Showing papers in "The Journal of Comparative Neurology in 1971"

Neuron‐glia relationship during granule cell migration in developing cerebellar cortex. A Golgi and electonmicroscopic study in Macacus rhesus

Abstract: The cytology of the postmitotic migratory granule cell and its relationship to Bergmann glial processes was examined with Golgi staining and electron microscopy in the three cardinal planes in the developing cerebellar cortex of Macacus rhesus at various late fetal and early postnatal ages. After final mitosis the granule cell body transforms from a nearly round shape in the superficial zone of the external granular layer to a horizontal bipolar form with elongated processes oriented longitudinally to the folium, at the outer border of the molecular layer. Another descending process develops, and the cell soma becomes a pyramid flattened in the plane longitudinal to the folium. The nucleus moves into the descending process and the cell soma assumes a vertically oriented spindle shape while migrating among previously formed parallel fibers deeper in the molecular layer, and finally attains a round shape again when it lies deep to the Purkinje cell layer. During these transformations, the cell cytoplasm becomes more voluminous and contains a prominent Golgi apparatus, numerous free ribosomes, mitochondria, multivesicular and dense bodies, and fascicles of microtubules Longitudinally oriented microtubules concentrated in the vertical leading process disappear by the time the cell soma enters the granular layer. The slender trailing process loss most of its cytoplasmic organelles, acquires microtubules and together with the horizontal processes forms the characteristic T-shaped axon. The axon forms synapses with Purkinje and stellate cell dendrites at a time when other granule cells are still migrating among them. During the entire course of their migration across the molecular layer, granule cells are directly apposed to vertically oriented Bergmann fibers belonging to the Golgi epithelial cells. The sequence of developmental stages indicates that Golgi epithelial cells are a type of protoplasmic astrocyte. The Bergmann fibers were present at all stages examined, and their constant apposition to granule cells suggests a role in the lartter's migration. Numerous electronluscent beady enlargements are seen along the fiber except at sites were the surface is in contact with migrating cells; probably these enlargements change position as the granule cells pass along the Bergmann fiber. Lamellate expansions also project from the main shaft of the glial fiber and envelop the synaptic sites on spines of Purkinje cell dendrites. These expansions seem more durable, and the young neuron appears to avoid collision with them by sprialling around the glial shaft during its descent to the granular layer. The neuron-glia relationship apparently provides the necessary conditions for the migration of the young granule cell. Especially at late developmental stages when the molecular layer is more than 250 μ wide and is densely packed with highly oriented cell processes that have already established synaptic connections.

The projection of the visual field to the lateral geniculate and medial interlaminar nuclei in the cat

Abstract: Detailed and complete projection maps of the visual field to the whole of the dorsal lateral geniculate (LGNd) and medial interlaminar nucleus (MIN) of the cat have been prepared by plotting the receptive fields of single units in the two nuclei with tungsten-in-glass microelectrodes. The standard projection maps show the pattern of isoazimuths (“horizontals”) and isoelevations (“verticals”) in the two nuclei. Particular attention has been given to the projection of the upper visual field to the posterior part of the LGNd/MIN complex where the shape and relationship of the cellular laminae are changing rapidly. A separate projection of the visual field to the nucleus perigeniculatus (NPG) is also described, but the retinotopic organization of this projection is not as precise as for the LGNd and the MIN. Most of the cells in the NPG are binocularly-activated and the receptive fields have ON/OFF centers. Further observations have been made concerning the distribution of the crossed and uncrossed fibers in the LGNd. In lamina B there is a thick dorsal zone of contralaterally-activated cells and below this is a zone in which ipsilaterally-activated cells are occasionally found. A few binocularly-activated cells were found in the vicinity of the interlaminar regions.

A study of normal and congenitally abnormal retinogeniculate projections in cats

Abstract: Retinogeniculate terminations have been studied by fiber degeneration and microelectrode mapping methods in normal cats and in Siamese cats in which the retinogeniculate pathway is congenitally abnormal. The normal representation of the visual field, including the monocular temporal crescent, has been determined. It has also been shown that there is a cellular discontinuity in lamina A which corresponds to the blind spot or optic disc. In normal cats four geniculate layers receive retinogeniculate terminals; two layers (A and C) receive contralateral and two layers (A1 and C1) receive ipsilateral afferents. In Siamese cats laminae A and C are normal. Lamina A1 is broken up into four main cell segments. Two of these receive a normal input from the ipsilateral temporal hemiretina; two receive an abnormal projection from the contralateral temporal hemiretina. The abnormal projection originates primarily from a vertical strip of retina about 20°–25° in width that lies just temporal to the area centralis. Within this abnormal projection a normal retinotopic sequence is maintained but, since this projection goes to the contralateral instead of the ipsilateral lamina A1, the abnormal segments of lamina A1 receive a mirror-image of the normal representation. Lamina C1 and the medial interlaminar nucleus receive an abnormal contralateral input from the temporal hemiretina similar to that found in lamina A1.

A quantitative study of morphological changes accompanying the initiation and progress of myelin production in the dorsal funiculus of the rat spinal cord.

Abstract: The dorsal funiculus in cervical spinal cords of rats from 3 to 120 days postnatal was studied in order to document and quantitate glial cell development and axonal growth as related to the initiation and progress of central myelination. Within the dorsal funiculus are three major and distinct tracts, each having distinct developmental trends and adult characteristics in terms of fiber sizes and amount of myelin. These tracts are the cuneate and gracile fasciculi and the cortico-spinal tracts. Glial cell counts and cross-sectional surface area determinations of each tract at increasing ages show that the initial rate of glial population increase is similar. However, each tract is unique in terms of the age at which a maximum population density is reached and the rate at which the expected population dilution takes place. An electron-microscopic examination indicates that oligodendrocytes constitute over 85% of the total glial population throughout the development period surveyed. As such, these cells are primarily responsible for the population density changes. The diameters of unmyelixgnated fibers, promyelin fibers and some myelinated fibers in these tracts were measured at 5, 10, 15, 20 and 120 days postnatal. This was done both for the purpose of relating glial population density changes with the initiation and decline of active myelination, and for determining whether or not a critical diameter for myelination exists in the CNS as was found in peripheral nerves (Matthews, '68). For each tract there is a characteristic sequence of events involving not only myelination, but also changes in diameter distribution just prior to the appearance of myelin and during the period of active myelin formation. These events coincide with the concentration and dilution of the glial population, but it is also evident that there is no critical and constant diameter in the CNS above which all axons are myelinated and below which all are unmyelinated. Myelin appears first on larger axons, but as the animal matures, it is found on progressively smaller axons until between 20 and 120 days, axons 0.2–0.4 μ in diameter acquire myelin. Thus, myelination begins with axons destined to be large and then extends down to those which enlarge very little prior to acquiring myelin and remain very small even in adult animals. Finally, from the determination, in adult rats, of the number of axons and oligodendrocytes in a defined volume of each tract and an estimation of internode length, the ratio of internodes to oligodendrocytes was calculated. The specific values obtained could vary by as much as ±50% and are only meant to serve as indicators of a trend. However, it is suggested that the number of internodes per oligodendrocyte may be inversely proportional to the length of the internode.

Ipsilateral afferents to the commissural zone of the fascia dentata, demonstrated in decommissurated rats by silver impregnation

Abstract: An ipsilateral pathway to the commissural zone of the dentate fascia has been demonstrated in the rat using the Fink-Heimer silver impregnation method. The pathway arises in one or both of the CA3c and CA4 hippocampal subfields. As lesions of these structures normally will cause degeneration of commissural fibers terminating in the dentate fascia, animals without commissural fibers were provided for this study. This was done by transecting the hippocampal commissures in eight day old rats which were allowed to survive until the adult stage at which time all stainable, degenerating commissural fibers had disappeared. Lesions involving the CA3c/4-subfields were then made. The resulting degeneration in the commissural zone of the dentate fascia was shown to be of purely ipsilateral origin. Fibers of this pathway display a spread along the longitudinal septotemporal axis of the hippocampal formation. The spread in the “septal” direction (ascent) is in general greater than the descent in the temporal direction, and the more “septal” the lesion is placed, the further does the degeneration extend in the septal direction. The most ascending fibers occupy a juxtagranular position along the medial crus of the dentate granule cells. The most descending (temporal) fibers are seen superficially in the commissural zone along the lateral crus. The pyramids of CA3c and the modified pyramids of CA4 are considered the most probable cells of origin of this system. The ipsilateral system may possibly be absent in normal rats. In view of the early age at which decommissuration was carried out in the experimental animals, axonal sprouting, resulting in the appearance of fibers which may normally be absent, cannot be excluded.

The telencephalon and hypothalamus of the bluegill (Lepomis macrochirus): evoked feeding, aggressive and reproductive behavior with representative frontal sections.

Abstract: Bluegills were stimulated electrically while swimming free in an aquarium containing other bluegills, a mirro, gravel and food. Stimulation sites have been plotted on representative frontal sections for which a nomenclature system was developed. Nestbuilding was evoked in both sexes by stimulation near the area dorsalis telencephali pars centralis, while strong after-responses were elicited from the ventral preoptic region. Stimulation in the preoptic region slightly rostral to the habenula simultaneusly inhibited aggressive behavior and evoked courtship. Feeding (snaping up prey, gravel or debris) and aggressive behavior (chasing and biting another bluegill) resulted from stimulation in the region surrounding the lateral recess of the third ventricle of the inferior lobe of the hypothalamus. In several cases feeding and aggressive responses alternated during stimulation; a similar pattern was observed as an after-response to stimulation in the nucleus rotundus. These results are discussed with regrard to stimulation in the nucleus rotundus. These results are discussed with regard to possible anatomical systems controlling reproductive, feeding and aggressive behavior in fishes.

Methods of fixation and the morphology of synaptic vesicles

Abstract: Cerebellar mossy, parallel, basket and Golgi axons were used to study the variables contributing to vesicle shape. It has been found that, when aldehydes are used as a primary fixative, synaptic vesicles can be either small round vesicles (less than 400 A in diameter), large round vesicles (400–500 A in diameter) or flat, with a ratio of large to small diameters of 2 or greater (500–600 A × 250 A). The proportion of round vesicles as well as the presence and the number of flat vesicles in each axon depend basically upon the osmotic pressure of the buffer. Concentration of aldehydes, duration of the fixation and dehydration, temperature of the fixative, etc. do not affect the synaptic vesicle shape. With buffers (phosphate and sodium cacodylate) of low osmolarity, mossy and parallel axons exhibit a round synaptic vesicle population and no flat vesicles are seen at all. With the same low osmolarity buffers, basket and Golgi axons have a synaptic vesicle population that is mainly round with a low proportion of flat vesicles. As the osmolarity of the buffers is increased, the number of flat vesicles in basket and Golgi axons increases. In mossy and parallel axons the flat vesicles are present with highest osmolarities but always in a lower proportion than in basket and Golgi axons. Quantitative observations indicate that each axon type, under given conditions of fixation, exhibits a mixed vesicle population with a characteristic vesicle ratio. Although this vesicle ratio is modified significantly with changes in the osmotic pressure of the buffer, each axon type exhibits a different and characteristic modification of its vesicle ratio. These observations show that the vesicle ratio and its changes in different conditions of fixation are useful parameters for classifying axon.

Origin and distribution of the amygdalofugal pathways in the rat: An experimental neuronatomical study

Abstract: The fields of origin of the amygdalofugal pathways in the albino rat were studied by using the Fink-Heimer technique to stain degenerating fibers and terminals in brains of animals sacrificed four and seven days after small unilateral lesions of the amygdale. A surprisingly restricted field of origin was found for the supracommissural stria terminalis — the component projecting to the ventromedial nucleus of the hypothalamus Only a lesion in the most posterior part of the cortical nucleus produced degeneration in this pathway. The postcommissural stria terminalis which apparently distributes to the bed nucleus of the stria terminalis and preoptic area originates in a more widespread area including parts of both the basolateral and corticomedial complexes. Although intense terminal degeneration could be seen within the amygdala following all lesions, long fibers projecting into the anterior amygdaloid area, lateral preoptic area and lateral hypothalamus were found only after lesions in which fibers of passage from periamygdaloid cortex could have been interrupted. Convincing evidence, therefore, of a long axon ventral amygdalofugal pathway of the rat was not found in this study.

Hippocampal efferents to the ipsilateral entorhinal area: an experimental study in the rat.

Abstract: A hitherto undescribed pathway from the hippocampus to the entorhinal area has been found in the albino rat in experimental studies by the silver-impregnation technique of Fink and Heimer ('67) and a modification there of by the present author ('70). Animals in which the hippocampal formation had been deprived of commissural and other afferents by a preliminary operation at the age of eight days were used to faciliate the search for the site of origin of the pathway. Lesions in various parts of the hippocampus showed the origin to be restricted to subfield CA3 in approximately the temporal third of the hippocampus. The axons run caudally in the stratum radiatum and stratum lacunosummoleculare, and terminate in the medial part of the entorhinal area in a distinct zone corresponding to layer IV of Lorente de No ('33, '34). By the aid of alternating series of sections impregnated with silver and incubated for acetyl-cholinesterase, the zone of termination was shown to be identical with the acetyl-cholinesterase positive band at the level of layer IV. In the dorso-ventral sense the fibers exhibit a topical organization, terminal degeneration at different levels of the entorhinal area depending on the levels of CA3 damaged. The mean course of the fibers from each level of CA3 seems to be roughly horizontal. A hippocampoentorhinal neuron circuit is proposed.

The olfactory connections of the lateral hypothalamus in the rat, mouse and hamster

Abstract: The afferent olfactory connections of the lateral hypothalamus of the rat were studied by producing lesions of olfactory cortex and staining for degeneration by the method of Fink and Heimer ('67) and by electropysiological recording of responses to olfactory bulb shock and odor stimulation. Direct connections from olfactory areas were found only in a ventrolateral part of the medial forebrain bundle. In the posterior hypothalamus the olfactory fibers turned dorsally and terminated in a more medial area. The region from which strong olfactory responses could be recorded coincided with the path of degenerating axons. Lesions of the olfactory tuercle of hamsters and mice produced a similar restricted pattern of degeneration.

An experimental study of ascending connections from the posterior group of thalamic nuclei in the cat.

Abstract: The cortical projections of the posterior group of thalamic nuclei have been studied in the cat by means of the Nauta technique. Small stereotaxic lesions introduced in such a manner as to cause no direct damage to the main thalamic nuclei adjoining the posterior group or to the overlying cortex, indicate the following pattern of projections: Only that part of the posterior group consisting of the suprageniculate and magnocellular medial geniculate nuclei, and particularly the region of transitions between the two, projects to the cortex. The cortical region of fibers is a band comprising the third auditory area (AIII) of Tunturi, the insular cortex, the banks of the anterior ectosylvian sulcus, zones A and B of Carreras and Andersson ('63) in the upper part of the anterior ectosylvian gyrus, the vestibular projection area, the suprasylvian fringe of Woolsey ('61). It is possible that different parts of the suprageniculate-magnocellular complex project to different parts of this cortical band. The suprageniculate-magnocellular complex and certain parts of the band of cortex to which it projects are regions of multi-sensory convergence. Although all parts of the posterior group as presently defined, have been damaged, no part seems to project to the first (SI) or second (SII) somatic sensory areas (other than AIII and zone B, which overlap SII). The main efferent connections of these parts of the poeterior group appear to be with the striatum. The results can be correlated to some extent with previous studies carried out with the method of retrograde cellular degeneration, but there are certain problems in relation to electrophysiological studies.

An analysis of the posterior group of thalamic nuclei on the basis of its afferent connections.

Abstract: The distribution of the axonal and terminal degeneration in the posterior group and principal nuclei of the thalamus of the cat has been studied with the Nauta technique following lesions of the major ascending sensory pathways and of most areas of the cerebral cortex. The cellular changes occurring in the same parts of the thalamus after damage of the cortex of the somatic, auditory and visual sensory areas have also been investigated. It has been found that the posterior group receives fibers from all parts of the cortex on the lateral surface of the hemisphere caudal to area 4, with the exception of areas 17, 18 and 19 of the visual cortex, and that cellular degeneration occurs in the posterior group after damage of the same areas of cortex. Both fiber and cellular degeneration can be found in the posterior group after a lesion confined to either the somatic sensory or auditory cortex. Experiments with smaller lesions have shown that all areas of the cortex which have been studied send fibers to parts of three distinct types of thalamic nuclei — to the relevant principal nucleus, to a part of the intralaminar group of nuclei or the posterior group, and to a part of the reticular nucleus. After larger lesions of the cortex cellular degeneration is always found in parts of these three types of nuclei. Ascending fibers in the somatic and auditory sensory pathways also terminate in the principal nuclei and in one or other part of the intralaminar nuclei-posterior group system but not in the reticular nucleus. There is a definite interrelationship in the somatic and auditory sensory systems between the site of termination of the ascending fibers of these pathways, the principal nuclei and parts of the posterior group in which these two pathways end, and the area of cortex to which these principal nuclei project and which, in turn, sends fibers back to them and to the posterior group. It is suggested that there is a similar relationship between the site of termination in the intralaminar nuclei of afferent fibers from subcortical structures, the principal nuclei in which the same afferent pathways end, and the area of cortex with which these principal nuclei are related. This appears to be true at least for the pathways from the cerebellum and globus pallidus to the ventrolateral nucleus and the relevant components of the intralaminar nuclei. On the basis of the experimental findings it is suggested that the posterior group should be included with the intralaminar group of nuclei, and that the region equivalent to the intralaminar nuclei-posterior group system for the visual cortex is the pretectum (either the whole or a part) or the nucleus of the optic tract. If this hypothesis is correct there is a continuous, well-organized projection of the neocortex upon the entire extent of the intralaminar nuclei-posterior group-pretectal area complex: prefrontal and limbic cortex being related to rostral intralaminar nuclei, areas 6 and 4 to the parafascicular, centre median and central lateral nuclei, the somatic sensory cortex to the medial division of the posterior group, the auditory cortex to the lateral division of the posterior group, the supra-sylvian cortex to the suprageniculate nucleus and intermediate division of the posterior group and the visual cortex to the pretectum and adjoining regions.

Quantitative cytoarchitectonic distribution of neurons, glia, and DNA in rat cerebral cortex

Abstract: A new technique combining microfluorometric DNA assays with differential cell counts was used to quantitate the intralaminar distribution of neuronal and non-neuronal cells (chiefly glial) in rat somatosensory cortex (Charles River 250 gm males, C D® strain). The intracortical amounts of DNA per unit fresh volume were calculated from the DNA contents of serial frozen slices of known volume sampled serially from the pial surface to white matter in frozen cortical cylinders; respective amounts per unit solids were calculated from predetermined dry weights of the slices. Cell counts were performed on serial horizontal sections from formalin-fixed cylinders stained by Nissl's method. Neuronal DNA and glial DNA were calculated based on the percentages of the respective cells counted. Total DNA averaged 5.43 μg/mg dry weight (1.19 μg mm3 fresh volume). Values were highest in layers II and IV. Neuronal DNA paralleled total DNA in its intracortical distribution and showed distinct peaks in layers II and IV. Glial DNA showed an even distribution. Glia exceeded neurons only in layers I and VIc. The mean neuron/glia ratio was 2.5. This method gives a more precise estimate of the absolute numbers of neurons and glia than can be obtained by histological methods alone, since DNA assays eliminate the need to correct the histological counts for volume changes during fixation and staining.

An autoradiographic study of cellular proliferation in degenerating rat optic nerve.

Abstract: Young adult rats were injected with tritiated thymidine, either before or after removal of one eye, to investigate: (1) the possibility of a leukocytic infiltration into degenerating optic nerve during the first six days following the operation, (2) the origin of the increased number of cells seen in degenerating tissue during the first few weeks after operation, and (3) the possibility of a change in the generation pattern of neuroglial cells in degenerating tissue. In order to investigate the possibility of a leukocytic invasion, rats were injected three times before enucleation to label a high percentage of circulating leukocytes while only labeling a few neuroglial cells. On the operated side of these animals, a small increase in the number of labeled cells above control values occurs only on the third day following enucleation. Another experiment shows that this increase can be explained by a change in the genratiion pattern of the neuroglial cells from two to four days postoperative (2–4 d.p.o.). In degenerating optic nerves, the number of labeled neuroglial cells increase almost tenfold in a 28 hour period from 2–3 d.p.o. While a week is required for a similar increase in normal optic nerve. From 1–3 d.p.o., astrocytes and astrocyte-like cells constitute 30–50% of the labeled cells observed in a pulse label while the remainder of the labeled cells (unclassifiable neuroglia) cannot be categorized as either astrocytes or oligodendrocytes in light micrographs. Our autoradiographic and morphologic studies indicate neuroglial proliferation during the first two weeks of degeneration can account for the numerical increase of cells in optic nerves undergoing Wallerian degeneration. There is no evidence for an important infiltration of leukocytes and/or pericytes into the optic nerve.

Timm's sulfide silver reaction for zinc during experimental anterograde degeneration of hippocampal mossy fibers.

Abstract: The boutons of the hippocampal mossy fibers stain particularly well with Timm's sulfide silver reaction for zinc and other metals. In the present study anterograde degeneration was produced in the mossy fibers in the rat by placing lesions in the fascia dentata, after which the Timm reaction was checked at different postoperative intervals. No unequivocal changes were seen as early as five hours after operation. Barely discernible blanching of the affected parts of the mossy fiber layer was observed after seven hours, a significant reduction of stainability was present after ten hours, and a nearly complete loss after 24 hours. The latter situation persisted for the rest of the period studied, viz., up to eight days after operation. Topographical coincidence of reduced Timm staining with areas of anterograde degeneration was verified by impregnating alternating sections of the sulfide treated tissue according to the reduced silver method of Fink and Heimer. These sections moreover confirmed that the affected boutons retain their structural identity for at least several days after the disappearance of the stainability with Timm's method. These findings are compatible with the concept that the zinc may be associated with some rapidly metabolized substance directly or indirectly involved in synaptic transmission.

Histogenesis of the substantia nigra, ventral tegmental area of Tsai and interpeduncular nucleus: an autoradiographic study of the mesencephalon in the rat.

Abstract: The origin of large neurons of the substantia nigra, ventral tegmental area of Tsai and interpeduncular nucleus was determined in three-week-old rats receiving a single injection of thymidine-H3 during gestation. These neurons underwent final mitotic division on embryonic days 11 through 15 with maximal production on days 14 and 15. Glia and the smallest type of granular neurons were produced from day 11 through 22. Cells in the ventral angle of the neuroepithelium were not labeled one hour after injection of thymidine-H3 in any of the series. Study of animals receiving a single injection of thymidine-H3 during gestation and killed at serial intervals thereafter showed that neurons forming the substantia nigra migrated from the middle third of the basal neuroepithelium and moved between existing cells in radial patterns. Production of neurons specifically for each division of the substantia nigra was not observed either in cross-section or rostrocaudally, nor was the destination of neurons related to their time of origin. The ventral tegmental area of Tsai and interpeduncular nucleus formed from neurons originating in the medial third of the basal plate and migrating almost to the ventral surface of the mesencephalon. The neurons then divided into two streams to create a pattern of an inverted fountain comparable to the distribution of neurons containing catecholamines. Some of these neurons may have contributed to the substantia nigra. The primordia in all three nuclear areas were first seen on embryonic day 18.

Survival of pattern vision after removal of striate cortex in the adult cat.

Abstract: Behavioral, anatomical and electrophysiological data are presented for three cats. One had complete removal of area 17 as evidenced by gross and histological examination of the remaining cortex and by the degeneration in the lateral geniculate body. Dorsal portions of areas 18 and 19 were essentially intact and much of the central and medial interlaminar nuclei of the lateral geniculate body survived. This cat had excellent pattern vision. So too did a cat in which all of the posterior suprasylvian gyrus, dorsal surface of the middle suprasylvian gyrus and much of anterior marginal gyrus had been extirpated. In contrast, an animal lacking area 18 and most of area 19 in addition to area 17, and thus having near “total” degeneration of the lateral geniculate body, was incapable of pattern discrimination. Photically evoked potentials could nevertheless be demonstrated throughout an extensive suprasylvian field in the latter animal. It is concluded that area 17 is not essential for pattern vision in the cat, but that in its absence, even in the case of ablations performed neonatally, cortex receiving major projection from the central and medial interlaminar nuclei, i.e., areas 18 and 19, is required.

Synapses made by myelinated fibers running to teleost and elasmobranch retinas.

Abstract: Myelinated fibers are described in teleost (carp, goldfish) and elasmobranch (dogfish) retinas which make synapses onto amacrine cell bodies and bipolar cell terminals. The fibers run in parallel with bundles of optic nerve fibers radiating from the optic disk until at some point they traverse the inner plexiform layer, turning again horizontally to course under the layer of amacrine cell bodies for 0.5–0.75 mm. En route each fiber makes several en passant synapses characterized by a cessation of the myelin sheath, a local increase in axonal diameter, an accumulation of agranular vesicles 300–400 A in diameter and increased densification of pre- and post-synaptic membranes. These fibers are not post-synaptic to any retinal element. The evidence that the myelinated fibers described form an efferent system is based on their resemblance in many particulars to the centrifugal fiber system innervating the pigeon retina. Degeneration experiments, however, could not distinguish conclusively between a true efferent system, originating in some central nucleus, and a recurrent collateral system branching from afferent optic nerve axons.

Rapid phase of axoplasmic flow and synaptic proteins: an electron microscopical autoradiographic study.

Abstract: Electro microscopic autoradiography was used to study the distribution of labeled proteins in the pigeon optic tectum, 12 hours after intraocular injection of 3H-1-leucine. More than 65% of the grains were detected over synaptic endings, in the fifth layer which is rich in retino-tectal axon terminals. In the first layer which contains retino-tectal fibers 70% of the grains were over axons. These data support the proposition that synaptic proteins migrate rapidly in the axon. Detailed examination showed that silver grains were predominatly located over the axolemma and agranular endoplasmic reticulum in axons, and over mitochondria and synaptic vesicles in neuronal endings.

Projection of dorsal column nuclei and spinal cord to brainstem and thalamus in the tree shrew, Tupaia glis.

Abstract: The aim of this study was to compare the projections of the dorsal column nuclei and spinal pathways to the brainstem and thalamus in Tupaia glis. Animals with unilateral lesions in the dorsal column nuclei or with lateral hemisections were perfused after 5 to 14 days survival time and sections were treated with Nauta or Fink/Heimer silver impregnation methods. The findings indicate that efferent fibers of dorsal column nuclei terminate not only in the thalamus but also in the dorsal accessory nucleus of the inferior olive and bilaterally in the external nucleus of the inferior colliculus. Some fibers terminate in periaqueductal gray and a few in pontine nuclei. In the diencephalon, efferents of the dorsal column nuclei were found to terminate in the posterior group (PO), ventroposterior nucleus (VP) and zona incerta. Spinal efferents were traced to the medial and dorsal accessory nuclei of the inferior olive, medullary and mesencephalic reticular formation, facial and vestibular nuclei, cuneiform nucleus, locus caeruleus, parabrachial nuclei and periaqueductal gray, and also to the external nucleus of the inferior colliculus. Evidence was found of more limited additional spinal projections to PO intralaminar nuclei and VP. The results of this study indicate that the dorsal column system, generally considered to be a phylogenetically new direct pathway to the thalamus, contains other components comparable to some of the spinal efferent connections with the brainstem. Moreover, even in this intermediate form, whose exact taxonomic position is unsettled, the dorsal column-medial lemniscus system to the thalamus appears to be of greater volume than the anterolateral spinothalamic connection.

Ascending brain stem projections of the anteroventral cochlear nucleus in the rhesus monkey.

Abstract: In a series of seventeen rhesus monkeys attempts were made to produce discrete stereotaxic lesions in the anteroventral cochlear nucleus (Av). Anterograde degeneration was described in detail in four cases with lesions confined within the cochlear complex to Av. Fibers decussating at pontine levels coursed exclusively in the trapezoid body. Degenerated fibers projected: ipsi-laterally to the lateral superior olivary nucleus; bilaterally to the preolivary nuclei; to the lateral side of the ipsilateral medial superior olive and the medial side of the contralateral medial superior olive; and to the contralateral medial trapezoid nucleus. A topographic projection upon the medial superior olive was demonstrated. Projections were bilateral but mainly crossed to the nuclei of the lateral lemniscus and central nucleus of the inferior colliculus; the posterior end of the ipsilateral ventral nucleus of the lateral lemniscus contained an island of profuse degeneration. A few fibers crossed in the commissure of the inferior colliculus. Few if any fibers from Av projected to the contralateral magnocellular medial geniculate.

The relations of ependyma to neurons and capillaries in the hypothalamus: a Golgi-Cox study

Abstract: Numerous basal processes of ependymal cells extend peripherally into every cell group and area of the hypothalamus of the four species of mammals examined: mouse, rat, rabbit and cat. With Golgi-Cox impregnation and Nissl counterstaining, ependymal cell processes appear to have a variety of forms and of intricate structural relationships with neurons and capillaries within the hypothalamus. It is proposed that hypothalamic ependymal cells and their processes function as a communication system between the cerebrospinal fluid of the third ventricle and neurons and capillaries within the hypothalamus. The role that such a system may play in the regulation of adenohypophysial function is discussed. It was also noted that in all hypothalamic cell groups, dendrites of some neurons extend to the ependymal layer. An unusual cell, resembling microglia forms, within the infundibular nucleus appears to be selectively impregnated by the Golgi-Cox technique employed. The cell is characteristic of the infundibular nucleus and, with rare exceptions, is confined to that cell group. Some of these spider-cells lie on the ependymal layer and also have endfeet extending to the ventricular surface of the ependyma.

A comparison of somatotopic organization in sensory neocortex of newborn kittens and adult cats

Abstract: To determine the state of functional development in the newborn kitten's somatic sensory system, the organization of mechanoreceptive projections to the sensorimotor cortex was compared to that of the adult Cat. Microelectrode mapping procedures were used. Projections from all contralateral body surfaces to the primary somatomotor cortex (SmI) are present at birth and respond to mechanical stimulation of the receptors. The somatotopic organization of these projections in the newborn kitten is similar to that in the adult cortex with respect to the cortical region receiving projections from each part of the body and to the detailed arrangement of the projections within each of these cortical subdivisions. The relative sizes of peripheral receptive fields, and the intensity of stimulation effective for eliciting a response were similar for projections in SmI cortex of both kittens and adults. At both ages receptive field sizes decreased as their locations approached the distal portion of the limbs or rostral part of the face. In adults and newborns, over 75% of the neuronal responses were elicited by gentle bending of the hairs or light touch to the glabrous skin surfaces. Other similarities between adult and newborn sensorimotor cortexes included: (a) receptive fields of projections to SmI cortex were of fixed, local field type; (b) projections to SmII cortex responded to mechanical stimulation of the receptors; (c) ipsilateral as well as contralateral body surfaces were represented in SmII cortex; (d) the columnar arrangement of neurons and their receptive fields were apparent in the SmI cortex; (e) the coronal sulcus formed a division between the representations of the forepaw and face. Differences between newborn kittens and adult cats included: (a) shorter latency from electrical stimulation of the skin to a SmI cortical response in adults; (b) projections to SmI cortex having “disjunctive” receptive fields were not found in newborn kittens but existed in the adults; (c) the diversity of receptive field types found in neurons of the adult postcruciate MsI cortex was not found in newborn kittens; (d) newborn subjects displayed less variability in the somatotopic organization of projections and less overlap in the receptive fields of projections to SmI cortex. It is suggested that the SmI cortex develops as a point-to-point reflection of the distribution of mechanosensitive receptors in the body and that the complexities in this organization seen in the adult cortex occur during postnatal development.

The role of the arcuate nucleus in the brain-pituitary-gonad axis.

Abstract: Recent evidence indicates that the arcuate nucleus of the hypothalamus is involved in the control of gonadotrophin secretion. In the present work the neurons of the arcuate nucleus were studied in normal and castrated adult male rats with the electron microscope. The neurons of normal animals appear quite ordinary in many respects and contain the same types of organelles that are common to neurons in general. In addition, however, many neurons contain structures resembling the chromatoid bodies commonly found in developing spermatids. There are also some peculiar features of nuclear structure such as nucleolar association with the nuclear envelope and the fragmentation of the nucleolus. Arcuate neurons of castrated animals show two variations, the most obvious of which is the occurrence of whoreled formations of closely apposed concentric cisternae of the smooth endoplasmic reticulum. These whorled bodies appear in several different forms. The simplest consist of complete uninterrupted cisternal rings. Variations from the simple form involve anastomoses between adjacent cisternal shells, areas in which the regular layered structure is obliterated by confluence of cisternal rings, areas of irregular spacing in which varying amounts of cytoplasm are trapped between adjacent rings, and the presence of semicircular incomplete outer rings. As many as five whorled bodies have been observed in a single cell. The whorled bodies in such a group are continuous with one another and with the common endoplasmic reticulum. Whorled bodies appear four days after castration, and by two weeks about one tenth of the neurons exhibit them. Very few whorled bodies appear in castrated animals that received daily injections of 2 μg testosterone propionate per gram body weight. Castration produced no obvious qualitative changes in the ependymal cells or their processes. The second variation resulting from castration is the presence of large populations of dense core vesicles in some of the neurons of the arcuate nucleus. Dense core vesicles are sparse in the neurons of normal animals. The significance of these variations is discussed. There is evidence to suggest that the whorled bodies may be an indication of enhanced synthetic activity following release from gonadal steroid inhibition. In any case, the whorled bodies label the cells in which they occur as direct links in the brain-pituitary-gonad axis.

The areas and layers of corticocortical terminations in the visual cortex of the Virginia opossum

Abstract: Visual cortex in the opossum was defined operationally as striate cortex and the total cortical area receiving ipsilateral projections from striate cortex. This area included all of Gray's ('24) peristriate cortex. In this study several areas were identified within Gray's striate and peristriate areas on the basis of changes in cytoarchitecture and parallel changes in thalamocortical fiber termination patterns. The layers of termination within these cortical areas, of the ipsilateral associational fibers, the commissural fibers and the thalamocortical fibers from the hemithalamus were determined by means of the Fink-Heimer stain. (1) Commissural fiber terminations occur in individual dense “bands” in certain regions of the different cytoarchitectural areas of visual cortex. These bands of commissural fiber terminations are separated by zones of cortex which receive only sparse commissural fiber terminations. The first band of commissural terminations is found in a zone of transitional cortex occupying lateral striate cortex and adjacent peristriate cortex. This band is characterized by terminations in all layers of cortex on the peristriate side and terminations circumscribing the lateral edge of layer IV on the striate side. A second commissural band of terminations lies in anterior and central peristriate areas with terminations in all layers except V. A cytoarchitectural delineation is present in central peristriate cortex between these two bands of commissural terminations. A third band with a laminar pattern of commissural terminations similar to the second band lies more laterally in other peristriate areas along the rhinal fissure and temporal cortex. These three bands broaden at their midpoints to fuse with one another. Commissural terminations are also found in a strip of peristriate cortex on the medial surface of the hemisphere. Characteristic of all commissural terminations in layer I is their restriction to the inner three-fourths of this layer. Subtotal lesions of visual cortex reveal homotopic and heterotopic commissural connections. Central striate cortex has few commissural interconnections. Most of this area receives a few commissural fiber terminations from the lateral portion of striate cortex and also from peristriate cortex. Fibers from the lateral region of striate cortex give rise to terminations which form the band about the striate border as may peristriate cortex adjacent to the lateral striate cortex border. Medial peristriate cortex has homotopic interconnections while the other peristriate areas have both heterotopic and homotopic interconnections. (2) the ipsilateral associational projections from striate cortex terminate mainly in layers I to IV in peristriate cortex. These terminations overlap the zones of peristriate cortex which receive sparse and dense commissural terminations. Degeneration in the lesioned hemisphere revealed tangential fibers in layer I that are present over a large extent of visual cortex. Thermal lesions of only layers I and II of striate cortex show that at least part of the ipsilateral association termination pattern arises from layer II. (3) In each cytoarchitectural area the corticocortical terminations are compared with the thalamocortical terminations and also with such axonal distributions described by Golgi and EM studies in other mammals. It is concluded that the visual cortex of the opossum has the cytoarchitectural subdivisions, and connectional substrate for at least two cortical representations of the visual field and that the fiber connections of the visual system of the opossum contain a basic organization present in other species.

Organization of subcortical projections of visual areas I and II in the rabbit. An experimental degeneration study.

Abstract: Sections prepared by the Nauta and Nissl methods have been used to study the subcortical distribution of axon and cell degeneration in rabbits after lesions in visual areas I and II (V I and V II) of the cerebral cortex. Degeneration was limited to the side of the lesions. Following lesions of either V I or V II, two distinct groups of degenerating axons were traced caudally. (i) One of these groups projected through the optic tract and its subjacent nuclei. The terminal portions of its axons were found to form zones of pericellular fiber (or boutonal) degeneration in the thalamic reticular nucleus (TRN), the ventral and dorsal lateral geniculate nuclei (LGv, LGd), the pulvinar (Pul), the nuclei praetectalis anterior and posterior (dorsal and lateral parts respectively), the nucleus tractus opticus, and the superior colliculus (SC). In the TRN, LGd, Pul, and nuclei praetectalis anterior and posterior the zones of degeneration were disposed into distinct columns. After lesions involving V II the terminal portions of these axons were also seen to form zones of pericellular fiber degeneration in the nuclei praetectalis and posterior (ventral and medial parts respectively), the ventrolateral thalamic nucleus, and the zona incerta. (ii) The second group of degenerating axons traversed the cerebral peduncle and the terminal portions of its axons were shown to form zones of pericellular fiber degeneration in the basal pons. Retinotopically organized projections from V I were recognized in the LGv, LGd, Pul, nuclei praetectalis anterior and posterior (dorsal and lateral parts respectively), and SC; and the evidence reveals the presence of similarly organized projections from V II. Other retinotopically organized projections from the visual areas could not be demonstrated. The data support the view that the collateral branches of visual cortical axons serve as a principal source of input to some of the cellular components receiving innervation from the visual areas. Cellular degeneration was confined to the LGd and then present only with lesions involving V I. With each such lesion, the cellular degeneration formed a distinct column within the LGd, and this column and the one consisting of pericellular fiber (or boutonal) degeneration were consistently found to overlap.

Stellate cells of the rat parietal cortex

Abstract: Stellate cells have rounded or oval cell bodies which contain nuclei bounded by a ruffled, and frequently indented, nuclear envelope. Te cytoplasm of these neurons is usually darker than that of pyramidal neurons because it contains a greater concetration of ribosomes. Where the perikaryal cytoplasm is thick, the granular endoplasmic reticulum is often arranged in parallel arrays. On the surface of the perikarya are three types of synapses: (1) ones with a wide cleft and a prominent postsynaptic density, (2) ones with a wide and straight synaptic cleft that lack a prominent postsynaptic density, and (3) ones with a narrow synaptic cleft and short synaptic complexes. The dendrites of stellate cells lack spines and frequently bear many synapses. On the thinner dendritic branches the type of synapse with a side cleft and a prominent postsynaptic density is most common. The cytoplasm of the dendrites is characterized by closely arranged microtubules.

The anatomy of the brain of the bottlenose dolphin (Tursiops truncatus). Rhinic lobe (rhinencephalon). I. The paleocortex.

Abstract: The bottlenose dolphin, Tursiops truncatus, lacks olfactory bulbs and peduncles as do the other members of the odontocete suborder of Cetacea. Nevertheless the dolphin as well as the other cetacean species studied possess a rhinencephalon or rhinic lobe consisting of prominent olfactory lobes and a very reduced hippocampus covered over, respectively, by small epistriatal (frontal, especially orbital lobes and insula) and huge epihippocampal (parietal, occipital and temporal lobes) Portions of the hemisphere. In the dolphin the demarcation of the rhinic lobe from each hemisphere bilaterad to it is particularly clear and consists of a continuous circular groove (rhinic cleft) composed of posterior parolfactory, anterior and posterior rhinal, rhinohippocampal, hippocampal and callosal segments. Along the trajectory of the rhinic cleft, the cytoarchitectonic demarcation of the paleocortex (olfactory lobes) and archicortex (hippocampus) from the neocortex in the border (limbus) of each hemisphere is equally clear. The rhinic lobe in Tursiops and other Cetacea so far examined thus appears to be a formation of the telencephalon whose distinctness in these species is dramatically emphasized. Topographic disposition of the cytoarchitectonic areas of the paleocortex in Tursiops, Which have not heretofore been described, has been found in this study to be essentially similar to that of other placental mammals. These areas of the paleocortical division of the rhinic lobe (Prepyriform, tubercular, diagonal and periamygdalar areas) are as easily differentiated from one another in this species as in many other mammalian forms.

Mutual contact inhibition of extension of chick sensory nerve fibres in vitro

Abstract: Methods were devised for measuring various aspects of the geometry of nerve fibre outgrowths from chick dorsal root ganglia in short-term plasma clot cultures. Optical birefringence was used as a measure of the magnitude and direction of stresses which developed within the plasma clots during the incubation period. The data obtained indicated that contact guidance of nerve fibres, along fibrin micelles of the medium, is not of prime importance in determining the courses of nerve fibres in non-fasciculated outgrowths. A mutual contact reaction, between nerve fibres, was observed using time lapse cine-photomicrography, and the patterns of nerve fibre outgrowths could be largely attributed to such a reaction. This contact reaction is similar, in many respects, to contact inhibition of locomotion in cultured fibroblasts; and it is proposed that the reaction be termed “contact inhibition of extension.”

Histogenesis of the cerebellar climbing fiber in the rat

Abstract: Early climbing fiber metamorphosis has been studied in 250 Golgi preparations of 5–12 day postnatal rat cerebellum, and in less numerous 12–18 day ones. EM controls were provided for the early phase covering maturation of Purkinje cytoplasm, status of axonal neuropil, and synapses between the evanescent nid structure and Purkinje soma membrane. Ramon y Cajal (1890, '11), Athias (1897) and others have contributed extensively to climbing fiber histogenesis. Our results are confirmatory but support more varied developmental detail including that of axonal collateralization within the granular layer, all of which may not persist to maturity. Distinguishing characteristics of climbing fibers are recognized early in histogenesis, including varicosities, redundancies in course, and a manner of branching called cross-over. The curvaceous path a climbing fiber pursues across the granular layer can be corrected at the ganglionic level by a horizontal segment having length equivalent to the offset. These and other redundancies may straighten out with areal expansion of cortical surface as compared to the restricted white matter base. While supporting multiple innervation of nids by local collateralizations proceeding from stem axons in white matter, the study does not preclude a one to one relationship between adult climbing fiber and Purkinje cell as basic design. Unknown factors are the relative amounts of local collateralization proceeding from several versus a single axon stem, and the extent to which branches are issued from a single fiber to different folia.