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Showing papers in "The Journal of Comparative Neurology in 1981"


Journal ArticleDOI
TL;DR: An atlas of the distribution of cholinergic cell bodies, fibers, and terminals, as well as cholinoceptive cells, in the central nervous system of the cat (excluding the cerebellum) is presented from results obtained in immunohistochemical work on choline acetyltransferase.
Abstract: An atlas of the distribution of cholinergic cell bodies, fibers, and terminals, as well as cholinoceptive cells, in the central nervous system of the cat (excluding the cerebellum) is presented from results obtained in immunohistochemical work on choline acetyltransferase. Cholinergic cell bodies are observed in more than forty areas, and cholinoceptive cells in sixty discrete areas of brain sections from the spinal cord to the olfactory bulb. The atlas is presented in seventy cross-sectional drawings of cat brain extending from the olfactory bulb to the upper cervical spinal cord.

848 citations


Journal ArticleDOI
TL;DR: The location, topographic organization, and function of the middle temporal visual area in the macaque monkey was studied using anatomical and physiological techniques, with the emphasis on central vision being similar to that found in striate cortex.
Abstract: The location, topographic organization, and function of the middle temporal visual area (MT) in the macaque monkey was studied using anatomical and physiological techniques. MT is a small, elliptically shaped area on the posterior bank of the superior temporal sulcus which can be identified by its direct inputs from striate cortex and by its distinctive pattern of heavy myelination. Its average surface area is 33 mm2, which is less than 3% of the size of striate cortex. It contains a complete, topographically organized representation of the contralateral visual hemifield. There are substantial irregularities in the detailed pattern of topographic organization, however, and the representation is significantly more complex than that found for MT in other primates. Much of MT is devoted to the representation of central visual fields, with the emphasis on central vision being similar to that found in striate cortex. Electrophysiological recordings have confirmed previous reports of a high incidence of direction selective cells in MT. The transition in functional properties, from cells lacking direction selectivity outside MT to direction selective cells within, occurs over a distance of 0.1–0.2 mm or less along the lateral border of MT. Such a transition does not occur along the medial border, however, as the cortex medial to MT contains many cells with strong direction selectivity. Nevertheless, this region differs from MT in its myeloarchitecture, its lack of inputs from striate cortex, and the large size of its receptive fields. These results demonstrate the existence of three distinct visual areas on the posterior bank of the superior temporal sulcus which can be distinguished on the basis of both physiological and anatomical criteria.

716 citations


Journal ArticleDOI
TL;DR: Signs of progressive development of the mossy fibers appeared to reflect, temporally and topographically, the developmental gradients followed by their parent granule cells.
Abstract: The postnatal development of the axons of the dentate granule cells--the so-called mossy fibers--was studied at the light microscopic level in Timm and Golgi preparations and also by transmission electron microscopy. In the Timm-stained material, there was a distinctive coloration in the hilus and incipient stratum lucidum, indicating the presence of mossy fibers, on the first postnatal day. Over the next two weeks, the stained areas became more extensive, the size and density of the stained particles increased, and the particles became more intensely stained. These signs of progressive development of the mossy fibers appeared to reflect, temporally and topographically, the developmental gradients followed by their parent granule cells. The Golgi material confirmed the presence of mossy fibers in the hilus on the first postnatal day. Fasciculi of mossy fibers were observed in the stratum lucidum of the 3-day-old hippocampus, and although these immature axons were devoid of large synaptic expansions, they did have prominent growth cones at their termini. Small expansions along the lengths of the axons first appeared on day 7 and these grew to approximately an adult size and complexity by about day 14. The postsynaptic component of the mossy fiber synapse, the "thorny excrescence," did not begin to emerge from the proximal portion of the pyramidal cell dendrites until sometime after day 9. At the electron microscopic level we observed, on the first postnatal day, small, immature mossy fiber expansions which made both symmetric and asymmetric contacts directly with dendritic shafts. These profiles, which were only one tenth the size of mature expansions, grew rapidly between postnatal days 1 and 9 and increased their mean area by a factor of five. On or about day 9, as the "thorny excrescences" emerged, the asymmetric synapses came to be associated with these spinous processes. Taken together, the Golgi and electron microscopic analyses support the suggestion that mossy fibers establish synaptic contact with pyramidal cell dendrites early in the postnatal period, several days before there is any indication of spine development. Furthermore, the "thorny excrescences" develop after the more typical, pedicellate spines have appeared on the distal pyramidal cell dendrites. Finally, while it is clear that the mossy fibers in our 21-day-old material are, for the most part, fully matured, a more subtle and protracted development of the system, long into adulthood, is indicated by the increased area and density of stained particles in the Timm preparations from adult animals.

581 citations


Journal ArticleDOI
TL;DR: The results demonstrate ELI in neurons which are heterogeneous in size, some probably functioning as interneurons and others as projection neurons in different areas of the CNS, suggesting that these pentapeptides serve diverse functions which include, in addition to nociception, the regulation of neuroendocrine, respiratory, auditory, vestibular, and olfactory functions.
Abstract: The immunocytochemical localization of enkephalin-like immunoreactivity (ELI) throughout the rat central nervous system (CNS) was investigated. The detection of ELI-containing structures was facilitated through the use of (1) brains from colchicine-treated rats, (2) the proteolytic pretreatment of sections with pronase and (3) the “double-bridge” staining technique. Our findings confirm the presence of ELI in perikarya, neuronal processes and terminals in many areas of the CNS. In addition, the localization of ELI-containing perikarya is reported for the first time in the following areas: the olfactory bulb, the olfactory tubercle, the lateral preoptic nucleus, several nuclei within the amygdaloid nuclear complex, the hippocampus, the neocortex, the cingulate cortex, the posterior mammillary nucleus, the medial nucleus of the optic tract, the brachium of the inferior colliculus, the ventral tegmental nucleus, the locus ceruleus, the subceruleal region, the lateral trapezoid nucleus, the nucleus reticularis lateralis, and lamina VII of the cervical spinal cord. Our results demonstrate ELI in neurons which are heterogeneous in size, some probably functioning as interneurons and others as projection neurons in different areas of the CNS. The location of these neurons within the brain suggests that these pentapeptides serve diverse functions which include, in addition to nociception, the regulation of neuroendocrine, respiratory, auditory, vestibular, and olfactory functions.

540 citations


Journal ArticleDOI
TL;DR: A cell‐by‐cell analysis of the magnocellular elements in hypothalami of fifty Long‐Evans (normal) and Brattleboro (diabetes insipidis) rats was done using the unlabeled antibody enzyme technique (PAP) with primary antisera directed against oxytocin, vasopressin, and the neurophysins.
Abstract: A cell-by-cell analysis of the magnocellular elements in hypothalami of fifty Long-Evans (normal) and Brattleboro (diabetes insipidus) rats was done using the unlabeled antibody enzyme technique (PAP) with primary antisera directed against oxytocin (OXY), vasopressin (ADH), and the neurophysins. The magnocellular neurons of the hypothalamus were found in the supraoptic (SON), paraventricular (PVN), and anterior commissural (ACN) nuclei, a number of accessory nuclei, and as individual cells in the anterior hypothalamic area. SON was divided by the optic tract into the principal part and retrochiasmatic SON. In retrochiasmatic SON a majority of the cells contained vasopressin. Within the principal part of SON oxytocin-producing cells tended to be found rostrally and dorsally, while the vasopressin cells were more common caudally and ventrally. PVN was divided into three subnuclei, the medial, lateral, and posterior subnuclei, on the basis of cellular morphology and peptide content. The magnocellular cells of the medial and lateral PVN were closely packed together and nearly round, while those of posterior PVN were more separated and fusiform in shape with their long axis running in a medio-lateral direction. Medial PVN consisted primarily of oxytocin-producing cells, while lateral PVN was formed by a core of vasopressin-producing cells with a rim of oxytocin cells. Posterior PVN contained largely oxytocin-producing cells. Both ADH and OXY cells were found in the accessory nuclei. In the Long-Evans rat the SON had, on the average, 1443 OXY and 3236 ADH cells; the PVN had 1174 OXY and 976 ADH cells; and the accessory magnocellular groups in the hypothalamus (including the ACN) had 1286 OXY and 552 ADH cells. The Brattleboro strain animal had similar numbers of cells in these nuclei. (The cells which contain ADH in normal animals were identified in the Brattleboro rat as large, neurophysin-negative cells.) Thus, a large fraction of the magnocellular oxytocin- and vasopressin-producing cells in the rat were located outside of the PVN and SON. One accessory cell group in particular, ACN, had 616 OXY cells, or about 50% as many as PVN. In each nucleus the sum of the numbers of OXY and ADH cells was approximately the number of neurophysin cells.

504 citations


Journal ArticleDOI
TL;DR: The results suggest that caudal area 8 may be involved in head and eye movements in response to visual stimuli, while its anterior subdivisions may beinvolved in directing the head and eyes in Response to auditory stimuli.
Abstract: The sources of ipsilateral afferents to subdivisions of one frontal eye field (Walker, '40a area 8) were studied with horseradish peroxidase (HRP) in macaque monkeys There were major differences in the distribution of cells projecting to the caudal and rostral parts of area 8 The majority (53%) of labeled cortical cells projecting to caudal regions were in visual association areas, and an additional 23% were in the ventral bank of the intraparietal sulcus, where neurons may have predominantly visual and visuomotor properties In contrast, rostral area 8 had a much lower percentage of its cortical input originating in visual association areas (5%) or in the ventral bank of the intraparietal sulcus (8%) After HRP injection in this rostral part, 21% of labeled cells were in auditory association areas and 13% in paralimbic regions, whereas labeling in these two types of cortex was negligible after HRP administration to caudal parts of area 8 The percentage of cells in other association regions (portions of the banks of the superior temporal sulcus, dorsolateral parietal, medial parietal, and prefrontal cortices) was higher in the rostral (53%) than in the caudal case (21%) The results suggest that caudal area 8 may be involved in head and eye movements in response to visual stimuli, while its anterior subdivisions may be involved in directing the head and eyes in response to auditory stimuli Furthermore, limbic input may also be relevant to the neural processing occurring in rostral frontal eye fields, perhaps by directing attention toward motivationally relevant stimuli

500 citations


Journal ArticleDOI
TL;DR: The changes occuring from the early to the late prenatal stages of development appear to be the result of an increase in number of cells and continued aggregation and migration of the labeled neurons.
Abstract: The immunocytochemical localization of tyrosine hydroxylase is examined at embryonic (E) days 18 and 21 in rat brain in order to determine changes in the distribution and cytology of neurons showing immunoreactivity for the enzyme during late prenatal development. As compared with earlier stages of development, the distribution and morphology of the tyrosine hydroxylase-containing neurons at E18 and E21 more closely resemble catecholaminergic neurons in the adult brain. The changes occurring from the early to the late prenatal stages of development appear to be the result of an increase in number of cells and continued aggregation and migration of the labeled neurons. The major differences in the distribution of labeled perikarya between E18 and E21 are in the olfactory bulb and cerebral cortex. In the olfactory bulb, tyrosine hydroxylase-containing neurons are not detected until E21. In contrast in the cerebral cortex, a few neurons are transiently labeled for the enzyme at E18, but are not detected at E21 and have not been reported in the adult brain. The most striking change in the tyrosine-hydroxylase labeled structures in the late prenatal period is the increase in detectable immunoreactivity in bundles of axons and in terminal aborizations. The orderly appearance of tyrosine hydroxylase-labeled axons in the neostriatum and cortex are discussed in relation to the formation of these two contrasting regions innervated by catecholaminergic neurons.

498 citations


Journal ArticleDOI
TL;DR: The representation of the visual field in the area adjacent to striate cortex was mapped with multi unit electrodes in the macaque using multiunit electrodes in each animal over several recording sessions.
Abstract: The representation of the visual field in the area adjacent to striate cortex was mapped with multiunit electrodes in the macaque. The animals were immobilized and anesthetized and in each animal 30 to 40 electrode penetrations were typically made over several recording sessions. This area, V2, contains a topographically organized representation of the contralateral visual field up to an eccentricity of at least 80 degrees. The representation of the vertical meridian is adjacent to that in striate cortex (V1) and forms the posterior border of V2. The representation of the horizontal meridian in V2 forms the anterior border of V2 and is split so that the representation of the lower visual field is located dorsally and that of the upper field ventrally. As in V1, the representation of the central visual field is magnified relative to that of the periphery. The area of V2 is slightly smaller than that of V1. At a given eccentricity, receptive field size in V2 is larger than in V1. The myeloarchitecture of V2 is distinguishable from that of the surrounding cortex. The location of V2 corresponds, at least approximately, to that of cytoarchitectonic Area OB. V2 is bordered anteriorly by several other areas containing representations of the visual field.

485 citations


Journal ArticleDOI
TL;DR: The isotope injection of the amygdala revealed a projection to the magnocellular moeity of the mediodorsal nucleus (MDmc) which is known to innervate the same ventromedial regions of the frontal lobe that receive direct connections from the amygdala.
Abstract: To elucidate the anatomical relationships between the frontal association cortex and the limbic system in primates, projections from the amygdala to frontal cortex were studied in the rhesus monkey using retrograde and anterograde tracing methods. Following injections of horseradish peroxidase (HRP) into the orbital prefrontal cortex, the gyrus rectus, the superior frontal gyrus, and the anterior cingulate gyrus of the frontal lobe, labeled neurons were found in the basolateral, basomedial, or basal accessory nuclei of the amygdala. None of these nuclei contained labeled neurons following HRP injections into the principal sulcus or the lateral inferior convexity of the frontal lobe. This selective distribution of amygdala connections was confirmed by injecting tritiated amino acids into the amygdala. Silver grains were present only over the orbital cortex and gyrus rectus on the ventral surface of the frontal lobe and over the superior prefrontal gyrus and anterior cingulate gyrus on the medial wall of the hemisphere, while the dorsolateral prefrontal cortex was free of radioactivity. The isotope injection of the amygdala also revealed a projection to the magnocellular moeity of the mediodorsal nucleus (MDmc) which is known to innervate the same ventromedial regions of the frontal lobe that receive direct connections from the amygdala. Although MDmc and amygdala project to the same cortical regions, their terminal fields are different. The direct amygdala input terminates in layer 1 in orbital cortex and gyrus rectus and layer 2 in the dorsomedial cortex and cingulate gyrus, while the thalamic input is primarily to layer 3 and, in some areas, also to the superficial half of layer 1. These findings indicate that the frontal lobe of rhesus monkeys can be subdivided into two separable cortical regions:(1) A ventromedial region including the anterior cingulate gyrus which receives both direct (amygdalo-cortical) and indirect (amygdalo-thalamo-cortical) input from the amygdala; and (2) a dorsolateral frontal region which is essentially devoid of either direct or indirect amygdalofugal axons. On the basis of its selective relationship with the amygdala, the ventromedial region may be considered the “limbic” portion of the frontal association cortex.

456 citations


Journal ArticleDOI
TL;DR: Following the injection of horseradish peroxidase into the ipsilaeral substantia nigra, 36 retrogradely labelled neurons in the striatum were characterized by Golgi staining and gold toning: each neuron was of the medium‐size, densely spinous type.
Abstract: Following the injection of horseradish peroxidase into the ipsilaeral substantia nigra, 36 retrogradely labelled neurons in the striatum were characterized (in three rats) by Golgi staining and gold toning: each neuron was of the medium-size, densely spinous type Prior to the injection of horseradish peroxidase, two of the rats had had lesions placed in the ipsilateral motor cortex, the third rat had had a lesion placed in the ipsilateral frontal and prefrontal cortex In the electron microscope, degenerating boutons of cortical neurons were found in asymmetrical synaptic contact with the spines of proximal and distal dendrites of all six of the identified striatonigral neurons that were studied Some of the degenerating boutons were small (diameter 01–03 μ), while others were larger (1–2 μ) An individual dendrite of a striatonigral neuron was in synaptic contact with very few degenerating boutons Local axon collaterals im the striatum could be traced from two of the identified striatonigral neurons that received degenerating cortical boutons These were studied in the electron microscope; their boutons formed symmetrical synapses with spines or dendritic shafts of other striatal neurons The synaptic boutons contained large, clear, round and pleomorphic vesicles The postsynaptic targets of these boutons morphologically resemble the dendrites of medium-size spiny neurons It is concluded that afferents from the cortex make monosynaptic contact with the dendritic spines of medium-size spiny striatonigral neurons and that such neurons have local axon collaterals in the striatum that form synapses with other spiny neurons

456 citations


Journal ArticleDOI
TL;DR: The widespread rostrocaudal extent of the pelvic primary afferent projection is consistent with the necessity for the integration of somatic and autonomatic elements from various levels of the lumbo‐sacral‐coccygeal spinal cord in the performance of pelvic visceral functions.
Abstract: The central distribution of visceral primary afferent fibers from the pelvic nerve of the cast and the relationship of these fibers to preganglionic neurons of the sacral parasympathetic neurons (SPN) have been studied. Horseradish peroxidase (HRP) applied to the cut pelvic nerve was detected ipsilaterally in preganglionic neurons and dorsal root ganglion cells (segments S1-S3), and in central afferent projections to Lissauer's tract (LT), the dorsal columns, the dorsolateral funiculus, and spinal gray matter. The afferent projections were strongest in the region of the SPN (S1-S3) but extended far beyond its limits (e.g., LT was labeled from L4 to Cx7). In the transverse plane, collateral fiber bundles formed a thin shell around the dorsal horn predominantly within lamina I and expanded into terminal fields in the gray matter. The more prominent lateral collateral projection (LCP) extended into laminae V and VI, whereas the medial one (MCP) ended in the dorsal commissure. In longitudinal planes these projections exhibited a periodicity with an interval of approximately 200 micrometer. The distribution of afferent collateral projections overlaps the regions where many preganglionic neurons and their dendritic extensions are located, and also areas known to contain interneurons involved in visceral pathways. A differential distribution of afferents within the SPN was noted where a higher intensity was observed in proximity to those neurons located in laminae V and VI, which innervate the colon, and a lower intensity near neurons located in Lamina VII which innervate the bladder. This is consistent with the known spinal control of colon reflexes and the supraspinal control of bladder reflexes. The widespread rostrocaudal extent of the pelvic primary afferent projection is consistent with the necessity for the integration of somatic and autonomic elements from various levels of the lumbo-sacral-coccygeal spinal cord in the performance of pelvic visceral functions.

Journal ArticleDOI
TL;DR: It is concluded that adrenergic inputs to the paraventricular nucleus may influence cells that project to the median eminence and to preganglionic autonomic cell groups in the medulla and spinal cord.
Abstract: The distribution of catecholaminergic fibers and cell bodies in the paraventricular and supraoptic nuclei of the hypothalamus was investigated with immunohistochemical methods in the adult albino rat. Sections through the nuclei were stained with antisera to the catecholamine synthesizing enzymes tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyltransferase (PNMT). The results suggest that adrenergic (PNMT-stained) fibers innervate the entire parvocellular division of the paraventricular nucleus, although the highest density of fibers was found in the medial part of the division. Only widely scattered adrenergic fibers are found in the magnocellular division of the nucleus and in the supraoptic nucleus. Noradrenergic fibers appear to innervate the periventricular zone of the paraventricular nucleus and those parts of the paraventricular and supraoptic nuclei that contain predominantly vasopressinergic neurons in both the normal and in the homozygous Brattleboro rat. Significant numbers--somewhat more than 500--of dopaminergic (TH-stained) neurons are found in the paraventricular nucleus; the cells are distributed throughout the nucleus but are concentrated in the medial and periventricular parts of the parvocellular division. Double-labeling experiments with the retrogradely transported tracer true blue indicate that between 4% and 8% of the dopaminergic neurons in the paraventricular nucleus project to the region of the dorsal vagal complex and/or thoracic levels of the spinal cord. It is concluded that adrenergic inputs to the paraventricular nucleus may influence cells that project to the median eminence and to preganglionic autonomic cell groups in the medulla and spinal cord. Noradrenergic inputs to the supraoptic and paraventricular nuclei may influence primarily vasopressinergic cells that project to the posterior lobe of the pituitary, as well as cells in the periventricular part of the paraventricular nucleus that project to the median eminence.

Journal ArticleDOI
TL;DR: Cells containing enkephalin‐like immunoreacactivity were found within the somata of three types of hippocampal neurons: granule cells of the dentate gyrus, occasional pyramidal shaped cells of field CA1 stratum pyramidale, and varied scattered interneurons.
Abstract: The distribution of enkephalin-like immunoreactivity in the hippocampal formation of the rat was analyzed. Two specific projection systems are described. The first emerges from the hilus of the dentate gyrus and appears to terminate with notably large boutons on the proximal apical and, to a lesser extent, basal dendrites of hippocampal regio inferior pyramidal cells. This projection corresponds in source, position, and character to the hippocampal mossy fiber system. The second axonal population enters the temporal hippocampal formation from the medial wall of the subicular complex and follows the hippocampal fissure to occupy stratum lacunosum-moleculare of the hippocampus proper and the distal third of the dentate gyrus molecular layer; this pattern corresponds to the distribution of afferent input from the lateral entorhinal cortex and/or perirhinal area. Lesions of the hilus or retrohippocampal area caused a selective depletion of immunoreactivity in the mossy fiber fields and molecular layers of the dentate gyrus, respectively. Enkephalin-like immunoreactivity was found within the somata of three types of hippocampal neurons: 1) granule cells of the dentate gyrus, 2) occasional pyramidal shaped cells of field CA1 stratum pyramidale, and 3) varied scattered interneurons. Of this last group, two types of interneurons were consistently seen. The first occupy the border between stratum radiatum and stratum lacunosum-moleculare and extend processes at right angles to the long axis of the pyramidal cell dentrites, whereas the second lie within stratum radiatum of field CA1 and extend processes in alignment with the long axis of the pyramidal cell dendrites. Cells containing enkephalin-like immunoreactivity were also observed in the subiculum and retrohippocampal region, most notably including layers II and III of the lateral entorhinal cortex-perirhinal area--the probable source of extrinsic immunoreactive input to the hippocampal formation. Intraventricular colchicine treatment intensified the immunoreactive staining of some hippocampal neurons but did not reveal any cell types not seen to be labeled in untreated rats.

Journal ArticleDOI
TL;DR: A cochleotopic organization of the projections is apparent for cochlear nucleus and superior olivary complex and the heaviest terminations of contralateral inferior Colliculus are medial and dorsal in inferior colliculus.
Abstract: The ascending auditory projections to central nucleus of inferior colliculus and its ventrolateral and dorsomedial subdivisions (ICVL and ICDM) have been studied in cat using both pressure and electrophoretic injections of horseradish peroxidase (HRP). The results indicate that the predominant ascending projections to inferior colliculus originate in (1) contralateral cochlear nucleus, (2) contralateral and ipsilateral lateral superior olive, (3) ipsilateral medial superior olive, (4) ipsilateral ventral nucleus of the lateral lemniscus, (5) ipsilateral and contralateral dorsal nucleus of the lateral lemniscus, and (6) contralateral inferior colliculus. In addition, ipsilateral cochlear nucleus, ipsilateral and contralateral intermediate nucleus of the lateral lemniscus, ipsilateral, and to a lesser extent contralateral, periolivary nuclei project to inferior colliculus. Of these nuclei, the lateral superior olive projects exclusively to ICVL and ipsilateral cochlear nucleus and contralateral inferior colliculus project mostly, if not exclusively, to ICDM. Many of these projections demonstrate a cochleotopic organization and frequency a nucleotopic organization as well. A cochleotopic organization of the projections is apparent for cochlear nucleus and superior olivary complex. A nucleotopic organization suggests that the heaviest terminations of contralateral inferior colliculus are medial and dorsal in inferior colliculus, of medial superior olive are dorsal and lateral, of superior olivary complex are rostral, of cochlear nucleus are caudal, and of ventral nucleus of the lateral lemniscus are caudal.

Journal ArticleDOI
TL;DR: Nine peptides examined had its own characteristic distribution within fibers in the gray and white matter and all peptides except for thyrotropin releasing hormone were observed in fibers in laminae I and II.
Abstract: The comparative distribution of nine peptides was examined in the L4 segment of the rat cord using the peroxidase antiperoxidase technique. The peptides examined were substance P, neurotensin, cholecystokinin, methionine-enkephalin, oxytocin, neurophysin, adrenocorticotrophin, thyrotropin releasing hormone, and vasoactive intestinal polypeptide. No transport blocking agents were used and in spite of this cell bodies containing substance P, neurotensin, cholecystokinin, and methionine-enkephalin were observed. All peptides except for thyrotropin releasing hormone were observed in fibers in laminae I and II. All peptides were present in the area around the central canal, lamina X. Each peptide had its own characteristic distribution within fibers in the gray and white matter.

Journal ArticleDOI
TL;DR: The retrograde axonal transport method has been employed to identify the cell bodies of cortical neurons projecting directly to the spinal cord in the monkey.
Abstract: The retrograde axonal transport method has been employed to identify the cell bodies of cortical neurons projecting directly to the spinal cord in the monkey. The investigation has focused on aspects of the laminar, columnar, and somatotopic organization of corticospinal neurons within each of the cytoarchitectural and functional subdivisions of the sensorimotor cortex. The principle findings of these experiments are that: (i) cortical regions containing cell bodies of corticospinal neurons are the first motor cortex (area 4), the first somatic sensory cortex (areas 3a, 3b, 1, and 2), and part of the immediately adjacent posterior parietal cortex (area 5), the second somatic sensory cortex, the supplementary motor cortex (the medial aspect of area 6), and the medial part of the posterior parietal cortex in a region termed the supplementary sensory area; (ii) corticospinal neurons display a somatotopic organization within each of these functional subdivisions of the sensorimotor cortex; (iii) all corticospinal neurons arise from layer V of the cortex; and (iv) corticospinal neurons within the first motor and first somatic sensory cortex oftern occur in clusters, perhaps reflecting a columnar organization in the sensorimotor cortex. These findings demonstrate the origins of the corticospinal system to be more extensive than previously recognized and show that a number of common features characterize the organization of corticospinal neurons in all cortical areas. Across cortical subdivisions, however, major differences exist in the extent of spinal segmental representations, in the manner in which corticospinal neurons occur in groups, and in the numerical density and sizes of corticospinal neurons. These aspects of the organization of the corticospinal system presumably reflect specialization of the different cortical areas in spinal cord sensory and motor control.

Journal ArticleDOI
TL;DR: The distribution of monoaminergic cell bodies in the brainstem of the cat has been examined with Falck‐Hillarp fluorescence histochemical technique and quantifications indicate that the IA cells make up about 70% of the medium‐sized cells in RD, 50% in RP, 35% in RCS and RO, 25% in LI, 15% in RM, and only 10% inRPo.
Abstract: The distribution of monoaminergic cell bodies in the brainstem of the cat has been examined with Falck-Hillarp fluorescence histochemical technique. Quantitative determinations indicate that the cat brainstem contains about 60,300 indolaminergic (IA) cells. The majority of these (about 46,700, or 77.5%) are located within raphe nuclei. The largest number is contained within nucleus raphe dorsalis (RD), accounting for around 24,300 IA cells, while raphe pallidus (RP) holds about 8,000, raphe centralis superior (RCS) 7,400, raphe magnus (RM) 2,400, raphe obscurus (RO) 2,300, linearis intermedius (LI) 2,100, and the raphe pontis (RPo) only some 280 IA cells. The IA cells represent, however, only part of the neuronal population of raphe nuclei, which, in addition, hold varying numbers of other medium-sized and small-sized neurons. Thus, quantifications in Nissl-stained material indicate that the IA cells make up about 70% of the medium-sized cells in RD, 50% in RP, 35% in RCS and RO, 25% in LI, 15% in RM, and only 10% in RPo. The substantial numbers of small-sized perikarya observed in all raphe nuclei may represent interneurons. Significant numbers of IA cells were consistently located outside the raphe nuclei at all brainstem levels. In all, these amounted to approximately 13,600, or 22.5% of the total number of IA cells. Thus, IA cells occurred in the myelinated bundles, and sometimes in reticular formation, bordering the raphe nuclei; in the ventral brainstem forming a lateral extension from the ventral raphe (RP, RM, RPo, RCS, and LI) to the position of the rubrospinal bundle; in the periventricular gray and subjacent tegmentum of dorsal pons and caudal mesencephalon; in the locus coeruleus (LC) complex; around the motor trigeminal nucleus; caudal to the red nucleus; and in the interpeduncular and interfascicular nuclei. The wide distribution of IA cells leads to a considerable mixing with catecholaminergic (CA) cell groups. Our observations on CA cell distribution are essentially in accordance with previous reports. Quantifications indicate that the LC complex contains about 9,150 CA cells, unilaterally. A previously unnoticed group of scattered CA cells was found in relation to the vestibular nuclei and extending dorsally toward the deep cerebellar nuclei.

Journal ArticleDOI
TL;DR: The medial (M) and posteromedial cortical (C3) amygdaloid nuclei and the nucleus of the accessory olfactory tract (NAOT) are disignated the “vomeronasal amygdala” because they are the only components of the amygdala to receive a direct projection from the accessory Olfactory bulb (AOB).
Abstract: The medial (M) and posteromedial cortical (C3) amygdaloid nuclei and the nucleus of the accessory olfactory tract (NAOT) are disignated the “vomeronasal amygdala” because they are the only components of the amygdala to receive a direct projection from the accessory olfactory bulb (AOB). The efferents of M and C3 were traced after injections of 3H-proline into the amygdala in male golden hamsters. Frozen sections of the brains were processed for autoradiography. The efferents of the “vomeronasal amygdala” are largely to areas which are primary and secondary terminal areas along the vomeronasal pathway, although the efferents from C3 and M terminate in different layers in these areas than do the projections from the vomeronasal nerve or the AOB. Specifically, C3 projects ipsilaterally to the internal granule cell layer of the AOB, the cellular layer of NAOT, and layer lb of M. Additional fibers from C3 terminate in a retrocommissural component of the bed nucleus of the stria terminalis (BNST) bilaterally, and in the cellular layers of the contralateral C3. The medial nucleus projects to the cellular layer of the ipsilateral NAOT, layer lb of C3, and bilaterally to the medial component of BNST. Projections from M to non-vomeronasal areas terminate in the medial preoptic area-anterior hypothalamic junction, ventromedial nucleus of the hypothalamus, ventral premammillary nucleus and possibly in the ventral subiculum. These results demonstrate reciprocal connections between primary and secondary vomeronasal areas and between the secondary areas themselves. They suggest that M, but not C3, projects to areas outside this vomeronasal network. The medial amygdaloid nucleus is therefore an important link between the vomeronasal organ and areas of the brain not receiving direct vomeronasal input.

Journal ArticleDOI
TL;DR: The cytoarchitecture of rat cingulate cortex is described, which includes the topographical distribution and layering patterns of Brodmann's areas 25, 32, 24, and 29a, b, c, and d.
Abstract: The cytoarchitecture of rat cingulate cortex is described. This includes the topographical distribution and layering patterns of Brodmann's areas 25, 32, 24, and 29a, b, c, and d. Area 24 is subdivided into a ventral area 24a and a dorsal area 24b, but an area 23 could not be identified between areas 24 and 29 An analysis of Golgi impregnations in areas 32, 24, and 29 demonstrates that most neuronal types recognized in neocortical areas are also present in cingulate cortex. Besides typical and inverted pyramidal cells, there is a wide variety of nonpyramidal cells, including multipolar, bitufted, and bipolar cells. Small multipolar cells with small somata, a dendritic tree limited to one or two layers, sparse to moderately spinous dendrites and one of two varieties of short axonal trajectories are present in layers I and II of areas 32, 24, and 29d. Medium multipolar cells occur mainly in layers III and V; they have extensive dendritic trees which traverse three or more layers, moderately spinous dendrites, and an axonal plexus which either ascends or descends in the cortex. Large multipolar cells are also frequent in layers III and V; their extensive dendritic trees are essentially spine free and they have axons which form dense terminations, particularly in the layer above the one in which the cell body is located Neurons with elongated somata and a primarily vertical orientation of the dendritic tree are either bitufted or bipolar. Bitufted cells are most frequent in layers II and III of areas 32, 24, and 29d. These cells have dendritic trees which form “hourglass shaped” fields, dendrites which are moderately spinous, and axons which form either extensive horizontal and vertical projections or are “chandelier” in form. Bipolar cells, in contrast, are found in layers II–V; their sparsely spinous dendrites form narrow dendritic trees which are oriented vertically and extend across four or more layers, and their axons have the same vertical orientation as the dendritic tree It is concluded that the form of the axonal arbors of nonpyramidal cells frequently mimics the extent and shape of their dendritic trees. Thus, small multipolar cells with limited, spherical dendritic trees may have axons which arch sharply and emit short, terminal branches. In contrast, medium and large multipolar cells have more extensive dendritic and axonal arbors which traverse two, three, or more layers. Of the fusiform cells, bitufted ones with their “hourglass” dendritic trees have extensive vertical and horizontally oriented axonal branches, while bipolar cells have narrow, vertically oriented dendritic and axonal arbors The granular layers II–IV of area 29c contain the following types of neurons: small and fusiform pyramids, medium-sized pyramids, large stellate cells, and medium multipolar cells. Fusiform pyramids are the only neurons unique to cingulate cortex. They are similar to the variety of pyramidal cells, but have an oval soma and only one basal dendrite which extends from the base of the cell body to arborize in layer IV. Large stellate cells differ from large multipolar cells in that they have densely spinous dendrites and axons which enter the white matter.

Journal ArticleDOI
TL;DR: The longer connections of the entorhinal cortex have been studied autoradiographically in a series of rats, each of which received a small injection of 3H-amino acids in one of the various cytoarchitectonic subfields of the entropy cortex.
Abstract: The longer connections of the entorhinal cortex have been studied autoradiographically in a series of rats, each of which received a small injection of 3H-amino acids in one of the various cytoarchitectonic subfields of the entorhinal cortex. The major findings can be summarized as follows. Whereas the projection of the lateral entorhinal area (LEA) to the dentate gyrus is broad in its longitudinal extent, the medial entorhinal area (MEA), and especially the ventral portion of this zone, projects in a more lamellar fashion. In the transverse plane the LEA preferentially projects to the inner (dorsal) blade of the dentate gyrus, while the MEA innervates both blades equally. Within the radial dimension, the entorhinal cortex projects to the dentate gyrus according to a medial to lateral gradient, with lateral portions of the LEA projecting along the pial surface and successively more medial portions of the entorhinal projecting closer to the granule cells. The commissural entorhinal to dentate projections are similar to the ipsilateral projections in location; however, they are considerably reduced in septotemporal extent and do not arise from cells in the ventral half of either LEA or the intermediate entorhinal area (IEA). The projection of the entorhinal cortex to Ammon's horn reflects the same longitudinal characteristics as the dentate projections. An alvear input which extends only to the pyramidal cells at the CA1-subicular junction was most noticeable at ventral hippocampal levels. Finally the extrahippocampal projections have been analyzed. These arise predominantly from cells in the LEA and project forward along the angular bundle to the piriform and periamygdaloid cortices, as well as the endopiriform nucleus, the lateral, basolateral, and cortical amygdaloid nuclei, the nucleus of the lateral olfactory tract, the olfactory tubercle, the anterior olfactory nucleus, the taenia tecta, and the indusium griseum. These extrinsic projections are to a large extent reciprocal to the major extrinsic inputs to the LEA.

Journal ArticleDOI
TL;DR: The anterograde transport of 3H proline and of horseradish peroxidase has been used to study the retinogeniculate pathway in normal adult ferrets and in young ferrets during postnatal development.
Abstract: The anterograde transport of 3H proline and of horseradish peroxidase has been used to study the retinogeniculate pathway in normal adult ferrets and in young ferrets during postnatal development. the lateral geniculate nucleus in adults shows a characteristic "carnivore" pattern, with layers A, A1, C, C1, C2, and C3, and a medial interlaminar nucleus recognizable either cytoarchitectonically or on the basis ofth retinogeniculate innervation. In addition, there is a well-defined, rather large perigeniculate nucleus. At birth the lateral geniculate nucleus is unlaminated and essentially all parts are reached by afferents from both eyes. The crossed component is by far the larger. It extends from the optic tract medially well into the perigeniculate field, in contrast to the uncrossed component which barely reaches the perigeniculate field. During the first 3 postnatal days the uncrossed fibers restrict their arbors to a small posterior and medial region, the precursor of the biocular segment of the nucleus. The crossed fibers gradually retreat from the region within which the uncrossed fibers have concentrated. Between the fourth and eighth postnatal days the field occupied by the ipsilateral component expands again to form a major focus that will define lamina A1 and a minor focus that will define C1. At this stage the crossed and the uncrossed fibers overlap at the borders of lamina A1 and the whole region of lamina C1 is also occupied by arbors of the crossed component. The perigeniculate field becomes clearly distinguishable from the lateral geniculate nucleus and the medial interlaminar nucleus is becoming clearly recognizable between days 3 and 8. Between days 8 and 15 the cytoarchitectonic borders between layers A and A1 become clearly defined, but the retinogeniculate axons from each eye still extend across this border. These axons retreat into their appropriate lamina after the 15th postnatal day an the nucleus reaches its essentially adult structure by about the fourth postnatal week. Segregation of retinofugal axons in the C layers occurs after segregation in the A layers, but many of the cells within the C layers show signs of cytological maturity earlier than those of the A layers. The nucleus undergoes a series of migrations and changes of shape as the ipsilateral and contralateral components become segregated. Whereas in teh newborn the nucleus is roughly comma-shaped and on the lateral aspect of the dorsal thalamus, in the adult it is "L"-shaped and mainly on the posterior aspect of the dorsal thalamus.

Journal ArticleDOI
TL;DR: The time of origin of neurons in the hippocampal region was determined in a series of rhesus monkeys exposed to a pulse of tritiated thymidine at a different time during ontogeny and sacrificed between the second and fifth month after birth.
Abstract: The time of origin of neurons in the hippocampal region was determined in a series of rhesus monkeys, each of which had been exposed to a pulse of tritiated thymidine (3H-TdR) at a different time during ontogeny and sacrificed between the second and fifth month after birth. No heavily labeled cells were found in the hippocampal region of animals exposed to 3H-TdR before embryonic day 33 (E33). Exposure to 3H-TdR given at E36 labels a few neurons in the deepest layers of the entorhinal area, and 3H-TdR given at E38 labels a small number of neurons in all hippocampal subdivisions. Although the first neurons are generated almost simultaneously throughout the hippocampal region, the proliferation ceases at a different time in each subdivision. The last neurons destined for the entorhinal area and presubiculum are generated between E70 and E75, whereas the last parasubicular neurons are generated between E75 and E80. The production of neurons that form the subiculum ends about two weeks earlier, between E56 and E65. Within the hippocampus, genesis of pyramidal cells ends between E70 and E80 in area CA1, between E56 and E65 in area CA2, between E65 and E80 in area CA1, between E56 and E65 in area CA2, between E65 and E70 in area CA3, and between E75 and E80 in area CA4. In contrast, the genesis of granule cells of the fascia dentata is considerably prolonged. It continues throughout the second half of gestation, declines steadily in the course of the first postnatal month, and tapers off during the next 2 months. There is a distinct inside-to-outside spatiotemporal gradient in the parahippocampal formation and in the stratum pyramidale of both the subiculum and hippocampus. In contrast, the spatiotemporal pattern of granule cell origin in the dentate gyrus is outside-to-inside. Furthermore, granule cells generated between E36 and E80 are distributed in a distinct suprapyramidal-to-infrapyramidal gradient, whereas those generated at later ages are distributed evenly throughout the fascia dentata. Correlation of the present findings with histological data on hippocampal neurogenesis in the human brain demonstrates that the timing and sequence of developmental events as well as spatiotemporal gradients are similar in both primate species.

Journal ArticleDOI
TL;DR: The ontogeny of callosal projection neurons in the rat parietal cortex was examined using the retrograde and anterograde transport of horseradish peroxidase (HRP), as well as Golgi and Nissl stains to compare to cortical maturation.
Abstract: The ontogeny of callosal projection neurons in the rat parietal cortex was examined using the retrograde and anterograde transport of horseradish peroxidase (HRP), as well as Golgi and Nissl stains. From postnatal day 0 (PND 0) to early PND 4, the callosal projection neurons are distributed as two continuous horizontal bands of cells which extend throughout the subplate in layers Va and Vc-upper VIa. Neurons within the cortical plate (CP), however, do not transport HRP from a contralateral injection site until PND 3 to early PND 4, when a few cells at the lower CP border are generally labeled. However, by late on PND 4, and more consistently by PND 5, several changes in the distribution of callosal projection neurons take place. First, cells at all levels of the CP become labeled in a sequential fashion, from the lower border upward. Second, gaps, or areas devoid of HRP, become apparent in layer IV of the barrel field area. Third, in the cortical areas containing the gaps, as well as in other areas which are destined not to be callosally connected in the adult, there is a noticeable decrease in the number of cells labeled with HRP. This decrease continues through PND 15 and possibly into adulthood. The foregoing developmental events are compared to cortical maturation as seen in both Golgi- and Nissl-stained material. By PND 15, the basic adult pattern of callosal projection neurons is established. The neurons reside mainly in layers III and Va, with fewer in layers II and Vc-upper VIa, and fewer still in the other cortical layers. They are aligned in vertical arrays in discrete areas of the cortex.

Journal ArticleDOI
TL;DR: While significant differences characterize the source of afferents to Rgc and NRM/Rmc, there is little to distinguish that between NRM and Rmc.
Abstract: In order to study the organization of the rostral medulla of the cat and its contribution to pain control mechanisms, we have examined the afferent connections of the midline nucleus raphe magnus (NRM), the laterally located nucleus reticularis magnocellularis (Rmc), and the nucleus reticularis gigantocellularis (Rgc) located dorsal to Rmc. Iontophoretic injections of HRP were made into the three regions; the distribution of retrogradely labeled neurons in brainstem and spinal cord was then mapped. While significant differences characterize the source of afferents to Rgc and NRM/Rmc, there is little to distinguish that between NRM and Rmc. The predominant spinal projection is to Rgc; fewer labeled neurons were recorded after injections into Rmc. In contrast, no significant direct spinal projection to NRM was found. All three regions receive input from widespread areas within the medullary and pontine reticular formation. The most pronounced differences in the distribution of retrogradely labeled neurons were found in the midbrain. The major projection to both NRM and Rmc derives from the periaqueductal gray (PAG) and from the adjacent nucleus cuneiformis. Labeled cells are concentrated in the dorsal and lateral PAG; few are found in the ventrolateral PAG. In contrast, Rgc receives few afferents from the PAG; however, after Rgc injections, many cells were recorded in the deep layers of the contralateral tectum. None of the injection sites produced significant labeling of the catecholamine-rich dorsolateral pontine tegmentum or of the nucleus raphe dorsalis. The demonstration of significant PAG projections to NRM/Rmc provides anatomical evidence for the hypothesis that opiate and stimulation-produced analgesia involves connections from PAG to neurons of NRM and Rmc which, in turn, inhibit spinal nociceptors.

Journal ArticleDOI
TL;DR: In macaque monkeys, just as in the cat, a geniculoprestriate projection system exists and it was suggested that there are two parallel systems of visual information processing from the LGN to the prestriate cortex, a direct one and an indirect one through the striate cortex.
Abstract: The enzyme horseradish peroxidase (HRP) was separately injected into striate, prestriate, inferotemporal, and parietal cortices in 19 macaque monkeys, and the lateral geniculate nucleus (LGN) was examined for retrograde transport. Labeled LGN cells were identified only in the animals, with HRP injections into the striate and prestriate cortex. Following injections into either of these regions, labeled cells were found in both parvocellular and magnocellular regions of the ipsilateral LGN only, in keeping with the topographic relation of HRP injection sites in the cortex to labeled areas in the LGN. It was also found that (1) labeled LGN cells were less numerous in both laminar and interlaminar zones following HRP injection into the prestriate cortex, whereas following HRP injection into the striate cortex labeled cells were found almost exclusively in the laminae, and localized to a wedge-shaped region; (2) following HRP injection into the prestriate cortex, the mean sizes of the labeled parvocellular and magnocellular cells, estimated in projected diameter, were almost the same, these means being significantly larger than the mean size of labeled parvocellular cells and much smaller than that of labeled magnocellular cells following HRP injection into the striate cortex; (3) the shapes of the labeled LGN cells following HRP injection into the prestriate cortex were ovoid, fusiform, or triangular (or multipolar), whereas those following HRP injection into the striate cortex were uniformly ovoid or round. The above findings following HRP injections into the prestriate cortex in normal monkeys were confirmed by HRP injections into the prestriate cortex of monkeys whose striate cortex had been removed several months prior to the injection; labeled cells were found in confines of areas of retrograde degeneration in the LGN and their labeling pattern was the same as that in intact animals. It was concluded that in macaque monkeys, just as in the cat, a geniculoprestriate projection system exists; it was suggested that there are two parallel system of visual information processing from the LGN to the prestriate cortex, a direct one and in indirect one through the striate cortex.

Journal ArticleDOI
TL;DR: The corticostriate projections of temporal areas TA, TE, TF, TG, 35, and 28 were studied in the rhesus monkey with the use of autoradiography to observe widespread projections to rostral as well as caudal parts of the striatum.
Abstract: The corticostriate projections of temporal areas TA, TE, TF, TG, 35, and 28 were studied in the rhesus monkey with the use of autoradiography. Widespread projections were observed to rostral as well as caudal parts of the striatum for all areas except area 28. For example, areas TA and TG have sizable projections to the medial or periventricular part of the head of the caudate nucleus, as well as to the medial part of the tail of this structure and the dorsally adjacent putamen. Areas TE and TF also were observed to send strong projections to the head of the caudate nucleus. In addition, they project to the rostral putamen. Both have projections to the tail of the caudate nucleus and caudal putamen. The widespread distribution of temporostriate axons to the rostral striatum suggests strongly that previous silver impregnation studies have not only underestimated the strength of the temporal cortical contribution to the corticostriate system, but also failed to identify the major projection zone of temporostriate axon terminals. For example, while all temporal cortical areas contribute projections to an organized topography in the tail of the caudate nucleus and the ventrocaudal putamen, they were observed consistently to have larger projections to the head of the caudate nucleus and rostral putamen. These results add to a growing body of evidence which demonstrates the existence of widespread nonmotor cortical input to the basal ganglia, and an organization of this input far greater in complexity than that demonstrated by earlier suppressive silver impregnation methods.

Journal ArticleDOI
TL;DR: Three divisions of the nuclei of the lateral lemniscus, a dorsal, an intermediate, and a ventral division are discussed, each of which receives a substantial projection from the medial nucleus of the trapezoid body.
Abstract: Afferents from the hindbrain auditory system to the nuclei of the lateral lemniscus were analyzed by the use of orthograde and retrograde axon-tracing techniques. Three divisions of the nuclei of the lateral lemniscus, a dorsal, an intermediate, and a ventral division are discussed. The dorsal nucleus of the lateral lemniscus is a recipient of afferents from cells located mainly in the superior olivary complex and the contralateral dorsal nucleus of the lateral lemniscus. It receives direct afferents from only a few cells in the cochlear nuclei. In sharp contrast, the ventral nucleus of the lateral lemniscus is the recipient of afferents from many cells in the contralateral ventral cochlear nucleus and from only a few cells in the superior olivary complex. Further, it receives no afferents from cells in the contralateral nuclei of the lateral lemniscus. The intermediate nucleus of the lateral lemniscus receives afferents from some cells in the cochlear nucleus and the superior olivary complex. It is unique among the three nuclei of the lateral lemniscus in that it receives a substantial projection from the medial nucleus of the trapezoid body.

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TL;DR: A germinal zone at the leading edge of sensory epithelium growth appears to persist into adult life in sharks, and published reports reinterpreted in light of this evidence suggest that such hair cell population growth may be expected in other anamniotes and that latent growth zones might persist in the ears of amniotes.
Abstract: In many animals the sensory hair cells of the inner ear are ultrastructurally variable within individual epithelia. This variation has been hypothetically related to both the function and the age of the individual cells. In this study, growth-related changes in hair cell populations were examined in the macula neglecta sensory epithelia of juvenile and adult sharks. Scanning electron microscopy demonstrated that more than 80% of the 200,000 hair cells in the adult's macula neglecta are produced postembryonically. Tritiated thymidine autoradiography and histological descriptions of the hair cells in this sound detector indicate that new sensory cells are produced in growth zones at the edges of the epithelia. The hair cells in those zones have small cell bodies, small and heterogeneous cilia complexes, and associations with small numbers of particularly thin nerve terminals. Their cytological features and their sparse innervation contrast with the features of the more numerous central cells in each epithelium, but appear to resemble the published descriptions of embryonically developing hair cells. Thus, a germinal zone at the leading edge of sensory epithelium growth appears to persist into adult life in sharks. Published reports reinterpreted in light of this evidence suggest that such hair cell population growth may be expected in other anamniotes and that latent growth zones might persist in the ears of amniotes.

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TL;DR: The proportion of neurons generated (no longer labeled) on specific embryonic days was determined quantitatively in 18 regions of the midbrain tegmentum in order to label in embryos the proliferating precursors of neurons.
Abstract: Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day E12 and 13 (E12 j3) until the day before parturition (E21 k2) in order to label in their embryos the proliferating precursors of neurons. At 60 days of age the proportion of neurons generated (no longer labeled) on specific embryonic days was determined quantitatively in 18 regions of the midbrain tegmentum. The neurons of the oculomotor and trochlear nuclei are generated concurrently on days E12 and 13. There was a mirror image cytogenetic gradient in these nuclei and this was interpreted as the dispersal of neurons derived from a common neuroepithelial source to the medial longitudinal fasciculus. Neurons in three other components of the tegmental visual system are produced in rapid succession after the motor nuclei. In the nucleus of Darkschewitsch peak production time was on day E12 and 13, extending to day E15; in the Edinger-Westphal nucleus the time span was the same but with a pronounced between days E13; finally, the neurons of the parabigeminal nucleus were produced between days E13 and E15 with a peak on day E14. The neurons of the periaqueductal gray were generated between days E13 and 17 with a pronounced ventral-to-lateral and lateral-to-dorsal gradient. In the red nucleus the neurons were produced on days E13 and E14 with a caudal-to-rostral gradient: the cells of the magnocellular division preceding slightly but significantly the cells of the parvocellular division. The neurons of the interpeduncular nucleus originated between days E13 and E15; the peak in its ventral portion was on day E13, in its dorsal portion on days E14 and E15. A ventral-to-dorsal gradient was seen also in both the dorsal and the median raphe nuclei in which neuron production occurred between days E13 and E15. The neurons of the pars compacta and pars reticulate of the substantia nigra were both produced between days E13 and E15 with a modified lateral-to-medial gradient. This gradient extended to the ventral tegmental area where neurons of the pars medialis were produced between days E14 and E16. With the exception of the central gray, neuron production was rapid and relatively early in the structures situated ventral to the midbrain tectum. A comparison of the cytogenetic gradients in the raphe nuclei of the lower and upper medulla, the pontine region, and the midbrain suggests that they originate from at least three separate neuroepithelial sources.

Journal ArticleDOI
TL;DR: The posterior lateral line lobe of two high‐frequency weakly electric fish, Apteronotus albifrons and Eingenmannia viriscens, was studied at the electron microscopic level to identifyerent input to the posterior lobe.
Abstract: The posterior lateral line lobe of two high-frequency weakly electric fish, Apteronotus albifrons and Eingenmannia viriscens, was studied at the electron microscopic level. The various cell types previously described by light microscopy (Maler, ′79) were identified on the basis of their unique position or by combined Golgi-EM. Afferent input to the posterior lobe was identified either by its location and generally accepted characteristics, e.g., parallel fibers in the molecular layer, or by making appropriate lesions and noting the degenerating terminals, e.g., primary electroreceptive afferents. The major cell types of the posterior lobe are as follows: (1) spherical cells—an electron-dense cytoplasm crowded with ribosomes and other organelles; (2) granule cells—a small pale soma; fairly electron-dense dendrites, and pale axon terminals with clustered pleomorphic vesicles; (3) pyramidal cells—a large pale soma with a well-developed golgi apparatus; pale dendrites with evenly distributed microtubules; the somatic dendrites of pyramidal cells have an exceptional quantity of coated vesicles, multivesicular bodies, and smooth endoplasmic reticulum; (4) polymorphic cells—a medium-sized electron-dense soma; the dendrites are easily recognized by their content of neurofilaments, while their axon terminals are distinguished by their increased electron density and tightly packed ovoid vesicles. Two types of primary electroreceptive afferents were identified: (1) Latency coder terminals were slightly electron-dense, with a small number of vesicles but large numbers of mitochondria; (2) Probability coder terminals were electron-lucent, with a large number of round synaptic vesicles; the diameters of these vesicles were always bimodally distributed. Afferent fibers to the molecular layer of the posterior lobe are organized as parallel fibers at the light microscopic level; ultrastructurally they are similar to parallel fibers of the cerebellum and make appropriate asymetric synapses on all apical dendritic trees within the molecular layer. The circuitry of the posterior lobe is summarized in Figure 17. Latency coders make gap junction contact only with spherical cells, which in turn receive strictly latency coder input. Probability coders make mostly asymmetric chemical synapses onto granule cell and pyramidal cell basilar dendrites. The granule cell axons make symmetric synaptic contacts with the somata and somatic dendrites of both basilar and non-basilar pyramids; they also synapse on the ascending apical and basilar dendritic processes of granule cells. These ascending processes of granule cells make gap junction contacts with the somata and somatic dendrites of only the non-basilar pyramids. The consequence of this basic circuit appears to be that the posterior lobe can detect and enhance the contrast of objects with either high conductivity (basilar pyramids) or low conductivity (non-basilar pyramids). The somatic dendrites of pyramidal cells were found to have extraordinary numbers of coated vesicles, and these were often associated with the postsynaptic densities of granule cell axons. The possible role of these coated vesicles in receptor recycling is discussed. All afferents of the posterior lobe end in specific laminae, and in a given lamina they usually terminate on all potential postsynaptic sites; this was defined as laminar specificity of synaptic connections. The latency coder to spherical cells contacts, and the granule cell ascending process to non-basilar pyramid contacts are both specific to particular cells within a lamina; this was defined as cellular specificity of synaptic connections. Other examples of both sorts of synaptic specificity are presented and discussed in relation to current concepts of neuronal development.