Showing papers in "The Journal of Comparative Neurology in 1965"

Autoradiographic and histological evidence of postnatal hippocampal neurogenesis in rats

Abstract: In the autoradiograms of young rats injected with thymidine-H3 many of the granule cells of the dentate gyrus were found labeled. The number of labeled cells declined rapidly with increased age at the time of injection. Histological studies showed the presence in young rats of a large germinal matrix of mitotic cells in the ependymal and subependymal layers of the third and lateral ventricles. The areal extent and cell population of this germinal pool declined rapidly from birth on, with a transient rise with a peak at about 15 days. During this latter period the number of “undifferentiated” cells near the granular layer of the dentate gyrus showed a rapid rise with a subsequent decline. The decline in the number of “undifferentiated” cells was accompanied by a rise in the number of differentiated granule cells. Cell counts in homologous parts of the dentate gyrus indicated a six-fold increase in the number of differentiated granule cells from birth to three months. We postulated that undifferentiated cells migrate postnatally from the forebrain ventricles to the hippocampus where they become differentiated. The possible functional significance of delayed hippocampal neurogenesis is discussed with reference to our finding of incorporation of testosterone-H3 by cells of the hippocampus, implicating that they may function as receptors of gonadal hormones.

A quantitative analysis of the distribution of ganglion cells in the cat's retina.

Abstract: Canglion cell density maps of the cat's retina have been constructed from whole-mounts of the retina stained with methylene blue. The main features of the maps are first, a great increase in density at the specialized central area, and second, a horizontally orientated “arm” of relatively high density extending from the central area into nasal and temporal retinae. The variation of ganglion cell size with density has been examined in the same preparations. This analysis showed that the cells are smallest at the central area, and increase in size as ganglion cell density decreases. Whole-mount preparations have also been made of the monkey's retina, allowing comparison between the central areas of cat and monkey retinae.

Distribution of corpus callosum and anterior commissure in cat and raccoon.

Abstract: The distribution of the forebrain commissures was studied using the Nauta-Gygax silver technique. Following total forebrain commissure transection in the cat the striate cortex or visual area I was remarkably free of degenerating fibers, while peristriate or visual area II showed dense degeneration. Somatic sensory arm and distal hindlimb areas appeared degeneration free while proximal leg and face areas revealed heavy degeneration. The somatic motor area of the anterior sigmoid gyrus contained dense numbers of degenerating fibers. The auditory areas of ectosylvian gyrus showed moderate degeneration over their entire surface except the most ventrally situated cortical areas which were degenerated free. Fibers from the corpus callosum also terminated in the dorsolatearal portions of the head of the caudate nucleus. The anterior limb of anterior commissure distributed mainly to the inner granular layer of the olfactory bulb. In addition, it disseminated considerable numbers of fibers in the anterior olfactory nucleus. The accessory olfactory bulb was degeneration free. The distribution of the forebrain commissures in the raccoon was very similar to the cat. The outstanding feature of the commissural pattern in the raccoon was the total absence of degenerating fibers in the lobular complex relating to the digits of the forepaw.

Sites and mode of termination of reticulo-spinal fibers in the cat. an experimental study with silver impregnation methods.

Abstract: Following lesions in the brain stem reticular formation in 20 cats the ensuing degeneration within the spinal cord has been studied with silver impregnation methods with special reference to the laminar organization of the gray matter described by Rexed ('52, '54). Reticule-spinal fibers do not arise in the mesencephalon. Pontine reticulo-spinal fibers descend in the ventral funiculus, almost exclusively homolaterally. Some cross to the contralateral side in the anterior commissure. Medullary reticulo-spinal fibers descend bilaterally in the ventral part of the lateral funiculus, mostly homolaterally. Both contingents of fibers descend the whole cord throughout. Pontine reticulo-spinal fibers are more numerous than medullary ones. Pontine fibers terminate bilaterally in lamina VIII and adjacent parts of lamina VII. Contralateral terminations are established mainly by way of fibers crossing in the anterior commissure. Medullary fibers terminate chiefly in lamina VII. A few terminations are found in lamina IX, possibly on large α-motoneurons and on small neurons. Reticulo-spinal fibers of both contingents terminate on cells of all sizes, on somata as well as on dendrites.

Electron microscopic study of the developing neuroblast of the dorsal root ganglion of the rabbit embryo

Abstract: The differentiation of the neuroblast of the spinal ganglion of the embryonic rabbit has been studied by phase, light, and electron microscopy from the period of migration of the cells from the neural crest until their transformation into unipolar neurons. The relatively undifferentiated migratory neuroblast, which has single primitive neurite, contains fine filaments and large numbers of ribonucleoprotein particles, but very little membranous endoplasmic reticulum. The presence in the Golgi-centriolar region of large numbers of neurotubules, which probably originate from the centriole, is one of the first signs of further maturation of the neuroblast. The neurotubles migrate into the neurite, where they become a prominent feature during development, particularly in the distal processes. Elements of the immature Golgi complex appear to participate directly in the formation of the membranous portion of the primitive Nissl substance, which develops during the bipolar period. A difference was noted in the fine structure of the processes of the transitional bipolar neuroblast; i.e., one neurite resembles an axon; whereas, the other contains granular endoplasmic reticulum typical of dendrites. The findings of this study are in accord with the concept that the unipolar process arises by constriction and elongation of perikaryal cytoplasm. Two neural cell types, a small cell having randomly disposed organelles, and a larger cell having large clumps of endoplasmic reticulum at the periphery, can be distinguished. The application of the Cajal reduced silver technique to embryonic ganglia, which were subsequently examined with the electron microscope, resulted in a random distribution of silver deposit throughout neural perikarya.

The anterior ventral cochlear nucleus.

Abstract: The anterior cochlear nucleus was examined with a view to describing its subdivisions. The brains of 29 adult rats were paraffin embedded, sliced at 16 μ and impregnated according to the protargol method of Bodian. From examination of this material the nucleus was divided into three major regions. Region III contained round cells with short dendrites which received as synaptic endings two or three bulbs of Held and many terminal rings. The cells of the region gave rise to small diameter (less than 1 μ) nerve fibers which entered the trapezoid body. This region appeared to be identical with region III of Lorente de No. Region II occupied the ventral one third of the nucleus and contained cells of various types, Synaptic endings in this region consisted principally of terminal rings of various sizes and complexities. Nerve fibers which originated in this region were between 1.0 μ and 2.2 μ in diameter and entered the trapezoid body. The region did not conform to region II of Lorente de No. Region I occupied the dorsal two thirds of the nucleus and contained medium and small cells. Synaptic endings consisted of pale, small bulbs of Held. This region differed from region I of Lorente de No.

Cellular localization of monoamines in the upper brain stem of the pigeon.

Abstract: With the help of a highly sensitive and specific fluorescence method developed by Falck and Hillarp, in combination with a pharmacological approach, it has been possible to demonstrate the presence in birds of specific Neurons of two distinctly different types, which in all probability form and store a primary catcholamine and 5-hydroxytryptamine respectively. The amines are in low concentrations in the cell bodies and axons but stored in very high concentrations in the terminals, especially in the abundant varicosities. At least three large ascending monoamine systems appear to be present within the upper brain stem. Many — if not most — of the ascending fibers arise in all probability from cell bodies within the mesencephalon and run rostrally mainly in the medial forebrain bundle. Two of the Neuron systems produce and store a primary catecholamine, one probably giving rise mainly to terminals within the hypothalamus and the preoptic area, the other within the corpus striatum. The remaining system produces and stores 5-hydroxytryptamine. The modified ependyma seems to consist — at least partly — of two types of cells forming and storing either a primary catecholamine or 5-hydroxytryptamine.

Organization of the first and the second somesthetic regions (si and sii) in the rat thalamus.

Abstract: Organization of the rat somesthetic thalamus was studied by a combination of electrophysiologic, stereotaxic, and histologic methods. A monopolar recording electrode was inserted numerous times in any one preparation to explore systemically those thalamic regions which receive somesthetic input. The tip of the electrode was small enough to detect unit activity as well as slow potentials. The recording sites were spaced at 250 and 300 μ distances by using sensitive microdrives in all stereotaxic dimensions. For each recording sire maps were made of the peripheral projection fields which, upon tactile stimulation, evoked strong, medium strong, or weak responses. Punctures made by the recording electrode were reconstructed from sections cut by the freezing method and the geometric arrangement of the recording sites within the thalamus was reconstituted. Two thalamic regions for somesthetic projection (SI and SII) were found in the rat thalamus. They are similar to the first and the second somesthetic areas previously described with the rat cerebral cortex. The thalamic regions encompass the ventrobasal nuclear complex. In the relatively large region of SI there is contralateral projection of the body only. The snout is extensively represented througout this projction region whereas the hindquarters project on a smaller amount of thalamic tissue found in the extreme anterolateral position of SI. Region SII is relatively small. It is situated posterolaterally to SI. The animal's body is represented anew but this time bilaterally; snout dorsomedially, hindquarters ventrolaterally.

Cellular localization of monoamines in the area postrema of certain mammals.

Abstract: The area postrema was studied using a highly sensitive and specific fluorescence microscopical method for the demonstration of certain biogenic monoamines. In all the species studied (rat, guinea-pig, rabbit, cat, dog, monkey) there occur small nerve cells containing a primary catecholamine. A varying number of catecholamine-storing nerve terminals can be demonstrated in all species. Many — if not all — of these seem to derive from catecholamine axons running in abundance just outside the area postrema. Against the background of earlier findings (Vogt, '54; Amin, Crawford and Gaddum, '54) of high levels of noradrenaline and 5-hydroxytryptamine thought to be present in glial cells in this organ it is concluded that these levels are not in accordance with the relatively small number of monoamine-containing structures demonstrated in area postrema. The explanation for this is in all probability that the area postrema tissue taken for biochemical determinations have been contaminated with surrounding brain tissue, very rich in catecholamine and 5-HT containing terminals. There is discussed in conclusion the possibility of adrenergic mechanisms being involved in the reflex path of central emesis.

Organization of the visual projection upon the optic tectum of some freshwater fish

Abstract: In four species of freshwater fish, bass, carp, bluegill and goldfish, the topographical relations of the visual field with the contralateral optic tectum were investigated, using a small light as stimulus in the visual field and recording the electrical response of the tectum with a metal microelectrode. The results show a precisely organized visual projection onto the contralateral tectum in which the anterior visual field lies anteriorly on the tectum, the temporal field posteriorly, the dorsal field medio-dorsally, and the ventral field in the latero-ventral part of the tectum. The projection was found to be essentially linear and uniform with no indication of a specialized area in the visual field in those species investigated. Some receptive fields extended into the anterior binocular visual field.

Effect of visual deprivation on the optic centers of growing and adult mice.

Abstract: The thickness of the visual cortex, the diameter of cell nuclei and the mean volume of internuclear material per nucleus in the visual cortex, geniculate bodies and superior colliculi were determined in growing and adult mice. The influence of prolonged stay in complete darkness was investigated. In the visual cortex of normal mice, a peak in nuclear size occurred 20–30 days after birth, followed by a peak in relative volume of internuclear material. In growing mice, reared in darkness from birth, a highly significant decrease in relative volume of internuclear material occurred in all visual centers. The decrease was greatest in the geniculate bodies and greater in the granular and supragranular layers of the cortex than in the infragranular. In the cortex, the decrease was most pronounced after two months and became less pronounced during prolonged stay in darkness. No similar normalization was observed in subcortical visual centers. In the same mice, visual deprivation caused a highly significant decrease in the thickness of the visual cortex and in the diameter of its cell nuclei. The decrease in nuclear diameter was greater in the granular and supragranular than in the infragranular layers of the cortex and exhibited a similar normalization during prolonged stay in darkness as the decrease in relative volume of internuclear material. In adult mice, visual deprivation caused decrease in internuclear material.

A fine structural analysis of the ventral nerve cord and associated sheath of Lumbricus terrestris L.

Abstract: This study is a fine structural analysis of the earthworm nervous system and its sheath. The bulk of the findings consists of the addition of fine structural detail to the extant descriptions of the general organization of this system. These findings were of particular interest, (1) that the nervous system possesses one basic type of supportive glial cell, (2) that the zonula occludens was not found anywhere in the structures studied here, and (3) that the sheath of the ventral giant axon is not myelin but consists of a thick covering of many tiny axons and synaptic terminals.

An autoradiographic study on the origin and fate of the sub-pial glioblast in the embryonic chick spinal cord.

Abstract: Gliogenesis in the spinal cord was studied in chick embryos ranging in age from 3 to 14 days of incubation using H3-thymidine autoradiography. It has been reported by the author that the neuron production of the spinal cord begins on the third day and ends at the eighth day of incubation. At eight days of incubation glioblasts with small dark round nuclei first appear in the sub-pial region. Using the selective labeling technique with H3-thymidine the author demonstrated that no transition exists from pial cells to sub-pial glioblasts. The glioblasts are produced from the matrix cells by their migration and transformation. These glioblasts mature into neuroglia (oligodendroglia and astrocytes), as development proceeds. The suggestion that the stage of neuroglia differentiation follows that of neuron production in development of the central nervous system has been reconfirmed.

The forebrain of the guinea pig in stereotaxic coordinates.

Abstract: A stereotaxic atlas has been prepared of the forebrain of the guinea pig (body weight 700–830 g) using a standard cat-monkey stereotaxic instrument. The coordinates used were the vertical interaural plane (APO) and the horizontal orbital-interaural plane (HO). The atlas consists of transverse sections of the brain taken at 0.5 mm intervals from A5 through A15.

Electroencephalogram of the chicken recorded from the skull under various conditions.

Abstract: Electroencephalographic studies were carried out on chickens to determine the normal electroencephalogram (EEC) patterns from wakefulness to sleep and the effect of anesthesia. Sixteen electrodes were fixed to the frontal and parietal bones. EEC was recorded under unstressed condition. In the excited state, fast waves of 30 to 60 cps and of low amplitude were predominant. In the resting period, these waves shifted to slower ones of 14 to 24 cps, the amplitude remaining low as in the excited state. As the bird fell asleep, three main stages could be distinguished according to the correlation between the EEC patterns and behavioral states. Under ether anesthesia, four stages could be distinguished according to the EEC patterns and the responsiveness to afferent stimuli. By increasing the dose of nembutal, the correlation between the EEC pattern and the depth of anesthesia was studied. The “spindle burst”, or “barbiturate burst,” and the “fast wave” shown in mammals by the injection of barbiturates were not observed in the chicken.

The medial longitudinal fasciculus and disturbances of conjugate horizontal eye movements in the monkey.

Abstract: In 16 monkeys attempts were made to produce localized unilateral and bilateral lesions in the medial longitudinal fasciculus (MLF) in the pons in order to study resulting disturbances of eye movements and fiber degeneration. Noteworthy physiological findings could be correlated with lesions and fiber degeneration in eight animals. Degeneration was studied by the Nauta technic. Bilateral lesions of the MLF between the abducens nuclei impair all horizontal eye movements, except convergence. Unilateral lesions of the MLF rostral to the abducens nuclei produce: (1) paresis of ipsilateral ocular adduction on attempted lateral gaze and (2) monocular horizontal nystagmus in the contralateral abducting eye. Bilateral lesions in the latter location produce these disturbances bilaterally. Paresis of ocular adduction resulting from lesions in the MLF is associated with ascending degeneration in the MLF projecting differentially upon cells of the ventral nucleus of the oculomotor complex, a cell group innervating the ipsilateral medial rectus muscle. Monocular horizontal nystagmus in the contralateral abducting eye appears to be a consequence of interruption of either: (1) descending fibers in the MLF, or (2) secondary vestibular fibers passing to the opposite abducens nucleus. Unilateral lesions of the MLF rostral to the abducens nucleus produce degeneration ipsilaterally in: (1) the nuclei of the extraocular muscles, (2) the interstitial nucleus (Cajal), and (3) parts of the ventral posterior inferior, ventral posterior medial, parafascicular, centromedian, and recticular nuclei of the thalamus.

The function of the tectum for attention to auditory stimuli in the cat

Abstract: Cats were trained to avoid a shock by moving from one to the other compartment of a double grill box at the onset of a compound signal which consisted of a soft low tone and a bright flashing light. After training on the compound signal unreinforced test trials were given on the tone alone and the light alone. By this procedure the relative potency of sound and light was established for normal cats and cats deprived of various structures in their auditory system. On the basis of this and other subsidiary experiments also reported here, several conclusions seem warranted: 1. In normal cats sound is a prepotent stimulus over light. 2. The prepotency of sound does not depend on the intensities of the competing stimuli. 3. Even with approximately 90% of the second order auditory fibers destroyed, sound is still prepotent over light. 4. Bilateral removal of auditory cortex does not affect the prepotency of sound. 5. Deep bilateral section of the brachia of the inferior colliculus and small bilateral lesions in the apices of the inferior colliculi abolish the prepotency of sound. 6. The loss of the prepotency of sound after midbrain lesions is not the result of a change in absolute threshold for the sound.

Geniculo‐striate connections in the rabbit. II. Cytoarchitectonic structure of the striate region and of the dorsal lateral geniculate body; organization of the geniculo‐striate projections

Abstract: Retrograde changes in the dorsal lateral geniculate body were studied following cortical radiation lesios. The cytoarchitectonic structure of the striate region is described. The peristriate as well as the striate areas are shown to receive projections form the dorsal lateral geniculate body. Thus — as far as this set of connections is concerned — the peristriate are is a subdivision of the striate region. It is further shown that the striate region as defined cytoarchitectonically is —to the extent that it was validated — coextensive with the cortical projection area of the dorsal lateral geniculate body. The dorsal lateral geniculate body is divided into an alpha and a beta sector. Evidence indicates that each vertical column of cells in the striate region receives projections from an appropriate geniculate column which extends throughout the thickness of the alpha sector. The alpha cell columns project upon the striate region in an orderly manner. Details of this organization are described. The cells of the beta sector also project upon the striate region. Whether the pattern of this projection is similar to that of the alpha sector or is more generalized has not been established. Some electrophysiological and experimental-anatomical evidence relevant to the findings is discussed.

“Descending” neuronal units in the commissure of the crayfish central nervous system; and their integration of visual, tactile and proprioceptive stimuli†

Abstract: The integrative properties of “descending” neuronal units in respect to visual, tactile and proprioceptive stimuli were studied at the commissure level of the crayfish central nervous system and 41 entities were established, bringing the total number of established descending entities at this level to 69. All but three of these are interneurons, over half of which have an entirely homolateral input. Altogether 227 interneurons have so far been established in the crayfish central nervous system, 73 of which extend through more than one of the studied levels. Compared to the thoracic-abdominal level, interneurons transmitting both anteriorly and posteriorly are very scarce. The properties of high order interneurons are discussed. In addition to those which respond to visual stimuli, or are multimodal, a number react only to mechanorecptive stimulation, and some of this latter type have peripheral sensory fields exclusively posterior to the recording level. A few interneurons, both visual and non-visual, exibit inhibitory phenomena of various kinds, again mirroring the findings in the mammalian central nervous system. Visual interneurons were shown to respond to specific types of optic stimulation such as movement of objects or changes in light intensity in correspondence with units found in the optic nerves of other decapod crustaceans.

Intralaminar, interlaminar, callosal and thalamocortical connections in frontal and parietal areas of the albino rat cerebral cortex.

Abstract: The present study represents an attempt to relate intracortical connections as seen with the Nauta degeneration method to those seen with the Golgi neuron stain. Lesions were placed in frontal or parietal cortex of 20 albino rats. Fourteen of the brains were prepared with the Nauta ('57) method or a modification of this method (Jacobson, '63). Only in parietal areas 3, 1, 2 were lesions limited to layers I through IV. In these brains the Nauta methods revealed only intercortical (callosal) and interlaminar connections (from II through IV to V and VI). Lesions which extended into layer V of forntal and parietal cortex showed the following connections: intercortical, interlaminar (connecting Vb to VIa); intralaminar fibers (spreading tangentially in V); extracortial to striatum and brain stem. A lesion into layer VI of frontal and parietal cortex showed more callosal and projection fibers, and the intracortical portion of the thalamocortical fiber was cut. Thalamocortical fibers ran tangentially and obliquely in VI vertically in V through I, and tangentially in I, and formed pericellular degenaration in layers VI through IIIb and preterminal degeneration in VI through IIIb, and I. The brains prepared with the Marchi or Gudden method did not show these details. In brains stained with the Golgi rapid method, axons of thalamic and cortical neurons were seen whose distribution corresponded to these connections.

The projection of afferent pathways on the thalamus of the rat.

Abstract: Electrophysiological techniques have confirmed that, except for differences in topographical organization, the projection of afferent pathways upon the thalamus of the rat is very similar to that found in higher mammals such as the rabbit, cat and monkey. Recording of evoked potentials has revealed a predominantly contralateral projection upon the ventrobasal complex, with an extensive snout region medially, foreleg representation ventromedially and hindleg and tail in a small lateral strip. There is a large bilateral projection of afferent pathways on the posterior thalamus—an area caudal to and partially co-extensive with the ventrobasal complex and medial to the medial geniculate body. The only sign of topographical organization in this area is a somewhat lateral representation of hindlegs and tail.

Localization of the terminals of the tongue afferents in the nucleus of the solitary tract.

Abstract: The nerves innervating the tongue were stimulated electrically and multineuron responses were recorded in the nucleus of the solitary tract. Stimulation of the chorda tympani and the IXth nerves evoked responses in the lateral and medial ipsilateral solitary nucleus in a rostral-caudal order. Responses to lingual nerve stimulation were found only in the lateral, larger-celled portion of the ipsilateral solitary nucleus overlapping the chorda tympani and the IXth nerve areas. Stimulation of the above three nerves also evoked somewhat longer latency responses in the ambiguus nucleus. Responses to lingual nerve stimulation were found in the XIIth nerve motor nucleus and the solitary nucleus at the level of the obex using high voltage levels of stimulation. The results were discussed in terms of the anatomical discreteness of the relays of the gustatory and the other tongue modalities in the solitary nucleus. These results were obtained in the white rats.

An electron microscopic study of terminal degeneration in the inferior olive of the cat

Abstract: An electron microscopic study has been made of terminal bouton degeneration in the inferior olive of the cat following interruption of afferent fibers to the olive. Bouton degeneration is found already on the second day, when the boutons show an increased density of the matrix and a close packing of synaptic vesicles. On the seventh day many mitochondria show marked changes. They disintegrate, and their fragments usually fill the bouton entirely. The synaptic vesicles in such boutons have lost their individuality. Most of the degenerating boutons found at later stages are similar to those found on the seventh day. Degeneration proceeds slowly in the boutons. Occasionally mitochondria and synaptic vesicles can be recognized even at the 112-day stage. At this time the degenerating boutons often show vacuolization. Where a degenerating bouton participates in a synaptic complex, thickening of the postsynaptic membrane is found even at the 112-day stage. The dendritic pits found at the 14- and 36-day stages and described in a previous publication (Walberg, '63b) are even more prominent at the one-hundred-twelfth day. Glial activity has not been observed. The relation between degenerating boutons and glial profiles, even at the 112-day stage, is similar to that found in unoperated animals. A very long period is obviously required for the lysis of the degenerating boutons.

Organization of the visual projection upon the optic tectum of a reptile (alligator mississippiensis).

Abstract: Electrical responses were recorded from the optic tectum of the alligator with steel microelectrodes, and the receptive field for each of a series of systematically spaced recording sites was delineated on a transparent plastic hemisphere positioned in front of the contralateral eye. A precise retinotopic relationship was determined with the inferior portion of the retina projecting onto the dorsal surface of the tectum, and the superior portion of the retina represented on the lateral and ventral aspects of the tectum. The equatorial line of the hemisphere is situated laterally and runs obliquely across the tectum from the rostrolateral pole to the caudomedial corner. The center of the visual field occupies a disproportionate amount of tectal space providing for functional magnification. Receptive field size and spacing diminish for the representation of the central region implying a retinal area for increased visual acuity. It is suggested that this alinearity between the visual field and the tectum is expressed in its fiber architecture and is probably a consequence of specialization of the eye rather than an evolutionary modification within the reptilian central nervous system.

Distribution of optic fibers in the cat.

Abstract: This study undertook to investigate pathways and connections of optic tract fibers in the pulvinar, hypothalamus, ventral lateral geniculate, pretectal region and superior colliculus. Thirty-five adult cats were utilized — 28 experimental subjects and seven controls. The right eye was removed and the cats allowed to survive for periods from three to 61 days. The chief method of investigation was the silver impregnation technique of Nauta-Gygax ('54), supplemented by Marchi and luxol-blue cresyl-fast-violet methods. Study of fiber patterns of degeneration in serial sections of the Nauta-Gygax preparations revealed no preterminal axonal degeneration in the hypothalamus or pulvinar. Portions of a completely crossed accessory optic tract as described by Hayhow ('59) were identified. Preterminal degeneration of fine collaterals of the larger optic fibers was found in the dorsal one-third of the lateral portion of the ventral lateral geniculate. Large areas of preterminal degeneration and many fibers of passage were observed in the pretectal region. Localized areas of pretermimal degeneration in this region were interpreted as belonging to the pretectal nucleus and to the nucleus of the optic tract. A large number of fine optic fibers was found terminating in the superficial stratum opticum of the superior colliculus. Two areas of preterminal degeneration lateral to the colliculus were interpreted as extension of the pretectal nucleus and as the nucleus olivaris colliculi.

The retinal structure of (Aotes trivirgatus) the owl monkey.

Abstract: This study reports the results of a light microscope examination of the eyes from 12 Aotes trivirgatus. Direct comparisons were made with the retinae of Macaca cynomologus and Macaca mulatta treated in the same way and stained at the same time. Both rods and cones are present in all Macaca retinae examined but never seen in the retinae of Aotes. The fovea of Macaca is described and the distribution of retinal but an increase in the number of ganglion cells in the fundus indicates an area centralis. Myelin staining is found in the optic fiber layer and inner plexiform layer of Aotes but not Macaca.

Auerbach's plexus of the rat cecum in relation to the germfree state.

Abstract: The cecum of germfree rats, after the second week of life, enlarges sixfold over that of conventional tank-raised controls. Poor muscle tone as well as dietary factors have been incriminated. We have studied the myenteric plexus of the cecum in conventional and germfree rats, in an effort to find a neuronal explanation of the phenomenon and to test whether the neurovegetative periphery is capable of adapting to the changing size. With routine and histochemical technics three salient features stood out: (1) The myenteric neurones in the cecum of the germfree rat on an average were three times larger than those of the controls (42 μ vs 16 μ). Some neurones of the germfree cecum attained giant size (over 150 μ). (2) They showed a lower DPNH diaphorase activity, unrelated to the increased cell size, (3) In the germfree rat cecum the meshes of the primary fiber plexus of Auerbach had increased in size along the antimesenteric border, while the network under the mesenteric attachment was smaller. The ratio between the network of the two sides was 1:12 in the germfree, 1:5 in the controls. We have concluded that the neurones of Auerbach's plexus in the germfree cecum are indeed less active metabolically — a factor which may perpetuate the cycle of cecal distention in these animals. The neurovegetative periphery in the cecum has shown itself capable to responding to the increased cecal volume by neuronal hypertrophy.

The cochlear nuclei in the common porpoise, Phocaena phocaena

Abstract: The structure of the primary cochlear nuclei in three specimens of the common porpoise, Phocaena phocaena, has been studied in transverse and sagittal sections stained for cells (Nissl) and myelin sheaths. A rudimental dorsal cochlear nucleus and a very large ventral cochlear nucleus were found. The large cochlear nerve (nine tenths of the entire VIII nerve) enters the rostral pole of the ventral cochlear nucleus within which it fans out to form ascending and descending fibers. Five subdivisions were distinguished in the ventral nucleus, viz., the anterior part, the posterior part, the dorsolateral part, the dorsomedial part, and the interstitial part. Great similarity exists between the Phocaena and other toothed whales with regard to the structure of the cochlear nuclei. Neither seems any principal difference to exist in this respect between the Phocaena and the landliving mammals, especially when compared with the primates which have likewise a poorly differentiated dorsal nucleus. The five subdivisions of the ventral nucleus of Phocaena presumably are the homologues of the subdivisions distinguished by Fuse ('13) and Lorente de No ('33) in the corresponding nucleus of terrestrial mammals. The enormous size of the ventral cochlear nucleus is the only reliable criterion observed that might reasonably be associated with the extraordinary sense of hearing in Cetacea.

An experimental study of the fornix and hypothalamo-tegmental tracts in the cat.

Abstract: Single electrolytic lesions were placed at various levels of the hippocampus, septum, and amygdala to elicit fiber degeneration from these structures in order to determine their efferent pathways to the hypothalamus. The Nauta silver Impregnation method for degenerated axons was used in this study. Fornix fibers of hippocampal origin were traced to the preoptic, dorsomedial, and posterior hypothalamic areas. Fornix fibers of septal origin were traced to preoptic, paraventricular, and ventromedial hypothalamic nuclei. Degenerated fibers from the baso-lateral amygdaloid nuclei were traced to the preoptic and ventromedial hypothalamic nuclei through the stria terminalis. Lesions were also placed in the anterior hypothalamic area, the dorsal hypothalamic area, the dorsomedial nucleus, the ventromedial nucleus, the paraventricular nucleus, and the posterior hypothalamic area. Degenerated fibers were traced from these nuclei to the midbrain tegmentum through the hypothalamo-tegmental tracts. The hypothalamus, then can be considered a way station for impulses from the limbic lobe to lower brain stem centers.

A degeneration study of the course and extent of the pyramidal tract of the opossum.

Abstract: The pyramidal tract was studied in 12 adult opossums. The method employed consisted of unilateral ablation of the motor cortex followed by selective staining of the resulting fiber degeneration with Nauta's silver technique. The results showed that in the upper part of its course the pyramidal tract followed a course similar to that found in other mammals. It descends in the internal capsule, cerebral peduncle, basal pons and the pyramids of the medulla oblongata where it decussates. It then continues to descend in the dorsal funiculus through the entire cervical cord. In the spinal cord fibers appeared to terminate among neurons at the base of the dorsal gray column. No degeneration could be traced directly into cranial and spinal nerve nuclei.