bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell generation, death, and retinal growth in the development of the hamster retinal ganglion cell layer
Authors: Sengelaub D. R. , Dolan R. P. , Finlay B. L. 
Published: January 2005

AbstractDuring the early postnatal period in the hamster, the retinal ganglion cell layer grows, establishes its central connections, and undergoes substantial cell loss. In this study, we describe the development of the retinal ganglion cell layer with particular attention to the creation of local specializations in cell density. Changes in the number and spatial distribution of cells identified by a single 3H thymidine injection were examined through the period of maximal cell loss (postnatal days 4–10) and at adulthood.The cells of the retinal ganglion cell layer are generated from embryonic day 10 to postnatal day 3. Overall, cell number in the ganglion cell layer increases by approximately 108,000 cells (223%) from postnatal day 1 to 5, because of continued migration of cells generated prenatally. Cell number decreases from postnatal day 5 to 10 (25%), coincident with the presence of degenerating cells. Cell type is correlated with day of generation: the largest cells, all having retinal ganglion cell morphology, are generated on embryonic days 10 and 11; intermediate‐sized cells predominantly of ganglion cell morphology on embryonic day 12; and smaller cells of displaced amacrine or glial cell morphology thereafter.At adulthood, the hamster retina shows a streaklike elevation of cell density through central retina. However, at the time of maximal cell number (postnatal day 5), cell density is uniform across the retina. During the period of cell degeneration, cells are lost in greater relative numbers from the retinal periphery. This cell loss occurs principally from the first‐generated cells (embryonic days 10 and 11), as shown by both changes in the distribution of labeled cells and by the spatial pattern of labeled degenerating cells. From postnatal day 10 to adulthood, relative cell density continues to decline in the periphery of the retina, thus suggesting that differential growth completes the production of the adult cell density distribution.
Origins of afferents to visual suprageniculate nucleus of the cat
Authors: Hicks T. P. , Stark C. A. , Fletcher W. A. 
Published: January 2005

AbstractSmall iontophoretic ejections of horseradish peroxidase (HRP) were made from recording‐multibarrel micropipette assemblies in areas of the cat's suprageniculate nucleus (SGn) that contained visually responsive neurones. The sources of afferents of the SGn were determined by locating the labeled cell bodies of neurones that were presumed to send their axons to the area of the SGn containing the light‐sensitive cells. The greatest concentration of labeled cell bodies was found in the granular insular cortex and the adjacent area of agranular insula. Most cells projecting to SGn from these areas were distributed in the middle and lower laminae. A second intensely labeled region was found in stratum opticum and stratum griseum intermediate of the superior colliculus. Other areas containing labeled cells that were distributed with intermediate density included the ventral thalamic nuclear complex (basal, medial, and lateral divisions), periaqueductal gray (PAG), zona incerta, and pretectal nuclei (posterior, medial, and anterior divisions). Sparsely labeled sites included the fields of Forel, substantia nigra (pars reticulata), peri‐insular cortex, superior colliculus (profundum), lateral suprasylvian cortex (posterolateral lateral suprasylvian, PLLS and posteromedial lateral suprasylvian, PMLS), anterior ectosylvian cortex, thalamic reticular complex, nucleus of the optic tract, basal part of the ventromedial hypothalamic nucleus, and the pontine reticular nucleus (oralis) and adjacent reticular formation. Together with previous electrophysiological and neuroanatomical studies, the findings suggest that the SGn provides an integrating link between limbic structures and certain modalities of sensory information.
Thalamostriatal projections from the ventral anterior nucleus in the dog
Authors: Tanaka Duke , Isaacson Lori G. , Trosko Beverly K. 
Published: January 2005

AbstractThalamostriatal projections from the ventral anterior nucleus (VA) were mapped by using autoradiographic and horseradish peroxidase techniques in the dog. Injections of tritiated leucine and proline into the lateral, central, and medial parts of VA resulted in anterograde label over the dorsolateral, midlateral, and dorsal parts of the head of the caudate nucleus, respectively. The dorsolateral and midlateral parts of the caudate contained the heaviest label. No silver grains were located over the medial or ventral parts of the caudate. Light to moderate label was located over the most dorsal part of the putamen. After injections of lectin‐conjugated horseradish peroxidase (WGA‐HRP) into the dorsolateral or intermediate areas of the head of the caudate, retrogradely labeled cells were present in the lateral and central parts of VA, respectively. In cases with dorsolateral caudate injections, labeled cells formed a narrow dorsoventrally oriented band located in the lateral part of VA whereas in the case with a larger injection into midcaudate, large numbers of labeled neurons were scattered throughout the central area of VA. Retrogradely labeled cells were also found in the rostral part of the ventral lateral nucleus (VL). Injections of WGA‐HRP into the medial part of the caudate resulted in only a few labeled cells located in the dorsomedial part of VA.Combining these data with those from other studies mapping neostriatal afferents from the cerebral cortex in the dog, it is apparent that the midlateral part of the caudate receiving input from VA also receives afferents from cortical area 6. Furthermore, the dorsolateral part of the caudate that receives input from the lateral part of VA also receives afferents from cortical area 4. These results indicate that the dorsal and lateral parts of the canine caudate nucleus may constitute important links in the transmission and integration of information related to complex motor activities.
Simple and complex retinal ganglion cell axonal rearrangements at the optic chiasm
Authors: Springer Alan D. , Mednick Adam S. 
Published: January 2005

AbstractThe rearrangements that retinal ganglion cell (RGC) axons undergo near the optic chiasm were determined by ablating either the nasal, temporal, dorsal, ventral, or peripheral retina. The axons of the remaining intact RGCs were then labelled with cobaltous lysine. RGC axons change their relationship with respect to the axes of the brain and with respect to one another. Toward the caudal end of the optic chiasm, the optic tract begins to rotate axially such that its rostral edge ultimately becomes located medially. Thereby, the column of ventronasal RGC axons shifts from a rostral to a medial position. In addition, columns of axons from other retinal sectors move with respect to one another. Ventrotemporal RGC axons, located initially at the caudal edge of the tract, move toward and come to be positioned laterally to, the column of ventronasal RGC axons. The column of dorsonasal RGC axons moves from the rostral to the lateral side of the column of dorsotemporal RGC axons. Concurrently, the axons within each column reorganize internally. Each chronological lamina of axons within a column twists such that the nasal and temporal axons within each column invert their positions with respect to the edges of the column. All of these reorganizations take place between the caudal end of the optic chiasm and the division of the main optic tract into the optic brachia. Furthermore, the rearrangements that occur do not involve any alterations in the positions of central and peripheral RGC axons with respect to the surface of the diencephalon. The results are discussed with respects to mechanisms that might influence the organization of the visual pathways.
Patterns of afferent synaptic contacts in the alligator lizard's cochlea
Authors: Mulroy Michael J. 
Published: January 2005

AbstractAfferent synapses on both free‐standing and tectorial hair cells in the alligator lizard's cochlea are described quantitatively. Semiserial sections were photographed with a transmission electron microscope. Hair cells together with their afferent nerves were reconstructed and morphometrically analyzed with the aid of a computer. Each afferent nerve forms many synapses with its hair cell. Tectorial afferents make more than twice the number of synapses with their hair cells as do free‐standing afferents. This suggests a possible neuroanatomical basis for the physiological difference in synchrony reported in these two types of auditory nerve fibers; namely, the greater the number of synapses the better a fiber is able to follow faithfully the response of its hair cell.
The organization of the pudendal nerve in the male and female rat
Authors: McKenna Kevin E. , Nadelhaft Irving 
Published: January 2005

AbstractMature male and female Sprague‐Dawley rats were used in this study to compare the organization of the pudendal nerve in the two sexes. Experiments included (1) incubating the cut pudendal nerve in diamidino‐2‐phenylindole HCl (DAPI), fast blue (FB), or horseradish peroxidase (HRP) and (2) injecting individual perineal muscles with these substances. In both sexes, incubation of the pudendal nerve labelled two motoneuron nuclei in the L5‐L6 segments of the spinal cord. These nuclei are the dorsomedial (DM) and dorsolateral (DL) cell columns described by Schrϕder (J. Comp. Neurol. 192:567–587, 1980). In agreement with previous studies, there were significantly more neurons in both nuclei in the male than in the female and the neurons were larger in the male. In both sexes, the DL and DM nuclei were characterized by a longitudinal dendritic structure. The DM nucleus also had numerous dendritic bundles extending across the midline, linking the DM nuclei bilaterally.Pudendal nerve afferent neurons were located in the L6 and S1 dorsal root ganglia. In the male, the afferent neurons were larger and more numerous. In both sexes, labelled pudendal afferent fibers in the spinal cord were located in the dorsal columns, the medial half of Lissauer's tract, the extreme medial edge of the dorsal horn, both ipsilaterally and contralaterally, and in a large terminal field in the dorsal gray commissure. No labelled afferents were seen in the intermediate or ventral gray.Perineal muscle injections established that there was no difference between males and females in the number of motoneurons innervating the external anal or urethral sphincters. In the female, urethral sphincter motoneurons accounted for almost all the DL motoneurons, and anal sphincter motoneurons accounted for almost all the DM motoneurons. The ischiocavernosus and bulbospongiosus muscles are vestigial in the female rat. In the male, neurons innervating the anal sphincter and bulbospongiosus muscles were intermingled in the DM nucleus. In contrast, in the DL nucleus, the urethral sphincter neurons were located in the lateral portion of the nucleus and the ischiocavernosus neurons were located in the medial portion.
Immunohistochemical localization of urotensin I/corticotropin‐releasing factor, urotensin II, and serotonin immunoreactivities in the caudal spinal cord of nonteleost fishes
Authors: Onstott Donna , Elde Robert 
Published: January 2005

AbstractNeurosecretory cells in the caudal spinal cord of fishes were first discovered in elasmobranches. However, most of the subsequent work on the caudal neurosecretory system has emphasized its morphology and function in teleosts. Two major peptides, urotensins I and II (UI and UII), have been isolated from this system in teleosts and their amino acid sequences have been determined. We have used immunohistochemical techniques to confirm and expand previous morphological and pharmacological findings regarding the phylogenetic occurrence and the anatomical organization of the caudal neurosecretory system and to localize putative neurohormonal products within its structural elements. UII‐immunoreactive neuronal structures were found in the holocephalan, Hydrolagus collei; the elasmobranches, Squalus acanthias, Dasyatis sabina, and Raja binoculata; the dipnoan, Protopterus annectens; the brachiopterygian, Erpetoichthys calabaricus; the chondrostean, Polyodon spathula; and the holosteans Lepisosteus platyrhinchus and Amia calva. UI/corticotropin‐releasing‐factor immunoreactive elements were detected in the caudal spinal cords of Petromyzon marinus, Raja binoculata, Polydon spathula, Lepisosteus platyrhinchus, L. osseus, L. platostomus, and Amia calva. In addition, in several of these species, immunohistochemical techniques have provided evidence for serotoninergic input to the caudal neurosecretory system.
Accurate reinnervation of motor end plates after disruption of sheath cells and muscle fibers
Authors: Kuffler D. P. 
Published: January 2005

AbstractAfter injury, regenerating motor axons grow back to form neuromuscular junctions at the original synaptic sites on muscle fibers. The pathways they grow along consist of basement membrane, Schwann cells, and perineurium that remained after degeneration of the original axons. All the factors necessary for directing axons to the original synaptic sites persist in muscles even after disruption of myofibers. The aim of the present experiments was to determine whether structural integrity of nerve sheath cells is required for precise reinnervation in the presence and absence of muscle fiber targets.The region of innervation of the cutaneous pectoris muscle of the frog was briefly frozen to eliminate all living cells from neuromuscular junctions, intramuscular nerve bundles, and from a 1–3‐mm length of the nerve trunk. Only extracellular matrices persisted within the frozen region of muscle and nerve. These consisted of the basement membrane sheaths of myofibers, of Schwann cells, and of perineurial cells and the small fragments of disrupted cells that were bound to them. In some preparations new muscle fibers developed within the basement membrane sheaths. Regenerating axons grew through the naked basement membrane sheaths of original Schwann cells, formed numerous branches, and contacted the myofibers precisely at the original synaptic sites. By 5 weeks 75% of the original synaptic sites became reinnervated; the terminals were indistinguishable from those at normal neuromuscular junctions. In contrast, preparations in which all muscle fibers were prevented from regenerating far fewer synaptic sites became reinnervated. Five weeks after cell damage axon terminals were at only 6% of these naked synaptic sites.These results show that the original nerve sheath cells need not be intact for restoration of the normal pattern of innervation and that the naked basal lamina has associated with it factors that direct the regenerating axons to the original synaptic sites. However, myofibers also play a role by contributing cues that significantly increase the rate of innervation of synaptic sites.
Cholinergic innervation of the cat striate cortex: A choline acetyltransferase immunocytochemical analysis
Authors: De Lima Ana Dolabela , Singer Wolf 
Published: January 2005

AbstractIn area 17 of adult cats the morphology, distribution, and synaptology of cholinergic elements were examined by immunocytochemical methods with a monoclonal antibody against choline acetyltransferase (ChAT). ChAT(+) fibers are present throughout the entire depth of the cortex but are particularly dense in layer I. Typically these fibers are very thin and possess numerous irregularly spaced varicosities. Except in layer I and deep layer VI, where the fibers tend to run parallel to the pial surface, they appear to be randomly oriented.At the electron microscope level, immunolabeling was present in unmyelinated fibers of irregular contour and diameter. Most of the ChAT(+) varicose profiles contained mitochondria and round vesicles; Synaptic complexes were relatively infrequent and tended to be of the symmetrical type. They were located mostly on dendritic shafts and only rarely on cell bodies and dendritic spines. Both pyramidal and nonpyramidal cells were found to be innervated by cholinergic afferents.These anatomical data are consistent with the known physiology of acetylcholine in the visual cortex, which indicates that it acts as a modulator of cortical excitability.
Optic fibers follow aberrant pathways from rotated eyes in Xenopus laevis
Authors: Grant Philip , Ma Pokay M. 
Published: January 2005

AbstractThe rotated eye paradigm has been a major experimental test of the neuronal specificity model for the development of ordered retinotectal connections in amphibians. In most studies, however, no optic fiber pathways were traced from rotated eyes and correlated with visuotectal projections. As an initial approach to this question, optic fibers from eyes rotated at different embryonic stages were traced with 3H‐proline autoradiography. Three experimental series were prepared: (1) in situ eye rotations, (2) isochronic transplants of eyes rotated between embryos at the same stage, and (3) heterochronic transplants of eyes rotated between embryos at different stages. Single or multiple optic fiber pathways developing from rotated eyes are identified by their sites of entry and trajectory in the brain. These include a normal chiasmatic (CH) pathway, and three aberrant pathways, identified as trigeminal (TR), diencephalic (DI), and oculomotor (OC). The latter three enter the brain ipsilaterally, some crossing contralaterally via commissural pathways. Depending on stage and type of operation, TR pathways develop in 50–100% of the animals, while CH pathways are more common after rotation at stage 21/22. The surgical procedure affects the initial trajectory of fibers from the retina, perturbs guidance cues in the surrounding orbit, and determines the patterns of optic pathways that develop. In most cases, optic fibers follow motor (oculomotor) or sensory (trigeminal) nerves, usually the first fibers encountered near the orbit by axonal pioneers exiting the retina. Evidently, optic fibers exhibit no pathway selectivity; any axon serves as a guidance cue. Tecta are innervated in about 50% of the cases, usually by fibers following abnormal trajectories from CH and OC pathways. The results suggest that the development of ordered visuotectal projections from rotated eyes is a complex process that may be independent of the trajectory of fiber arrival. Unless pathways and visuotectal maps are directly compared in each animal, however, the question remains open because we still do not know which anomalous pathways, if any, correlate with ordered projections.
The motor trigeminal nucleus of the rat: Analysis of neuronal structure and the synaptic organization of noradrenergic afferents
Authors: Card J. Patrick , Riley Joseph N. , Moore Robert Y. 
Published: January 2005

AbstractThe organization of the rat motor trigeminal nucleus (MTN) and the morphology of noradrenergic afferents terminating in this cranial motor nucleus were analyzed with light and transmission electron microscopy. Two morphologically distinct types of neurons are present in the MTN. Large multipolar neurons are the most prevalent cell type and are distributedd uniformly throughout the nucleus. The morphology of these cells is identical to that of motor neurons described previously in both the brainstem and spinal cord. The neurons are characterized ultrastructurally by a light, organelle‐rich cytoplasmic matrix containing numerous cisternal arrays of rough endoplasmic reticulum (RER) and a centrally placed spherical nucleus containing a single prominent nucleolus. Approximately 80% of the surface of these cells is contacted by axon terminals. The second major class of neuron consists of small spherical and fusiform cells that are located predominantly at the peripheral borders of the MTN. These cells are significantly smaller than motor neurons and exhibit only scattered axosomatic contacts. This small cell population appears to be composed of two distinct subclasses of neurons that probably represent interneurons and gamma motor neurons.The MTN neuropil contains four morphologically distinct classes of axon terminals that are characterized by either spherical or pleomorphic vesicles within cytoplasm that is lucent or dense. Quantitative morphometric analysis demonstrated differential distribution of each of the four terminal types upon motor neuron somata and dendrites. Intracerebral injection of 5‐hydroxydopamine into the brainstem tegmentum immediately adjacent to the MTN labeled axon terminals containing spherical vesicles and a lucent axoplasmic matrix. Intracerebral injection of the neurotoxin 6‐hydroxydopamine resulted in degeneration of the same terminal population and thus confirmed that noradrenaline‐containing axons innervating the MTN exhibit a distinctive terminal morphology. The number of synaptic complexes exhibited by noradrenergic terminals did not differ significantly from other terminal populations in the MTN.
Laminar organization of ON and OFF regions and ocular dominance in the striate cortex of the tree shrew (Tupaia belangeri)
Authors: Kretz R. , Rager G. , Norton T. T. 
Published: January 2005

AbstractThe organization of ON and OFF responses and ocular dominance in the striate cortex of the tree shrew was electrophysiologically investigated by using flashed, stationary visual stimuli presented monocularly to either the ipsilateral or contralateral eye. We measured cortical multi‐unit activity at 25‐μm intervals with glass‐insulated platinum‐plated tungsten microelectrodes. Penetrations were made perpendicular to the cortical layers and the responses were quantitatively analyzed in layers IIIc to V. In sublayers IIIb, IIIc, and upper V, phasic responses of approximately equal magnitude occurred to both light ON and light OFF (ON‐OFF regions). In layer IV, tonic as well as phasic responses were often evoked by the flashed spot of light. In sublayer IVa stronger responses occurred to light ON than to light OFF (ON region) while in sublayer IVb stronger responses occurred to light OFF than to light ON (OFF region). In an ON region, the increased neural activity that occurred at light ON was often accompanied by a decrease in activity below baseline level at light OFF. A similar decrease often occurred in an OFF region at light ON. Recordings from the region of the cell‐sparse cleft in layer IV were characterized by ON‐OFF responses, signalling a transition zone between sublayers IVa and IVb. In addition, the responses to stimulation of the ipsilateral eye typically were very weak in the cleft region. In the other regions examined, the multi‐unit activity generally was driven binocularly with slightly greater responses being elicited by the contralateral eye. We conclude that the ON‐center and OFF‐center afferent pathways that are organized at the retinal level remain generally segregated in the tree shrew through the first synapse in the striate cortex. In addition, our recordings confirm that a horizontal organization of ocular dominance occurs in layer IV of the striate cortex in tree shrews.