bluuebunny/crossref_metadata_2025_split huggingface dataset:
Origin of spinal cord axons in the lizard regenerated tail: Supernormal projections from local spinal neurons
Authors: Duffy Mark T. , Simpson Sidney B. , Liebich Diana R. , Davis Brian M. 
Published: January 2005

AbstractDuring tail regeneration most lizards also regenerate the tail spinal cord. The regenerated spinal cord primarily contains neuroepithelium (i.e., the ependymal tube which forms the central canal) and descending axons. The present experiments identify the source of the axons in the regenerated spinal cord. Application of HRP to normal tail spinal cord resulted in labeled cells in the nucleus paraventricularis, the interstitial nucleus of the fasciculus longitudinalis medialis, the nucleus ruber, the medullary reticular formation (including raphe nuclei), as well as in vestibular nuclei. HRP applied to the regenerated spinal cord labeled only 4% of the cells seen in normal animals, and these were confined to rhombencephalic nuclei. The lack of labeling of more rostral nuclei was not due to the death of descending neurons. Application of HRP immediately rostral to the regenerated spinal cord resulted in the labeling of a normal, and in some cases, greater than normal, number of neurons.To quantify the origin of axons in the regenerated spinal cord, electron microscopic montages of the regenerated spinal cord were made and the number of axons counted, before and after various spinal lesions. Only lesions within one spinal segment of the regenerated spinal cord had a significant effect on the number of axons in the regenerated tail spinal cord. This indicated that most of the regenerated axons were of local spinal origin. A significant increase in the number of labeled local spinal neurons was revealed following application of HRP to a regenerated tail spinal cord. These results suggest that while various portions of the lizard central nervous system can grow axons into the regenerating tail spinal cord, the great majority of axons in the regenerate are of local origin and that some of these arise from neurons that do not normally possess descending projections. Finally, to test whether new neurons were participating in the regeneration process, 3H‐thymidine was injected during the regrowth of the tail. No labeled spinal cord cells were conclusively identified as neurons. Thus, the regenerating lizard tail spinal cord exhibits robust axonal sprouting from neurons near the site of a spinal transection in a manner reminiscent of sprouting in the mammalian CNS. This sprouting can develop into descending spinal projections that extend for significant distances into the regenerated tail spinal cord and provides a unique model for exploring the requirements for successful axon growth in an adult vertebrate CNS.
Development of olivocerebellar fibers in the clawed toad, Xenopus laevis: A light and electron microscopical HRP study
Authors: Van Der Linden J. A. M. , Ten Donkelaar H. J. , De Boer‐van Huizen R. 
Published: January 2005

AbstractAn anterograde tracer study was undertaken to provide a light‐ and electron microscopical description of climbing fiber development in the clawed toad, Xenopus laevis, ranging from premetamorphic stages to the adult state. The inferior olive was unilaterally labeled with horseradish peroxidase and the contralateral climbing fiber morphology investigated. At early stages of development, only undifferentiated fibers were observed in the rostral alar plate. At later stage, these fibers form large varicosities, which contact presumed cerebellar Purkinje cells. Finger‐like protrusions arising from the Purkinje cell somata penetrate the climbing fiber varicosities and form synaptic specializations at these contact sites. In older tadpoles, a large variety of climbing fiber morphologies was found displaying a mediolateral gradient. At dorsolateral cerebellar areas long and straight climbing fibers follow the Purkinje cell primary dendrites. However, in ventromedial areas pericellular baskets or nests were found on presumed Purkinje cell somata. These pericellular nests were found throughout development but were not observed in adult animals. Both pericellular nests and real climbing fibers make synaptic contacts on spiny protrusions of the Purkinje cell's somatic or dendritic surface. In several cases, labeled as well as unlabeled climbing fiber profiles were observed on the same Purkinje cell, indicating multiple, convergent innervation. Also, divergent Purkinje cell innervation was found. In conclusion, this study shows that anuran climbing fiber development encompasses stages and processes similar to those observed in mammals. The only principal difference with climbing fiber development in mammals is the low degree of synchrony observed in anurans.
Ultrastructure of the mammillotegmental projections to the ventral tegmental nucleus of gudden in the rat
Authors: Hayakawa Tetsu , Zyo Katuya 
Published: January 2005

AbstractThis study examines the termination pattern of axons from the medial mammillary nucleus within the ventral tegmental nucleus of Gudden (TV) in rats by using anterograde transport of horseradish peroxidase conjugated with wheat germ agglutinin (WGA‐HRP) and visualized with tetramethylbenzidine. The neuropil of TV contains three classes of axodendritic terminals, that is, terminals containing round, flat, and pleomorphic synaptic vesicles. These types make up 55.6%, 26.1%, and 18.3%, respectively, of all normal axodendritic terminals. Injection of WGA‐HRP into the medial mammillary nucleus permits ultrastructural recognition of anterogradely labeled terminals within the TV. More than 80% of the labeled terminals contain round synaptic vesicles and form asymmetric synaptic contacts, whereas about 16% contain flat synaptic vesicles with symmetric synaptic contacts. There are a few labeled terminals with pleomorphic vesicles and only a few axosomatic terminals. Almost all labeled terminals are small, having diameters of less than 1.5 μm. Compared with the distributions of normal and labeled terminals with round vesicles, there is an increase of the percentage of labeled terminals with round vesicles on the intermediate dendrites (1‐2 μm diameter) and a decrease on the distal dendrites (less than 1 μm diameter). Anterogradely labeled axon terminals often contact retrogradely labeled dendrites.These results suggest that the medial mammillary neurons send mainly excitatory as well as a few inhibitory inputs to the dendrites of TV and have direct reciprocal contacts with the TV neurons.
Development of retinotopy in projections from the eye to the dorsal lateral geniculate nucleus and superior colliculus of the wallaby (Macropus eugenii)
Authors: Marotte L. R. 
Published: January 2005

AbstractThe development of retinotopy in projections from the eye to the dorsal lateral geniculate (dLGN) and superior colliculus (SC) has been studied in the marsupial wallaby. Discrete retinal lesions were made and the remaining retinal projections were traced with horseradish peroxidase in animals at stages ranging from just after optic innervation of the dLGN and SC to the time when the projections are mature.Topographically organised projections could be recognized a few weeks after axons first reached the dLGN and SC with a topographically discrete projection from nasoventral retina recognized later than from dorsal, dorsotemporal, temporal, and temporoventral retina. Over time there was an increase in precision of the retinotopy as judged by an increase in sharpness of the borders of filling defects in the projection labelled with horseradish peroxidase. Refinement of the projection from temporal retina preceded that from nasal retina in both the dLGN and SC and in the former occurred concomitantly with the segregation of eye‐specific terminal bands. Refinement was complete 16 weeks after birth, prior to eye opening at around 20 weeks after birth. Inequalities in retinal representations in both nuclei were present from the time retinotopy could first be detected. This was before the inequalities in retinal ganglion cell distribution, which underly these representations in the adult, were obvious.Retinotopy and inequalities in retinal representation characteristic of the adult are present from a very early stage in the protracted development of visual projections in the wallaby. Refinement may involve death of inappropriately projecting cells, pruning of inappropriately projecting axon arborizations or could be achieved by growth of the retinorecipient neuropil. Temporonasal differences in the time course of refinement may reflect gradients of maturation in the retina.
Delineation of a brain nucleus: Comparisons of cytochemical, hodological, and cytoarchitectural views of the song control nucleus HVC of the adult canary
Authors: Gahr Manfred 
Published: January 2005

AbstractThe present investigation used stable area‐specific, neuronal properties instead of Nissl stain to delineate the boundaries of the nucleus hyperstriatalis caudal c (HVc) in the telencephalon of the adult male canary. Immunocytochemical procedures combined with retrograde tracing labeled a large population of perennial long‐projecting neurons that contain estrogen receptors in the canary HVc. The HVc area defined by the distribution of these neurons was congruent with the HVc area defined in Nissl‐stained sections during the breeding period. The HVc area defined in Nissl‐stained preparations showed an extensive seasonal change in size, confirming previous results Nottebohm: Science, 214:1368–1370, '81. In contrast, the HVc area defined by the distribution of the estrogen receptor containing long‐projection neurons showed little or no seasonal change in size. Because these neurons are permanent, the HVc seems to be of rather constant size year round. The internal morphology of the HVc, however, undergoes seasonal alterations, which are reflected in changes in size of the HVc area distinguishable in Nissl‐stained sections. The combination of cytoarchitectural criteria of Nissl‐stained preparations with area‐specific cytochemical and hodological markers to delineate the boundaries of a brain nucleus might give new insights in the partitioning and neural plasticity of brain areas.
Origins and terminations of bulbospinal axons that contain serotonin and either enkephalin or substance‐P in the North American opossum
Authors: Reddy V. K. , Cassini P. , Ho R. H. , Martin G. F. 
Published: January 2005

AbstractWe have shown previously that some enkephalin, substance‐P, and serotoninergic neurons in the medullary raphe and adjacent reticular formation project to the spinal cord in the opossum. In the present study we have combined the retrograde transport of True Blue and immunofluorescence histochemistry to determine whether methionine enkephalin or substance‐P containing bulbospinal neurons are serotoninergic. Furthermore, we have used the same immunofluorescence protocol to determine whether spinal axons cocontain the same substances.Neurons that immunostained for both enkephalin and serotonin were observed in many brainstem nuclei. However, those that projected to the spinal cord were limited to the nuclei raphe magnus and obscurus, and the ventral part of nucleus reticularis gigantocellularis, pars ventralis. Neurons that immunostained for both substance P and serotonin were fewer in number, but some of the ones in the above nuclei and within the nucleus raphe pallidus, projected to the spinal cord.Spinal axons exhibiting both enkephalin‐ and serotonin‐like immunoreactivity were observed in the superficial laminae of the dorsal horn, lamina X, and the intermediolateral cell column, whereas those showing both substance‐P and serotonin‐like immunoreactivity were seen primarily in lamina X, the intermediolateral cell column, and the ventral horn. Some of the axons in the ventral horn were in close apposition to presumed motoneurons. Comparison of the above results with those obtained from previous studies of bulbospinal projections has allowed us to infer the origins of axons that innervate different spinal targets.
Differential growth and remodelling of ganglion cell dendrites in the postnatal rabbit retina
Authors: Wong Rachel O. L. 
Published: January 2005

AbstractThe postnatal dendritic maturation of small field type 1 (SF1), medium field type 1 (MF1) and type 2 (MF2), and large field type 1 (alpha) ganglion cells in the rabbit retina was compared qualitatively and quantitatively. Dendritic tree structure was revealed by intracellular injection of the fluorescent dye Lucifer yellow, and the stained cells were then morphologically separated on the basis of soma area, dendritic field size, total dendritic length, number of nodes, and mean internodal distance. Cells in the visual streak and an area inferior to the streak were sampled from retinae between birth and adulthood.The dendrites of all studied classes of rabbit ganglion cells were extensively covered by short spine‐like appendages. As in cat retina, many dendritic spines disappeared by the end of the third postnatal week, at which stage the adult dendritic form could be recognised. However, there was differential loss in the number of spines from the dendrites of the four cell classes. In both the streak and inferior retina, adult SF1 cells had the same number of spines/dendritic unit length througout postnatal life, whereas MF1 and MF2 ganglion cells lost at least half of their number of spines/unit dendritc length by maturity. Alpha ganglion cells lost virtually all their dendritic spines by adulthood. In both retinal locations, there were small changes in the number of nodes (dendritic branch points) of small field and medium field ganglion cells but alpha cells lost between 70 to 80% of their nodes by adulthood. The dendrites of ganglion cells with contrasting morphology thus undergo differential remodelling during postnatal maturation. The completion of the period of dendritic remodelling coincided with the first appearance of adult receptive field organisation, suggestion, suggesting that structural remodelling, in particular that involving dendritic spines, may be associated with the development of the cell's synaptic circuitry.The dendrites of neighbouring postnatal ganglion cells in the rabbit retina also grow by different amounts; the increase in dendritic tree area, total dendritic length, and mean internodal distances of alpha cells exceeded that of small field and medium field cells in corresponding retinal positions. This implies that retinal dendrites elongate by active growth rather than by “passive stretching.”.
Synaptic organization of neurotensin immunoreactive amacrine cells in the chicken retina
Authors: Li Hai‐Biao , Lam Dominic Man‐Kit 
Published: January 2005

AbstractImmunohistochemistry was utilized to investigate the light and electron microscopic localization of neurotensinlike immunoreactive (NT) amacrine cells in the chicken retina. The NT cells possess oval cell bodies (7 μm in diameter) that are located in either the second or third tier of cells from the border of the inner nuclear and inner plexiform layers. The processes of such cells extend into the inner plexiform layer where they ramify as a narrow plexus in sublamina 1 and as a broad plexus in sublaminas 3 and 4. Additionally, stained processes are observed occasionally within sublamina 5.At the ultrastructural level, NT‐positive somas exhibit a rather dense and evenly distributed peroxidase reaction product throughout their cytoplasm. The nucleus of NT amacrine cells possess a round, unindented nuclear membrane. NT‐immunoreactive processes in the inner plexiform layer interact synaptically only with non‐NT cells. NT processes receive synaptic input mainly from the processes of amacrine cells and to a lesser degree from bipolar cells. The large majority of NT‐stained varicosities form presynaptic contacts onto the processes of amacrine cells, but are also presynaptic to bipolar cell axon terminals. Moreover, each of the above synaptic relationships can be identified in each of sublaminas 1 and 3 to 4 of the inner plexiform layer. In addition, NT processes are presynaptic to processes devoid of synaptic vesicles that may originate from ganglion cells. Finally, NT processes occasionally form synaptic contacts onto somas situated in the most proximal row of the inner nuclear layer.
Distribution and synaptic organization of serotoninergic and noradrenergic axons in the lateral geniculate nucleus of the rat
Authors: Papadopoulos Georgios C. , Parnavelas John G. 
Published: January 2005

AbstractAntisera raised against the monoamines serotonin (5‐HT) and noradrenaline (NA) were employed in a study designed to provide a detailed description of the distribution, morphology, and synaptic organization of the serotoninergic and noradrenergic afferents in the lateral geniculate nucleus (LGN) of the rat. The distribution patterns of the two types of immunoreactive fibers were distinct and largely complementary to each other. NA axons were particularly concentrated in the dorsal lateral geniculate nucleus (LGd), with the ventral lateral geniculate nucleus (LGv) and the intergeniculate leaflet (IGL) receiving substantially fewer fibers. In contrast, 5‐HT axons, although present throughout the LGN, were preferentially concentrated in the LGv and IGL.5‐HT and NA axon terminals and axonal varicosities, examined in single and serial ultrathin sections, formed conventional synapses in the extraglomerular neuropil. The types of synapses and the nature of the postsynaptic targets were different for the two monoamines. 5‐HT afferents formed asymmetrical synapses on dendritic spines and shafts of both presumptive relay cells and interneurons but established symmetrical synapses on cell bodies. However, NA afferents formed almost exclusively symmetrical synapses on dendritic spines and shafts and made no contacts with cell bodies.The present findings suggest that the 5‐HT and NA afferents of the rat LGN, which are likely to influence certain stages of visual processing, exhibit distinct organizational principles and act at restriced sites as do other classical neurotransmitter systems.
Synaptic organization in the adult ferret medial superior olive
Authors: Brunso‐bechtold J. K. , Henkel C. K. , Linville C. 
Published: January 2005

AbstractThe ultrastructure of the medial superior olive (MSO) was studied in the adult ferret. The synaptic terminals were categorized on the basis of morphology and their distribution determined. There are three types of synaptic terminals: R terminals, containing round vesicles; Ov terminals, containing ovoid vesicles; and P terminals, containing vesicles of varying morphologies. R terminals are the dominant terminal type on both the somata and dendrites. Ov and P terminals are equally prevalent on the dendrites; however, P terminals are significantly more common than Ov terminals on the somata. Furthermore, P terminals are significantly more common on the somata than on the dendrites. These results suggest that there is some segregation of types of afferent synapses on MSO cells.
Morphology of single intracellularly stained axons terminating in area 3b of macaque monkeys
Authors: Garraghty Preston E. , Sur Mriganka 
Published: January 2005

AbstractWe have studied the morphology of single thalamocortical axons innervating area 3b of postcentral somatosensory cortex in macaque monkeys. We recorded from axons in the white matter below the representation of the hand in postcentral cortex in two monkeys (Macaca fascicularis) by using micropipettes filled with horseradish peroxidase (HRP). When an axon was recorded, we delineated its receptive field and determined its modality, and if cutaneous, whether it was slowly or rapidly adapting (SA or RA). We then impaled the axon and injected it with HRP. We recorded and successfully injected many more RA than SA axons, possibly because of differences in their true proportions. The RA axonal arbors varied in mediolateral extent from 350 to 800 μ with a mean of 600 μ One of the RA axons gave rise to four separate arbors spanning 2.5‐3.0 mm of cortex. The single SA axon we recovered was 370 μ in width. We suggest that the individual terminal zones underlie the columnar parcellation of the somatosensory cortex. The presence of arbors spanning several such columns suggests that all regions within the arbor may not be equally effective in driving cortical cells under normal conditions, and such arbors may provide the substrate for a cortical response to alterations in the pattern of input.
Statistical analysis of corticopontine neuron distribution in visual areas 17, 18, and 19 of the cat
Authors: Bjaalie Jan G. , Diggle Peter J. 
Published: January 2005

AbstractThe spatial organization of visual corticopontine neurons was studied both at a “large scale” (in relation to cortical visual field maps) and at a “small scale” (in relation to cortical modular organization). Large injections of horseradish peroxidase‐wheat germ agglutinin were made in the pontine nuclei. In complete series of sections from parts of areas 17, 18, and 19, the position of each retrogradely labeled neuron was recorded with an x‐y plotter connected to the microscope stage. Each cell was thus given a set of x, y, and z coordinates. After alignment of the sections, three‐dimensional computer reconstructions of the distribution of the labeled cells were made. With program RPOP (developed by Blackstad and Bjaalie, ′88), the reconstructions were studied with different rotations, scaling, etc. In addition, section‐independent parts of reconstructions were isolated („windows”︁) and further analyzed. Curved parts were automatically unfolded for inspection of distribution patterns and determination of cell densities. The spatial distribution of the labeled cells was analyzed within small windows, where density gradients are negligible.We confirm and extend previous demonstrations of a large‐scale aggregation of visual corticopontine cells due to density gradients by showing that densities of corticopontine neurons increase linearly as a function of distance from paracentral to lower visual field representations in area 17 (and partly in areas 18 and 19). We demonstrate that density gradients are steeper in area 17 than in area 18. For example, clear‐cut differences between the areas in mediolateral density gradients are found. These findings are discussed in relation to the different visual field maps of the areas and the existence of a similar visual field representation in corticopontine projections from different visual areas.The type of small‐scale distribution (randomness or non‐randomness, aggregation into clusters, bands, etc.) was studied with statistical methods. Such analysis shows that the labeled cells within small zones are non‐randomly distributed in all three areas. In most cases, the analysis indicates an aggregated spatial distribution. A possible relationship to the cortical map of direction selectivity is discussed. To our knowledge, this study is the first to combine the use of three‐dimensional computer reconstructions of a population of labeled neurons, with subsequent statistical analysis of apatial point (cell distribution) patterns.