摘要:

AbstractThe developmental mechanisms that allow physiological coding of acoustic pitch have remained unexplained. Cochlear hair cells that have different structures respond to different sound frequencies and synapse with neurons that project to different locations in the brain. How do these hair cells develop appropriate structures, and how are the connections between specific hair cells and the neurons that code for their pitch sensitivities matched? We have investigated one aspect of this by denervating embryonic chicken ears, before the time of hair cell production, and then transplanting them to the aneural chorioallantoic membrane of host embryos where they have continued to develop. We report that vestibular and auditory hair cell phenotypes differentiate appropriately and that correct gradients of hair cell structural phenotypes, as expressed in stereocilia bundles, develop in the cochleae of these denervated ears. Therefore, the normal development of gradients in hair cell stereocilia properties must be controlled by location‐specific cues originating in the ear itself. Neuronally directed modification of target cell phenotypes is not required for the quite specific phenotype development represented by the stereocilia bundles of individual hair cells and the connectional matching in the numerous distinct peripheral information lines of the auditory syste

ISSN:0092-7317    

DOI:10.1002/cne.902880402

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractPositional markers in the tectum, which are thought to guide growing axons to their target sites, have been proposed to be induced by axons, to be only transiently associated with the tectal cells, and then lost after long‐term denervation periods (Schmidt:J. Comp. Neurol.177: 279–300, '78). To further investigate this concept, retinal axons were induced to regenerate into ipsilateral tecta which had been deprived of their retinal afferents for shorter (0–4 months) and longer periods (4–8 months). The paths of HRP‐labeled regenerating axons of known retinal origin were traced and used as an operational test to decide whether the axons might navigate under the influence of positional markers. Two different kinds of experiments were performed:The axons from a subpopulation of all ganglion cells in the retina were labeled by applying a small crystal of HRP at defined retinal regions. Independent of the denervation period of the tectum, the labeled regenerating axons traveled in abnormal but nonrandom routes. In early regeneration stages, axons exhibited signs of exploratory growth. They extended branches equipped with growth cones and filopodia into various regions of the tectum. In late regeneration stages, the axons lost these branches, exhibited U‐turns and bends, and ended in terminal arbors in the retinotopic target region. These findings suggest that the axons travel under the influence of tectal positional markers and that these markers are not transient.Axons from a surgically created temporal hemiretina were labeled by application of HRP to the optic nerve to test whether the temporal axons might expand into the caudal tectum in long‐term‐denervated tecta. The HRP‐labeled axons coursed over rostral and midtectal regions. Instead of invading the caudal tectum they bent and terminated in the rostral tectal half. These results add further support for the conclusion that the path of regenerating retinal axons is governed by long‐lasting

ISSN:0092-7317    

DOI:10.1002/cne.902880403

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractIn this study the pattern of projections from the rostral intralaminar thalamic nuclei to the cerebral cortex was examined in the cat by autoradiography. Injections of tritiated proline and leucine were placed into the central lateral, paracentral, central medial, and para‐stria medullaris nuclei.After injections into the central lateral nucleus, label is present on the lateral side within the presylvian sulcus, in most of the suprasylvian gyrus, including the adjacent lateral and suprasylvian sulci, and in the posterior corner of the ectosylvian gyrus. On the medial side, label is present in the orbitofrontal (Of), precentral agranular (Prag), anterior limbic (La), retrosplenial (Rs), and postsubicular (Ps) areas, as defined by Rose and Woolsey ('48a). The cingulate gyrus also contains label throughout (part of which was defined as the “cingular area,” Cg, by Rose and Woolsey, '48a). Label is also found on both banks of the splenial and cruciate sulci. In addition, label is present within the lateral gyrus, on both its lateral and medial sides.The paracentral projections are similar to the central lateral input. On the lateral side, label is found within the presylvian sulcus, suprasylvian gyrus and adjacent lateral and suprasylvian sulci, and posterior ectosylvian gyrus. Medially, label is present in the Of, Prag, La, Cg, Rs, and Ps areas, and within the cruciate and splenial sulci, and in portions of the lateral gyrus.Following injections of the central medial nucleus, label is present in the presylvian sulcus; but in contrast to the central lateral and paracentral projections, the suprasylvian gyrus is labeled only in its posterior part. The central medial nucleus also projects to the posterior lateral gyrus, both laterally and medially. Also, the central medial nucleus projects heavily to rostral cortical zones, which include the Of, Prag and La areas, cruciate sulcus, and the rostral cingulate gyrus.The para‐stria medullaris nucleus projects only to the presylvian sulcus and orbitofrontal cortex laterally, but, medially, has an extensive input similar to the central lateral and paracentral projections in that label is present in the Of, Prag, La, Cg, Rs, and Ps areas, in the cruciate and splenial sulci, and in the posterior lateral gyrus.The laminar distribution of label is as follows: the central lateral, paracentral and para stria medullaris nuclei project primarily to layers I and III, whereas the central medial nucleus projects to layers I and VI. In addition, the central lateral projection has a patchy appearance in the retrosplenial and postsubicular c

ISSN:0092-7317    

DOI:10.1002/cne.902880404

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractSomatosensory cortex reorganizes following restricted deafferentation so that deprived neurons acquire new receptive fields. Electrophysiological data suggest that a decrease in inhibition might be one of the mechanisms contributing to these changes. This hypothesis was tested by evaluating quantitatively glutamic acid decarboxylase (GAD) immunoreactivity and cytochrome oxidase (CO) activity in normal and partially deafferented rat hindlimb somatosensory cortex. In normal animals, there were laminar differences in the frequencies of GAD+cells that correlated with the levels of CO activity. Two weeks after transection of the sciatic nerve, CO levels were reduced in all layers of the hindlimb somatosensory cortex contralateral to the nerve transection whereas the frequencies of GAD+cells were unchanged except in layer IV where a 16% decrease was observed. This observation is consistent with the hypothesis that the expression of GAD in layer IV is partially controlled by the amount of afferent input. The ability of novel inputs to develop stable patterns of excitation in deafferented somatosensory cortex may depend upon the reduction of GABAergic inhibition which follows deafferentation.

ISSN:0092-7317    

DOI:10.1002/cne.902880405

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractRetinal horizontal cells receive synaptic input from photoreceptors and provide a pathway for lateral interactions in the vertebrate retina. In nonmammalian retinas, the H1 horizontal cells appear to use γ‐amino butyric acid (GABA) as their neurotransmitter. The transmitter used by mammalian horizontal cells, however, remains to be identified. In the present study, we have employed in situ hybridization to examine whether cat retinal horizontal cells contain L‐glutamic acid decarboxylase (GAD) mRNA and hence might use GABA as their transmitter. In the cat retina, labeled cell bodies were found in the inner nuclear layer and the ganglion cell layer. No labeled cells were found in the photoreceptor layer. In the inner nuclear layer, labeled somata were present at two locations. The majority of them (∼72%) were located in the vitread side of the inner nuclear layer bordering the inner nuclear layer/inner plexiform layer boundary. A second class of labeled cells in the inner nuclear layer (∼20%) had larger somata and were present at the inner nuclear layer/outer plexiform layer boundary. Double labeling experiments with antisera to parvalbumin, a horizontal cell marker, showed that these perikarya belonged to horizontal cells. RNA blot analysis showed that cat retina contains a single species of GAD mRNA that is about 4 kb in size. These data show that in addition to GABAergic amacrine, displaced amacrine, and interplexiform cells described previously, horizontal cells contain GAD mRNA and may use GABA as their neurotransmitter. Hence, GABA may be a transmitter that is involved in lateral inhibition in both nonmammalian and mammalian

ISSN:0092-7317    

DOI:10.1002/cne.902880406

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractTo investigate indirect pathways to ganglion cells we studied the starburst amacrine cell network and its relationship to the alpha ganglion cell. Starburst cells were identified by an antiserum to choline acetyltransferase and alpha cells by injection of Lucifer yellow. The density ofonandoffstarburst cells peaks at the area centralis and decreases with eccentricity by a factor of seven. The fine amacrine processes, interrupted by distinct varicosities, arborize in a planar fashion in the inner plexiform layer. Theonnetwork, at the junction of strata 3 and 4, and theoffnetwork, in stratum 2, have a similar appearance. Neighboring starburst processes run in intimate association to form a network of bundles. As bundles cross each other, loops of irregular size and shape are formed. The loops are smallest in the area centralis and increase by a factor of three towards the periphery; correspondingly, bundle length per unit area decreases with eccentricity. However, the number of varicosities/bundle length stays constant with eccentricity as does the number of processes per bundle. Segments of the starburst network associate over fairly long distances with dendrites of alpha ganglion cells. About 26% of the alpha ganglion dendritic tree shows such association, and this is significantly greater than would be expected if the alpha and starburst processes were independent. We conclude that the functional unit of the starburst cell is a linear bundle of processes and that the starburst network may connect synaptically to the alpha cell.

ISSN:0092-7317    

DOI:10.1002/cne.902880407

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractWe have employed transneuronal transport to examine the anatomical relationships between the deep cerebellar nuclei and 2 cortical motor areas: the primary motor cortex and the arcuate premotor area (APA). In the same animals, we have also examined the patterns of labeling in the thalamus and the red nucleus to provide evidence for the potential routes of transneuronal transport to the cerebellum.When the appropriate technical procedures were employed, cortical injections of wheat germ agglutinin conjugated to horseradish peroxidase (WGA‐HRP) resulted in transneuronal labeling within portions of the contralateral deep cerebellar nuclei. Injections into the primary motor cortex labeled neurons in the dentate and in the 2 subdivisions of the interpositus. Injections into the APA labeled neurons in the dentate and in only the posterior subdivision of the interpositus. In most instance, dentate neurons were more intensely labeled following the cortical injections than interpositus neurons.The transneuronal labeling observed in the dentate nucleus was topographically organized. The dentate region that was labeled following injections into the “arm area” of the APA was caudal and ventral to the dentate region that was labeled following injections into the “arm area” of the primary motor cortex. This observation provides evidence for two “arm areas” in the dentate: one anatomically related to the APA, and the other related to the primary motor cortex.More than one route of transport may be responsible for the labeling of cerebellar neurons. We propose that the labeling observed in the dentate nucleus reflects the pattern of connections in the cerebellothalamocortical pathways that link the dentate with the cerebral cortex. Thus, our observations support the concept proposed by Schell and Strick (J. Neurosci.4: 539–560, '84)—that the cortical targets of the dentate nucleus include both the primary motor c

ISSN:0092-7317    

DOI:10.1002/cne.902880408

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe distribution of pancreastatin immunoreactivity was investigated in porcine brain, spinal cord, dorsal root ganglia, and pituitary. In the brain, immunoreactive cell bodies were present in many areas including the cortex, basal ganglia, hippocampus, thalamus, hypothalamus, mesencephalic reticular formation, cerebellum, and medulla oblongata. Immunoreactive fibres were most abundant in the globus pallidus, stria terminalis, entopeduncular nucleus, hippocampus, and in the substantia nigra. In the spinal cord, immunoreactive cells were found in laminae IV±IX. Immunoreactive fibres were concentrated in the dorsal horn. Pancreastatin immunoreactivity was localised to fibres and small cells (5–10% of the total) in the dorsal root ganglia. In the posterior pituitary, many immunoreactive fibres were present and in the anterior lobe subsets of gonadotrophs and thyrotrophs were pancreastatin‐immunoreactive. The localisation of pancreastatin showed a parallel distribution with chromogranin A. Coexistence of pancreastatin with calcitonin generelated peptide (CGRP) immunoreactivity in cell bodies in the spinal cord, including motoneurones, and with CGRP or galanin immunoreactivities in dorsal root ganglion cells was also noted. The differential pattern of pancreastatin immunostaining was reflected in the extractable levels of peptide with highest concentrations in the cortex (55.8 ± 6.0 pmol/g wet weight, mean ± S.E.M.), thalamus (60.0 ± 5.0 pmol/g), hypothalamus (54.4 ± 6.5 pmol/g), and anterior pituitary (2,714 ± 380 pmol/g). Characterisation of pancreastatin immunoreactivity in the hypothalamus and pituitary by gel permeation and high‐pressure liquid chromatography revealed multiple molecular forms, one of which was indistinguishable from natural porcine pancreastatin. The widespread distribution of pancreastatin immunoreactivity suggests this peptide may play a part in several neuroendocrine, autonomic, somatic, and sensory functions, and its colocalisation with chromogranin A is consistent with a precursor‐product

ISSN:0092-7317    

DOI:10.1002/cne.902880409

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractA small discrete concentration of actin filaments in the connecting cilium of vertebrate photoreceptors appears to have a role in the morphogenesis of the phototransductive disk membranes (Williams et al., '88). We have visualized these actin filaments in rat rod photoreceptors by decorating them with myosin subfragment‐1. At the site of disk morphogenesis, we observed a cluster of short filaments, with various orientations and their faster growing (barbed) ends at the ciliary plasma membrane. Their association with the liplike structure of an early nascent disk is consistent with their apparent involvement in the initiation of disk môrphogenesis. A few longer decorated filaments extended along the core of the connecting cilium, away from the site of disk morphogenesis, implying that they might have some function other than the shaping of a new disk. Most of the antiactin label was found in the region of the short filaments. The alpha‐actinin immunolabel coincided with that of actin, suggesting that the filaments may be crosslinked by alpha‐a

ISSN:0092-7317    

DOI:10.1002/cne.902880410

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY

摘要:

AbstractThe cholinergic and monoaminergic innervation of the lateral geniculate nucleus (GL) and other thalamic nuclei in the cat was examined by using immunocytochemical and tract‐tracing techniques. Cholinergic fibers, identified with an antibody to choline acetyltransferase (ChAT), are present in all layers of the GL. They are fine in caliber and exhibit numerous swellings along their lengths. The A layers, the magnocellular C layer, and the medial interlaminar nucleus are rich in cholinergic fibers that give rise to prominent clusters of boutons, while the parvicellular C layers contain fewer fibers that are more uniformly distributed. The interlaminar zones are largely devoid of ChAT‐immunoreactive fibers. Double‐label experiments show that cholinergic projections to the GL originate from two sources, the pedunculopontine reticular formation (PPT) and the parabigeminal nucleus (Pbg). The PPT contributes cholinergic fibers to all layers, while Pbg projections are limited to the parvicellular C layers.The lateral geniculate nucleus has a much greater density of cholinergic fibers than the other principal sensory nuclei: the density of fibers in the A layers is more than three times greater than that in the ventral posterior nucleus (VP) or the ventral division of the medial geniculate nucleus (GMv). In contrast, serotonin (5‐HT)‐immunoreactive fibers are distributed with equal density across the principal thalamic nuclei, while tyrosine hydroxylase (TH)‐immunoreactive fibers (presumed to contain norepinephrine) are noticeably less dense in the GL than in the others. Monoaminergic fibers also differ from cholinergic fibers in their laminar distribution within the GL: both TH‐ and 5HT‐immunoreactive fibers are distributed evenly across the layers and interlaminar zones and are slightly more abundant in the parvicellular C layers than in the other layers.Other thalamic nuclei rich in cholinergic fibers include the pulvinar nucleus, the ventral lateral geniculate nucleus, the intermediate nucleus of the lateral group, the lateral medial and suprageniculate nuclei (Graybiel and Berson:Neuroscience5: 1175–1238, '80), and the paracentral and central‐lateral components of the intralaminar nuclei. This pattern matches the distribution of projections from the PPT and is similar, but not identical, to the pattern of acetylcholinesterase staining. The fact that most of the nuclei rich in cholinergic fibers have been implicated in visual sensory or visual motor functions suggests that cholinergic projections from the reticular formation play an especially important role in visua

ISSN:0092-7317    

DOI:10.1002/cne.902880411

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1989

数据来源: WILEY