Showing papers in "The Journal of Comparative Neurology in 1967"

Experimental study of the projections of the nucleus of the tractus solitarius and the area postrema in the cat.

Abstract: Projections from the area postrema and adjacent parts of the medial solitary nucleus are demonstrated with the Nauta method following lesions limited exclusively to these structures. Experiments are controlled with lesions involving adjacent bulbar regions, cerebellum, and spinal cord. Ascending pathways in the dorsal and lateral columns of the spinal cord project ipsilaterally to the area postrema and bilaterally to a para-alar nucleus in the ventral periphery of the nucleus gracilis. Neurons in the area postrema project mainly inspilaterally to the dorsal and medial regions of the medial solitary nucleus. Neurons in the posterior half of the medical solitary nucleus project ipsilaterally to the lateral solitary nucleus, dorsal vagal nucleus, ambigus, retrofacial nucleus, and dorsal and lateral bulbar reticular formation. Projections to nuclei intercalatus and prepositus hypoglossi, bilaterally, and to the ipsilateral dorsal tegmental nucleus by way of the dorsal longitudinal fasciculus are also shown. No direct projections to the diencephalon are demonstrated. Control lesions in the dorsal column nuclei reveal projections to the contralateral inferior olive and thalamic reticular and ventrobasal nuclei, but not to the projection sites of the solitary nucleus. Evidence is given to support the hypothesis that ascening visceral pathways are interruped in the bulbar reticular formation and dorsal tegmental nucleus before reaching the diencephalon. Correlations are suggested with functional aspects of the central autonomic and reticular activating systems.

Thalamic afferents from the spinal cord and trigeminal nuclei. An experimental anatomical study in the rat.

Abstract: Degeneration studies after making lesions involving the spino-thalamic pathways indicate that the projection from any level of the cord to the ventrobasal complex differs from that of the medial lemniscus in that it is less dense and ends largely in the rostral one third in a topographical pattern. Additional projections from all levels of the cord end in the nuclei pretectalis anterior, centralis lateralis, medialis dorsalis and in the medial geniculate body pars medialis and dorsal part of the posterolateral complex. Fibers from the rostral few segments of the cord, possibly from the lateral cervical nucleus, end in addition in the caudal part of the ventrobasal complex and sparsely in the parafascicular-centrum medianum complex and zona incerta. Heavy degeneration was found in all the brains in the brainstem reticular formation. The tritgeminal sensory nuclei project heavily to the dorsomedial cell band of the ventrobasal complex and sparsely to the neighboring part of the posterolateral complex. There is no evidence of a projection from any level of the trigeminal sensory complex to any part of the intralaminar nuclei.

Extensive cortical depth measurements and neuron size increases in the cortex of environmentally enriched rats

Abstract: This study is another in a series of investigations attempting to define the changes in the brain as a consequence of environmental manipulation. Cortical depth and neuron size measurements were taken on brains of rats from enriched (ECT) and impoverished (IC) environments. Celloidin embedded, 10 μ, transverse sections of formalin fixed rat brains were stained wiith thionin. Ten representative sections from each brain were taken, utilizing subcortical landmarks to insure uniform sampling. Cortical depths were measured on microslide projected drawings beginning at the midline and proceeding laterally. The number of readings per hemisphere ranged from 41 to 46. The greatest increases in depth were found in the sections from the posterior commissure landmark. At this position the increases in four regions, proceeding medially to laterally, were as follows: A, 5.2% (p < 0.001); B, 6.3% (p < 0.001); C, 3.2% (p < 0.01); D, 1.6% (NS). Perikarya and nuclear size measurements were taken with a planimeter on microfilm projected outlines. The cortex was divided into upper, middle and lower levels, and within each third, cell size increases were noted, with the outer third showing the greatest increases. The ECT perikarya were greater than the IC by 17.7% (p < 0.001) in the upper level, by 7.2% (p < 0.05) in the middle level, and by 11.6% (p < 0.01) in the lower level.

Relation between the number of myelin lamellae and axon circumference in fibers of vagus and sciatic nerves of mice.

Abstract: Nerve fiber populations of the vagus and sciatic nerves of mice were classified according to the number of myelin lamellae present in the sheaths. This method for classifying fiber populations was superior to others used previously since it provided a more sensitive procedure for the analysis of individual fibers and better control over the technical factors involved in tissue processing. The relationship of the number of myelin lamellae in the sheath to axon circumference was found to be linear. In fresh tissue there was one myelin lamella for every 0.24 μ increase in axon circumference above da value of 2.32 μ (the mean circumference of an average-sized nonmyelinated fiber). A formula was proposed which may be useful for understanding how axons control myelin development and interpreting developmental stages, as well as for evaluating pathologic conditions affecting the peripheral nervous system. The critical diameter above which fibers were found to be myelinated was about 0.8 μ for fixed nerve and 1.1 μ for fresh nerve. The ratio of axon diameter to fiber diameter ranged between 0.5 and 0.9 and was not related to fiber size.

The development of hippocampal and dorsolateral pallial regions of the cerebral hemisphere in fetal rabbits. I. Fifteen millimeter stage, spongioblast morphology

Abstract: The structure of the cerebral hemisphere of 15 mm rabbit embryos was studied with aniline and Golgi stains. Three layers of successively less denselypacked cells were identified in aniline stained sections–matrix, intermediate, and marginal laminae. In the matrix lamina two types of cells were identified in Golgi impregnations: (1) neuroblasts with axons ascending to the intermediate and marginal laminae, (2) spongioblasts attached to the ventricular surface by a short proximal process. Two varieties of spongioblasts can be distinguished according to the mode of termination of long distal processes: (1) typical spongioblasts with claviform enlargements terminating at the pial surface, (2) freely-arborizing spongioblasts with multiple short processes arborizing in the intermediate and marginal laminae. The terminal arbors of freely arborizing spongioblasts, here recognized for the first time, may represent either the growing processes of immature spongioblasts destined to reach the pial surface, or an apparatus having special relations to the embryonic vessels and nerve processes. In the intermediate lamina, pyramidal cells outline the plan of the cortex and subcortical white matter. They have apical dendrites that ascend and ramify in the marginal lamina and axons which descend and turn toward the base of the hemisphere. Neurons with ascending axons are also present, and elements with horizontal axons are located in both the marginal and intermediate laminae.

Somatotopic organization in the spinal trigeminal nucleus, the dorsal column nuclei and related structures in the rat.

Abstract: The medulla of the anesthetized rat was explored with with fine (25.4 μ) wire electrodes from C1 rostrally to the cerebellar penduncles. Concurrently, the body surface and the buccal cavity were mechanically stimulated with delicate probes. Descriptions of peripheral fields and characteristics of evoked discharges were recorded. Histological evidence revealed that the dorsal column nuclei yeilded responses to stimulation of the limbs, trunk, posterior face and pinna. The spinal trigeminal nucleus indicated an input from the face and from buccal cavity components, while the solitary nucleus disclosed an input originating in the tongue and, less often, in other oral structures. In addition, loci in adjacent portions of the reticular formation gave responses to mild stimulation of many peripheral regions. Most of the body projected to every level of the medulla studied. The projection was typically homolateral, and fields of many sizes were represented throughout the longitudinal extent of each nucleus. The amount of bulbar tissue devoted to any region of the body appeared to be related to the innervation density of that region. The results support the concept that the nuclei can be regarded together as a functional unit which resembles the primary tactile systems of the thalamus and the cortex in somatotopic organization.

Thalamic afferents from the dorsal column nuclei. An experimental anatomical study in the rat

Abstract: The distribution of axons originating in the dorsal column nuclei has been studied using the Nauta technique on brains witth lesions restricted to small parts of the gracile and cuneate nuclei. The caudal area of each nucleus projects contralaterally to the ventrobasal complex in a topographical manner and in small amount to the pars medialis of the medial geniculate body. In addition, the rostral part of each nucleus sends axons to the contralateral zona incerta, anterior pretectal nucleus and posterolateral complex within the diencephalon as well as to the collicular plate and pontine protuberance of the brain stem. There is no clear evidence of a projection to the area comparable to the posterior thalamic complex of the cat. This work establishes the identity of some of the cytoarchitectonic divisions of the rat diencephalon, and indicates that the rostro-caudal differences shown for the dorsal column nuclei are reflected in their ascending projections.

Patterns of fiber degeneration in the dorsal lateral geniculate nucleus of the cat following lesions in the visual cortex.

Abstract: Golgi preparations show a group of relatively fine axons ending in the dorsal lateral geniculate nucleus. These, the type I axons, are characterized by many short collateral terminal branches and form a well oriented plexus within the lateral geniculate nucleus. Individual axons distribute terminals to more than one geniculate lamina and some can be seen to come from the region of the internal capsule. Four or more days after damage to the visual cortex, the Nauta method shows relatively fine degenerating fibers that approach the lateral geniculate nucleus from a rostral direction. Some pass straight into lamina a, While others enter the three major laminae via the central interlaminar nucleus. The appearance of this degeneration suggests that the type I axons are cortico-genciulate, as does the sequence of the diencephalic degenerative changes. Thus, relatively coarse corticofugal fibers to the lateral thalamus and tectum show heavy degeneration within three days. The fine axons in the lateral geniculate nucleus show slight, early degeneration after three days, extensive degeneration after four days. They are possibly collaterals of the coarser corticofugal fibers. A second group of coarse fibers which runs laterally from the lateral geniculate nucleus shows early degeneration after four days but does not show consistent and clear degeneration until five or more days. Since retrograde cell changes are already recognizable after four days the third group is regarded as geniculo-cortical.

The superior olivary complex and audition: A comparative study

Abstract: The sizes of the three major nuclei of the mammalian superior olivary complex were examined in a number of different species and variations in size were related to the relative prominence of haring and vision in each species. Size was measured by counting neurons in the several nuclei and by measuring the diameter of the eyes. The lateral superior olive was large in Microchiroptera(3850–4340 cells), guinea pig (3780), cat (3360) and chinchilla (3220); of intermediate size in macaque (1830), rat (1430) and squirrel monkey (1300); and small in gerbil (1220), mouse (1190), hedgehog (1090), squirrel (1000) and hamster (980). These data suggest that this nucleus is necessary for complex auditory discriminations (echolocation in Microchiroptera, for example) and that its size is not primarily determined by the taxonomic order of the animal. The medial nucleus of the trapezoid body was large in cat (5910), guinea pig (5840), hedgehog (4620) and chinchilla (4590); of intermediate size in rat (3870), Microchiroptera (3700) and macaque (3120); and small in squirrel monkey (2600), squirrel (2700), gerbil (2680), mouse (2270), and hamster (2130). The size of the nucleus was not related to sensory development or the size of the other olivary nuclei. The size of the medial superior olive was found to be highly correlated with the size of the VIth nucleus and eye diameter.

Pattern and field in cortical structure: the rabbit.

Abstract: Previous attempts at classification of cortical neurons have been based on a number of anatomical characteristics, some of doubtful physiological significance. In seeking a functionally more relevant scheme, we have based our classification on three neural attributes; (a) size and shape of the dendritic domain, (b) presence or absence of dendritic spines, and (c) intra or extra-cortical trajectory of the axon, as revealed in Golgi stained material. Our data indicate that neurons with extra-cortically projecting axons (long axons) invariably possess spine-rich dendrites forming domains with remarkably regular horizontal parameters (i.e. modular domains). Cells with axons limited to intra-cortical paths (short axons) are characterized by spine-poor or spine-free dendrites forming domains which are highly variable in size and shape. These two categories appear dependant on structural characteristics related both to input and output functions of cortical neurons, and are called Class I and II, respectively. The significance of synaptic arrangements along horizontal and vertical components of Class I dendritic modules are compared with those for Class II cells, and possible relationships between dendritic structure and temporo-spatial activity patterns are considered.

Histogenesis of the dorsal and ventral cochlear nuclei in the mouse. An autoradiographic study.

Abstract: The time, site of origin and migration pathways of neuroblasts destined for the dorsal and ventral cochlear nuclei in the mouse have been determined autoradiographically. Neurons of the dorsal cochlear nucleus arise on gestation days 10 through 13, neurons of the ventral cochlear nucleus on days 10 through 14. Neurons of both nuclei arise within the primitive ependyma of the caudal extent of the primary rhombic lip at the level of the lateral recess; neurons of the dorsal cochlear nucleus arise caudal to neurons of the ventral cochlear nucleus. Granular cells arise on days 12 through 18 within the primitive ependyma of the secondary rhombic lip at the same levels.

Electron microscopic studies of the dentate gyrus of the rat. II. Degeneration of commissural afferents

Abstract: Experimental degeneration of the commissural afferents to the dentate gyrus of the rat has been studied using the electron microscope. Four and six days after unilater fimbrial section, unequivocal degeneration of axon terminals is found in the inner part of the molecular layer of the dentate gyrus of the opposite side. The affected endings are in synaptic contact both with the shafts of the granule cell dendrites and with the short dendritic spines which occur on the granule cell dendrites in this part of the molecular layer. These degenerating terminals show changes ranging from an increased axoplasmic density with aggregation of the synaptic vesicles, to a complete disappearance of the vesicles and mitochondria, and the engulfment of the endings by glycogen-containing processes of glial cells. There is no proliferation of neurofilaments at any stage during this degeneration. Glial processes in the vicinity of degenerating axon terminals show reactive changes in the form of swelling and accumulation of glycogen, and probably proceed to phagocytosis of the degenerating nerve endings. On the side of the lesion the glial cells also show fibril proliferation, an even greater accumulation of glycogen, and a variety of ingested cellular debris.

Cortical projections from the dorsal lateral geniculate nucleus of cats

Abstract: Lesions were placed in the dorsal lateral geniculate nucleus of cats (LGN) and cortical degeneration studied with a modified Nauta method. Besides local degeneration attributable to the electrode track, dense projections to Areas 17 and 18 ipsilateral to the lesion were found. Medium or dense degeneration was found on both banks of the suprasylvian fissure ipsilaterally and light degeneration widely distributed in Area 19 and on the suprasylvian and posterior ectosylvian gyri. In addition to commissural degeneration homotopic to the electrode track, degenerating fibers were found in the visual areas of the opposite hemisphere, suggesting the presence of a crossed geniculo-cortical pathway.

An electron microscope study of types of receptor in the chick retina.

Abstract: Rods, double cones which comprise a principal and an accessory cone, and two types of single cones occur in the chick retina. The rod is narrow and contains a paraboloid, a basal nucleus and a small synaptic body with long synaptic lamellae. The principal cone has a pale-staining oil droplet and is aligned against an accessory cone, which has a paraboloid, no oil droplet, but a small granular vesicle instead. The synaptic body of the principal cone is large and partly surrounds that of its associated accessory cone. The synaptic body of the accessory cone has a long process extending into the outer plexiform layer. Single cone type I has a dark oil droplet and the mitochondria in the ellipsoid are dense with cristae. Single cone type II has a lighter-staining oil droplet and fewer cristae. The synaptic bodies of both types of single cone lie vitreal to those of rods and double cones. Fibres connect the synaptic body to the nuclear region in single cones and accessory cones, but not in rods and principal cones. Another type of synaptic body, which is not that of a receptor, occurs in the outer plexiform layer. Groups of small vesicles, like those in the synaptic body, occur near the base of the inner segments; synaptic vesicles may originate here. Muller cells separate each receptor, except the members of a double cone, at the outer limiting membrane and may position the receptors in relation to the pigment epithelium to allow a radial orientation of the inner and outer segments.

Formation and differentiation of the external granular layer of the chick cerebellum.

Abstract: To examine the formation and differentiation of the external granular layer, chick embryos ranging in age from two to 20 days were treated with tritiated thymidine and sacrificed after various time intervals By studying the migration of the labeled cells at different stages of development, the following observations were made: (1) cells originating from the neuro-epithelial layer along the ventricular surface of the cerebellar plate migrate through previously formed cell layers of neuroblasts to the surface; (2) the development of the lateral portion of the cerebellar plate is approximately 24 hours more advanced than that of the medial region, thus explaining the appearance of the external granular layer first laterally and then medially; (3) at no time during development can a proliferation center be found in the ventrolateral angle of the fourth ventricle Based on theses results, it is concluded that the cells of the external granular layer originate from the neuroepithelium bordering the ventricular surface of the cerebellar plate and migrate from this position straight to the surface No evidence for a surface migration from the ventrolateral angle in a dorsomedial direction can be found Shortly after the formation of the external granular layer at day six, its cells begin to proliferate During this period, which lasts until day 15, relatively few cells leave the external granular layer to migrate inwards After this day a massive inward migration occurs, and the cells of the external granular layer differentiate into the granular cells and perhaps the glia cells In the internal granular layer they intermingle with the Purkinje cells and Golgi II neurons, which originate in the neuro-epithelial layer between days three and six of development Shortly after hatching, when the external granular layer has fulfilled its function in cell production, it disappears

The structure and function of the Haarscheibe

Abstract: Haarscheiben have been studied in several species, using light and electron microscopy as well as electrophysiological techniques. These specialized plates of epidermis contain many Merkel Cell-neurite complexes arranged just above the basement membrane and beneath a row of colmnar cells. The adequate stimulus for evoking responses in the sensory nerve fibers serving Haarscheiben is pressure upon the tylotrich (hair) which, in turn, compresses the Haarscheibe, a highly sensitive, slowly adapting, modality-specific touch receptor. The pattern of distribution and innervation of Haarscheiben in rats has been mapped. The ultrastructure of the Merkel cell-neurite complex reveals that myelinated neurites lose their myelin within a few microns of the epidermis and penetrate the basement membrane, to end as disciform terminals upon the bases of Merkel cells. Merkel cells probably serve an important function in transducing mechanical force into neural action potentials, and their cytoplasmic granules may play a role in this function.

Mitotic division of neuroglia in the normal adult rat.

Abstract: Twenty-four adult rats were given an injection of 3H-thymidine at 4.00 p.m. and sacrificed two at a time everyhour for the next 12 hours. Another 24 adult rats were similarly treated but after inejction at 4.00 a.m. The brainswere fixed by immersion in Bouin fluid. Sections were stained with hematoxylin-eosin and radioautographed. In another experiment two animals were sacrificed two and nine hours respectively after 3H-thymidine injection and the brains were fixed in formalin. The sections were stained by silver impregnation and radioautographed. One hour after 3H-thymidine injection, a number of glial nuclei were labeled: all were in intrphase. By 2–3 hours, labeled mitotic figures appeared and increased in number with time. From 4–5 hours after injection on, pairs of labeled nuclei were seen in increasing numbers. This sequence of events, which was observed with slight differences in the two main groups, indicated that labeled glia nuclei go through mitotic division. It is concluded that a low degree of mitotic activity continually takes place in the glial population of adult rats. About one fifth of the divisions seem to be in microglia. Most of the others seem to occur in cells of the oligodendrocyte family.

Ascending projections of the lateral lemniscus in the cat and monkey

Abstract: The ascending connections of the lateral lemniscus were studied in the cat and squirrel monkey (Saimiri sciureus). In both species, the central nucleus of the inferior colliculus receives a massive projection from the lateral lemniscus. Only a few lemniscal fibers were found to terminate in the external nucleus of the inferior colliculus. The commissure of the lateral lemniscus originates from the dorsal nucleus of the lateral lemniscus and projects to the contralateral dorsal nucleus and the contralateral central nucleus of the inferior colliculus. No lemniscal fibers were seen ascending in the inferior brachium or terminating in the principal division of the medial geniculate body. A bundle of fibers was observed, however, which passed medial to the inferior brachium and terminated in the magnocellular or internal division of the medial geniculate. The bundle degenerated after lesions confined to the lateral lemniscus and is probably identical with the central acoustic tract of earlier workers. Evidence is presented that the fibers of the bundle are of spinal origin. Since the lemniscal fibers which ascend to the thalamus appear to be non-auditory, it is suggested that the inferior colliculus is an obligatory relay station in the classical auditory system and that the inferior brachium is the only ascending pathway of the system to project upon the thalamus.

Comparative fine structure of vertebrate neuroglia: Teleosts and reptiles

Abstract: Electron microscopic examination of aldehyde perfused fish and reptile brains reveals the presence of three distinct varieties of glial elements; ependyma, astrocytes and oligodendrocytes. Ependymal cells line the ventricular cavity, possess cilia and extend long fibrillar processes to the pial surface. Several cytoplasmic organelles and specialized plasma membrane contacts are unique to this glial variety. Astrocytes possess long processes which can be traced as pericapillary and sub-pial end-feet. Their cytoplasm contains fine filaments (less than 100 A) and quantities of glycogen granules. Oligodendrocytes display only occasional long processes and usually have thin cytoplasmic rims, especially when related to myelinated axons. A wide range of nuclear and cytoplasmic matrix densities, numerous free ribosomes and an extensive microtubular system characterize these cells. On the basis of distinctive cytoplasmic organelles it appears possible to establish the homology of lower vertebrate and mammalian glial elements.

Observations on the fine structure and distribution of presumptive baroreceptor nerves at the carotid sinus.

Abstract: Comparative nerve fiber counts show that the areas of the carotid bifurcation receiving a rich innervation correspond in extent to areas of the vascular wall with a thinned and elastic tunica media. Presumptive baroreceptor nerves within the carotid sinus wall were examined by electron microscopy in normal rabbits and also after superior cervical ganglionectomy and/or Hering's nerve transection. The glossopharyngeal (baroreceptor) nerve terminals are either denuded of a cellular covering or are thinly clothed in Schwann cell cytoplasm, and are intimately related over wide areas to at least three sinus wall components: to elastin at the medio-adventitial border, to collagen in the inner one-half of the adventitia, and to the surfaces of isolated adventitial smooth muscle cells. These muscle cells also receive a terminal innervation from the superior cervical ganglion. There is no nervous penetration of the sinus tunica media. The spatial arrangement of the adventitial muscle cells and their associated sensory and motor nerves simulates a smooth muscle spindle, possibly constituting a morphological basis for an efferent control of baroreceptor output. The baroreceptor nerve terminals contain large accumulations of mitochondria, and also myelin figures and small dense bodies resembling glycogen granules. Evidence is presented that baroreceptor impulses may be conveyed from the sinus wall in both myelinated and nonmyelinated nerve fibers.

The course and termination of the striae of Monakow and held in the cat

Abstract: The course and termination of the stria of Monakow and stria of Held were studied with Nauta-Gygax technique following a localized lesion of the dorsal cochlear nucleus in the cat. A dense preterminal degeneration within all homolateral primary cochlear nuclei and a tract of degenerated fibers crossing the restiform body dorsally were found. This tract divides in two branches forming the stria of Held and stria of Monakow. The stria of Held followed the course described by classical anatomists. In the homolateral side, the stria gave terminals to the medial and lateral preolivary nuclei, lateral superior olive nucleus and retro-olivary groups. In the contralateral side, preterminal degeneration was found in the medial preolivary nucleus and medial retro-olivary group. The stria of Monakow is essentially crossed pathway given numerous terminals to the contralateral dorsal retro-olivary group, rostral part of the lateral preolivary nucleus, the ventral and dorsal nuclei of the lateral lemniscus, and nucleus of the inferior colliculus.

Architectonic studies of the telencephalon of Iguana iguana

Abstract: With the atrophy of the aquatic olfactory organ and the increased complexity of locomotion, the amphibian telencephalon was reorganized from a structure dealing primarily with olfaction, to the reptilian structure functioning at four levels of organization. The primary olfactory centers are retained, and the posterolateral and medial basal regions become specialized as secondary olfactory centers. The anterolateral basal regions are reorganized as primary association centers of somatic information. A dorsal component develops due to the convergence of sensory modalities, and a ventral component develops which influences tectal centers. Three pallial elements are recognized which function as part of the primary and secondary association systems. The lateral pallial element (pyriform cortex) is functionally related to the secondary olfactory system. Part of the medial pallial element (dorsomedial hippocampal cortex) is functionally related to the secondary olfactory system while the other part (dorsal hippocampus) is related to the secondary association system. The secondary association system, which integrates all sensory modalites, has evolved along two lines in reptiles. The sauropsid line has lost the motor elements of the dorsolateral component of the dorsal pallium. The dorosomedial component of the dorsal pallium retained its motor elements and functions with the hippocampus as a transitional cortical structure. In the theropsid line, the motor elements of the dorsolateral component were retained in a system which bypasses the older tectal motor system.

Excess vitamin A and development of the cerebral cortex

Abstract: In previous experiments excess vitamin A, administered to pregnant rats during the early stages of gestation, was found to interfere with the mitotic activity of the neuro-epithelial cells bordering the neural groove. The result was exencephaly and anencephaly in a high percentage of the newborn. The present work was undertaken to examine the influence of hypervitaminosis A on the behavior of the neuro-epithelial cells of the cerebral hemisphere and the subsequent migration and differentiation of the neuroblasts during the later stages of development. Swiss-Webster mice were treated with large doses of vitamin A on days 14 and 15 of gestation. When subsequently the cell cycle of the neuro-epithelial cells lining the lateral ventricle of 15-day fetuses was determined, vitamin A was found to increase both the duration of the mitosis and DNA synthetic period. In comparison with the controls, the total generation time was prolonged by approximately 40%. Since almost all neuroblasts of the cerebral cortex originate in the neuro-epithelial zone bordering the lateral ventricle, the total number of neuroblast formed is in all probability less than normal. Indeed, prelimiinary data on the number of cells present in the cerebral cortex of 10-day postnatal rats treated with excess vitamin A toward the end of pregnancy showed a decrease in cell density, indicating either a reduction in the number of cells formed or a degeneration of existing cells. In a second experiment Swiss-Webster mice were treated with excess vitamin A during three successive days in the second half of pregnancy. The cerebral cortex of the newborn was examined one to ten days after birth. Histological examination revealed a rather sharply delineated zone of abnormal cells characterized by a lightly stained cytoplasm, a thick nuclear memberane, a desely stained nucleoplasm and several dark chromatin bodies. When the position of the zone containing the abnormal cells was analyzed and correlated with the day of formation in the neuroepithelial zone, it was found that the affected cells were neuroblasts already present in the cortex before the vitamin treatment was started. This indicates that excess vitamin A, given to pregnant mice during the later stages of gestation, influences the development of the cerebral cortex, not only by interfering with the production of cells in the neuroepithelial zone, but also by affecting the differentiation of existing neuroblasts. As a result of these anomalies, some of the newborn appeared to have abnormal patterns of behavior.

Motor function and the corticospinal tracts in the dog and raccoon

Abstract: Following unilateral somatomotor cerebral cortex ablation in three raccoons and ten Beagle dogs similar functional deficits of hypotonia, hypokinesia and dysmetria limited to the side opposite the lesion were observed in both species. Only in the raccoon was a loss of digital manipulative ability of the contralateral forepaw observed. The Nauta-Gygax method was used to trace corticospinal projections into the grey matter of the spinal cord. In both species preterminal degeneration was found ipsilaterally and contralaterally in Rexed's laminae V, VI, VII and VIII. Furthermore, in the raccoon preterminal corticospinal degeneration was followed into the dorsal portion of contralateral lamina IX at the level C7–8. Although direct corticospinal projections to motoneurones of lamina IX occur in greater quantity and in increasing quantity with increasing complexity of digital abilities among the primate species, it appears that such connections are not limited phylogenetically to primates and probably are correlated with the ability of a species to manipulate the digits. Comparison of these anatomical findings with those reported for the cat revealed a progressive ventral shift of corticospinal terminations in ventral horn neuronal groups from cat to dog to raccoon, specifically into lamina IX in the raccoon. No single pattern of corticospinal terminations appears typical for the Order Carnivora. Data on dogs varying in age from one month to adult support the suggestion that there is a direct correlation between some motor cortex functions and postnatal maturation of corticospinal connections.

Number and distribution of the apical dendritic spines of the layer V pyramidal cells in man.

Abstract: The number and the distribution of the apical dendritic spines was investigated in the layer V pyramidal cells of the human cerebral cortex. This study was carried out in the motor cortices of an 8-month fetus, a premature infant, and a newborn, 15-, 19- and 45-day-old infants; in the somesthetic cortex of a newborn infant; and in the auditory cortex of a newborn infant. This study has shown: (a) that the number of spines increases with the age, (b) that the spines are distributed along the apical dendrites in a characteristic manner which, graphically represented, consists of a curve with three distinct deflexions, (c) that the spine-distribution along the apical dendrites of the layer V pyramidal cells is similar in all cases studied regardless of their age or their cortical location (motor, somesthetic and auditory cortices), (d) that the distribution of the spines along the apical dendrites appears to depend on the nature of the dendrite, (e) that the sequence of the mean number of spines maintains an exponential relationship with the distance from the cell body for the first and second deflexions of the spine-distribution curves. The significance of the distribution of the spines along the apical dendrites of the layer V pyramidal cells is discussed. A new method is presented and its possible application to the study of the normal development and pathoIogical conditions of the cerebra1 cortex is suggested.

The development of hippocampal and dorsolateral pallial regions of the cerebral hemisphere in fetal rabbits. III. Twenty‐nine millimeter stage, marginal lamina

Abstract: The structure of the cerebral hemisphere of 29 mm rabbit embryos was stuided with aniline and Golgi stains. Particular attention was devoted to the structure of the marginal lamina. In aniline stained sections it is a light, relatively acellular layer at the surface of the embryonic cerebral hemisphere and corresponds to layer I, the molecular layer, of the adult cerebral cortex. Even in early embryonic stages the marginal lamina consists mainly of terminal remifications of pyramidal cell apical dendrites and ascending axons. This layer of neuropile is of particular interest since it greatly precedes the development of other cortical zones rich in axons and dendrites. The reasons for the precocious development of dendritic branches at this level are unknown but may be related to the presence of ascending axons of nerve cells in the cortical plate or to horizontal cells. Large and small horizontal neurons are the only intrinsic cells at this level. Axons are present on the small elements, but were seen only infrequently on large cells. Some of the latter are similar to Cajal-Retzius cells of perinatal stages, but have relatively few ascending branches.

Cytoarchitecture of the frontal lobe of the squirrel monkey.

Abstract: Six Saimiri sciurea brains were studied. Coronal, horizontal, and sagittal sections were stained with cresyl violet. The frontal lobe map shows, anterior to the cental sulcus, a triangular area 4, agranularis giganto-pyramidalis (FA). Anterior to area 4 is area 6, frontalis agranularis (FB), which differs from area 4 by the absence of Betz cells. Rostral to area 6 is area 8, frontalis intermedia (FC), a narrow, thick band of cortex, with a faint layer IV. Anterior to area 8 the cortex becomes thinner and more granular, its cells are smaller and this region is subdivided into area 9, frontalis granularis (FD), and area 10, fronto-polaris (FE). Area 44 (FCBm) is on the inferior frontal gyrus, this cortex is granular limb of the arcuate sulcus is thin and granular, contains very large pyramidal cells in layers V and III: area 8a (FDT). The orbital cortex posteriorly shows an evident loss of layer IV; area 11 (FF). Area 50 is a narrow band of koniocortex in the inner wall of the fronto-parietal operculum. On the gyrus rectus the cortex develops allocortical characteristics with a heavy layer V, area 12 (FG). The characteristics of limbic cortex (mesocortex) are present on the cingulate gyrus, area 24 (LA). Area 25 is found in the subcallosal region.

Unit analysis of the pretectal nuclear group in the rat

Abstract: Unit responses to visual stimuli in the pretectal region of the rat were investigated with steel microelectrodes. Most units could be classified into two broad categories; “phasic” (brief on and off discharges) and “tonic-on” (sustained discharge during the visual stimulus). The responsive region appears to be coextensive with the n. praetectalis anterior (Pta) which can be divided into a dorsal portion containing “phasic” units and a ventral portion containing “tonic-on” units. The projection of the contralateral visual field is a mirror reversal of the field projection onto the superior colliculus. “Tonic-on” units may suserve total luminous flux detection necessary for the pupillary reflex. The topographical organization of units within Pta, as well as their diverse properties may account for residual visual function in animals with extensive lesions of the main visual pathways.

The subcortical distribution of optic fibers in Saimiri sciureus (squirrel monkey).

Abstract: 1. The optic subcortical connections in a new world monkey (Saimiri sciureus) have been examined with the Nauta and Glass silver impregnation. 2. Terminal degeneration following optic nerve sectioning reveals a laminated dorsal cell mass, which contains separate points of termination for crossed and uncrossed optic fibers. 3. Experimentally it can be shown that the two magno-cellular laminae have separaate connections. The most ventral lamina (lamina 1) receives contralatieral fibers, lamina 2 ipsilateral fibers. The dorsal cell mass in the normal material undivided shows experimentally the following lamination: layers 4 and 6 receive contralateral fibers while layers 3 and 5 receive ipsilateral fibers. 4. Further points of termination for optic impulses are: the nucleus pregeniculatus, the nucleus limitans, and the superior colliculi (stratum poticum). 5. Fibers of the accessory optic system are crossed entirely and terminate in the nucleus of the accessory optic tract.

The distribution of 5′‐nucleotidase in the brain of the mouse

Abstract: The distribution of the enzyme 5′-nucleotidase in the brain of the mouse is described in detail. The structures showing the greatest amount of activity are the corpus striatum, the substantia gelatinosa, the lateral longitudinal stria, the nodulus of the cerebellum and parts of the retina. In the cerebellum in particular, and to some extent in the hippocampus, the distribution is such as to suggest that the enzyme may be actively involved not only in simple biochemical processes but possibly also in some neurophysiological function.