bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of corticogeniculate synapses in the cat
Authors: Weber Arthur J. , Kalil Ronald E. 
Published: January 2005

AbstractThe development of corticogeniculate synapses was studied in 16 cats ranging in age from newborn to adult. Tritiated proline was injected into areas 17 and 18 of the visual cortex in order to label corticogeniculate terminals in lamina A of the dorsal lateral geniculate nucleus. The labeled terminals were then characterized ultrastructurally using electron microscopic autoradiography.Labeled synaptic profiles were found in newborn kittens, indicating that corticogeniculate connections are present in the cat at birth. Morphologically, however, many corticogeniculate endings in newborn and 1‐week‐old kittens are different from those in older animals in that they do not form well‐defined terminal boutons, and their synaptic vesicles are often loosely packed. In kittens 2 weeks of age and older, corticogeniculate axons end as RSD terminals exclusively; i.e., they are relatively small in size and contain round, densely packed synaptic vesicles, and occasionally an electron‐dense mitochondrion (Guillery: Z. Zellforsch. 99: 1–38, '69). However, not all RSD terminals in the LGN represent input from visual cortex. Injections of 3H‐proline into the mesencephalic reticular formation also label RSD terminals selectively in the lateral geniculate nucleus.At all ages corticogeniculate axons make synaptic contacts with dendrites exclusively, and they are always presynaptic. This suggests that the essential pattern of corticogeniculate synapses is formed early and is not altered during subsequent development. Quantitatively, there is no significant change in the size of corticogeniculate terminals or their synaptic vesicles in kittens 2 weeks of age (the youngest measured) and older. In contrast, the synaptic contact lengths of these terminals decrease about 28% between 2 and 12 weeks. During this same period there is approximately a twofold increase in the density of corticogeniculate terminals in the neuropil of lamina A. Since the volume of neuropil in lamina A increases almost fourfold between 2 and 12 weeks, the doubling of corticogeniculate terminal density represents about an eightfold increase in terminal number. After 12 weeks there is little change in the length, density, or number of corticogeniculate synaptic contacts, which suggests that the morphological development of the corticogeniculate pathway is essentially complete by this age.
Relationship between natural variations in motoneuron number and body size in Xenopus laevis: A test for size matching
Authors: Sperry David G. 
Published: January 2005

AbstractDuring normal development, tadpoles of Xenopus laevis demonstrate large variations in body size that are carried through metamorphosis. This variation in size exists at the stages when lumbar lateral motor column (L‐LMC) motoneurons are produced and when neuronal cell death in this neuron population occurs. Body size, hindlimb size, motoneuron number, and motoneuron size (i.e., neuron nuclear cross‐sectional area) were measured in animals from three developmental stages: one prior to significant amounts of cell death, one at the peak rate of cell death, and one after cell death. The hypothesis that neuron population size is matched to peripheral size was tested by using the natural size variation found at each of these stages.The ranges of values for the measurements at the three stages were large. Significant correlations between body size and motoneuron number, as well as between motoneuron number and muscle fiber number, were present after cell death. Since these correlations emerged as cell death reduced neuron numbers, size matching may have occurred and cell death may have adjusted the L‐LMC motoneuron population's size to variation in body size. In addition to the correlations between body size and motoneuron number at the end of cell death, neuron numbers before and after cell death were significantly correlated among groups of siblings. The possibility that the number of neurons after cell death was also influenced by differences in the number of L‐LMC progenitors is discussed.
The entorhinal cortex of the monkey: I. Cytoarchitectonic organization
Authors: Amaral D. G. , Insausti R. , Cowan W. M. 
Published: January 2005

AbstractAs an essential preliminary to a series of experimental studies of the afferent and efferent connections of the monkey entorhinal cortex, we have carried out a detailed analysis of its cytoarchitectonic organization. Primarily on the basis of features observed in Nissl‐ and fiber‐stained preparations, supplemented with Golgi‐stained material and preparations stained for heavy metals by Timm's method and histochemically for acetylcholinesterase, the entorhinal cortex has been divided into seven fields that are named according to their rostrocaudal and mediolateral positions except for one rostrally located field that is named for the prominent input that it receives from the olfactory bulb. At rostral levels, the entorhinal cortex is marked by a number of morphological inhomogeneities. The neurons tend to be organized in patches that are surrounded by large, thick, radially oriented bundles of fibers. At caudal levels, the entorhinal cortex has a more distinctly laminated appearance, reminiscent of that in the neocortex, and most of the neurons and fiber fascicles are arranged in discrete radial columns. The cortical region adjoining the entorhinal cortex laterally, which is commonly known as the “perirhinal cortex,” is in fact composed of two separate fields corresponding to areas 35 and 36 of Brodmann. Area 35 occupies the fundus and part of the lateral aspect of the rhinal sulcus. Area 36 extends from the lateral bank of the rhinal sulcus into the inferior temporal gyrus, where it borders fields TA and TE rostrally, and field TF of the parahippocampal gyrus caudally. The surface extents of each of the entorhinal fields have been determined by making “unfolded” two‐dimensional maps of the region and measuring the areas with a computerized digitizing system.
The entorhinal cortex of the monkey: II. Cortical afferents
Authors: Insausti R. , Amaral D. G. , Cowan W. M. 
Published: January 2005

AbstractThe entorhinal cortex of the monkey is commonly viewed as the major link between the cerebral cortex and the other fields of the hippocampal formation. Until recently, however, little was known about the origins of the cortical projections to the entorhinal cortex, and most of the available information is still based on degeneration studios. We have carried out a systematic analysis of these connections by placing small injections of the retrograde tracer wheat germ agglutinin conjugated to horseradish peroxidase into each of the fields of the entorhinal cortex of the Macaca fascicularis monkey, Retrograde labeled cells were observed in several areas of the frontal and temporal lobes, the insula, and the cingulate cortex. In the frontal lobe, the greatest number of labeled cells were observed in the orbital region and specifically in areas 13 and 13a: labeled cells were also seen in areas 14, 11, and 12. In the dorsolateral frontal cortex, labeled cells were observed mainly in the rostral half of area 46; occasionally cells were also seen in areas 9, 8, and 6. In the cingulate cortex, labeled cells were observed in area 25, area 32, and rostral levels of area 24; fewer cells were observed at caudal levels of area 24 or in area 23. The retrosplenial region (areas 30 and 29), including its caudal extension along the rostral calcarine sulcus and its ventral extension into the temporal lobe, contained numerous labeled cells. In the temporal lobe, retrogradely labeled cells were arranged in two rostrocaudally oriented bands. Rostral to the hippocampal formation, the first band encompassed the priform and periamygdaloid cortices and areas 35 and 36; the labeling in area 36 was continuous to the temporal pole. At more caudal levels this band was located immediately lateral to the hippocampal formation and included areas 35 and 36 rostrally and areas TH and TF caudally. The second band was situated in the superior temporal gyrus where labeled cells were observed in several distinct cytoarchitectonic fields, including the parainsular cortex in the fundus of the inferior limiting sulcus. In the insula proper, retrogradely labeled cells were seen mainly in the rostral or agranular division; far fewer were observed in the dysgranular and granular insula. Whereas there is little available physiological information concerning many of the cortical regions that project to the entorhinal cortex, on anatomical grounds they may be generally characterized as poly sensory associational regions.
Organization of sensory and motor nuclei of the trigeminal nerve in lampreys
Authors: Koyama Hiromichi , Kishida Reiji , Goris Richard C. , Kusunoki Toyokazu 
Published: January 2005

AbstractAnterograde and retrograde HRP transport were used to elucidate the primary central projections of the trigeminal nerve in a lamprey, Lampetra japonica, by application to the ophthalmic, apical, basilar, suborbital, and mandibular branches of the trigeminal nerve. (1) Most of the trigeminal and a few facial ganglion cells were labeled. The ganglion cells of each nerve were distributed in separate areas within their respective ganglia. (2) Some ipsilateral medullary and spinal dorsal cells were labeled after HRP application to the ophthalmic and apical nerves, but there was no contralateral labeling. (3) Most of the neurons of the trigeminal motor nucleus were labeled, and when the apical or the basilar nerve was labeled, in each case a cluster of small motor neurons was found ventrolateral to the classic motor nucleus. (4) Miscellaneous neurons were found scattered along the course of the descending trigeminal tract and nucleus in all cases except after application to the mandibular branch. The shape, size, and distribution patterns of these neurons were varied, and several characteristics indicated that they were sensory in nature. (5) In the rostral part of the medulla, sensory fibers of each nerve showed restricted localization within the descending trigeminal tract and nucleus. When compared to the distribution of the same fibers in the hagfish Eptatretus burgeri, another member of the cyclostomes, the distribution pattern in the lampreys studied was closer to the type seen in gnathostomes.
Early postnatal development of glial cells in the canine cervical spinal cord
Authors: Lord Kim E. , Duncan Ian D. 
Published: January 2005

AbstractTo study qualitative and quantitative changes in the glial cell population of young postnatal dogs, the cervical spinal cords of 20 beagle pups, ranging in age from 1 to 28 days, were prepared for light and electron microscopy. Glial cells in the lateral corticospinal tract were classified and quantified directly on the electron microscope. Quantification was performed by means of a stereological method designed to correct for sampling bias, and glia were classified according to morphological criteria as immature glial cell precursors, light and dark oligodendrocytes, astrocytes, and microglia.Glial cell precursors, which include undifferentiated glioblasts, oligodendroblasts, and astroblasts, predominated in the first few days after birth, constituting 43% of the glial cell population, and then declined to less than 5% by 28 days. Light and dark oligodendrocytes differed morphologically in their electron density and the appearance of their organelles. Light oligodendrocytes increased slightly prior to myelination, and then declined, whereas dark oligodendrocytes continued to increase throughout the 4‐week period and became the predominant cell type at 28 days (66%). In contrast to the oligodendroglial population, the sizes of the astroglial and microglial cell populations were relatively stable.This study shows that the population of immature glial cell precursors, abundant at birth in the lateral corticospinal tract, appear to be differentiating primarily into oligodendroglia, because this population exhibits a rapid increase in size, and relatively little change occurs in the astrocyte population. The trends in glial cell development in the dog are similar to those reported for rodents, although there may be some variation in the maturation and activity of oligodendrocytes.
Changing glial organization relates to changing fiber order in the developing optic nerve of ferrets
Authors: Guillery R. W. , Walsh C. 
Published: January 2005

AbstractThe structures of the developing eye‐stalk and the relationships of early retinofugal fibers as they pass through the stalk, chiasm, and tract have been studied by light and electron microscopical methods in fetal ferrets aged 23–27 days. The early eye‐stalk can be divided into two parts: a narrow extracranial part has a narrow lumen and is lined by few cells, whereas a thicker intracranial part has a wider lumen and is lined by several rows of cells. At the earliest stages no axon bundles are recognizable in the stalk, but fibers of the supraoptic commissure are already beginning to cross the midline in the diencephalon. Subsequently, as retinofugal axons invade the stalk, the glia of the extracranial part of the stalk have an interfascicular distribution and axon bundles are separately encircled by glial cytoplasm. In the intracranial part, as in the chiasm and tract, the glial cells occupy a periventricular position and send slender radial cytoplasmic processes to the subpial surface; these pass between groups of axons that here lie immediately deep to the subpial glia. Whereas axonal growth cones have no evident preferred distribution in the extracranial stalk, they tend to accumulate near the pial surface intracranially. The boundary between the two types of organization shifts as development proceeds so that the interfascicular glial structure of the early extracranial stalk first encroaches upon the intracranial parts and later appears in the chiasm. The characteristic adult arrangement of fibers in an age‐related order in the optic chiasm and tract, but not in the optic nerve, can be understood if axonal growth cones are guided toward the pial surface by radial glia but not by interfascicular glia. From the distribution of the growth cones, this is what appears to happen.
Early uncrossed component of the developing optic nerve with a short extracerebral course: A light and electron microscopic study of fetal ferrets
Authors: Guillery R. W. , Walsh C. 
Published: January 2005

AbstractDuring the study of the developing optic nerve described in the preceding paper (Guillery and Walsh, '87), small bundles of nerve fibers were seen passing between the optic nerve and the ipsilateral hypothalamus of 24‐to 27‐day‐old prenatal ferrets. The bundles appear before any other fiber groups of the retinofugal pathway and are identifiable while the main portions of the retinofugal system are growing into the optic tracts. The bundles, made up of 50 or more axons, leave the optic nerve, emerge through the otherwise continuous layer of subpial glia and through the basal lamina of the nerve, run a short, naked, extracerebral course among collagen fibers and presumed fibroblasts, and then re‐enter the central nervous system, passing rostrally and dorsally to the superficial parts of the ipsilateral hypothalamus away from the region of the chiasm. These fibers represent the earliest link between the optic nerve and the brain, but their course is not followed by the majority of retinofugal fibers developing later, which pass toward one or the other optic tract.
Amacrine cells in the ganglion cell layer of the cat retina
Authors: Wässle Heinz , Chun Myung Hoon , Müller Frank 
Published: January 2005

AbstractFollowing transection of the optic nerve, ganglion cells in the cat retina undergo retrograde degeneration. However, many small profiles (≤ 10 μm) survive in the ganglion cell layer. Previously considered to be neuroglia, there is now substantial evidence that they are displaced amacrine cells. Their density increases from approximately 1,000 cells/mm2 in peripheral retina to 7,000 cells/mm2 in the central area. Their total number was found to be 850,000, which is five times the number of ganglion cells and also five times the number of astrocytes.Uptake of 3H‐muscimol followed by autoradiography labelled 75% of the displaced amacrine cells; hence, the majority seem to be GABAergic. Immunocytochemistry with an antibody directed against choline‐acetyltransferase labelled approximately 10% of the displaced amacrines in the peripheral retina and 17% in the central area. Uptake of serotonin (5–HT) followed by immunocytochemistry was found in 25–30% of displaced amacrines. NADPH diaphorase histochemistry labelled approximately 5% of displaced amacrine cells. The sum of the various percentages makes colocalization likely. Intracellular injection of Lucifer Yellow under microscopic control revealed that displaced amacrine cells constitute several morphological types.
Thalamic and corticocortical connections of the second somatic sensory area of the mouse
Authors: Carvell George E. , Simons Daniel J. 
Published: January 2005

AbstractThalamic and corticocortical connections of the second somatic sensory area (SII) in the mouse cerebral cortex were investigated by means of the retrograde transport of horseradish peroxidase. Focal injections of the enzyme were made in physiologically determined locations within the parietal cortex. Results show that SII receives substantial inputs from topographically appropriate regions within the ipsilateral ventrobasal nucleus and from the ipsilateral posterior group. The limb representation, which was previously found to be responsive to auditory stimulation, received inputs also from the medial division of the medial geniculate body. The SII face representation, which is largely unresponsive to auditory stimuli, received little or no input from the medial geniculate body. SII injections yielded retrograde labeling in the topographically appropriate region in the first somatic sensory area (SI), and SI injections retrogradely labeled cells in SII in a pattern consistent with previous electrophysiological maps. Homotypical regions within SI and SII therefore appear to be reciprocally interconnected. SII also receives inputs from the ipsilateral motor cortex and from contralateral SI and SII. Finally, injections into the SI paw but not face regions yielded retrograde labeling in the thalamic ventrolateral nucleus. Thus, the distal limb representations in SI and SII each receive inputs from a third major relay nucleus (i.e., medial geniculate to SII, ventrolateral nucleus to SI) whereas the face representations do not. These results indicate a close functional interrelationship between homotypical areas in SI and SII, though the two areas differ in several important respects. It is proposed that SII in mice may complement the function of SI by helping to define the overall sensory context in which detailed tactile discriminations are made.
Golgi study of the primate substantia nigra. I. Quantitative morphology and typology of nigral neurons
Authors: Yelnik Jerome , François Chantal , Percheron Gerard , Heyner Simone 
Published: January 2005

AbstractNeuronal morphology was analyzed in the pars compacta, reticulata, and lateralis of the substantia nigra of humans and macaques. Golgi‐impregnated dendritic arborizations, reconstructed from serial sections, were described by using topological, metrical, and geometrical parameters measured in three dimensions. Morphological parameters were statistically analyzed. Cell bodies and axons were also described.The primate substantia nigra comprises few local circuit microneurons. It consists mainly of large projection neurons having large cell bodies and sparsely branched dendritic arborizations. In all subdivisions, “complex endings” and “thin processes” can be found on nigral dendrites. Axons of large neurons occasionally had initial collaterals that never form profuse arborizations. Pars reticulata neurons had a cell body surface of 520 μm2, 4 dendritic stems, and 13 dendritic tips. The total dendritic length (L) was 7,100 μm, the highest dendritic length (Lm) 1,200 μm, and the mean length of dendritic segments 320 μm. Pars lateralis neurons were similar except for their larger cell bodies (650 μm2) and longer dendritic segments (440 μm). Pars compacta neurons had larger cell bodies (860 μm2), thicker and more numerous (5 stems, 19 tips), and longer dendrites (L = 10,500 μm; Lm = 1,400 μm). Large neurons of monkeys had the same topological characteristics as human neurons but shorter dendrites. The overall shape of arborizations was highly variable and not characteristic in any subdivision.A hierarchical typology of nigral neurons is proposed, which comprises two neuronal species, the compacta and reticulata species, and a lateralis subspecies. Pallidal neurons (Yelnik et al., '84) belong to the reticulata species. The position of these species in relation to higher hierarchical levels is discussed.
Quantitative autoradiography of muscarinic and benzodiazepine receptors in the forebrain of the turtle, pseudemys scripta
Authors: Schlegel Jerry R. , Kriegstein Arnold R. 
Published: January 2005

AbstractThe distribution of muscarinic and benzodiazepine receptors was investigated in the turtle forebrain by the technique of in vitro receptor autoradiography. Muscarinic binding sites were labeled with 1 nM 3H‐quinuclidinyl benzilate (3H‐QNB), and benzodiazepine sites were demonstrated with the aid of 1 nM 3H‐flunitrazepam (3H‐FLU). Autoradiograms generated on 3H‐Ultrofilm apposed to tissue slices revealed regionally specific distributions of muscarinic and benzodiazepine binding sites that are comparable with those for mammalian brain. Dense benzodiazepine binding was found in the anterior olfactory nucleus, the lateral and dorsal cortices, and the dorsal ventricular ridge (DVR), a structure with no clear mammalian homologue. Muscarinic binding sites were most dense in the striatum, accumbens, DVR, lateral geniculate, and the anterior olfactory nucleus.Cortical binding sites were studied in greater detail by quantitative analysis of autoradiograms generated by using emulsion‐coated coverslips. Laminar gradients of binding were observed that were specific for each radioligand; 3H‐QNB sites were most dense in the inner molecular layer in all cortical regions, whereas 3H‐FLU binding was generally most concentrated in the outer molecular layer and was least dense through all layers in the dorsomedial cortex. Because pyramidal cells are arranged in register in turtle cortex, the laminar patterns of receptor binding may reflect different receptor density gradients along pyramidal cell dendrites.