摘要:

AbstractThe thalamic projections to somatic sensory‐motor (SSM) cortex and adjacent cortical areas of the Virginia opossum were studied using anterograde and retrograde axoplasmic transport techniques. Large injections of horseradish peroxidase and/or tritiated amino acids were made in the parietal cortex to identify all of the thalamic nuclei that are interconnected with this large cortical area. Very restricted injections were then made in physiologically identified subdivisions of SSM cortex, in the remaining posterior portion of parietal cortex, and in the anteriorly adjacent postorbital cortex.The results show that the parietal cortex is reciprocally connected with a number of thalamic nuclei. Different combinations of these thalamic areas project to specific subregions within the parietal field. All parts of the SSM cortex, which occupies the anterior four‐fifths of parietal cortex, receive input from the ventrobasal complex (VB), the ventrolateral complex (VL), the central intralaminar nucleus (CIN), the central lateral nucleus (CL), and the ventromedial nucleus (VM). We could detect no segregation of VL and VB inputs in any part of SSM cortex. Projections from all of these thalamic nuclei, except VM. show at least some degree of topographic organization. Anterior‐posterior strips of SSM cortex receive input from clusters of thalamic neurons that extend dorsoventrally and rostrocaudally through VB and VL. The posterior one‐fifth of the parietal cortex (the posterior parietal area) receives input from VL, the posterior nuclear complex, and the lateral complex, as well as input from CL, CIN, and VM. Postorbital cortex receives input mainly from intralaminar, midline, and medial thalamic nuclei. We conclude that the projection field of VB in the parietal cortex coincides precisely with the first somatic sensory area (SI) as defined by single unit studies (Pubols et al., '76). The VB projection field also delineates the area of the first motor (MI) representation. Thus, there is no separation of SI and MI cortex in the opossum. The posterior parietal area lies outside of SSM cortex and has thalamic connections similar to the posterior parts of parietal cortex in other

ISSN:0092-7317    

DOI:10.1002/cne.901980302

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

年代:1981

数据来源: WILEY

摘要:

AbstractThe projections of the ventrobasal complex (VB), the ventrolateral complex (VL), and the central intralaminar nucleus (CIN) to the somatic sensory‐motor (SSM) cortex of the Virginia opossum were studied with light and electron microscopic autoradiographic methods. VB, VL, and CIN have overlapping projections to SSM cortex and each one also projects to an additional cortical area. Unit responses to somatic sensory stimulation and the areal and laminar distribution of axons in cortex is different for VB, VL, and CIN, but the axons from each form similar round asymmetrical synapses, predominantly with dendritic spines.As in other mammals, VB units in the opossum have discrete, contralateral cutaneous receptive fields. VB projects somatotopically to SSM cortex and also projects to the second somatic sensory representation. Within the cortex, VB axons terminate densely in layer IV and the adjacent part of layer III. A few axons also terminate in the outermost part of layer I and the upper part of layer VI. Most VB axon terminate upon dendritic spines (86.6%), but they also contact dendritic shafts (10%) and neuronal cell bodies (3%).Neurons in VL have no reliable response to somatic stimulation under our recording conditions. VL projects to the SSM cortex and to the posterior parietal area. Throughout this entire projection field VL fibers terminate in layers I, III, and IV most densely, and sparsely in the other cortical layers. The density of termination in the mid‐cortical laminae is quite sparse compared to VB, but the projection to layer I is considerably greater. Nearly all (93%) of VL axons contact dendritic spines, the remainder (7%) end dendritic shafts.CIN is a thalamic target of ascending medial lemniscal, cerebellar, spinal, and reticular formation axons. Neurons in CIN respond to stimulation restricted to a particular body part, but typically responses may be evoked from larger areas and at longer latencies than neurons in VB that are related to the same body part. CIN neurons require a firm tap or electrical stimulation within their receptive field to elicit a response in the anesthetized preparation. CIN axons terminate throughout the entire parietal cortex, but unlike VB and VL, CIN fibers end almost exclusively in the outer part of layer I. Approximately 21% of CIN fibers contact dendritic shafts in layer I, which is twice the percentage of shafts contacted by VL or VB axons. All of the other CIN synapses are formed with dendritic spines.These experiments demonstrate three different pathways to SSM cortex. The results suggest that each projection has a unique role in controlling the patterns of activity of neurons within the SSM cor

ISSN:0092-7317    

DOI:10.1002/cne.901980303

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

年代:1981

数据来源: WILEY

摘要:

AbstractHorseradish peroxidase (HRP) histochemistry was used to visualize cells afferent to the bullfrog torus semicircularis. These afferent cells are located in several sensory and nonsensory nuclei. The sensory structures which project to the torus are mainly auditory nuclei, with the major input coming from the ipsilateral superior olive. A very small contralateral projection is also present. In addition, afferents arise from the contralateral, and to a lesser extent ipsilateral, dorsal acoustic nucleus and nucleus caudalis, both primary eighth nerve nuclei. A vestibular input is also apparent in that HRP‐positive cells were seen in the magnocellular vestibular nucleus and among elongated bipolar cells at the ventral border of the eighth nerve nuclei. In addition, the torus receives somatosensory input from the contralateral perisolitary band. Afferents from spinal cord cells proved difficult to visualize. Nonsensory areas throughout the brain innervate the torus as well. In the medulla, HRP‐positive cells were present bilaterally in both medial and lateral reticular areas. The tegmentum contributes a major input from the superficial isthmal reticular nucleus and a minor input from the tegmental fields. Commissural toral projections are also present. Descending forebrain input arises from the pretectal gray bilaterally, the ventral half of the ipsilateral lateral pretectal nucleus, and, possibly, from the ipsilateral posterior thalamic nucleus. HRP‐positive cells were also occasionally seen in the posterior tuberculum, ventral hypothalamus, and caudal suprachiasmatic preoptic area. Finally, a telencephalic projection from the ipsilateral anterior entopeduncular nucleus is pr

ISSN:0092-7317    

DOI:10.1002/cne.901980304

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

年代:1981

数据来源: WILEY

摘要:

AbstractAs a sensory response to starvation or overcrowding,Caenorhabditis eleganssecond‐stage larvae may molt into a developmentally arrested state called the dauer larva. When environmental conditions become favorable for growth, dauer larvae molt and resume development. Some mutants unable to form dauer larvae are simultaneously affected in a number of sensory functions, including chemotaxis and mating. The behavior and sensory neuroanatomy of three such mutants, representing three distinct genetic loci, have been determined and compared with wild‐type strain. Morphological abnormalities in afferent nerve endings were detected in each mutant. Both amphid and outer labial sensilla are affected in the mutant CB1377(daf‐6)X, while another mutant, CB1387(daf‐10)IV, is abnormal in amphidial cells and in the tips of the cephalic neurons. The most pleiotropic mutant, CB1379(che‐3)I, exhibits gross abnormalities in the tips of virtually all anterior and posterior sensory neurons. The primary structural defect in CB1377 appears to be in the nonneuronal amphidial sheath cells. The disruption of neural organization in CB1377 is much greater in the adult than in the L2 stage. Of all the anterior sense organs examined, only the amphids are morphologically affected in all three mutants. Thus, one or more of the amphidial neurons may mediate the sensory signals for entry into the dauer larva stage in normal animals. Using temperature‐sensitive mutants we determined that the same defects which block entry into the dauer stage also prevent recovery of d

ISSN:0092-7317    

DOI:10.1002/cne.901980305

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

年代:1981

数据来源: WILEY

摘要:

AbstractThis work represents an attempt to elucidate structural features of electrophysiologically characterized, individual cat dorsal spinocerebellar tract (DSCT) neurons by using intracellular application of horseradish peroxidase (HRP).Intracellular recordings and HRP injections were made in DSCT neurons of the Clarke's column in cat lumbar (L3) spinal cord. The units were identified by antidromic invasion following electrical stimulation of the ipsilateral dorsolateral funiculus at C1. In addition, sensory inputs to the DSCT neurons were determined by natural (adequate) stimuli applied to the hind limb with intact innervation.The morphological analysis is based on data obtained from 19 well‐stained electrophysiologically identified neurons located in Clarke's column. Thirteen of these units received excitatory sensory inputs from muscle receptors, two were activated by cutaneous afferents only, and four had a convergent (muscle + cutaneous) input. The DSCT‐muscle cells were equivalent to the large Clarke cells (class C of Loewy, '70). Their dendrites were oriented primarily in the rostrocaudal direction (up to 2500 μm) and appeared generally smooth except for some branchlets. In four of these cells, the axon was traced into the lateral funiculus. In light microscopic analysis there was no evidence that axon collaterals arose from these axons during the initial trajectory through the spinal grey matter. The four DSCT‐convergent neurons were similar in shape to the DSCT‐muscle units although they appeared to have somewhat smaller cell bodies. Of the two DSCT‐cutaneous neurons one was found to be of the B type, with the dendritic tree having fewer branches and oriented mainly in the medio‐lateral direction. The other cell, however, turned out to be similar in appearance to the C type Cl

ISSN:0092-7317    

DOI:10.1002/cne.901980306

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

年代:1981

数据来源: WILEY

摘要:

AbstractRecent evidence suggests that the main olfactory bulb projects caudally beyond the prepiriform cortex and the cortical amygdaloid nuclei to the region of the piriform lobe called the parahippocampal area. Included within this area is the entorhinal cortex, which is composed of six major subdivisions. Since question remain as to which of these subdivisions receives centripetal fibers from the bulb, we reexamined these projections using autoradiography and HRP histochemistry and correlated the sites of termination with the cytoarchitecture of the entorhinal cortex.The results indicate that olfactory bulb axons reach all parts of the parahippocampal area, including the cortex which forms the medial and lateral banks of the amygdaloid sulcus (area TR), and both subdivisions of the laterally located entorhinal cortex (28L' and 28L). Also, label is observed over the more medially located fields of the entorhinal cortex, including the cortex posterior to the cortical amygdaloid nucleus (28M'), as well as the ventrolateral parts of medial entorhinal cortex (28M). In addition, evidence of label occurs over the full extent of the trasition zone (28i) which separates areas 28L and 28M. These results suggest that the olfactory bulb has a more extensive projection to the parahippocampal area in the rat than previously thought, and may provide at least some input to all of the parahippocampal areas which project to the hippocampal formation.

ISSN:0092-7317    

DOI:10.1002/cne.901980307

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

年代:1981

数据来源: WILEY

摘要:

AbstractLarge or “giant” neurons (average somatic diameter>22μm) of the dorsal cochlear nucleus (DCN) have been carefully described in this light (LM) and electron (EM) microscopic study of normal Nissl‐stained and Golgi‐impregnated cat brain stems. These neurons can be roughly classed by somatic shape (width:length ratio = r) as elongate (r<0.65), ovoid (0.65

ISSN:0092-7317    

DOI:10.1002/cne.901980308

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

年代:1981

数据来源: WILEY

摘要:

AbstractMicrolesions (30–275 microns in diameter) were placed in VLPm of the cat and the terminal axonal degeneration in SI cortex was stained using the Fink‐Heimer I technique. Following each of these microlesions, small, localized patches or subcolumns of degeneration, relativly light in density, were observed within laminae IIIb and IV of SI when viewed in the coronal plane. In addition, a few degenerating fibers ascended to lamina I. These multiple subcolumns had distinct radial boundaries and were narrow in the mediolateral plane (80–120 microns in width) but elongated rostro‐caudally (2500–3000 microns in length). Localized patches of degeneration were separated at their widest points by a distance of 500 microns medio–laterally, but at various rostro–caudal levels of SI were observed to merge into larger columns of degeneration (250–400 microns) and then separate again into smaller multiple patches (i.e., a “zebra‐like” pattern).Small injections of HRP into the forelimb region of area 3b or rostral area 1–2 of SI resulted in the labeling of small, discrete clusters of neurons in the ventral regions of VPLm. The clusters examined ranged in size from 140–350 microns in medio–lateral diameter and were elongated rostro–caudally (up to 500 microns in extent); virtually all cells within a cluster appeared labeled, but not equally so.A pattern of HRP labeling different from that observed following area 3b and rostral area 1–2 injections was observed following injections into more caudal regions of area 1–2 and into SII cortex. The labeling that resulted from these injections was not in the form of neuronal clusters but instead labeled cells tended to be scattered in more dorsal regions of VPLm. This scattering did not appear to be random since the labeled neurons were grouped within the same general area of VPLm. Labeling was distributed throughout a number of cell clusters, comprising only a small proportion of cells within each cluster. The pattern of labeling seen after caudal area 1–2 and SII injections differed only in its rostro–caudal extent within VPLm. SII injections generally resulted in labeling along the full rostro–caudal dimension of VPLm.A differential organization of the anatomy of thalamocortical projections to the various subdivisions of SI and to SII was noted in this study. It is postulated that the multiple, discrete patches of degeneration in laminae IIIb and IV of SI represent a portion of the somatosensory cortical columns and that the HRP‐labeled clusters seen in VPLm following area 3b and rostral area 1–2 injections are the

ISSN:0092-7317    

DOI:10.1002/cne.901980309

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

年代:1981

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901980301

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

年代:1981

数据来源: WILEY