摘要:

AbstractWith the aid of a polyclonal antibody specific for Calbindin D‐28k, we studied the distribution of this calcium‐binding protein in the central auditory system of the mustached bat,Pteronotus parnellii. Components of the cochlear nucleus (CN) that were calbindin‐positive (cabp(+)) included the root of the auditory nerve, multipolar and globular bushy cells in the anteroventral CN, multipolar and octopus cells in the posteroventral CN, and small and medium‐size cells in the dorsal CN. Not stained were spherical bushy cells of the anteroventral CN and pyramidal/fusiform cells in the dorsal CN.In the superior olivary complex, labeled cells were found in the lateral and medial nuclei of the trapezoid body, the ventral and ventromedial periolivary nuclei, and the anterolateral periolivary nucleus. No cellular labeling was seen in the lateral superior olive. In the medial superior olive, only marginal cells were cabp(−). Labeled fibers could be seen surrounding the ghosts of unlabeled cells in both the latter nuclei.Most cells in the intermediate nucleus and the columnar division of the ventral nucleus of the lateral lemniscus were cabp(+). However, the dorsal nucleus was cabp(−). A group of cabp(+) cells was also seen in the paralemniscal zone.The inferior colliculus had a relatively low density of cabp(+) cells. Labeled cells were more common in the caudal half of the central nucleus, and in the external nucleus and dorsal cortex.In the auditory thalamus, nearly every cell in the medial geniculate body was cabp(+), but those in the suprageniculate nucleus and in the posterior group did not stain.Small cells in the intermediate layer and giant cells in the deep layers of the superior colliculus were densely cabp(+). In the pons, cabp(+) cells and neuropil could be seen in the medial and lateral pontine nuclei (pontine gray).In conclusion, calbindin‐like immunoreactivity was found in most of the brainstem auditory system, as well as in regions associated with acoustic orientation or control of vocalization. However, except for a minority of cells of the medial superior olive, it is conspicuously absent from the nuclei receiving binaural input below the level of the inferi

ISSN:0092-7317    

DOI:10.1002/cne.903130102

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

年代:1991

数据来源: WILEY

摘要:

AbstractVestibular axons form synapses on a restricted area of the lateral dendrite of the Mauthner cell, a large, identified brainstem neuron found in fish land amphibians. The differentiation of the vestibular nerve, medullary neuropil, and Mauthner cell of the axolotl (Ambystoma mexicanum) was studied to understand better the means by which this synaptic specificity arises. The Mauthner cell first extends a medial process and then a lateral dendrite. The latter initially elongates as a simple process and later sends out branches. As the lateral dendrite grows, vestibular axons enter the brainstem to form one of the earliest of several discrete axon fascicles that course longitudinally through the neuropil. The fascicles, many of which are identifiable on the basis of their location and axonal morphology, are the precursors of the longitudinal tracts of the mature salamander. The lateral dendrite grows dorsally over the orthogonally oriented fascicles, making contact with each at a characteristic time and place. The first afferents to form synapses do so on the soma and proximal lateral dendrite; subsequent afferent groups terminate more distally. Axons within a given fascicle form synapses with the Mauthner cell in a discrete and initially homogeneous domain. As dendritic branches form and the organization of the longitudinal fascicles becomes more complex, the homogeneity of axons terminating on a given region of the Mauthner cell surface is lost, but no major rearrangement or migration of terminals is apparent. These observations are consistent with both active recognition and passive spatiotemporal models of synaptic site specificity.

ISSN:0092-7317    

DOI:10.1002/cne.903130103

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

年代:1991

数据来源: WILEY

摘要:

AbstractAfferents often form synapses on restricted regions of their target cells. The connections between vestibular axons and the Mauthner cell are an example of this sort of specificity. The Mauthner cells are a pair of identifiable central neurons in certain fish and amphibians. In the axolotl (Ambystoma mexicanum), the large vestibular axons form club endings on only one portion of one dendrite of the Mauthner cell. During development, this specific distribution might result from nothing more than when and where the growing axons and dendrite meet (spatiotemporal model). Alternatively, the distribution might reflect constraints on where the developing axons may grow (axon segregation model) or form synapses (active recognition model). As a test of the spatiotemporal model, ears and vestibular ganglia from older embryos (Harrison stage 33/34–) were unilaterally grafted in place of prospective ear/ganglion placodes of younger embryos (stage 23). Light and electron microscopic examination revealed that the axons precociously entered the brain and formed synapses on the Mauthner cell. Similarly, grafts from younger to older embryos resulted in a delay. In both situations, mapping the club endings on the mature Mauthner cells of 21–mm larvae revealed a distribution similar to that of the contralateral control cells. Thus precocious and delayed afferent arrival did not alter the eventual localization of the synapses. These results conflict with the spatiotemporal model and imply that the vestibular axons are either restricted to a certain region of the neuropil or capable of recognizing a specific region of the Mauthner cell surf

ISSN:0092-7317    

DOI:10.1002/cne.903130104

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe acidic dipeptideN‐acetylaspartylglutamate (NAAG) was identified immunohistochemically within neurons of the visual pathways of two adult macaque monkeys which had undergone midsagittal sectioning of the optic chiasm 6 or 9 years earlier. In both temporal and nasal retinae, amacrine cells, including some displaced amacrine cells, expressed NAAG immunoreactivity. In temporal but not nasal retina, retinal ganglion cells were stained, as were their dendrites in‐the inner plexiform layer, and their axons in the optic nerve fiber layer. In nasal retina, the ganglion cells had degenerated because they were axotomized by the optic chiasm section. In the target regions of the retinal ganglion cells, the superior colliculus and the lateral geniculate nucleus (LGN), both neuropil and cell bodies were stained. In LGN, staining was confined to layers 2, 3, and 5, that is, to the layers innervated by the intact ipsilateral pathway. Immunoreactivity was also seen in the cells of layers 2, 3A, 4B, 5, and 6 of area 17 and layers 3 and 5 of area 18. The neuropil was stained in all layers of area 17, but more heavily in layers 1, 2, 4B, the bottom of 4Cβ, 5B, and 6B. Within 4C the staining was patchy; in tangential sections there were alternating bands of light and dark label which matched the ocular dominance bands demonstrated by cytochrome oxidase histochemistry in adjacent sections. This banding pattern is consistent with the presence of NAAG in geniculocortical terminals of the intact ipsilateral pathway and the absence of such terminals for the contralateral pathway, which had undergone transneuronal degeneration due to the optic chiasm sectioning. Overall, our results for monkey are very similar to those in cat and suggest that NAAG or a structurally related molecule may have a prominent role in the communication of visual signals at retinal, thalamic, and cortical le

ISSN:0092-7317    

DOI:10.1002/cne.903130105

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe studied the sources of thalamic projections to prefrontal areas of nine rhesus monkeys with the aid of retrograde tracers (horseradish peroxidase or fluorescent dyes). Our goal was to determine the proportion of labeled neurons contributing to this projection system by the mediodorsal (MD) nucleus compared to those distributed in other thalamic nuclei, and to investigate the relationship of thalamic projections to specific architectonic areas of the prefrontal cortex. We selected areas for study within both the basoventral (areas 11, 12, and ventral 46) and the mediodorsal (areas 32, 14, 46, and 8) prefrontal sectors. This choice was based on our previous studies, which indicate differences in cortical projections to these two distinct architectonic sectors (Barbas, '88; Barbas and Pandya, '89). In addition, for each sector we included areas with different architectonic profiles, which is also relevant to the connectional patterns of the prefrontal cortices.The results showed that MD included a clear majority (over 80%) of all thalamic neurons directed to some prefrontal cortices (areas 11, 46, and 8); it contributed just over half to some others (areas 12 and 32), and less than a third to area 14. Clusters of neurons directed to basoventral and mediodorsal prefrontal areas were largely segregated within MD: the former were found ventrally, the latter dorsally. However, the most striking findings establish a relationship between thalamic origin and laminar definition of the prefrontal target areas. Most thalamic neurons directed to lateral prefrontal cortices, which are characterized by a high degree of laminar definition (areas 46 and 8), originated in the parvicellular and multiform subdivisions of MD, and only a few were found in other nuclei. In contrast, orbital and medial cortices, which have a low degree of laminar differentiation, were targeted by the magnocellular subdivision of MD and by numerous other limbic thalamic nuclei, including the midline and the anterior. Thus topographic specificity in the origin of thalamic projections increased as the laminar definition of the target area increased. Moreover, the rostrocaudal distribution of labeled neurons in MD and the medial pulvinar also differed depending on the degree of the laminar definition of the prefrontal target areas. The rostral parts of MD and the medial pulvinar projected to the eulaminate lateral prefrontal cortices, whereas their caudal parts projected to orbital and medial limbic cortices. Selective destruction of caudal MD is known to disrupt mnemonic processes in both humans and monkeys, suggesting that this thalamic‐limbic prefrontal loop may constitute an important pathway for memor

ISSN:0092-7317    

DOI:10.1002/cne.903130106

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe cellular localization of mRNAs for nerve growth factor (NGF), brain‐derived neurotrophic factor (BDNF), and neurotrophin‐3 (NT3), in the rat central olfactory system was evaluated with in situ hybridization of35S‐labeled cRNA probes. In the main olfactory bulb, low levels of NGF and BDNF mRNA expression were detected. NGF mRNA was restricted to the glomerular region while BDNF mRNA was predominantly localized to the granule cell layer. No cellular hybridization to NT3 cRNA was seen. The accessory olfactory bulb did not express detectable levels of mRNA for any of the three related neurotrophic factors. Areas which receive olfactory nucleus and in layers 2 and 3 of rostal piriform cortex. BDNF mRNA expression in these areas appeared more robust than that of NGF mRNA, while NT3 mRNA was not detectable. In contrast, tenia tecta exhibited dense labeling with the cRNAs for all three neurotrophic factors. The localization of NGF mRNA to primary target neurons of the olfactory nerve in the periglomerular region of the main olfactory bulb suggests that bulb cells may influence the ingrowth and continual turnover of olfactory sensory afferents. However, as there is a strong correlation between the distribution of neurotrophic factor mRNAs within rostral olfactory structures and the distribution of centrifugal cholinergic neurons of the basal fore

ISSN:0092-7317    

DOI:10.1002/cne.903130107

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

年代:1991

数据来源: WILEY

摘要:

AbstractWe have shown previously that rubral axons can grow around a lesion of their spinal pathway in the developing opossum and that a critical period exists for that plasticity (Martin and Xu, Dev Brain Res 39:303, 1988). Since most rubrospinal neurons degenerate after axotomy during the critical period, we have proposed that plasticity results primarily from growth of late arriving axons around the lesion rather than regeneration of cut axons (Xu and Martin, J Comp Neurol 279:368, 1989). In the present study, we used a double‐labeling paradigm to test that hypothesis.Four groups of pouch young opossums received bilateral or unilateral injections of Fast Blue (FB) into the caudal thoracic or rostral lumbar cord (T12–L2) at different ages in order to label rubrospinal neurons. Three or 4 days later, the rubrospinal tract was transected unilaterally, four to five segments rostral to the injection(s). If the injection was unilateral, the lesion was made ipsilateral to it. The animals were maintained for about 1 month before a second marker, Diamidino Yellow (DY), was injected, usually bilaterally, between the FB injection(s) and the lesion. The animals were maintained for about 5 days before sacrifice and sections through the red nucleus and spinal cord were examined with a fluorescence microscope.During the critical period for plasticity, only a few rubral neurons contralateral to the lesion were labeled by FB alone, supporting our previous contention that most axotomized neurons degenerate. In contrast, many neurons were labeled by DY alone, indicating that their axons were not present in the caudal cord at the time of the FB injection and that they grew around the lesion during the 1 month survival to incorporate DY. A few double‐labeled neurons were also found. One interpretation of such neurons is that they survived axotomy, as evidenced by the presence of FB, and supported axons which grew around the lesion to take up DY. Another interpretation is that they supported late growing axons which incorporated residual FB as well as DY. In order to choose between these alternatives, a similar double‐labeling paradigm was carried out, but with removal of FB at the time of the lesion. Since a few neurons were still double labeled, we conclude that regeneration of cut axons also contributed to rubrospinal plasticity.Our results support our previous suggestion that developmental plasticity of the rubrospinal tract results primarily from growth of late arriving axons around the lesion, but they also suggest that regeneration of cut axons

ISSN:0092-7317    

DOI:10.1002/cne.903130108

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe postnatal development of cholinergic afferents to the superior colliculus in neonatal cats was studied by using acetylcholinesterase (AChE) histochemistry, choline acetyltransferase (ChAT) immunohistochemistry, and retrograde transport of horseradish peroxidase (HRP). In the adult cat, the pattern of AChE staining was laminar specific. AChE was distributed continuously in thestratum griseum superficiale(SGS) but was organized as patches in thestratum griseum intermediate(SGI). Diffuse AChE staining also was present in thestratum griseum profundum(SGP) and the dorsolateral periaqueductal gray (PAG). At birth, however, AChE staining was barely detectable in the SGS and, aside from a few isolated labeled neurons, was absent from the SGI, SGP, and PAG. By 7 days postnatal (dpn), staining in the SGS was more apparent but did not change appreciably in the deeper laminae. A substantial increase in AChE staining occurred in the SGS at 14 dpn (several days after eye opening), at which time patches in the SGI first became apparent. By 28 dpn, the complete laminar‐specific adult AChE staining pattern was present, though the staining intensity did not reach the adult level until 56 dpn.A protracted maturation of both AChE staining and ChAT immunoreactivity also was observed in the sources of cholinergic afferents to the superior colliculus, which include the parabigeminal nucleus, and the pedunculopontine (PPN) and lateral dorsal tegmental (LDTN) nuclei. AChE and ChAT‐immunoreactive staining in each nucleus was weak at birth but increased during the ensuing 2 weeks. At 21 dpn, however, ChAT immunoreactivity virtually disappeared in the parabigeminal nucleus and significantly decreased in PPN and LDTN. The ChAT immunoreactivity in these nuclei then gradually increased reaching maximum levels by 28 dpn. At 35 dpn, AChE staining showed a significant, though temporary (4 weeks), decrease in the parabigeminal nucleus, but not in the PPN and LDTN, that subsequently increased to the adult level of staining at 70 dpn.The absence of AChE in the SGI in neonatal animals was correlated, at least in part, with a paucity of neurons in the brainstem cholinergic cell groups labeled by retrograde transport of HRP from the superior colliculus. Injections of HRP into the superior colliculus retrogradely labeled many neurons in the parabigeminal nucleus, but few, if any, neurons in the PPN or LDTN at 1 dpn. Retrogradely labeled neurons also were observed in the substantia nigra pars reticulata, albeit fewer in neonates than in adults. By contrast, extensive projections from all cholinergic cell groups were demonstrated by similar injections in adults, including neurons that were double‐labeled with retrograde HRP and ChAT immunoreactivity.These findings indicate that the cholinergic projections to the rat superior colliculus undergo considerable postnatal development. The superficial to deep developmental chronology may be related to the functional dichotomy between the different laminae. The results suggest that the influence of basal ganglia‐related structures on visuomotor behaviors associated with the deeper laminae of the superior colliculus may develop after the major sensory afferent and brainstem efferent projections are

ISSN:0092-7317    

DOI:10.1002/cne.903130109

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe development of calcitonin gene‐related peptide‐like immunoreactive (CGRP‐LI) nerves was studied in neonatal and adult rat corneas stained immunohistochemically according to an avidin biotin peroxidase procedure. At birth, rat corneas already contained dense plexuses of CGRP‐LI nerve fibers. Most of the nerves entered the cornea in 12–15 prominent stromal nerve bundles located at regular intervals around the circumference of the cornea. Fibers in these bundles entered the epithelium approximately midway between the limbus and the center of the cornea and supplied extensive central and pericentral areas of the tissue. In addition, smaller numbers of axons entered the cornea individually and in small fascicles located in between the larger bundles and supplied mainly peripheral territory. In the epithelium, the CGRP‐LI nerves formed a complex, highly anastomotic meshwork that ramified uniformly throughout central and peripheral areas of the tissue. Fibers in the plexus gave origin to numerous short, stout terminal axons that extended into the adjacent epithelium in all directions with no preferred orientation. During the first week of neonatal life, several changes in CGRP‐LI innervation occurred: (1) the innervation density of the central and pericentral cornea increased relative to the peripheral cornea; (2) intraepithelial axons became progressively longer, increased in branching complexity, and oriented preferentially towards the center of the cornea; and (3) a dense innervation of the corneoscleral limbus and, in particular, the branches of the marginal artery, developed. Midway through the second week of life, immature versions of Corneal epithelial “leashes,” the dominant feature of the adult corneal innervation, were first observed. Over the next 10 days, the leash formations in the central and pericentral cornea gradually became more complex and gave rise to greater numbers of terminal axons, compared to developing leashes in the peripheral cornea. The mature pattern of corneal CGRP‐LI innervation was reached on day 21 and remained constant (except for compensatory growth‐related elongation of axons) for at least the first 6 months of life. Transection of the ophthalmomaxillary nerve or neonatal administration of the sensory neurotoxin capsaicin resulted in the total loss of CGRP‐LI staining from the cornea. In contrast, removal of the superior cervical ganglion had no effect on corneal CGRP‐LI staining. The extraordinary density and complexity of the CGRP‐LI innervation of the rat cornea demonstrated at all stages of development in this study suggests that these nerves may play important roles in corneal sensory, re

ISSN:0092-7317    

DOI:10.1002/cne.903130110

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

年代:1991

数据来源: WILEY

摘要:

AbstractElectrophysiological recordings were made at a large number of sites in the primary somatosensory cortex of six anesthetized raccoons. A high density of penetrations (110–229 per animal), within or near the representation of the fourth digit, allowed identification of three cortical regions with different physiological properties: aglabrous zone, containing a highly detailed, somatotopically ordered representation of the glabrous surface of the digit; rostral to this aclaw‐dominant zone, in which the neurons at most penetrations respond to stimulation of the claw of the fourth digit, but may also receive input from the hairy skin or surrounding glabrous skin; and a more rostralmultidigit zone, in which the neurons respond to stimulation of two to five digits, with the dominant digit usually being the one represented caudally (i.e., the fourth digit at most of the sites sampled here). Claw‐dominant zones with receptive fields restricted to digit three or five are also found rostral to the representations of the glabrous skin of the corresponding digit. The glabrous and claw‐dominant zones constitute a complete map of the fourth digit. The multidigit region presumably is a separate map, since its neurons have different spatial convergence, higher thresholds, and a lower incidence of slowly adapting inputs than those in the claw‐dominant and glabrous zones. A comparison between animals with lesions of the basal forebrain and intact animals found no differences in the organization of these zones or in the responses to peripheral input, suggesting that cholinergic inputs to the cortex are not essential to these properties. The detailed description of these regions and the proposed terminology should resolve some inconsistencies in the use of the term “heterogeneous zone” in

ISSN:0092-7317    

DOI:10.1002/cne.903130111

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

年代:1991

数据来源: WILEY