摘要:

AbstractWe explored the course and termination of primary vestibular afferent fibers within the brainstem of the guinea pig by means of anterograde axonal transport of horseradish peroxidase (WGA‐HRP). Primary vestibular afferent fibers distribute within the entire vestibular nuclear complex, with the exception of the dorsal part of the lateral vestibular nucleus. The superior vestibular nucleus is characterized by the concentration of terminals within its central part. Although terminal labeling is weaker within the periphery, no area completely lacks primary input. The lateral vestibular nucleus can be divided into a ventral and a dorsal part; within the ventral part small and giant cells receive primary afferent fibers, whereas no significant terminal labeling occurs in the dorsal part. The medial vestibular nucleus shows the most uniform labeling, although the lateral part of its rostral third has a few more terminals than the medial half. Primary projection to the descending vestibular nucleus is widespread, although in its rostrodorsal part it is less impressive. Of the small cell groups commonly associated with the vestibular nuclear complex, only group y receives abundant primary input. Whereas group z completely lacks labeled fibers as well as terminals, single primary axons can be observed passing groups x and f. However, no terminals can be found within the borders of these two cell groups. Scanty projections can be detected within the prepositus hypoglossi nucleus, as well as within the external cuneate nucleus, the cochlear nucleus, the abducent nucleus, and parts of the reticular formatio

ISSN:0092-7317    

DOI:10.1002/cne.902930202

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractRabbit retinas were fixed with mixed aldehydes and examined for the fluorescence of catecholamines. Labeled cell bodies were present in the layer of the amacrine cells. A band of fluorescent processes was present in layer 1 of the inner plexiform layer. Weaker labeling was present in two deeper strata, one near the middle of the inner plexiform layer (presumably layer 3) and one at the juction of layers 4 and 5. Immunohistochemistry showed tyrosine hydroxylase (TH) to be present in the same cells and the same strata of the inner plexiform layer as the endogenous catecholamines. Exposing the retina to exogenous dopamine or norepinephrine resulted in stronger labeling in the middle and deep levels of the inner plexiform layer. At the same time a second population of amacrine cell bodies became visible.Catecholamine fluorescence contained in the amacrine cell bodies was used as a guide to their injection with Lucifer yellow CH. The filled dendritic arbors revealed two main types of cells. The type 1 cells are monostratified at the most distal level of the inner plexiform layer. They have relatively uncomplicated, radially branching dendritic trees. They are the cells densely stained by immunohistochemistry with antibodies against. TH. The type 2 cells are tristratified, with minor branching in layer 1 of the inner plexiform layer and major branching in the two deeper sublayers. The descending dendrites follow a complicated course, and it is not uncommon for intermediate dendrites to cross between strata more than once.The relationship of the cells to their dendritic plexuses was further studied in retinas in which the aldehyde‐induced fluorescence of catecholamines was photoconverted to a diaminobenzidine product. The type 1 cells were found to dominate the plexus of dendrites in layer 1 of the inner plexiform layer. The catecholaminergic plexuses in the middle and deep levels of the inner plexiform layer are formedf by dendrites of the type 2 cells.The position of every type 1 cell was mapped in retinas stained with antibodies directed against TH. In one retina we counted 5,613 type 1 cells, distributed evenly across the retina. In another retina, all of the catecholamine‐accumulating cells were counted. There were 9,058 with a distribution that peaks in the visual streak. The type 1 cells appear to be the dopaminergic cells previously studied by others and thought to regulate the flow of information from rod bipolar cells to ganglion cells. The low density and wide spread of type 2 cells suggests that they, too, perform a generalized control function, presumably a novel one that dictates their intricate, tristratified sh

ISSN:0092-7317    

DOI:10.1002/cne.902930203

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractImmunocytochemistry with an antiserum directed against serotonin (5‐HT) was used to assess the development of the representation of the body surface in the rat's primary somatosensory cortex (S‐I). Within 1 hour of birth (P‐O), 5‐HT‐positive fibers were present in the marginal zone, the cortical plate, and developing layers V and VI. Immunoreactivity in the marginal zone consisted of a thin band of coarse fibers oriented parallel to the pia. Only a small number of isolated fibers were visible in the cortical plate. A denser network of both coarse and fine fibers could be seen in presumptive layers V and VI. By the first hour of P‐1, 5‐HT‐positive axons in the deeper cortical plate were organized into a crude representation of the rat's body surface. At this age, aggregates of fibers corresponding to the head, lower jaw, trunk, and forepaw could be clearly distinguished. These regions of dense 5‐HT immunoreactivity consisted primarily of fine caliber axons that had invaded the lower part of the cortical plate. Dense aggregates of fine caliber axons were also visible in developing layers V and VI. Coarse 5‐HT‐positive fibers were visible in all layers, but they did not appear to contribute to the pattern that corresponded to the body surface. By the first hour of P‐2, the map of the body surface in S‐I was more refined and a row‐related organization of 5‐HT‐immunoreactive fibers was visible in the portion of the cortex representing the vibrissa pad. The laminar distributions of coarse and fine caliber serotoninergic axons at this age were essentially the same as on P‐1. By P‐2.5 (60 hours after birth), patches of 5‐HT‐positive fibers corresponding to individual vibrissa follicles were clearly evident. These consisted of dense aggregates of fine caliber axons that were centered in presumptive layer IV, but which also extended above and below this lamina. Over the next 3 days, the pattern continued to mature. By P‐4, dense 5‐HT labelling was also visible in the secondary somatosensory cortex (S‐II). By the beginning of P‐5, clusters of fibers corresponding to more rostral facial hairs and individual digits within the forepaw representation could also be discerned. By P‐12, the differential distribution of 5‐HT fibers in S‐I was no longer visible. Thus, immunocytochemistry for serotonin showed a representation in S‐I homeomorphic with the body surface prior to the age at which it can be discerned with other methods thought to reveal thalamocortical axons.Transection of the infraorbital nerve (ION) on the day of birth altered the organization of the vibrissal representation in the contralateral cortex from the earliest age at which it could be detected by 5‐HT immunocytochemistry in normal animals. Hawever, the departure from the normal organization was gradual. Row‐related organization was clearly visible in the cortices of rats sacrificed on P‐3, but not in those of rats that were killed on P‐5. These results suggested that the organization of the 5‐HT innervation of the cortex may be guided by thalamic afferents and further that some aspects of this guidance persist. albeit temporarily, after ION transection on P‐0.The 5‐HT immunoreactivity that we observed in the developing somatosensory cortex was not contained in thalamocortical axons. Unilateral electrocautery of the ventrobasal thalamus on P‐4 did not reduce the density or alter the pattern

ISSN:0092-7317    

DOI:10.1002/cne.902930204

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

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 CN

ISSN:0092-7317    

DOI:10.1002/cne.902930205

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractTwo apical unidirectional and 16 basal bidirectional papillar hair cells of the yucca night lizard,Xantusia vigilis, were serially sectioned for transmission electron microscopy (TEM) to determine the pattern of hair cell innervation. The 16 bidirectional hair cells (central group) were sectioned across the entire width of the papilla and consisted of four complete hair cells in each of the first three rows and the upper (or neural) half of the four hair cells in the fourth or last row. Both hair cell types were nonexclusively innervated, i.e., each afferent nerve fiber innervated two or more hair cells. The apical unidirectional hair cells were innervated by six or seven different afferent nerve fibers and five or six efferent fibers. The afferent nerve fibers made an average of 52.5 synapses/hair cell. In the central group of 16 bidirectional hair cells, 25 different afferent nerve fibers innervated an average of 4.5 hair cells. The average number of hair cells innervated by the eight afferent nerve fibers limited to the central group was 5.4. An unusual finding was the presence of gap junctions directly interconnecting more than half the hair cells in both papillar segments. In the bidirectional hair cell region, it was possible to count the number of gap junctions between 24 contiguous hair cells. The average number of gap junctions was four per hair cell, and all bidirectional hair cell were either directly or indirectly interconnected by gap junctions. The possible function of a nonexclusive type of hair cell innervation and the presence of large numbers of gap junctions are discussed.

ISSN:0092-7317    

DOI:10.1002/cne.902930206

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

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 anur

ISSN:0092-7317    

DOI:10.1002/cne.902930207

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThis study analyzes the structural variability of granule cells in the monkey fascia dentata. The hippocampi of three adult rhesus monkeys (Macaca mulatta) and two 1‐year‐old female baboons (Papio anubis) were used for a combined Golgi/electron microscope (EM) study. The results were compared with other Golgi/EM studies on dentate granule cells in small laboratory animals.Whereas the granule cells in small rodents form a relatively uniform population of neurons, we observed a much greater variability of granule cell morphology in monkeys. This variability concerned the size of the cell body, the length and thickness of apical dendrites, the spine density, and the occasional occurrence of basal dendrites. The dendritic length of individual granule cells largely depended on their position in the highly convoluted granular layer. These convolutions caused significant variations in the thickness of the molecular layer and consequently in the length of individual granule cell dendrites. Granule cells with thick dendrites densely covered with spines could be differentiated from those exhibiting much thinner dendritic processes and moderate spine numbers. About 10% of granule cells in the monkey fascia dentata exhibited basal dendrites. Occasionally in the hilus ectopic granule cells were observed that gave rise to long apical dendrites traversing the granular layer. The axons of granule cells, the mossy fibers, entered the hilus, where they gave off several collaterals.In contrast to the light microscopic variability, subtypes of granule cells revealed similar fine structural characteristics, i. e., a round nucleus lacking indentations, a thin rim of cytoplasm, and characteristic spine formations. Large complex spines and smaller, “stubby” spines were observed on apical as well as basal dendrites. This suggests that characteristic spine formations were not induced by specific afferent fibers. All synaptic contacts on spines were of the asymmetric type, whereas both symmetric and asymmetric synapses occured on cell bodies and dendritic shafts.Unlike in rodents, we found a large variability of granule cells in the primate fascia dentata. This variability has to be considered in neropathological studies of this ce

ISSN:0092-7317    

DOI:10.1002/cne.902930208

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractPrevious studies of growth cones in invertebrates have shown that they become larger and more complex when changing direction in response to cellspecific contacts (Bentley and Caudy, '83; Raper et al., '83b; Caudy and Bentley, '86). In pathways of the vertebrate nervous system, analogous regions, termed “decision regions,” have been identified in which axons change direction and their growth cones become more elaborate than when tracking along straight trajectories (Tosney and Landmesser, '85a; Bovolenta and Mason, '87). In order to assess the generality of these principles to the mammalian CNS, we studied the morphology of growth cones and their interactions with the environment in the developing corpus callosum. Given the straight pathway that callosal axons could use to navigate across the callosum, one might predict that later arriving axons would extend on those growing out earlier and that therefore, by analogy with previous studies, many growth cones would have simple tapered morphologies. Surprisingly, however, virtually all growth cones in the callosal white matter, regardless of age or position, were complex with broad lamellipodial veils and/or numerous, often lengthy filopodia. Only growth cones entering the cortical target were consistently smaller. As seen in the EM, the predominant elements in the callosal pathway are other axons and growth cones; we found no evidence for specialized contacts. These results suggest that there is no specific decision region for the fiber population as a whole; rather it is possible that in this mammalian CNS pathway individual growth cones respond independently to molecular cues broadly distributed in the callo

ISSN:0092-7317    

DOI:10.1002/cne.902930209

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractThe ventral striatum is considered to be that portion of the striatum associated with the limbic system by virtue of its afferent connections from allocortical and mesolimbic areas as well as from the amygdala. The efferent projections from this striatal region in the primate were traced by using 3H aminoacids andPhaseolus vulgaris‐leucoagglutinin (PHA‐L). Particular attention was paid to the topographic organization of terminal fields in the globus pallidus and substantia nigra, the projections to non‐extrapyramidal areas, the relationship between projections from the nucleus accumbens and the other parts of the ventral striatum, and the comparison between ventral and dorsal striatal projections.This study demonstrates that in monkeys a circumscribed region of the globus pallidus receives topographically organized efferent fibers from the ventral striatum. The ventral striatal fibers terminate in the ventral pallidum, the subcommissural part of the globus pallidus, the rostral pole of the external segment, and the rostromedial portion of the internal segment. The more central and caudal portions of the globus pallidus do not receive this input. This striatal output appears to remain segregated from the dorsal striatal efferent projections to pallidal structures.Fibers from the ventral striatum projecting to the substantia nigra are not as confined to a specific region as those projecting to the globus pallidus. Although the densest terminal fields occur in the medial portion, numerous fibers also extend laterally to innervate the dorsal stratum of dopaminergic neurons of the substantia nigra and the retrorubral area. Furthermore, they project throughout the rostral‐caudal extent of the substantia nigra. Projections from the medial part of the ventral striatum reach the more caudally located pedunculopontine tegmental nucleus. Thus unlike the above described terminals in the globus pallidus, the ventral striatum project widely throughout the substantia nigra, a fact that indicates that they may contribute to the integration between limbic and other output systems of the striatum.Finally, the ventral striatum projects to non‐extrapyramidal regions including the bed nucleus of the stria terminals, the nucleus basalis magnocellularis, the lateral hypothalamus, and the medial

ISSN:0092-7317    

DOI:10.1002/cne.902930210

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY

摘要:

AbstractIn macaques, the frontal eye field and the recently defined supplementary eye field play a role in the production of eye movements. Whereas the structure and function of the frontal eye field are well understood, little is known about the supplementary eye field. The goal of this study was to determine the connections of the physiologically defined supplementary eye field. In each case, the location of the supplementary eye field was determined by using intracortical microstimulation, the borders were marked with small electrolytic lesions, and horseradish peroxidase conjugated to wheat germ agglutinin was injected into the supplementary eye field. After the tissue was incubated with tetramethyl benzidine, it was determined that in three cases the injection site was confined to the physiologically defined supplementary eye field.The present results indicate that the supplementary eye field is reciprocally connected with the claustrum, ventral anterior nucleus, including pars magnocellularis, nucleus X, posterior subdivision of the ventral lateral nucleus, multiform, parvocellular, magnocellular, and densocellular subdivisions of the medial dorsal nucleus, central lateral nucleus, parafascicular nucleus, and suprageniculate‐limitans complex. The supplementary eye field projects to the putamen, caudate, reticular nucleus of the thalamus, central densocellular nucleus, zona incerta, subthalamic nucleus, rostral interstitial nucleus of the medial longitudinal fasciculus, parvocellular part of the rednucleus, intermediate and deep layers of the superior colliculus, central gray, cuneiform nucleus, mesencephalic reticular formation, pontine gray, nucleus reticularis tegmenti pontis, and nucleus reticularis tegmenti pontis, and nucleus reticularis pontis oralis.The supplementary eye field is reciprocally and bilaterally connected with periprincipal and inferior prefrontal cortex, with periarcuate cortex, including the frontal eye field, the frontal ventral region, and with postarcuate premotor cortex, and cortex surrounding the supplementary eye field, including the supplementary motor area. The supplementary eye field is also reciprocally connected ipsilaterally with cortex in and around the cingulate sulcus and the intraparietal sulcus, whereas cortex within the superior temporal sulcus projects to the supplementary eye field.The connections of the physiologically defined supplementary eye field are compared to previously demonstrated connections of the supplementary motor region and of the physiologically defined frontal eye field. Comparisons between the connections of the frontal and supplementary eye fields reveal that both regions are connected with structures related to visuomotor functions, but the frontal eye field has more extensive connections with vision‐related structures, and the supplementary eye field has more extensive connections with structures related to prefrontal and skeletomotor functions. Such connectional differences suggest functional differences between these two sensorimotor regions of the frontal l

ISSN:0092-7317    

DOI:10.1002/cne.902930211

出版商:Wiley‐Liss, Inc.    

年代:1990

数据来源: WILEY