Showing papers in "The Journal of Comparative Neurology in 1974"

Topographic atlas of catecholamine and acetylcholinesterase-containing neurons in the rat brain. I. Forebrain (telencephalon, diencephalon).

Abstract: A complete stereotaxic neuroanatomical atlas of the rat hindbrain was prepared using transverse serial sections stained with Luxol fast blue and cresyl violet. Catecholamine-containing cell bodies and fiber terminals were identified by the histofluorescence method. The acetylcholinesterase distribution was histochemically localized. A detailed stereotaxic atlas of the catecholaminergic and acetylcholinesterase-containing structures is presented.

Sequence regularity and geometry of orientation columns in the monkey striate cortex

Abstract: The striate cortex of the macaque monkey is subdivided into two independent and overlapping systems of columns termed “orientation columns” and “ocular dominance columns.” The present paper is concerned with the orientation columns, particularly their geometry and the relationship between successive columns. The arrangement of the columns is highly ordered; in the great majority of oblique or tangential microelectrode penetrations the preferred orientations of cells changed systematically with electrode position, in a clockwise or counterclockwise direction. Graphs of orientation vs. electrode track distance were virtually straight lines over distances of up to several millimeters; such orderly sequences were often terminated by sudden changes in the direction of orientation shifts, from clockwise to counterclockwise or back. The orientations at which these reversals occurred were quite unpredictable. Total rotations of 180–360° were frequently seen between reversals. In tangential or almost tangential penetrations orientation shifts occurred almost every time the electrode was moved forward, indicating that the columns were either not discrete or had a thickness of less than 25–50 μ, the smallest order of distance that our methods could resolve. In penetrations that were almost perpendicular to the surface, the graphs of orientation vs. track distance were relatively flatter, as expected if the surfaces of constant orientation are perpendicular to the cortical surface. Stepwise changes in orientation of about 10° could sometimes be seen in perpendicular penetrations, each orientation persisting through several clear advances of the electrode, suggesting a set of discrete columnar subdivisions. The possibility of some kind of continuous variation in orientation with horizontal distance along the cortex was not, however, completely ruled out. Occasionally a highly ordered sequence was broken by an abrupt large shift in orientation of up to 90°. Shifts in ocular dominance occurred roughly every 0.25–0.5 mm and were independent of orientation shifts. In multiple parallel penetrations spaced closer than about 250 μ the slopes of the orientation vs. track distance curves were almost the same; reconstruction of these penetrations indicated that the regions of constant orientation are parallel sheets. On crossing perpendicular to these sheets, a total orientation shift of 180° took place over a distance of 0.5–1.0 mm. Column thickness, size of shifts in orientation, and the rate of change of orientation with distance along the cortex seemed to be independent of eccentricity, at least between 2° and 15° from the fovea. A few penetrations made in area 17 of the cat and in area 18 of the monkey showed similar orderly sequences of receptive-field orientation shifts.

Uniformity of monkey striate cortex: a parallel relationship between field size, scatter, and magnification factor.

Abstract: This paper is concerned with the relationship between orientation columns, ocular-dominance columns, the topographic mapping of visual fields onto cortex, and receptive-field size and scatter. Although the orientation columns are an order of magnitude smaller than the ocular-dominance columns, the horizontal distance corresponding to a complete cycle of orientation columns, representing a rotation through 180°, seems to be roughly the same size as a left-plus-right ocular dominance set, with a thickness of about 0.5–1 mm, independent of eccentricity at least out to 15°. We use the term hypercolumn to refer to a complete set of either type (180°, or left-plus-right eyes). In the macaque monkey several penetrations were made at various eccentricities in various parts of the striate cortex subserving the fovea, parafovea and midperiphery. As observed many times previously, in any vertical penetration there was an apparently random scatter in receptive-field positions, which was of the same order of magnitude as the individual receptive fields in that part of the cortex; the field size and the scatter increased in parallel fashion with eccentricity. The movement through the visual field corresponding to a 1 mm horizontal movement along the cortex (the reciprocal of the magnification factor) also increased with eccentricity, in a manner that was strikingly parallel with the increase in receptive field size and scatter. In parts of the cortex representing retina, at least out to about 22° from the fovea, a movement along the cortical surface of about 1 mm was enough to displace the fields so that the new position they collectively occupied half overlapped the old. Such an overlap was thus produced by moving along the cortex a distance about equal to the thickness of a left-plus-right set of ocular-dominance columns, or a complete 180° array of orientation columns. It therefore seems that, independent of eccentricity, a 2 mm × 2 mm block of cortex contains by a comfortable margin the machinery needed to analyze a region of visual field roughly equal to the local field size plus scatter. A movement of 2–3 mm corresponds to a new visual field region and to several new sets of hypercolumns. The cortex thus seems remarkably uniform physiologically, just as it is anatomically.

Retrograde axonal transport and the demonstration of non-specific projections to the cerebral cortex and striatum from thalamic intralaminar nuclei in the rat, cat and monkey.

Abstract: The intralaminar nuclei of the thalamus have been examined particularly in the rat but with additional observations in the cat and squirrel monkey, with a view to determining the extent of their connections with the cerebral cortex and/or striatum. Cells in the intralaminar and other thalamic nuclei were labeled by retrograde axonal transport of the enzyme, horseradish peroxidase, from injection sites of varying size in the cerebral cortex and striatum. This system provides a useful means of determining certain parameters of the horseradish peroxidase technique. It is concluded that the degree of retrograde labeling of a cell is primarily dependent upon the number and concentration of its axon terminals in the vicinity of the injection site. Injections of the striatum in the rat and monkey cause intense labeling of many cells in the intralaminar nuclei. Conversely, injections in the medial, frontal and parietal cortex of all three species, though leading to heavy labeling of many cells in the appropriate thalamic relay nuclei, result in only light labeling of relatively few cells in the intralaminar nuclei. Cells in a single intralaminar nucleus, however, though showing a broad topographical relationship, can be labeled from quite wide areas of the cerebral cortex. These results are consistent with the view that the intralaminar nuclei (including the parafascicular and centre median) project densely to the striatum and sparsely and diffusely upon the cerebral cortex.

Connections of the median and dorsal raphe nuclei in the rat: an autoradiographic and degeneration study.

Abstract: Ascending and descending projections from the median and dorsal raphe nuclei of the midbrain were mapped in the albino rat, using reduced-silver stains after lesions or the autoradiographic technique following injections of tritiated proline. In all major respects the two techniques gave the same results. The majority of the ascending projections sweep ventrally from the raphe nuclei, then curve rostrally to course through the ventral tegmentum and into the medial forebrain bundle (MFB). Others radiate through the mesencephalic reticular formation (RF) and central grey, turning ventrally at the posterior thalamic border to enter the subthalamus. From the MFB, fibers branch into the hypothalamus, preoptic areas, anterior amygdala and olfactory tubercle, while some fibers enter the fornix or the stria terminalis. Many fibers continue rostrally in the MFB, joining the diagonal bands of Broca to reach the septal nuclei or, further rostrally, the cingulum bundle. Fibers in the cingulum bundle turn caudally around the genu of the corpus callosum, some branching into the cell-free layers of the pregenual cortex. Runing caudally, then curving around the splenium, the cingulum bundle projection sprays out into the subiculum and in some cases a projection into the hippocampus is seen. Other ascending projections include one to the habenular nuclei through the fasciculus retroflexus. Projections to the mediodorsal, parafascicular and reuniens nuclei of the thalamus were also noted. Descending projections were observed to the dorsal tegmental nucleus and locus coeruleus and diffusely to the pontine reticular formation and caudal central grey. No projections were seen below the level of the facial nerve nucleus and none were observed to the cerebellum, caudal raphe nuclei or cranial nerve nuclei.

Ontogeny of monoamine neurons in the locus coeruleus, raphe nuclei and substantia nigra of the rat. I. Cell differentiation

Abstract: The onset of cell differentiation in the locus coeruleus, dorsal and medial raphe nuclei, and substantia nigra (zona compacta) was studied using the technique of long-survival H3-thymidine autoradiography to date neurogenesis. Pregnant female rats were injected with isotope on day 10, 11, 12, 13, 14, 15, 16 or 17 of gestation. Litters were born on day 22 and allowed to survive for 30 days. Brains were prepared for the fluorescence histochemical demonstration of monoamines or fixed by formalin perfusion. Autoradiography was carried out on sections adjacent to those in which monoamine-nuclear groups were identified by the fluorescence method and also on sections from perfused brains, which were used to facilitate cell counting. The norepinephrine cells of the locus coeruleus began to differentiate (presence of heavily labelled cells) on days 10–13 of gestation, with a peak of heavy labelling on day 12, whereas the 5-HT cells of the raphe nuclei and the dopamine cells of the substantia nigra began differentiating on days 11–15. In the dorsal raphe nucleus, the peak of heavy labelling occurred on day 14, whereas in the medial nucleus this took place on days 13–14. The substantia nigra, on the other hand, peaked on day 13. Cell differentiation was also studied in the cerebellar Purkinje cells and hippocampal macroneurons (pyramidal and polymorph cells) of areas CA3 and CA4, to which the locus coeruleus has been reported to project. Differentiation of these cells commenced on days 14–15 (Purkinje cells) and 13–18 (hippocampal cells), with both cell types peaking on day 15, a full three days after the peak of heavy labelling in the locus coeruleus. Evidence is discussed for the possible neurotrophic role of monoamine neurons in the neurogenesis of monoaminergic receptive cells.

The retrograde intraaxonal transport of horseradish peroxidase in the chick visual system: a light and electron microscopic study.

Abstract: Retrograde transport of horseradish peroxidase (HRP) from the region of retinal genglion cell axon terminals back to the cell bodies has been studied by light and electron microscopy. After injection of HRP into the chick optic tectum, it was taken up by axon terminals and unmyelinated axons as well as by other processes and cell bodies of the outer tectal layers. Subsequently the HRP was obseved in vesicles, multivesicular bodies, cup-shaped organelles and small tubules within axons in the stratum opticum, optic tract, optic nerve and optic fiber layer of the retina with accumulation in the retinal ganglion cell bodies. Pinocytosis of extracellular HRP along the axon shaft was rare. After a short postinjection interval, HRP was found in organelles within the axons of the optic nerve but not in the extracellular spaces. After larger injections or longer postinjection intervals, extracellular HRP diffused from the injection site to the back of the eye, but none was found in the extracellular spaces of the retina; ganglion cells were the only cells of the retina which contained HRP product. HRP disappeared from the cell bodies 3–4 days after transport. These findings suport the concept of intraaxonal retrograde movement of HRP. Within axons the vesicles carrying HRP frequently were partially or completely surrounded by a regualr array of microtubules. Doses of colchicine greater than 5–10 µ/eye administered 4 days before tectal injection of HRP interfered with the uptake and/or transport of HRP. HRP also moved in an anterograde direction in membrane-bound vesicles within the ganglion cell axons, although apparently more slowly and in smaller quantities than in the retrograde direction. The localization of HRP in neurons of the isthmo-optic nucleus following intravitreal injections has also been studied. The marker enzyme was found in neuronal cell bodies 4 hours after injection, indicating a rate of retrograde transport of at least 84 mm/day in these neurons.

Astrocyte-specific protein and neuroglial differentiation. An immunofluorescence study with antibodies to the glial fibrillary acidic protein.

Abstract: The topographical features of the neuroglial network in the mature rat CNS and the differentiation of fibrous neuroglia in the neocortex and hippocampus have been studied by immunofluorescence using antibodies to the glial fibrillary acidic (GFA) protein. In the mature brain and spinal cord the distribution and appearance of neuroglia as observed with immunofluorescence were similar to those described by Weigert ('95) using his method for astrocytic fibers. In the developing rat immunofluorescence started to appear on the surface of the neocortex in the first week after birth. In 9-day-old rats a continuous external glial membrane had formed by immunofluorescence. Immunofluorescence of the perivascular glial membrane appeared later. Blood vessels completely surrounded by a fluorescent membrane were not observed in the middle cortical layers before the eighteenth day of life. An unexpected finding in the hippocampus was the sudden appearance in the 8-day-old rat of a radial system of immunofluorescent fibers crossing the granular layer and extending in the molecular layer. The radial fibers were still present in the adult rat. However, they became widely spaced and thus less prominent than in the immature animal. In fetal rats immunofluorescent fibers first appeared in the medial wall of the lateral ventricles on the eighteenth post-conceptionaly day. The radial system of glial fibers extending from the ventricles to the surface of the brain and characteristic of this stage of development was not stained by immunofluorescence.

A radioautographic study of the efferent pathways of the nucleus locus coeruleus.

Abstract: The projections of neurons in the nucleus locus coeruleus (LC) of the rat were traced by radioautography following stereotaxic injections of 3H-proline. An ascending bundle consisting of a dense cluster of labeled axons accompanied the medial forebrain bundle (MFB) into the lateral hypothalamus. Rostral to the anterior commissure, the labeled fibers contributed to other major pathways: the stria terminalis to the amygdala, and the cingulum bundle and the supracallosal stria to the cingulate cortex, subiculum, and hippocampus. The rest of the ascending fibers terminated diffusely in the pyriform cortex and frontal neocortex. In addition, a lateral group of labeled fibers entered the cerebellum through the superior cerebellar peduncle and terminated around the Purkinje cell somata and in the molecular layer. Descending fibers which entered the medulla either terminated around brainstem nuclei or passed into the ventral portion of the spinal cord. In all areas except the brainstem, the labeling was unilateral with respect to the injection site. This distribution of label from LC provides direct confirmation for connections which have been difficult to visualize in their entirety by any other histological or cytochemical method.

The neuronal architecture of the cochlear nucleus of the cat.

Abstract: A detailed parcellation of the entire cochlear nucleus of the cat was prepared with the Nissl and Protargol methods in the form of a cytoarchitectonic atlas. Neuronal cell types were characterized in rapid Golgi impregnations. Golgi impregnations were used to define the specific features of the mature neuronal types. Neurons from the Golgi preparations were systematically mapped according to type and location in serial sections. These neurons were then plotted in corresponding positions in the cytoarchitectonic atlas. This combined Golgi-Nissl approach provides a scheme in which neuronal types, defined in terms of a number of functionally significant features, can be precisely localized within the cochlear nucleus.

Structure of layer IV in the somatosensory neocortex of the rat: description and comparison with the mouse.

Abstract: The cytoarchitecture of layer IV of SmI neocortex of the rat has been studied in sections parallel and perpendicular to layer IV. The neurons of layer IV are arranged into discrete multicellular units, called barrels, which we have previously described in both mouse and rat. Using the barrels as markers, it is possible to outline precisely a cytoarchitectonic field—the barrel field—which (1) is confined to SmI. (2) has a consistent appearance from hemisphere to hemisphere, and (3) contains at least 220 barrels. A special region of the barrel field has been identified—the posteromedial barrel subfield (PMBSF)—in which the barrels are arranged in five rows and are larger than elsewhere. However, in contrast to other barrels in the rat barrel field and to the barrels that make up the PMBSF in the mouse, the PMBSF barrels in the rat are filled with small neurons nearly throughout the thickness of layer IV. From experimental evidence, it has been possible for the first time to establish consistent homologies between small groups of neocortical neurons in layer IV. The most surprising finding is that homologous barrels in the PMBSF of two closely related species, the rat and the mouse, have such a different cytoarchitectonic appearance. On the basis of this observation, we suggest that a careful study of these PMBSF barrels in the mouse, the rat and other species may provide a clue to understanding how neocortical neuronal circuits of varying complexity are assembled.

The telencephalon, diencephalon, and mesencephalon of the canary, Serinus canaria, in stereotaxic coordinates

Abstract: A stereotaxic atlas of the telencephalon, diencephalon and mesencephalon of the canary, Serinus canaria, was prepared for use in anatomical and behavioral experiments. Canaries have a complex vocal and behavioral repertoire many of whose components are under hormonal control in the male, and are therefore useful for many physiological and anatomical experiments. They are available commercially, breed easily in captivity, are quite hardy and respond well to anesthetic and surgical procedures. The atlas consists of 30 frontal plates from the frontal pole to the level of the motor nucleus of the trigeminus. One sagittal plate is included for reference purposes. Six birds (three males and three females) with marking lesions were used to make the atlas. Their brains were embedded in albumin-gelatin media, cut at 50 and 25μ and stained with cresyl violet for cell bodies, Weil stain for myelinated fibers and the Fink-Schneider method for unmyelinated fibers. Plates were drawn from the cresyl violet series and labeled using all three stains. The completed atlas was tested for accuracy by making 12 small lesions in a number of predetermined discrete loci in several birds and evaluating their placement. Eleven of these lesions were found to be within the targeted structure. The results of this test, combined with the results of experiments in over 50 birds, have shown the atlas to be accurate in 80% of all cases.

An autoradiographic study of the efferent connections of the ventral lateral geniculate nucleus in the albino rat and the cat.

Abstract: The efferent connections of the ventral lateral geniculate nucleus (LGNv) of the albino rat and the cat have been studied using the autoradiographic method for tracing axonal pathways. Following the injection of 3H-proline or 3H-leucine into the LGNv of the rat, label transported in the rapid phase of axonal flow was found bilaterally in the olivary pretectal nuclei, the lateral terminal nuclei of the accessory optic system, and the ventral portion of the suprachiasmatic nuclei of the hypothalamus, and ipsilaterally in the rostrolateral portion of the superior colliculus. Since these regions are known to receive a direct projection from the retina, comparisons have been made of the distribution of silver grains in autoradiographs of each region following injections of 3H-proline into the eye and into the LGNv; in every nuclear region except the superior colliculus the grain distributions were found to overlap precisely and, in the suprachiasmatic nuclei there also appears to be a similarity in the relative intensity of the input to the nuclei on the two sides. In the superior colliculus, the retinal fibers end mainly within the more superficial laminae, whereas those from the LGNv are distributed mainly to the deeper layers where they overlap the projection from the striate and peristriate cortex. The LGNv has also been found to project to the zona incerta on the same side and to the contralateral LGNv, In the cat a similar set of projections to the lateral terminal nuclei of the accessory optic tract, the suprachiasmatic nuclei, and the pretectal areas of both sides has been found, together with a projection to the ipsilateral superior colliculus and the zona incerta of both sides. No evidence could be found in either species for a projection from the LGNv to the visual cortex.

Ordered arrangement of orientation columns in monkeys lacking visual experience.

Abstract: The main object of this study was to see whether ordered sequences of orientation columns are present in very young visually naive monkeys. Recordings were made from area 17 in two macaque monkeys three and four weeks of age, whose eyes had been closed near the time of birth. The first monkey was born normally, but one day elapsed before eye closure could be done. The second was delivered by Cesarean section and the lids sutured shut immediately. The results in these two animals were very similar; in both, highly ordered sequences of orientation shifts were present, and were in no obvious way different from those seen in the adult. For example, average values for the size of orientation shifts, for the horizontal component of the distance between shifts, and for the slopes of orientation vs. track distance curves, were all similar to adult values. This indicates that the ordered column system is innately determined and not the result of early visual experience. In these two monkeys and a third one, sutured at two days and examined at 38 days, most of the cells seemed normal by adult standards, with simple, complex or hypercomplex receptive fields, showing about the same range in orientation specificity as is found in adults. About 10–15% of cells showed abnormalities similar to those seen in monkeys binocularly deprived of vision for longer periods. Furthermore, all three deprived monkeys showed a decided lack of cells that could be influenced from both eyes, whereas a normal three-week-old control animal seemed similar to the adult, with binocular cells comprising over half of the total population. A monkey deprived by binocular closure from the third to the seventh week also showed a diminution in number of binocularly influenced cells, suggesting that the deprivation from birth resulted in a deterioration of innate connections subserving binocular convergence. To be sure that the abnormalities in the deprived animals represented a deterioration of connections, we recorded from 23 cells in a normal two-day-old monkey: here the ocular dominance distribution of cells was about the same as in the adult, and the response characteristics of the cells were normal by adult standards.

Anatomical organization of pretectal nuclei and tectal laminae in the cat

Abstract: Seven nuclei of the pretectum in the cat have been identified and described using material stained for cytoarchitecture and myeloarchitecture, and these have been related to comparable nuclei in other species. These nuclei are termed (1) N. pretectalis anterior, pars compacta and (2) pars reticularis, (3) N. p. medialis, (4) N. p. posterior, (5) N. tractus opticus, (6) N. p. subopticus and (7) N. p. olivaris. Fink-Heimer stains of terminal degeneration following enucleation indicate that retinopretectal fibers terminate primarily contralaterally in nuclei 4, 5 and 7, and in nuclei 5 and 7 ipsilaterally. At least seven laminae in the superior colliculus have been identified by cytoarchitecture: I. Stratum zonale (two sublayers), II. S. griseum superficiale (three sublayers), III. S. opticum, IV. S. griseum profundum, VII. S. album profundum. The lateral nucleus of the periaqueductal gray might be included as the eighth tectal lamina. Ninety percent or more of the terminal degeneration following enucleation is found on the contralateral side, primarily in the first sublayer of lamina II, with small amounts in the second sublayer; the sparse ipsilateral degeneration is limited to the second sublayer.

Restitution of function and collateral sprouting in the cat spinal cord: the partially hemisected animal

Abstract: The hypothesis that collateral sprouting might be correlated with recovery of function was tested by a combination of behavioral and anatomical studies. Partial hemisections, sparing the dorsal columns, were made between T12 and L1 of cat spinal cord. Initially, all reflex and locomotor hindlimb activity was depressed ipsilaterally. During two postoperative weeks behavioral and electromyographic responses increased in response to intrinsic reflex elicitation but not to descending or crossed reflex elicitation. Marked improvement in use of the limb occurred as intrinsic reflex activity increased and became, in some cases, hyperactive. The status then remained stable for ten months. Since intrinsic reflexes are mediated by ipsilateral dorsal roots, the intraspinal distribution of L5 or L6 dorsal roots was determined by degeneration methods ten months after hemisection or by quantitative radioautography 20 days after hemisection. By both methods, the dorsal root distribution was found to be asymmetrical in the spinal gray. It was greater on the experimental side and the distribution was altered, having a greater distribution medially in Rexed's lamina VI and laterally in lamina VII. These anatomical changes are considered as signs of collateral sprouting from dorsal roots in response to degeneration of descending tracts on the same side. Dorsal root distribution to dorsal horn (laminae I–IV), motor nuclei, and nucleus gracilis is symmetrical. Regions of increased and of expanded dorsal root input can be correlated with electrophysiologically determined location of interneurons in the path of cutaneous reflexes and of stretch reflex facilitation. Behavioral and anatomical changes were selective; intrinsic reflexes recovered or became hyperactive and ipsilateral dorsal roots showed evidence of collateral sprouting during the recovery period, although a causal relationship between the two cannot be proven, by the present experiments.

Hippocampal development in the rat: cytogenesis and morphogenesis examined with autoradiography and low-level X-irradiation.

Abstract: The cytogenesis and morphogenesis of the rat hippocampus was examined with the techniques of 3H-thymidine autoradiography, cell pyknosis produced by low-level X-irradiation, and quantitative histology. The procedure of progressively delayed cumulative labelling was used for autoradiography. Groups of rats were injected with four successive daily doses of 3H-thymidine during non-overlapping periods ranging from birth to day 19. They were killed at 60 days of age, and the percentage of labelled cells was determined. The pyramidal cells of Ammon's horn and the polymorph cells of the dentate gyrus are not labelled postnatally, confirming earlier conclusions of their prenatal origin. In the dentate gyrus, 85% of the granule cells are formed postnatally, with 45% forming during the first week. The majority of the small cells of the dentate molecular layer and of the Ammonic strata oriens, radiatum, and lacunosum-moleculare are formed during the second week. As an aid to locating the proliferative compartments of the hippocampus during development and to characterize the time course of both cell differentiation and morphological development, rats ranging in age from gestation day 17 to postnatal day 103 were killed six hours after one exposure to 200r X-rays, and the pyknotic cells were counted. Cell pyknosis in Ammon's horn reaches a maximal level prenatally and declines rapidly during the early postnatal period. Cell pyknosis in the dentate gyrus reaches its highest level during the second postnatal week and declines gradually with some radiosensitive cells still present in the adult. Immature granule cells are also at their highest level during the second postnatal week, while mature granule cells gradually accumulate to attain asymptotic levels at around two months of age. The alignment of the pyramidal cells to form the characteristic curvature of Ammon's horn occurs shortly after pyramidal cell cytogenesis is completed. Conversely, the sharp fold in the dentate gyrus is apparent from the day of birth onward, before the completion of granule cell cytogenesis. Possible mechanisms for the morphological development of the dentate gyrus along with a consideration of the possible migratory route of granule cell precursors is also discussed.

Corticofugal projections from the visual cortices to the thalamus, pretectum and superior colliculus in the cat.

Abstract: Small lesions were placed in visual cortical areas 17, 18, 19, 20, 21, 7, and Clare-Bishop in the cat, and the sites of terminal degeneration seen with Fink-Heimer technique were plotted in thalamus, pretectum and superior colliculus. No degeneration was found in these sites after area 20 lesions; lesions in the other cortical areas gave different patterns of degeneration. Two major patterns were present, one from lesions in 17–18, one from lesions in 21, 7 and C-B, with degeneration from 19 forming a transition between the two groups. Areas 17, 18 and 19 project to the dorsolateral geniculate nuclear complex (LGNd); areas 21, C-B and 7 do not. Area 17 projects to the laminar part, area 18 to both laminar and interlaminar (NIM) parts, and 19 only to NIM. The corticogeniculate projections from all three areas are topically organized anteroposteriorly, and at least that from area 17 is topically organized mediolaterally. Areas 17 and 18 project topically to a columnar locus of the medial pulvinar (=lateral posterior) nucleus which ventrally includes that area known as the posterior nucleus. Area 19 has a double columnar projection to this part of the thalamus, one in the medial and one in the lateral pulvinar area. The medial column lies medial to that from 17–18, and appears to overlap the termination of the ascending projection from the superior colliculus. Cortical areas 21, C-B and 7 also have a double projection to the pulvinar. These findings indicate that the corticorecipient neurons in both medial and lateral sectors of the pulvinar are organized so that dorsal neurons are activated by stimuli in upper visual fields (lower retina) and ventral neurons by stimuli in lower fields (upper retina). Areas 17 and 18 project to the external layer of the ventrolateral geniculate (LGNv) nucleus, 19 to both external and internal layers, and 21, C-B and 7 to internal layer only. The pretectal projection from 17–18 is limited to its caudal pole chiefly in the posterior pretectal nucleus (NPP), and also in the nucleus of the optic tract (NOT). Area 19 fibers terminate in NPP, NOT and also in the reticular part of the anterior pretectal nucleus (NPAr). Those from 21 and C-B end primarily in NPAr, and from area 7 in both reticular and compact parts of NPA. These corticopretectal systems all appear to be organized topically. Areas 17, 18 and 19 have a double termination in the superior colliculus, a focal pattern in the superficial layers (chiefly lamina II), and a diffuse pattern in deeper layers (laminae IV, V, VI). The superficial pattern only provides the retinotopical matching with the optic afferents. All other cortical areas project diffusely to the deep layers. After lesions in 21 and C-B, the superficial foci are larger and centered in lamina III; after area 7 lesions this focal degeneration is centered in laminae III and IV and spread over much of the width of the colliculus. Degeneration to pontine nuclei and inferior olive was not examined.

The adrenergic innervation of the rat thalamus as revealed by the glyoxylic acid fluorescence method

Abstract: The adrenergic innervation of the thalamus, epithalamus, metathalamus, and subthalamus in the rat has been investigated by means of the recently introduced glyoxylic acid fluorescence method. Many areas of the thalamus and adjoining regions, that appear sparsely innervated by catecholamine (CA) fibers in specimens processed according to the standard Falck-Hillarp formaldehyde method, were found to be richly supplied with such fibres in the glyoxylic acid-treated specimens. Moreover, the glyoxylic acid method allows the tracing of the CA axons from the cell bodies up to the terminals, and in combination with stereotaxic lesions the following CA systems to the thalamus could be established: 1 The locus coeruleus system. Most of these axons ascend in the so-called dorsal tegmental bundle through the mesencephalon and the zona incerta into the medial forebrain bundle. From this bundle branches were traced along several routes, giving rise to extensive terminal systems in many thalamic, metathalamic and pretectal areas, most notably the anterior, ventral and lateral nuclear complexes, and the medial and lateral geniculate bodies. 2 The dorsal periventricular bundle, which constitutes a previously not described adrenergic component of the dorsal longitudinal fasciculus. This system originates in cell bodies (defined as the A11 cell group) in the dorsal raphe region, the central gray of the mesencephalon, and in the periventricular gray of the caudal thalamus. The axons ascend within the dorsal longitudinal fasciculus and give rise to a thalamic and hypothalamic periventricular system, projecting to medial and midline thalamic, epithalamic and pretectal regions. 3 Part of the terminals in the paraventricular thalamic nucleus was identified with a non-locus projection from cell bodies in the pontine or medullary reticular formation. 4 A system of delicate, probably dopamine-containing axons was revealed in the caudal thalamus, the zona incerta and the dorsal and anterior hypothalamus. This system probably originates in the dopamine cell bodies of the diencephalic A11 and A13 cell groups, forming a hitherto unknown intradiencephalic dopaminergic system. The adrenergic afferent systems to the thalamus can, to a large extent, be regarded as adrenergic components of known ascending reticular projections. The information on the adrenergic systems obtained with the glyoxylic acid method revealed new features of the organization of the thalamic projections from the brain stem reticular formation.

Restitution of function and collateral sprouting in the cat spinal cord: the deafferented animal.

Abstract: Unilateral hindlimb deafferentation is followed initially by generalized loss of all reflex and useful function. As useful movement returns, certain descending reflexes recover and become hyperactive: crossed reflexes do not. Recovery of movement and reflex hyperactivity are then abolished by subsequent destruction of the ipsilateral descending systems. Although there is no sprouting from contralateral dorsal roots, bilateral degeneration of descending systems is asymmetrical, being greater in density and distribution on the previously deafferented side. Collateral sprouting to certain spinal laminae apparently took place during the recovery period from the same source which mediated reflex hyperactivity; the ipsilateral descending systems. A substantial descending projection to Clarke's nucleus was found only on the experimental side, however, suggesting that a central feedback system replaced the abolished peripheral feedback. If functional, this might subserve recovery of the ability to maintain a limb position. Chronically deafferented cats which are then transected show, for the first time, hyperreflexia of crossed responses, which develops gradually during the first week post-transection. It may be related to sprouting of contralateral dorsal roots for contralateral ganglion injection with 3H-proline gives a larger than normal ipsilateral distribution of grain density over the commissural nuclei. It is suggested that recovery and hyperactivity of reflex responses underlie the recovery of useful movement and that reflex recovery may be related to collateral sprouting. It is also suggested that both the reflex and the anatomical response to a given lesion is restricted to only one of the remaining systems and is therefore a specific rather than a generalized response.

Cytoarchitecture and somatic sensory connectivity of thalamic nuclei other than the ventrobasal complex in the cat

Abstract: This study is a re-examination, using autoradiographic and axonal degeneration methods, of the distribution of spinal, dorsal columnlemniscal and cortico-thalamic fibers within the thalamus of the cat. The emphasis was placed upon making an exact cytoarchitectonic delineation of regions outside the ventrobasal complex which receive spino-thalamic fibers and corticofugal fibers arising in the sensory-motor regions of the cerebral cortex. It is concluded, in agreement with Boivie ('70, '71a,b) that spino-thalamic fibers arising below the level of the lateral cervical nucleus terminate, not in the ventrobasal complex, but in a recognizable portion of the ventrolateral complex adjacent to the ventrobasal complex. This region appears to be also the thalamic relay for Group I muscle afferents. Combined experiments in which, in the same animal, the dorsal column-lemniscal path was labeled autoradiographically and the spino-thalamic path by the Nauta method, indicate virtually no overlap of the two systems in the ventral nuclear complex. Spinal fibers also end in the medial division of the posterior group (Pom), which extends posteriorly as a small-celled zone along the ventromedial aspect of the magnocellular medial geniculate nucleus. Reports of spinal terminations in the magnocellular nucleus proper may result from a failure to recognize the extent of Pom. A third part of the thalamus receiving spinal fibers consists of a posteriorly situated group of large, deeply staining cells belonging to the central lateral nucleus which lie mainly posterior to the internal medullary lamina and which, as Mehler ('69) has mentioned, have previously been confused with the centre median and parafascicular nuclei. Corticofugal fibers arising in the somatic sensory cortex terminate in both the ventrobasal complex and the spinal part of the ventrolateral complex as well as in the central lateral nucleus and Pom and this confirms the work of Rinvik ('68a). Those arising in the motor cortex terminate only in (a different part of) the ventrolateral complex and in the centre median nucleus.

Fine structure of dendritic and axonal growth cones in embryonic chick spinal cord.

Abstract: Our preliminary electron microscopic observations of embryonic chick spinal cord indicate that the majority of synapses in the cervical cord at the fourth and sixth days of incubation are found in the marginal layer rather than the mantle layer. These findings raise two basic questions about the type of connections in the marginal zone during the first week of development: are all these early synapses axondendritic, and are synaptic junctions present on axonal and dendritic growth cones? Since criteria for distinguishing between axonal and dendritic growth cones are scarce or nonexistent, serial section electron microscopy was employed to definitively identify the two types of terminals. Two types of dendritic growth cones are present in the marginal layer during the first week of development. The first type is distinguished by a dendritic stalk which expands into a club-shaped or bulb-like terminal. A characteristic feature of this type of dendritic ending is the presence of numerous vesicles which vary in diameter from about 1000 A to 2500 A. Its cytoplasm has a floccular appearance and is frequently electron lucent. In contrast, the second type of dendritic terminal is electron dense, has a consistently homogeneous appearance, and usually lacks the large vesicles of the first type. The shape of the second type is a finger-like process (filopodium) roughly of the same diameter as the main dendritic trunk. Evidence is presented that some dendritic growth cones observed in this study represent growing, motile processes rather than quiescent enlargements. Synapses on dendritic growth cones are quite numerous and, in addition, the first synapses on dendrites appear to form on growth cones. The hypothesis is put forward that synapses on dendritic growth cones. The hypothesis is put forward that synapses on dendritic growth cones are incorporated onto the dendritic trunk as the terminal continues to grow. Axonal growth cones may be distinguished from dendritic growth cones on the basis of their overall morphology and their cytoplasmic components. An axonal growth cone is, in general, a larger and more irregular structure than the dendritic terminal. This irregularity is due to the large number of processes radiating away from the terminal enlargement or varicosity. While dendritic terminals almost always have finger-like projections, processes of axonal growth cones are more often sheet-like extensions of cytoplasm (folipodia). Another important difference between axonal and dendritic growth cones is that ribosomes in axonal varicosities are infrequently encountered and rarely aggregated into polysomes as in dendritic terminals. Axonal growth cones are occasionally observed to be presynaptic to a dendrite during the first week of development.

Motor and sensory flight neurones in a locust demonstrated using cobalt chloride.

Abstract: The central projections of motor and sensory neurons involved in the control of the wing beat in locusts have been analysed using cobalt chloride introduced axonally. From sections fo cobalt material, components of particular neuropile regions can be identified. The cobalt method offers an important advance in the analysis of insect neuropile. The flight motor neurones in the mesothoracic ganglion are all basically similar in shape, with no clear distinction between elevator and depressor neurones. All have a highly branched dendritic tree which ramifies extensively through the dorsal neuropile. A neurone innervating a particular muscle can be recognised in different individuals by characteristic features but the pattern of dendritic branching is variable. Neurones involved in both flight and walking have some branches in a deeper layer of neuropile than those concerned only with flight, where the branches lie superficially. Sensory projections from the flight sense organs are complex but compact and their positions in the neuropile are very predictable. They have large interganglionic components. The stretch receptors and wing sense organ projections lie mainly in the dorsal neuropile, whereas the other thoracic sensory receptors project ventrally, with branches to the dorsal neuropile at a few specific points. Associations between certain branches of sensory and motor neurones are demonstrated and their implications for the organisation of the flight reflexes discussed. It is suggested that parts of the motor neurone dendritic tree may be functionally equivalent to interneurones.

The upper layers of the superior colliculus of the rat: A Golgi study

Abstract: A number of questions deriving from a previous electron microscopic study of the superficial layers of the rat superior colliculus pointed out the need for a comprehensive study of the cell types of the superior colliculus and their detailed morphology. In the present Golgi study the cells of the superficial layers of the superior colliculus were found to be of five major types; marginal cells, horizontal cells, narrow field vertical cells, wide field vertical cells, and stellate cells. Some of these categories were further subdivided. Each cell type has a distinctive set of dendritic field characteristics, a regional distribution, and consistent axon characteristics. The horizontal cells were found to have a preference in the orientation of their dendrites along the vertical and horizontal axes of the visual field projection upon the superior colliculus. It is argued that the horizontal cells are the presynaptic elements in the majority of the dendrodendritic synapses.

Unmyelinated axons in the ventral roots of the cat lumbosacral enlargement

Abstract: The ventral roots L7 and S1 of the cat spinal cord were examined with the light and electron microscopes. Differences in the morphology of Schwann cells associated with large myelinated fibers and with small myelinated or unmyelinated fibers were observed. The blood vessels were largely encircled by pericytes. The most noteworthy finding was that 29% of the axons in these roots were unmyelinated. These unmyelinated axons were greatly reduced in number proximal but not distal to a ventral rhizotomy. Furthermore, they were reduced in number following dorsal root ganglionectomy, but not after dorsal rhizotomy, sympathectomy or peripheral nerve section. It is concluded that the ventral roots of the lumbosacral enlargement contain a large population of unmyelinated fibers originating from dorsal root ganglion cells.

Synaptogenesis in the photoreceptor terminal of the mouse retina.

Abstract: Observations are presented of a combined light and electron microscopic study of synaptogenesis in the photoreceptor terminal of visuallycompetent mice. Our study suggests that photoreceptor synaptogenesis in these retina progresses through a sequence of postnatal changes which leads to the ordered arrangement of processes within the adult photoreceptor terminal. On the 5th postnatal day, neuronal processes from synaptic contacts with a photoreceptor terminal, usually in the vicinity of a synaptic ribbon. Following the formation of synaptic contacts, the processes invaginate into the photoreceptor terminal, maintaining their position, lateral to a synaptic ribbon. Beginning on about the 10th day, a central process enters the terminal to yield a triad configuration which is a characteristic of a mature photoreceptor terminal. The formation of triads is essentially complete by the 14th postnatal day. Our observations suggest that horizontal cell processes form synaptic contacts with the photoreceptor terminal before bipolar cell dendrites, implying that the horizontal cells mature in advance of the bipolar cells. This possibility is discussed in terms of the appearance of the electroretinogram (ERG) in the developing mouse retina.

Synaptic organization in the dorsal cochlear nucleus of the cat: A light and electron microscopic study†

Abstract: This report describes some observations of the synaptic organization of one region of the cat dorsal cochlear nucleus (DCN). The large “fusiform cell” and its innervation from the cochlea are emphasized. The morphology of the mature fusiform cell and its postnatal development are described in rapid Golgi impregnations of perfusion-fixed littermate cats. The mature features are correlated with profiles of fusiform cell bodies, apical dendrites, and basal dendritic trunks in electron micrographs from adult cat brains. Small neurons and granule cells are also identified in electron micrographs. In Golgi impregnations, axons of small cells and granule cells may terminate upon fusiform cells. Six classes of axons can be distinguished in rapid Golgi impregnations of the DCN. Two classes are of cochlear origin. One axonal class arises from small cells. The sources of the remaining axonal classes have not been identified in this study. Primary afferents can terminate as large, mossy endings in the DCN neuropil. They can also participate in axonal nests along with axons and dendrites of small cells. In electron micrographs, four synaptic endings can be distinguished. Primary cochlear fibers end in large terminals with asymmetrical synaptic complexes and round, clear vesicles. Primary axons can end in glomeruli, resembling those of the cerebellum, or in synaptic nests which are conglomerates of neuronal processes including other types of endings. The origins of the other synaptic types are not yet known. According to this study, primary afferent input could influence fusiform cells directly or indirectly, via small cells and granule cells.

The connections between horizontal cells and photoreceptors in the retina of the cat: electron microscopy of Golgi preparations.

Abstract: Electron microscopy of Golgi preparations reveals that the dendritic terminals of horizontal cells in the cat's retina are connected only to cones. The axon terminals of these horizontal cells connect exclusively to rods. Dendritic and axonal terminals of horizontal cells penetrate the photoreceptor endings to become lateral elements of the invaginations. In addition this study suggests that each cone is in contact with more than one horizontal cell and that each rod connects to more than one axon terminal system. The horizontal cells of the cat are similar to those of the rhesus monkey in that the rod and cone connections are segregated to different portions of these cells.

Synaptic interactions of identified nerve cells in the spinal cord of the sea lamprey.

Abstract: As part of a continuing study on the organization of the lamprey nervous system, two additional groups of interneurons have been identified by physiological and morphological criteria in the isolated spinal cord of Petromyzon marinus. These and other identified nerve cells were tested for synaptic interactions using separate intracellular microelectrodes for stimulation and recording. 1 Edge cells were identified by their unusual location in the lateral fiber tracts of the spinal cord. Their axons extended rostrally either on the ipsilateral or contralateral side of the cord. 2 Some edge cells showed polysynaptic EPSP's and IPSP's after stimulation of sensory dorsal cells, but interactions with other identified neurons were rare. A single cell was excited by a giant interneuron. One edge cell produced IPSP's in a contralateral edge cell, and another produced IPSP's in lateral cells on the opposite side of the spinal cord. Thus, some edge cells have an inhibitory function. 3 Lateral cells were distinguished from giant interneurons and edge cells by their cell bodies in the lateral grey of the spinal cord in the gill and trunk regions, their ipsilateral dendrites, and their long ipsilateral axons extending as far as the tail. 4 Lateral cells were excited and inhibited polysynaptically by sensory dorsal cells and, in turn, produced weak IPSP's in unidentified neurons. Stimulation of lateral cells produced neither visible movements peripherally nor synaptic potentials in other lateral cells, in giant interneurons, or in edge cells. 5 Giant interneurons were previously identified on the basis of their cell bodies in the caudal half of the spinal cord, their bilateral dendrites, and their long contralateral axons extending towards the brain. Giant interneurons exhibited unitary composite EPSP's when more caudal giant interneurons were stimulated. The two components of the EPSP were due to electrical and chemical transmission. Under the electron microscope a contact between a dendrite of one giant interneuron and the probable axon of another had separate junctions resembling chemical and electrical synapses. 6 Intracellular stimulation of sensory dorsal cells produced both monosynaptic and polysynaptic EPSP's in giant interneurons. Some dorsal cells produced unitary composite EPSP's Giant interneurons are part of a convergent, multispecific sensory system extending towards the brain.

Topographical localization in the olivo-cerebellar projection: an electrophysiological study in the cat.

Abstract: Micro-electrodes have been used to record the antidromic responses generated in olivary neurones by electrical stimulation of their axon terminations in the cerebellar cortex. This electrophysiological technique, in combination with precise histological methods for locating postions of the micro-electrode tip, has been used to reinvestigate the topography of much of the olivo-cerebellar projection. The results are partly in accord and partly in conflict with those of earlier investigations in which purely anatomical techniques were employed. In general, the terminations of a circumscribed group of olivary neurones have been found to be located within a longitudinal strip of the cerebellar cortex. Such strips frequently ignore the anatomical landmarks which divide the cerebellar cortex into lobules. The axons of a number of individual olivary neurones have been found to branch to provide a termination in both the anterior and the posterior lobe of the cerebellum. It was also found that olivary neurones projecting to a particular area of cerebellar cortex were in some cases situated in neighbouring regions of more than one of the main anatomical subdivisions of the olive (principal olive and medial and dorsal accessory olives). The discrepancies between the present findings and those made earlier are discussed.