Abstract: The fine structure of the dentate gyrus of the rat has been studied in glutaraldehyde perfused material. With the exception of the short axon association cells, the major components of each of the three layers of the gyrus have been identified, and a detailed account is given of the synaptic organization of the dentate granule cells. The granule cells have most of the features typical of small neurons and although they contain no large aggregates of granular endoplasmic reticular they exhibit a variety of cisternal specializations. In the granule cell layer numerous axo-somatic and axo-dendritic synapses have been observed, and on occasion a single presynaptic fiber has been seen to contact the soma of one cell and a proximal dendrite of another. In the inner part of the molecular layer the majority of synapses are upon the main dendritic shafts of the granule cells but many also contact short dendritic spines. In the outer two-thirds of this layer most presynaptic fibers end upon long dendritic spines some of which are characterized by a prominent projection from the subsynaptic surface into the presynaptic process. The unmyelinated axons of the granule cells establish many en passant contacts with dendrites and spines of CA4 pyramids before ending in large presynaptic bags which may contain a number of large agranular vesicles (up to 2,000 A in diameter) and vesicles with dense cores.

Abstract: Following lumbosacral dorsal rhizotomies (L1, L5, L6 and S1), fiber degeneration could be traced throughout three rostro-caudal regions of nucleus gracilis by utilizing the Nauta method. In rostral region, fiber degeneration was less dense and localized with greater intersegmental overlap than in middle region, where roots terminated in fairly specific cell clusters. Little could be stated about the caudal region because of sparsity of terminal degeneration. Fiber degeneration in rostral region appeared to be distributed primarily in the dendritic fields while that in the middle region terminated on both cell somata and dendrites. Overlap of dermatomes in periphery and centrally in nucleus parallel each other. Throughout the nucleus, greatest overlap of root distribution was encountered in more ventral regions. A root supplying a more distal dermatome (e.g. L6) compared to a more proximal one (e.g. L1), terminates more densely and dorsally in the nucleus. An occasional degenerated fiber passed into the contralateral gracile nucleus at obex level. Root degeneration proceeded, ipsilaterally, into rostro-dorsal regions of lateral cuneate, cuneate, and caudo-lateral regions of 2 nuclei. Bilateral degeneration from all roots, excepting S1, was noted in rostral pole of subnucleus caudalis and the subnucleus interpolaris of spinal trigeminal complex and nucleus reticularis parvicellularis. The pathway to the spinal trigeminal and parvicellular nuclei was undetermined. The concept of the non-homogenous organization of the gracile nucleus was supported.

Abstract: The innervation of rat vibrissae has been studied by light and electron microscopy. Nerve fibers enter the external root sheath and become associated with Merkel cells. Merkel cells are specialized sheath cells containing many secretory granules apposed to the neurite. These secretory granules are PAS-positive and diastase-resistant in light microscopic preparations. The neurite at the level of the Merkel cell is expanded and contains masses of mitochondria. As contrasted to nerve fibers in glabrous skin, the neurite does not penetrate deeply into the external root sheath but appears to terminate at the level of the Merkel cells. The neurite-Merkel cell complex is interpreted as representing a mechanoreceptor.

Abstract: In the prelaminar region of adult cat optic nerve, silver impregnation revealed a macroglial cell population consisting solely of small fibrous astrocytes. Electron microscopically the cells were characterized by abundant processes containing closely packed filaments and occasional glycogen granules; their perikarya contained few organelles, glycogen particles were conspicuous but not abundant, and their cytoplasmic and nucleoplasmic matrices were of low density. The laminar region contained typical fibrous astrocytes. These cells were characterized by similar processes and matrices but their perikarya contained filaments and were richer in organelles whose orientation was primarily radial. The postlaminar region contained both astrocytes and oligodendrocytes. The latter were identified as cells characterized by the absence of filaments and glycogen, the presence of canaliculi, dense cytoplasmic and nucleoplasmic matrices and perikarya very rich in organelles, whose orientation was primarily circumferential. The presence of filaments and/or glycogen on the one hand, and of dense matrices on the other hand, seemed to be mutually exclusive and provided diagnostic criteria for astrocytes and oligodendrocytes respectively. Bivalent forms were not seen. Cells usually identified as microglia were not seen. The relationship between astrocytes and finely myelinated nerve fibers in the lamina cribrosa indicates a sheath-supporting role. Astrocytes are probably generally concerned with the isolation and insulation of neurons and their processes. Oligodendrocytes may be concerned with the energetic support of neurons and their processes.

Abstract: By means of autoradiography the time, site of origin and migration pathways of neuroblasts destined for three nuclei in the hindbrain of the mouse have been determined. The cells of the nuclei griseum pontis and corporis pontobulbaris arise on gestation days 12 through 16 in the rhombic lip from the obex to the lateral recess. Most cells migrate within 48 hours via the pontobulbar body to the base of the pons to form the nucleus griseum pontis; some migrate only a short distance along the pathway and collectively form the nucleus corporis pontobulbaris. Most cells of the nucleus reticularis tegmenti pontis (Bechterew) arise in the primitive basal ependymal plate of the pons on gestation days 12 and 13 and migrate ventrally into the tegmentum. Some probably arise at the rhombic lip and migrate via the pontobulbar body to the base of the pontine flexure where they turn dorsally into the tegmentum.

Abstract: Studies with the light microscope (Am. J. Path., 34: 631, '58) indicated that an injection of endotoxin into the carotid artery of a rabbit alters the blood-brain barrier allowing the distribution of subsequently injected colloidal iron throughout the cerebral cortex. The present investigation by electron microscopy determined the distribution of the colloidal iron oxide in the normal and endotoxin altered cerebral capillaries of rabbits. Four hours prior to the intracarotid injection of saccharated iron oxide the animal received an injection via the same artery of either 50 μg gram-negative endotoxin or a control dose of normal saline. The animals were sacrificed at times from 15 minutes to two hours after the injection of iron oxide and samples of the cerebral cortex were processed for electron microscopy by routine methods. In those animals that did not receive endotoxin, the colloidal iron was limited to the lumen of the cerebral capillaries and occasional large endothelial vacuoles. None of the iron was found in the endothelial pinocytotic vesicles. In the endotoxin animals the iron oxide particles were found in quantity in the capillary endothelium phagosomes, the basement membrane, and in astrocytes and their processes. The fine structure of the cerebral capillary is reviewed and evidence is presented in support of the hypothesis that the barrier mechanism for colloidal tracers lies in a unique property of the brain's endothelial pinocytotic vesicles.

Abstract: Each nucleus ambiguus of the rabbit contains about 1,500 cells and is approximately 4 to 5 mm long. The author confirms the previously described division of the nucleus into a rostral compact formation, 1.6 mm long, and a caudal diffuse formation occupying the remainder of the nucleus. He further subdivides the compact formation into a lateral part, the principal column, and a medial part, the medial column. These divisions and the cytological differences between the cells in different divisions are illustrated. The cells in the medial column are more similar in appearance to those of the diffuse formation, with which they probably form a continuous column, than to those of the principal column, which are smaller, and have less distinct Nissl granules.

Abstract: This study represents an attempt to reconcile recent quantitative findings of large amounts of monoamines in the earthworm with early histological findings of only small numbers of chromaffin cells in that animal. Using the highly sensitive and specific fluorescence method for the histochemical localization of monoamines, it has been demonstrated that the earthworm nervous system contains large numbers of monoaminergic neurons. At least one-tenth of the motor and interneuronal population in a typical ganglion of the ventral nerve cord contain either serotonin or primary catecholamines. In addition a large number of neurons containing a primary catecholamine form an extensive sensory system with their cell bodies in the epidermis and their axons terminating in the ventral nerve cord.

Abstract: Studies were made of decrease of neurons and proliferation of glial cells in the dorsal nuclei of lateral geniculate body of 32 rabbits and 12 cats who had undergone unilateral ablation of visual cortex up to 50 weeks prior to sacrifice. Results show that degeneration occurred in 80% of neurons in rabbit lateral geniculate body within three days, and 95% disappeared within four weeks. In comparison, degeneration was present in only 70% of neurons in the cat nucleus at the seventh post-operative day, and about 26% remained normal up to the fiftieth week. Glial cell reactions were differential and complex: astrocytes showed rapid proliferation with gradual return to normal, while oligodendrocytes and microglia increased more slowly, maintaining a high level over 50 weeks.

Abstract: The degeneration pattern in the rabbit following transection of the olfactory bulb or peduncle at various levels was studied by the Laidlaw method of Nauta. Degenerating axons were observed in the crossing of the anterior limb of the anterior commissure and in the lateral olfactory tract following olfactory bulb lesions which did not damage the anterior olfactory nucleus. Evidence was found for termination of the olfactory tract fibers over all parts of the anterior olfactory nucleus, the rostral and lateral parts of the olfactory tubercle, the anterior continuation of the hippocampus, the nucleus of the lateral olfactory tract, and the prepyriform areas 1, 2, and 3, the periamygdaloid areas 1, 2, part of 3, and 5, and the entorhinal axeas 1, 2, and 4 of Maximillian Rose. When the anterior olfactory nucleus was damaged degeneration was found in the contralateral olfactory bulb and anterior olfactory nucleus and parts of the ipsilateral neocortex adjacent to the rhinal fissure, limbic system (medial septal nucleus and anterior continuation of the hippocampus), pyriform lobe cortex, and lateral preoptic area. The results differ in particulars from those of previous investigators.

Abstract: The diameter of cell nuclei and mean volume of internuclear material per nucleus were determined in the auditory cortex in growing and adult mice. The influence of stay in complete darkness for 2–4 months was investigated. In growing mice, a decrease in nuclear size and relative volume of internuclear material was observed after two months in the dark from birth. Prolonged stay in the dark caused an increase in nuclear size and internuclear material, and the hypotrophy of the auditory cortex was succeeded by hypertrophy after four months in the dark from birth. In adult mice, reared in darkness for three months from four to seven months of age, similar hypertrophy of the auditory cortex was recorded. Compared to the findings in the striate cortex of visually deprived mice (in a previous investigation), the initial hypotrophy of the auditory cortex after visual deprivation was less pronounced than the hypotrophy of the auditory cortex after visual cortex. In the latter, no late hypertrophy occurred after prolonged stay in the dark, and hypotrophy was found in the adult, visually deprived mice, and not hypertrophy as in the auditory cortex. The possibility of compensatory auditory training and cortical hypertrophy is discussed.

Abstract: Electrophysiological characteristics of the visual system have been investigated on an ascending phylogenetic scale in submammalian vertebrates. In cyclostomes and plagiostomes the only system of vision is retino-tectal. In lampreys spread of excitation from visual centers to descending paths of the spinal cord occurs readily, as a manifestation of diffuse, primitive brain. As a result of progressive cephalization, a new retino-thalamo-cortical system arises in amphibia and reptilia. The retino-tectal system, however, retains its leading role. Optic tectum visual potentials are of short latency, displaying stability of pattern and aptitude to reproduce stimulation rhythm, making them comparable to primary responses of the mammalian cortex. The phylogenetically more recent retino-thalamocortical system has not attained structural or functional maturity. Due to its diffuse organization, visual potentials generated in the surface cortical layer are of long latency, displaying aptitude to fatigue and recruiting on rhythmical stimulation, sensitivity to nembutal; being unlike the primary responses of the mammalian cortex, they should rather be regarded as responses of a non-specific type. Electrical stimulation of dorsal thalamic structures in the frog, turtle and varanus also fails to evoke cortical responses of a primary type. In the course of phylogenetic development, the retino-thalamo-cortical system evidently goes through a stage (amphibia, reptiles), when representation of the function of vision is of a mainly non-specific nature.

Abstract: Cerebellar afferents from the inferior olivary nuclei arise from about one million nerve cells. This figure was determined by counts and estimates carried out on four complete series of human brain-stem sections of a new-born, a three-month-old infant, a 42-year-old male and a 56-year-old male. Cell frequencies in all four cases were nearly identical. About 7% of this total belongs to the two accessory nuclei, believed to project to the archeocerebellar cortex. Cell sizes differ between the main and the two accessory olivary nuclei, the former having a mean cell size of about 400 μ2, the latter about half this size. Comparing infant and adult cell size, there is a threefold increase in volume from infancy to adulthood. Packing density of nerve cells in the infants is about twice that of the adults. The ratio of nerve cells to glia cells is 1:4 in the adults and 1:6.7 in the infants.

Abstract: The choroid plexuses of the neotenous salamander, Necturus maculosus, were examined by light and electron microscopy. Their epithelium was found to consist of a single layer of flattened to cuboidal cells resting upon a well-developed, continuous basement membrane. The cytoplasm of a typical epithelial cell contained, besides a large, centrally-placed nucleus, numerous mitochondria, an extensive agranular endoplasinic reticulum, prominent Golgi complexes and a variety of dense bodies. In addition, occasional clusters of ribosomes, lipid droplets, fascicles of fine filaments and numerous glycogen granules were present within the cytoplasm. Specializations of the apical (ventricular) surfaces of the epithelial cells included an irregular brush border, cilia, and minute, possibly micropinocytotic, invaginations of the plasma membrane. Surfaces of contacts between epithelial cells were specialized by “tight junctions” desmosomes, and complex inter dictations of the apposed plasma membranes. The interstitial space separating the epithelial layer from the thin-walled, non-fenestrated plexus blood vessels contained a mesh-work of collagen fibrils and a variety of connective tissue cell types. Electron dense Thorotrast particles were found to traverse the endothelial walls of the blood vessels and accumulate within the interstitial spaces within 30 minutes after being injected into the blood stream. The epithelial basement membrane, however, apparently prevented the tracer particles from reaching the epithelial cells, and the ventricular spaces beyond, as long as five hours after injection.

Abstract: The postnatal changes in the cross-sectional area of the cortex and white matter in the median sagittal section of the cerebellum of mouse were studied quantitatively. That of the cortex increases about 20 fold from birth to maturity, increasing slowly during the first five days following birth, then sharply during the next five days to resume slow increase again after the tenth day. There is very little increase after the fifteenth day. That of the white matter increases only four-fold during the same period. By the end of the second week it has attained only half of its adult value and continues to increase even after the thirtieth day. The increase in the cross-sectional area of the cerebellar cortex is mainly due to rapid expansion of the cortical surface which forces the white matter to be arranged into medullary rays (actually ridges) to keep in contact with the rapidly expanding cortex, thus cerebellar fissures are formed. The number of mitotic figures (uncorrected for fragments) in the superficial granular layer in a median sagittal section 10 m thick increases from about 22 at birth to a peak of 230 at seven days then falls to less than 36 at 15 days of age, after which the entire layer disappears.

Abstract: Degenerative changes in the cerebellum of the cat have been observed electron microscopically 2 to 30 days after surgical lesions were placed in the inferior or middle cerebellar peduncles or after undercutting or isolating cerebellar folia. The changes were confined to the mossy fibers of the white matter and granular layer except when Purkinje cells were damaged buy undercutting. Mossy fiber terminals in the glomeruli underwent two kinds of change. Either the synaptic vesicles and mitochondria coalesced into dense clumps with loss of mitochondrial outer membranes and proliferation of cristae, or the vesicles and miotochondria disappeared leaving a swollen terminal containing only a few large pleomorphic vesicles and small dense polygonal bodies. Neurofilaments proliferated and filled a few terminals but most of the neurofilamentous hypertrophy and proliferation was confined to myelinated axons. Some phagocytosis of degenerated endings was observed and mild fibrous gliosis occurred in the glomeruli. All of the changes observed in the present study have been reported in degenerating synapses and axons elsewhere in the central and peripheral nervous system, but there appeared to be more pleomorphism and less predictability of changes in the cerebellar cortex than have been noted in other single areas of the central nervous system.

Abstract: The parvocellular portion of the lateral geniculate nucleus (LGN) in the squirrel monkey (Saimiri sciureus) is a relatively unlaminated mass of cells . In order to determine whether a concealed laminar structure might exist, one eye was removed in each of three squirrel monkeys . Transneuronal degeneration did not appear prominent in the LGN of the animal which was allowed to survive for six months, but in the two animals which survived for one year six laminae were clearly present. There was transneuronal degeneration in layers 1, 4 and 6 contralateral to the enucleation, and 2, 3 and 5 ipsilaterally . Lack of interlaminar fiber masses prob- ably accounts for the apparent absence of lamination in the normal parvocellular mass . Lamination is a conspicuous feature of

Abstract: In a previous study a low molecular weight basic protein, isolated from guinea pig brain, was shown to be localized in the myelin of adult nervous tissue. An antigenically similar protein was present in the central nervous system of a variety of mammals, the chicken and the frog. In the present study, the ability of the nervous system of the albino rat to react specifically with the fluorescent anti-basic protein antibody was investigated during fetal and postnatal development. Although earlier stages were examined, the spinal cord of the rat was first observed to react with the antiserum in the twenty-first day of gestation. Ultrastructural studies indicated that well formed myelin, and mature and immature synapses were present in the cervical cord at this time. A positive immune reaction was detected two days before a noticeable Weigert reaction was obtained; the sequence and spatial pattern of labeling with both techniques was similar, however. It was observed that the nucleolus and cytoplasmic web of dorsal root ganglion cells first reacted with the antiserum at a time immediately preceding the onset of rapid myelination of axonal fibers in the ganglion. The immune reaction in the cell body of the large ganglion cells diminished rapidly with the cessation of rapid myelination. The relationship of the findings to the present concept of myelinogenesis is discussed.

Abstract: Examinations were made by means of the Golgi-Cox method of the developing neuronal elements of the cortex of the dog during the first ten weeks of life. The neuronal elements undergo gradual morphological differentiation during the first week. From 2–4 weeks of age the most dramatic changes in the development of dendritic arborizations occur. After this time the changes are slower with terminal maturation of cellular elements, cessation of neuronal growth and final organization of apical and basilar dendrites and their collaterals. Comparison with the development of the kitten shows close similarity in the development of canine and feline neocortex. In dogs, however, an essentially mature neocortex is not reached until after four weeks of age. The relation of these data to biochemical and electrophysiological development and behavioral patterns in the young dog is discussed.

Abstract: The ganglionic sheath is structured upon a complex fibrocellular framework. A tridimentional network of anastomosed connective tissue lamellae constitutes the extracellular space. In the deep ganglionic region these lamellae display alkaline phosphatase activity. Sheath cells appear embedded in network fenestrae. The most peculiar of these are the superficial voluminous globular cells. Its cytoplasm appears built of a lipoprotein network containing glycogen and “lipofuscin pigments.” These two latter substances appear to undergo seasonal changes. The gland cells seem to be unicellular endocrine glands, containing many droplets giving positive reaction for carbohydrates, lipids and proteins. Muscle cells are placed throughout the sheath. The cytoplasm gives an intense reaction for proteins but does riot exhibit myofibrilles. These cells could play an important role in ganglonic movements and in addition could modify the amplitude of the extracellular sheath space. Pigment cells, containing melanin granules, are distributed among the other sheath cells. Cellular groups of the sheath show many large spheroidal mitochondria and sudanophilic droplets. These cells could be involved in the synthesis of some unknown substance or/and in metabolic transport across the sheath. Glial cells are located under the sheath and surrounding the entire neuronal surface. The cytoplasm appears connected with alkaline phosphatase and with an acidic substance. The histochemical and topographical characteristics of these cells point to their role in metabolic transportation, mechanical support and nervous homeostasis.

Abstract: The distribution of the internal carotid circulation of the macaque brain was studied by using a method of intracarotid dye injections which produced no appreciable disturbance of the dynamics of the cerebral circulation. The areas in cortical and diencephalic structures supplied by the carotid circulation are described and displayed semidiagrammatically in a set of figures. The carotid artery supplies most of the lateral and mesial surfaces of the cerebral hemisphere, whereas the hemispherical portion supplied by the posterior cerebral artery is confined to the occipital and inferior temporal region. Left and right internal carotid territories overlap widely across the midline in cortical areas due to the existence of a single pericallosal arterial trunk formed by the junction of both anterior cerebral arteries. In the diencephalon the segregation of the territories of the left and right internal carotid arteries is sharp, except in its anterior-most portion. The pattern of internal carotid supply to the thalamus is somewhat variable, the most lateral structures are most consistently supplied by this vessel, whereas the more medial structures, even those lying far rostral within the thalamus, are supplied by the posterior cerebral artery. The territories of the two vessels overlap considerably within the thalamus. In a certain number of animals, the posterior cerebral artery is part of the internal carotid, rather than of the vertebral-basilar system.

Abstract: The development of cutaneous innervation in the rat and the rat and the mouse has been studied by silver techniques. In particular, the innervation patterns of adult and of perinatal skin have been compared. From the second parental day until the sixth postnatal day, the relatively thick epidermis is freely penetrated by nerve fibers; thereafter, the nerve endings appear to be confined to the dermis. The intra-epidermal axons are directed obliquely, with a rough (and not exact) correspondence to the plane of future emergence of the hair shafts. The appearance of a transitory development of intra-epidermal nerves elsewhere.