ISSN:0092-7317    

DOI:10.1002/cne.901920302

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

年代:1980

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.901920303

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe medullary electromotor nucleus (EMN) ofSternarchus albifronswas studied at the light and electron microscopic levels. The EMN consists of a dense meshwork of myelinated axons and glial elements with interposed large neurons; it is provided with an abundant supply of capillaries. Two types of essentially adendritic nerve cells were distinguished on the basis of size: giant neurons (approx. 70 μm in diameter) and large neurons (approx. 30 μm in diameter). Their population ratio is 1:4. Only giant cells are labelled following the injection of retrograde tracer into the spinal cord; they are therefore identified with the so‐called “relay cells” of other gymnotids. Tracer experiments further suggest that the descending axons of these relay cells give off collateral branches throughout the elongated spinal electromotor nucleus. In contrast, the large cells remain unlabelled and therefore lack spinal projections; they most likely correspond to “pacemaker cells”.The perikaryal surface, including axon hillock and proximal part of initial segment of both types of EMN cells, is contacted by clusters of synaptic terminals and astrocytic processes. Two main varieties of synaptic terminals occur: (1) large endings and (2) ordinary end feet with standard size (S‐type) and variable size (Sv‐type) clear, spherical vesicles. The junction between large endings and EMN cells is characterized by the combination of gap junctions and surrounding intermediate junctions whose freeze‐fracture characteristics were morphometrically analyzed. The large endings were formed by nodes of Ranvier as well as by fiber terminations, and synchronization within the EMN may be achieved by presynaptic fibers. Some of the contacts occur directly on the initial segment, which could allow activity to bypass the soma.It is concluded that the electromotor system ofSternarchusis comprised of a rapid conduction pathway where medullary pacemaker and relay cells as well as spinal electromotor neurons are coupled by synapses with gap junctions. In contrast to the spinal electromotor neurons, the medullary EMN cells receive synapses with morphological characteristics of chemical transmission, and the S‐type and Sv‐type terminals may possibly correspond to Gray's Type I and Type II synapses, respectively. These synapses may be involved in modulation of the electric orga

ISSN:0092-7317    

DOI:10.1002/cne.901920304

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe pattern of projection of the rat medial lemniscus was studied by axonal transport labeling following injections of tritiated leucine, proline and/or adenosine, or of horseradish peroxidase for retrograde identification of the neurons of origin. The vast majority of neurons in the gracile, cuneate, and principal trigeminal nuclei contribute to an almost totally crossed projection primarily to the thalamic ventrobasal complex. Additional thalamic components were traced to specific sites within the “posterior group”, including a medial component largely traversed by lemniscal axons and a caudolateral component lying between the principal nucleus of the medial geniculate and ventral nucleus of the lateral geniculate. We have designated this latter zone “intermediate geniculate”, distinguishing a somatosensory portion of the geniculate group on the basis of its myelo‐and cytoarchitecture, as well as its connections.Other projections replicated in several animals included the zona incerta and nearby sectors of the substantia nigra; three distinct mesencephalic arrangements within the deep layers of the superior colliculus, the external nucleus of the inferior colliculus, and the intercollicular nucleus; the anterior pretectal nucleus; dorsal sectors of the inferior olivary complex and the ipsilateral cerebellar cortex. The results are compared with findings in other species (with emphasis on the caudal thalamic region) in an attempt to resolve some of the apparent inconsistencies in nom

ISSN:0092-7317    

DOI:10.1002/cne.901920305

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe relationship between stimulus intensity and response latency implies that the relative time of arrival of input to binaurally sensitive locican vary over a range significantly longer than the interaural delays resulting from the travel time of sound between the ears. To investigate the effect of such potentially long inter‐arrival time intervals, responses of binaurally sensitive neurons in auditory cortex of cats were examined over relatively long interaural delays. Two kinds of interaural delay functions were observed. One kind involved a sharp transition to a reduced response rate over a narrow range of interaural delays, while the other involved a gradual reduction of response rate over a relatively prolonged range of interaural delays. The amount of suppression was found to be a sensitive function of both interaural delay and the relative intensity of the stimuli delivered to the two ears. The pattern of suppression across a binaural response was stationary with respect to the excitatory contralateral stimulus over wide ranges of interaural delay. In addition, certain characteristics of a group of cells generally responsive only to binaural stimulation are described. A model is proposed which accounts for the observed stationarity of the response suppressio

ISSN:0092-7317    

DOI:10.1002/cne.901920306

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

年代:1980

数据来源: WILEY

摘要:

AbstractLight and electron microscopy have been used to study the projections of dendrites from motoneurons in lumbar segments of the spinal cord of the frog following administration of horseradish peroxidase to cut ventral roots. Processes originating from motoneurons crossed to the opposite side of the spinal cord via the anterior commissure and made contact with dendrites and motoneuronal somata. Typically, in segments 6 to 8 the crossing dendrites showed irregular enlargements in diameter.Electrophysiological recordings were obtained both extracellularly from ventral roots and intracellularly from motoneuronal somata. In Ringer's solution containing 1 mM calcium, stimulation of a lumbar ventral root elicited population responses with early and late components in the ventral root of the opposite side of the same segment. Only the early, short latency component remained in calcium deficient Ringer's solution. In calcium‐containing Ringer's solution, intracellular recording from an antidromically activated motoneuron showed an action potential with a short latency; this response was followed by excitatory postsynaptic potentials (epsps) from which action potentials could be generated. Contralateral ventral root stimulation also elicited in the same motoneuron a short latency action potential that was rarely followed by epsps. The short latency responses, that were elicited by stimulation of ventral roots of either side persisted in calcium‐deficient Ringer's solution, but the epsps were abolished. Contralaterally elicited short latency responses were eliminated by section of the anterior commissure.We believe that electrically mediated crossed interactions among lumbar motoneurons may serve as a means of coordinating muscle groups of opposite sides that are used in movements that require bilateral synchronization, such as jumping and swimm

ISSN:0092-7317    

DOI:10.1002/cne.901920307

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

年代:1980

数据来源: WILEY

摘要:

AbstractSupraependymal cells (SECs) of the young hamster's third ventricle have been examined by scanning and transmission electron microscopy. Of special interest were cells with the surface morphology and ultrastructure of macrophages, which were found in largest numbers in 12–15‐day‐old females and males. In the ciliated areas SECs are generally smooth and rounded; in nonciliated areas, they frequently have surface ruffles, blebs and microprocesses. SECs were frequently seen to be dividing or fusing. The macrophage‐like cells are characterized by prominent Golgi zones and numerous large vacuoles, and frequently contain inclusions in their cytoplasm which resemble intraventricular cell processes, cytoplasmic protrusions from ependymal cells and cellular debris. We have demonstrated that supraependymal macrophage‐like cells phagocytose latex beads injected into the ventricles of the brain.Supraependymal cells from 12‐day‐old hamsters were grown in tissue culture. Phagocytic, cytochemical and surface ultrastructural studies were then done sequentially on the same population of cells. These studies revealed the cells to be actively phagocytic as well as strongly esterase positive and peroxidase negative, consistent with their classification in the macrophage/monocyte category. The surface ruffles, ridges and microprocesses were also characteristic of the SECs seen in situ with scanning electron microscopy and of the macrophages cultured from the peritoneum and peripheral blood of the same hamsters.On the basis of cellular morphology, cytochemical staining characteristics and functional response to exposure to foreign particles both in situ and in cell culture, we have demonstrated that supraependymal cells of the third ventricle of the hamster are phagocytes that resemble cells of the macrophage/monocyte line. It is suggested that they constitute a resident macrophage system of the ventricles

ISSN:0092-7317    

DOI:10.1002/cne.901920308

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

年代:1980

数据来源: WILEY

摘要:

AbstractThirty rabbit embryos and two neonates (E18‐P1) received micropipette injections of3H‐Leucine into the occipital region of one hemisphere and were killed after 0.5–5 hours. Incorporated tracer was demonstrated by autoradiography of serial sections of the brains. The first axons were seen in the intermediate zone of the developing cerebral cortex, on day E20, and by day E22 they reached the internal capsule. The entire cortico‐peduncular bundle and a short branch of the superficial (thalamic) bundle were labeled on day E24. On day E25, additional branches directed to claustrum, thalamus (deep bundle), and cerebellum were distinguished. By day E28 the first indications of terminal field development were observed. One day before birth (E30), the neonate pattern of subcortical pathways was fully established and silver grain condensations were present over most of the subcortical target areas.Subcortically, the axons followed preferentially preexisting fiber tracts. There was a period of at least 2–3 days between the arrival of the supplying bundles at the target sites and the onset of terminal field formation: The axon bundles grew first towards more distal targets, and even beyond, before terminal fields developed proximally. Transient axon bundles reaching the cerebellar paraflocculus and traveling along the pyramidal tract and the external and extreme capsules failed to form terminal fields and disappeared around birth. The data suggest that growth of long axonal tracts and the development of terminal fields are separate phenomena possibly regulated by different m

ISSN:0092-7317    

DOI:10.1002/cne.901920309

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe somatotopic organization of the vestibulospinal tract (VST) and the percentages of cells of the lateral vestibular nucleus (LVN) contributing fibres to different regions of the spinal cord of the rat have not been studied before. These problems are investigated using the technique of retrograde cellular degeneration. Varying degrees of spinal cordotomies were performed at upper cervical, thoracic, and lumbar segments in 75 adult rats of Wistar strain. The animals were killed after varying survival periods and the brain stems were processed in the usual way. Chromatolytic neurons were observed in the ipsilateral lateral vestibular nucleus, and no such neurons were seen contralaterally. Following lumbar lesions, reacting neurons were condensed in the caudal two thirds, while with cervical and thoracic lesions, such neurons occupied more cranial levels in the nucleus. It is concluded that vestibulospinal fibres projecting to lumbosacral segments arise from the caudal two thirds of the nucleus, while those projecting to cervical and thoracic segments come from the cranial two thirds, those to the cervicals arise from the most cranial levels. The dense lumbosacral projection was attributed to the role played by the vestibulospinal fibres in maintaining extensor tonus of antigravity musculature, especially in the rat, which can effectively stand on its hindlimbs and use its free forelimbs for handling and examining objects.

ISSN:0092-7317    

DOI:10.1002/cne.901920310

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

年代:1980

数据来源: WILEY

摘要:

AbstractMicroelectrode recordings were made in the binocular portion of the tree shrew striate cortex to determine how orientation selective cells are distributed topographically in area 17 of this species. Seventy‐five percent of the cells sampled were activated well by elongated visual stimuli and were quite selective for stimulus orientation. Ninety‐five percent of the orientation‐selective cells had orientation tuning ranges (Wilson and Sherman, '76) between ± 5° and ± 40° from their optimal orientation.Orientation‐selective cells with the same or similar optimal orientations were distributed in cortex in a columnar manner (Hubel and Wiesel, '62), as determined from electrode penetrations nearly normal to the cortical surface. Penetrations parallel to the cortical surface revealed a highly ordered representation of optimal stimulus orientation, generally characterized by sequential changes in optimal orientation with electrode movement across the striate cortex. In addition, relatively consistent differences were observed in the rates and patterns of orientation shift on these penetrations depending on the direction of electrode movement across the cortex. Penetrations parallel to the 17–18 border yielded moderate‐to‐high rates of orientation change (mean slope = 434°/mm), with the changes genearlly progressing through a complete clockwise or counterclockwise cycle of 180° or more before a major reversal in the direction of orientation shift was encountered. In contrast, penetrations perpendicular to the border yielded low‐to‐moderate slopes (mean slope = 239°/mm). On these penetrations a more limited range of optimal orientations (<180°) was usually encountered, due to frequent reversals in the direction of orientation shift. Also, extended regions (100–200 μm long) of constant optimal orientation were observed in these penetrations. The different patterns of orientation change found on these orthogonal penetrations across the striate cortex indicate that the orientation column system in this species is anisotropically organized with respect to the 17–18 border. Further, the regions of constant optimal orientation frequently encountered on penetrations perpendicular to the 17–18 border suggest that the anisotropy is subserved by a system of elongated zones of iso‐orientation arranged approximately

ISSN:0092-7317    

DOI:10.1002/cne.901920311

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

年代:1980

数据来源: WILEY