bluuebunny/crossref_metadata_2025_split huggingface dataset:
External morphology of pouch young opossum brains: A profile of opossum neurogenesis
Authors: Ulinski Philip S. 
Published: December 2004

AbstractAn outline of opossum brain development was prepared by studying the external morphology of 27 pouch young opossum brains which were from one to 81 postnatal days old. Opossum brain development goes through three morphologically defined periods. (1) An embryonic period extends from conception to the third postnatal day. The brain is not much more than a neural tube at birth, but by the third day it has undergone a longitudinal compression which gives it the shape of an adult brain. (2) A period of regional differentiation extends from the fourth day to about the sixtieth day. All of the grossly visible adult brain structures sequentially appear within each brain region during this period. For example, the rhinal and orbital fissures appear on the dorsolateral cerebral hemispheres at about day 30; the di‐telencephalic fissures appear on the ventral brain surface at about the fifth day; the olfactory tubercles begin to appear by the eighth day; the hypothalamus attains its adult proportions by about the fifth day, but does not differentiate into its adult components until after the thirtieth day; the cerebellum has all of its adult components by the fortieth day. (3) A period of maturation extends from about the sixtieth day to weaning. Minor finishing changes take place in some brain structures during this period. For example, the trapezoid body is more clearly demarcated and the parafloccular lobes of the cerebellum become more prominent.
Terminal arborizations of retinotectal axons in the bullfrog
Authors: Potter H. D. 
Published: December 2004

AbstractIn the optic tectum of Rana catesbeiana four laminae of myelinated fibers in the superficial zone of the optic tectum (laminae B, D, F, and G: Potter, ′69) are identified as retinal axons on evidence from patterns of degeneration following contralateral eye removal. After survival times of 5 to 22 days Cajal's block method II shows either fragmentation or abnormal beading of the axons in the four laminae and the paraffin‐Nauta method shows coarse granules, representing axonal debris, in these laminae.Golgi impregnations of terminal arborizations arising from fibers in laminae B, D, F, and G show three major types of branching patterns. The arbors are horizontally flattened and are elongated in the same direction as the parent fibers. Densely branched (DB) arbors have stem fibers in laminae B and D and are distributed within the same and adjacent laminae. Widely branched (WB) and thin, straight (TB) arbors have stem fibers in laminae F and G and are distributed mainly in the two laminae of origin with some overlap into adjacent layers of cells and fibers. The horizontal dimensions of DB arbors are 30 μ–70 μ by 100 μ–200 μ, whereas the WB arbors are more variable in overall dimensions. The TB arbors consist of long thin stem axons that give off infrequent terminal specializations in the form of forked or spiny appendages. Numerous terminal forks are present on the WB arbors but are rare on the DB arbors. Swellings and varicosities, that probably represent synaptic specializations, are particularly numerous on the long tertiary branches of DB arbors.
The fine structure of neurons and synapses in the motor nuclei of the cat spinal cord
Authors: McLaughlin Barbara J. 
Published: December 2004

AbstractThe normal synaptic organization of the motor nuclei in the cat lumbosacral spinal cord was examined by light and electron microscopy. Neurons could be classified into three categories on the basis of their size in Nissl stained sections. In neurofibrillar stained sections, seven neurofibrillar rings were observed, on the average, to lie upon large neurons and proximal dendrites in the motor nuclei. Electron microscopic examination revealed no apparent differences in the fine structure of the three neuronal cell types. In contrast the synaptic covering, as determined by the actual number of synaptic contacts or “active” zones, varied greatly. Less than half of the perikaryal surface of large neurons was covered by “active” zones and very few or no “active” zones covered the perikaryal surface of smaller neurons.The synaptic knobs contacting neuronal cell bodies and dendritic processes were classified into seven morphological types on the basis of vesicle shape, the presence of neurofilaments, and the nature of the subsynaptic specializations. Synaptic contacts occurred more frequently on proximal dendrites and less frequently on perikarya and distal dendrites. Rounded vesicle knobs outnumbered flattened vesicle knobs on distal dendrites, while the reverse was true on cell bodies and proximal dendrites. Two quite large synaptic knobs were characteristically observed. One knob, occurring predominantly on cell bodies and proximal dendrites, exhibited an apposed subsynaptic cistern and elaborate subsynaptic granular endoplasmic reticulum. The other synaptic knob, the least commonly found of all synaptic types, appeared primarily on proximal dendrites and exhibited multiple synaptic contacts with specialized subsynaptic densities. No axo‐axonal synaptic contacts were observed in the motor nuclei.
Visual cortex of the grey squirrel (Sciurus carolinensis): Architectonic subdivisions and connections from the visual thalamus
Authors: Kaas J. H. , Hall W. C. , Diamond I. T. 
Published: December 2004

AbstractThalamic projections to the visual cortex of the grey squirrel were studied by retrograde degeneration in the lateral geniculate and the pulvinar nuclei. The lateral geniculate was found to project to architectonic area 17 which also corresponds to visual area I as defined by its retinotopic organization. The projection is spatially organized in a precise way, and for every cortical point there is a corresponding column in the lateral geniculate which extends from border to border. For the binocular sector of area 17 the lateral geniculate column lies in the trilaminar part of the lateral geniculate, while for the uniocular sector the column lies in the bilaminar sector of the lateral geniculate. The pulvinar projects to several architectonic areas, areas 18 and 19 and to two or more temporal areas below area 19. This projection is roughly topographic but follows the sustaining pattern. When the squirrel is compared to the tree shrew and hedgehog what emerges is a conception of those changes in the visual system which arose as a result of adaptation to an arboreal habitat.
Early neuron differentiation in the mouse olfactory bulb. I. Light microscopy
Authors: Hinds James W. 
Published: December 2004

AbstractOlfactory bulb development in mouse embryos from day 10 of gestation (E10) to E15 was studied with 1 μ plastic sections and Golgi impregnations. Olfactory nerve axons reach the presumptive olfactory bulb region of the cerebral vesicle at E12, the same time that the first young neurons (postmitotic neuroblasts) are seen in the newly‐formed intermediate (mantle) layer. By E14 many of the presumptive mitral cells are oriented tangential to the surface and have grown a long axon that enters the lateral olfactory tract on the surface of the presumptive piriform cortex.The following probable sequence of differentiation of mitral cells was determined from Golgi impregnations of E14 and E15 animals: (1) After regrowth of an internal and external process following rounding up at mitosis, the nucleus and perikaryon of certain ventricular cells migrate into the deepest portion of the intermediate layer and start to re‐orient into a tangential orientation. This stage is called the primitive radial stage.(2) The growth of tangential processes combined with withdrawal or atrophy of external and internal primitive radial processes follows to produce cells in the pre‐axonic tangential stage. (3) The tangential cells then acquire a long, thin, unbranched process (axon) oriented towards the lateral olfactory tract and a larger, branching process (dendrite) running in the opposite direction. This stage is called the tangential mitral cell stage. (4) Radial re‐orientation of the perikaryon and dendrites of these cells and external migration of the perikaryon results in cells in the radial mitral cell stage.
The subependymal layer and neighboring region in the brain of the young rat
Authors: Privat A. , Leblond C. P. 
Published: December 2004

AbstractThe subependymal layer found below the ependyma of the lateral ventricle, as well as the border area separating the layer from corpus callosum and caudate nucleus, were investigated in the brain of 40‐ and 80‐gm rats with the help of the electron microscope.The subependymal layer is composed of cells packed under the ependymal epithelium. These cells undergo division frequently. They are characterized by an irregular nucleus with patches of ill defined chromatin and a scanty cytoplasm rich in free ribosomes. These features are suggestive of immaturity, although the presence of processes indicates some degree of differentiation.The border area is characterized by the presence of cells scattered among neuronal and glial processes. The cells in 40‐gm rats include a few neuroblasts and, in both 40‐ and 80‐gm rats, neurons and neuroglia, as well as numerous cells which resemble the cells of the subependymal layer or appear intermediate between them and oligodendrocytes or astrocytes. Such transitional cells are also found in corpus callosum and caudate nucleus.It is suggested that cells may leave the subependymal layer, cross the border area and enter white and gray matter while undergoing differentiation. Perhaps neuroblasts arise from these cells in the younger group studied (40‐gm rats). In both groups, most of these cells seem to differentiate into astrocytes and oligodendrocytes.
Changes in the dorsal lateral geniculate nucleus of the squirrel monkey after unilateral ablation of the visual cortex
Authors: Wong‐Riley Margaret T. T. 
Published: December 2004

AbstractYoung adult squirrel monkeys were subjected to unilateral occipital lobectomies, and were allowed to survive for 3 to 42 days. Both light and electron microscopic techniques were employed to examine orthograde as well as retrograde changes in the ipsilateral dorsal lateral geniculate nucleus. Three stages of degenerative change were described. During the early stage (third to fourth post‐operative day) there were early signs of corticogeniculate terminal degeneration. During the intermediate stage (fifth to eighth day) most of the RS (small axonal terminals with round vesicles) or corticofugal endings were seen to undergo a sequence of degenerative change: swelling or irregularity of the synaptic vesicles; electron dense disintegration; and finally the engulfment by glial elements. The small myelinated axons also become electron dense at this stage, and there were early signs of retrograde degeneration. The late stage was characterized by severe changes and final disappearance of the geniculocortical relay neurons as well as their axons and dendrites. Concurrently, most of the RS terminals were also removed from the LGN, and there was considerable re‐organization of the rest of the synaptic population.
Thalamic projections of the superior colliculus in the rhesus monkey, Macaca mulatta. A light and electron microscopic study
Authors: Partlow G. D. , Colonnier M. , Szabo J. 
Published: December 2004

AbstractThe projections of the superior colliculus to the thalamus have been studied in the monkey, Macaca mulatta, with anterograde degeneration techniques. The superior colliculus has been shown to project to the inferior nucleus of the pulvinar in a topographical manner with the lower visual field represented dorsomedially and the upper field ventrolaterally. The peripheral zone is located along the medial border and the fovea at the dorsolateral angle adjacent to the lateral geniculate nucleus. The superior colliculus also sends a dense projection to the ipsilateral intralaminar complex, i.e., to the parafascicular, central lateral and paracentral nuclei, and a lesser projection to the same contralateral nuclei. Degenerating tectal fibers were also found in the lateral geniculate nuclei. Four types of vesicle containing profiles were observed in the inferior pulvinar and paracentral nucleus. The large RL and small RS terminals contain round vesicles of uniform size and form asymmetric contacts mainly with large and small dendrites respectively. The F terminal contains a mixture of small round and flat vesicles. It forms symmetric contacts with dendrites and cell somata. The P profile is very pale and contains a relatively sparse population of vesicles showing a great variation in size. It forms symmetric contacts with medium to large dendrites. It is frequently found postsynaptic to the other types, especially the RL terminal, and is regularly seen as the intermediate element of serial and triadic synaptic arrangements. The experimental electron microscopic study has shown that many fibers from the superior colliculus terminate as RL profiles, undergoing direct dense degeneration, in both the inferior pulvinar and the paracentral nucleus. Others probably end as smaller RS terminals.
An autoradiographic study of the organization of the efferet connections of the hippocampal formation in the rat
Authors: Swanson L. W. , Cowan W. M. 
Published: December 2004

AbstractThe efferent connections of the hippocampal formation of the rat have been re‐examined autoradiographically following the injection of small quantities of 3H‐amino acids (usually 3H‐proline) into different parts of Ammon's horn and the adjoining structures. The findings indicate quite clearly that each component of the hippocampal formation has a distinctive pattern of efferent connections and that each component of the fornix system arises from a specific subdivision of the hippocampus or the adjoining cortical fields. Thus, the precommissural fornix has been found to originate solely in fields CA1‐3 of the hippocampus proper and from the subiculum; the projection to the anterior nuclear complex of the thalamus arises more posteriorly in the pre‐ and/or parasubiculum and the postsubicular area; the projection to the mammillary complex which comprises a major part of the descending columns of the fornix has its origin in the dorsal subiculum and the pre‐ and/or parasubiculum; and finally, the medial cortico‐hypothalamic tract arises from the ventral subiculum. The lateral septal nuclei (and the adjoining parts of the posterior septal complex) constitute the only subcortical projection field of the pyramidal cells in fields CA1‐3 of Ammon's horn. There is a rostral extension of the pre‐commissural fornix to the bed nucleus of the stria terminalis, the nucleus accumbens, the medial and posterior parts of the anterior olfactory nucleus, the taenia tecta, and the infralimbic area, which appears to arise from the temporal part of field CA, or the adjacent part of the ventral subiculum. The projection of Ammon's horn upon the lateral septal complex shows a high degree of topographic organization (such that different parts of fields CA1 and CA3 project in an ordered manner to different zones within the lateral septal nucleus). The septal projection of “CA2” and field CA3 is bilateral, while that of field CA1 is strictly unilateral. In addition to its subcortical projections, the hippocampus has been found to give rise to a surprisingly extensive series of intracortical association connections. For example, all parts of fields CA1, CA2 and CA3 project to the subiculum, and at least some parts of these fields send fibers to the pre‐ and parasubiculum, and to the entorhinal, perirhinal, retrosplenial and cingulate areas. From the region of the preand parasubiculum there is a projection to the entorhinal cortex and the parasubiculum of both sides. That part of the postsubiculum (= dorsal part of the presubiculum) which we have examined has been found to project to the cingulate and retrosplenial areas ipsilaterally, and to the entorhinal cortex and parasubiculum bilaterally.
Visual cortical areas mediating form discrimination in the cat
Authors: Sprague J. M. , Levy J. , Diberardino A. , Berlucchi G. 
Published: December 2004

AbstractCats were trained pre‐ and/or postoperatively on flux and pattern discriminations, and were examined in a series of visuomotor tests which measured attention and orientation to, and following and localization of stationary and moving stimuli, in a free situation and in a perimetry test.Cortical lesions were placed in areas 17 and 18, or in the middle and posterior suprasylvian gyri and sulci–areas 19, 20, 21, 7 and lateral suprasylvian cortex (LSA), as delineated by cyto‐ and myeloarchitecture, and by electrophysiological mapping.After removal of all of area 17 and up to 90‐95% of 18, postoperative learning of flux and pattern discriminations is at a high level, although in some cases slowed. Visuomotor behavior is normal. Such lesions result in severe atrophy only of laminae A, AI and C in the lateral geniculate nuclear complex (LGNd).The neuronal systems for perceiving and discriminating simple, large planime triepat terns and forms, and for mediating visually guided behavior characteristic of this species lie outside of areas 17‐18. The cortices primarily responsible for form discrimination in the cat include those in the suprasylvian gyri and sulci.After lesions which removed areas 19, 20, 21 and LSA, sparing most of 37‐18, form discriminations based on orientation or shape were prolonged or absent. Although these animals showed slow tracking and poor depth judgment, the visual fields were full and they had good sensory and perceptive capacity as seen in normal flux and near normal pattern (gratings) discrimination. Such lesions result in severe atrophy in lateral and inferior pulvinar complex. Although these nuclei receive visual input primarily from the superficial laminae of the superior colliculus and certain nuclei of the pretectum, both areas 19 and LSA receive a dual input from pulvinar and parts of LGNd.Whether these marked deficits in form discrimination after suprasylvian lesions are due to involvement of certain crucial areas of this extensive cortex, or whether all are involved in some integrated fashion, is not yet completely clear. Removal of 19, 21 and parts of LSA are followed by similar (but somewhat less marked) deficits of both retention and learning. Lesion in area 20 alone (cortical target of the lateral pulvinar) leaves retention of preoperatively learned discriminations intact but results in prolonged initial learning.Previous work by the present authors has shown similar deficits in form discrimination in the cat after lesions in the pretectumsuperior colliculus. These data, together with the present findings appear to support the hypothesis that the midbrainpulvinarcortieal pathways provide the first stage in simple, coarse form perception and discrimination in this species.
An autoradiographic study of the development of the entorhinal and commissural afferents to the dentate gyrus of the Rat
Authors: Fricke R. , Cowan W. M. 
Published: December 2004

AbstractThe development of the entorhinal, ipsilateral associational, and commissural afferents to the dentate gyrus have been studied autoradiographically, following the injection of small amounts of tritiated proline into the medial and lateral parts of the entorhinal cortex, and into fields CA3c and CA4 of the hippocampus, ia series of rats, on the third, sixth, and twelfth postnatal days. Clear labeling of the entorhinal afferents was found at the third postnatal day, and from the earliest stage studied the afferents from the two parts of the entorhinal cortex appear to be spatially segregated within the stratum moleculare of the dentate gyrus: the fibers from the lateral entorhinal areà occupying the outermost one‐third, or so, of this stratum, while those from the medial entorhinal cortex occupy its middle zone. The ipsilateral hippocampo‐dentate associational pathway is present at the third postnatal day, but the commissural projection (which shares wiht it the inner part of the stratum moleculare) could not be labeled until the sixth postnatal day. By the twelfth day the characteristic adult pattern of distribution of the terminals of the two hippocampo‐dentate pathways is established. although this pattern is best accounted for on the basis of a temporal competition for the available synaptic sites on the proximal parts of the dendrites of the granule cells, the spatial segregation of these two fiber systems from those arising in the entorhinal cortex, is probably due to the selective fasciculation of fibers in each group of afferents and to their early cytochemical specificity.
An ultrastructural analsis of neurites in the basal lamina of capillaries in the chinchilla cochlear nucleus
Authors: McDonald Donald M. , Rasmussen Grant L. 
Published: December 2004

AbstractIn an ultrastructural study of the chinchilla anteroventral cochlear nucleus (AVCN), we found innervated capillaries in the layer of granule cells that comprises the dorsolateral portion of the AVCN and forms a cap over the principal portion of the nucleus. In 66% of 215 capillaries we examined in the granule cell layer of various levels of the AVCN, we found structures having ultrastructural features of axons that (l) were within the brain parenchyma and were in direct contact with the pericapillary basal lamina, or (2) were separate from the adjacent neuropil and, often in the company of astrocytic processes, were completely enveloped by the pericapillary basal lamina. An analysis of serial sections confirmed that neurites within the pericapillary basal lamina were in continuity with neurites in the brain parenchyma. Most neurites within the basal lamina of capillaries were next to pericytes, but some neurites were next to endothelial cells. None of the neurites adjoining capillaries had the abundance of synaptic vesicles typical of autonomic vasomotor nerve endings and synaptic terminals. Consequently, they may be sensory, responding perhaps to changes in hydrostatic pressure or chemical composition of the blood or cerebrospinal fluid. However, we cannot exclude the possibility that neurites which accompany capillaries in the AVCN terminate elsewhere. In the AVCN the innervation of capillaries is restricted to the superficial layer of granule cells. In none of 177 capillaries of the principal portion of the AVCN did we find an example of a neurite in contact with the pericapillary basal lamina, a pericyte, or an endothelial cell, although it was sometimes necessary to examine specimens at various angles of tilt to confirm that the pericapillary glial sleeve was continuous. Furthermore, we found no innervated blood vessels among 266 capillaries examined in the granular and molecular layers of the cerebellar cortex.