摘要:

AbstractRetinal projections and visual thalamo‐cortical connections were studied in the subterranean mole rat, belonging to the superspeciesSpalax ehrenbergi, by anterograde and retrograde tracing techniques. Quantitative image analysis was used to estimate the relative density and distribution of retinal input to different primary visual nuclei. The visual system ofSpalaxpresents a mosaic of both regressive and progressive morphological features. Following intraocular injections of horseradish peroxidase conjugates, the retina was found to project bilaterally to all visual structures described as receiving retinal afferents in non‐fossorial rodents. Structures involved in form analysis and visually guided behaviors are reduced in size by more than 90%, receive a sparse retinal innervation, and are cytoarchitecturally poorly differentiated. The dorsal lateral geniculate nucleus, as defined by cyto‐ and myelo‐architecture, cytochrome oxidase, and acetylcholinesterase distribution as well as by afferent and efferent connections, consists of a narrow sheet 3–5 neurons thick, in the dorsal thalamus. Connections with visual cortex are topographically organized but multiple cortical injections result in widespread and overlapping distributions of geniculate neurons, thus indicating that the cortical map of visual space is imprecise. The superficial layers of the superior colliculus are collapsed to a single layer, and the diffuse ipsilateral distribution of retinal afferents also suggests a lack of precise retinotopic relations. In the pretectum, both the olivary pretectal nucleus and the nucleus of the optic tract could be identified as receiving ipsilateral and contralateral retinal projections. The ventral lateral geniculate nucleus is also bilaterally innervated, but distinct subdivisions of this nucleus or the intergeniculate leaflet could not be distinguished. The retina sends a sparse projection to the dorsal and lateral terminal nuclei of the accessory optic system. The medial terminal nucleus is not present.In contrast to the above, structures of the “non‐image forming” visual pathway involved in photoperiodic perception are well developed inSpalax. The suprachiasmatic nucleus receives a bilateral projection from the retina and the absolute size, cytoarchitecture, density, and distribution of retinal afferents inSpalaxare comparable with those of other rodents. A relatively hypertrophied retinal projection is observed in the bed nucleus of the stria terminalis. Other regions which receive sparse visual input include the lateral and anterior hypothalamic areas, the retrochiasmatic region, the sub‐paraventricular zone, the paraventricular hypothalamic nucleus, the anteroventral and anterodorsal nuclei, the lateral habenula, the mediodorsal nucleus, and the basal telencephalon. These results indicate that the apparently global morphological regression of the visual system conceals a selective expansion of structures related to functions of photoperiodic perception and photo‐neuroendocrine regulation.We suggest that the evolution of an atrophied eye and reduced visual system is an adaptively advantageous response to the unique subterranean environment. Factors favoring regression include mechanical aspects, metabolic constraints, and competition between sensory systems. The primary advantage of sensory atrophy is the metabolic economy gained by the reduction of visual structures which do not contribute significantly to the animal's fitness. ©

ISSN:0092-7317    

DOI:10.1002/cne.903280302

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

年代:1993

数据来源: WILEY

摘要:

AbstractSomatic motor neurons begin to express the transmitter synthesizing enzyme, choline acetyltransferase (ChAT) and the low‐affinity nerve growth factor receptor (NGFR) during embryonic development. However, as motor neurons mature in postnatal life, they lose immunoreactivity for NGFR and acquire a motor neuron‐specific epitope that is recognized by the monoclonal antibody, MO‐1. The present study was undertaken to examine the effect of nerve injury in adult rats on these three developmentally regulated markers in two populations of somatic motor neurons.Unilateral transection, ligation, or crushing of the sciatic nerve resulted in a loss of MO‐1 binding and a concomitant rise in immunoreactivity for NGFR within axotomized motor neurons in lumbar levels of the spinal cord. These changes, detectable within 5 days following nerve injury, are reversed with reinnervation, but persist if reinnervation is prevented by chronic axotomy. Thus, regulation of the expression of NGFR and the MO‐1 epitope appears to be critically dependent upon interactions between motor neurons and target muscles. These observations are also consistent with the idea that during regeneration, neurons may revert to a developmentally immature state; in motor neurons, this state is characterized by the presence of NGFRs and the absence of the MO‐1 epitope.Transection of the hypoglossal nerve, a purely motor nerve, resulted in a similar loss of MO‐1 binding and a selective rise in NGFR immunoreactivity in neurons within the ipsilateral hypoglossal motor nucleus. In addition immunoreactivity for ChAT was also lost in axotomized hypoglossal motor neurons. In contrast, injury to the sciatic nerve, which bears both sensory and motor axons, did not result in any detectable change in ChAT immunoreactivity in spinal motor neurons. © 1993 W

ISSN:0092-7317    

DOI:10.1002/cne.903280303

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

年代:1993

数据来源: WILEY

摘要:

AbstractCholinergic innervation of the human cerebellum was investigated immunocytochemically by using a polyclonal rabbit antiserum against choline acetyltransferase. Immunoreactive structures were found throughout the cerebellar cortex but were localized predominantly in the vermis, flocculus, and tonsilla. These included (1) a population of Golgi cells in the granular layer; (2) a subpopulation of mossy fibers and glomerular rosettes; (3) thin, varicose fibers closely associated with the Purkinje cell layer and the molecular layer; and (4) a relatively dense network of fibers and terminals contributing to the glomerular formations in the granular layer. In the cerebellar nuclei, some cells stained positively for choline acetyltransferase, and a terminal field pattern could be detected with a distinct but sparse network of varicose fibers. Acetylcholine appears to be a primary transmitter in the vestibulocerebellar pathways at several levels, which may account for the potent effects of muscarinic antagonists in diminishing vestibular vertigo in humans. © 1993 Wiley‐Liss, I

ISSN:0092-7317    

DOI:10.1002/cne.903280304

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

年代:1993

数据来源: WILEY

摘要:

AbstractWe examined the organization of descending projections from the inferior colliculus (IC) to auditory brainstem nuclei and to pontine and reticular nuclei in the rat by employing the anterograde axonal tracerPhaseolus vulgaris‐leucoagglutinin (PHA‐L). Small PHA‐L injections into cytologically defined subnuclei of the IC revealed that each subnucleus has a unique pattern of efferent projections.The central nucleus of the IC projects in a topographic order to the dorsal nucleus of the lateral lemniscus (DLL), the rostral periolivary nucleus (RPO), the ventral nucleus of the trapezoid body (VNTB), and the dorsal cochlear nucleus (DCN). It is assumed that this topography represents a cochleotopic arrangement. The external cortex of the IC projects to the nucleus sagulum (Sag), the RPO, the VNTB, and the DCN. Minor projections were found to pontine and reticular nuclei. Efferent fibers from the dorsal cortex of the IC terminate mainly in the Sag, while other nuclei of the auditory and extra‐auditory brainstem receive only minor projections. The intercollicular zone sends a moderate number of fibers to the DLL and very few, if any, to the remaining auditory brainstem nuclei. In contrast, fairly strong projections from the intercollicular zone to the reticular formation were found.The present data demonstrate that the four subnuclei of the IC have a differential pattern of descending projections to nuclei in the pontine and medullary brainstem. These parallel colliculofugal pathways, assumed to belong to functionally separate circuits, may modulate auditory processing at different levels of the auditory neuraxis. © 1993 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903280305

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

年代:1993

数据来源: WILEY

摘要:

AbstractComparative studies of growth cone morphology may provide insight into the mechanisms underlying motility and navigation in vivo. Here we analyzed the morphology of a unique set of growth cones in the embryonic medicinal leech,Hirudo medicinalis. The comb or C‐cell is a transient cell found as a bilateral pair in each midbody segment. Early in development, from embryonic day (E)7 to E11, each C‐cell adds and orients about 70 parallel growth cones that remain relatively nonmotile until E12 when rapid process outgrowth is initiated. Individual C‐cells from E10 to E14 were injected with Lucifer yellow and growth cones were traced with a camera lucida. Growth cone morphology was quantified from the drawings. Lamellar regions increased in area with age and change in extension rate. Young, relatively nonmotile growth cones had numerous short filopodia in many orientations, while at highly motile stages filopodial number decreased, length increased, and orientation became more restricted in the direction of outgrowth. Thus, while filopodia were distributed symmetrically, such that the average filopodial angle was predictive of the direction of outgrowthat all stages, younger (relatively nonmotile) growth cones project more filopodia in many directions than do older more motile growth cones. These results suggest that: (1) alterations in morphology may reflect developmentally regulated changes in extension and the local environment, (2) these growth cones maintain a large area for environmental sampling as they increase extension rate, even as filopodia become more restricted in orientation, and (3) C‐cell growth cones might progressively alter their affinity for local cellular cues as they initiate rapid and directed outgrowth. The C‐cell of embryonic leech may provide a relatively simple system in which to test these ideas experimentally. © 1993 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903280306

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe total numbers of neurons and glial and endothelial cells in five rat spinal cords were estimated by stereological techniques.Each spinal cord was divided into 12 slabs of equal length. One transverse and one oblique slice was cut from each slab. The volumes of gray and white matter of each cord were then estimated by point‐counting techniques on the transverse slices. By means of optical disectors and systematic sampling, the numerical densities of different cell types were estimated on 35 m̈‐thick plastic sections from the oblique slices. The total cell number was calculated by multiplying the numerical density by the total volume of gray and white matter.On average there were 15.1 and 21.1 million cells in white and gray matter, respectively. Of the cells in gray matter, 6.4 million were judged to be neurons, 4.3 million to be endothelial, and 10.3 million to be glial. Of the neurons, 1.7 million were located in the cervical region, 2.5 million in the thoracic, 1.6 million in the lumbar, and 0.6 million in the sacro‐coccygeal region.The methods used are simple to perform, and the counting necessary to obtain a reliable estimate of cell number from one spinal cord can be carried out during the course of 1 day. The only major problem is reliable criteria for unambiguous cell classification. © 1993 Wiley‐

ISSN:0092-7317    

DOI:10.1002/cne.903280307

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

年代:1993

数据来源: WILEY

摘要:

AbstractDuring normal development of the mammalian forebrain, the paired cerebral hemispheres are initially separated midsagittally by the connective tissue‐filled longitudinal fissure. During subsequent stages, the hemispheres fuse as basal lamina is remodeled and fibroblasts are eliminated from the fissure to create new central nervous system (CNS) territory in the midline. Two axon pathways, the corpus callosum and dorsal callosal stria, eventually use this region as part of their pathway. In order to assess the possible role of glial cells in the fusion process and in the guidance of axons in this and several other areas of the forebrain, we have analyzed the developing brain in timed cat and mouse embryos with immunohistochemical and morphological techniques. With the use of astroglial‐specific antibodies and electron microscopy, we have visualized two distinct, primitive astroglial structures associated with the cerebral midline, and seven more associated with other specific brain regions. The way in which one of these structures moves as a column along the hemispheric midline in synchrony with seam formation suggests the possibility that during morphogenesis of the telencephalon, astrocytes may aid in the fusion process. In addition, the compact assemblage, early appearance and location of this and the other glial structures in relation to well defined neuroanatomical landmarks or axon pathways suggest that they may transiently compartmentalize relatively large regions of the CNS and organize certain developing fiber systems by acting as guides or barriers at critical stages of ontogeny. © 1993 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903280308

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

年代:1993

数据来源: WILEY

摘要:

AbstractIn the developing spinal cord of the frog,Xenopus laevis, a population of interneurons assumes a pattern that represents a previously undescribed level of organization. Glyoxylic acid treatment and immunocytochemistry show that the neurons contain catecholamines and their synthetic enzyme, tyrosine hydroxylase. Cells are located within the ependymal layer of the floor plate region of the larval spinal cord. The cells have several processes including a long one that projects toward the brain without fasciculating with other labeled processes. In addition, the cytoplasm of the catecholaminergic cells extends into the central canal, showing that they are a population of cerebrospinal fluid‐contacting neurons.The spatial domain of catecholaminergic neurons starts abruptly at the boundary between the hindbrain and spinal cord and continues to the tip of the tail. The neurons occupy two longitudinal columns within the sheet of floor plate cells, which includes cells that do not exhibit the catecholaminergic phenotype. Unlabeled cells are intercalated between catecholaminergic cells in each column, giving the labeled cells the appearance of being spaced along the length of the spinal cord. This general arrangement is evident at the time of hatching. Spatial analysis showed that the position of cells along a column is not random. The nonrandom behavior is due to cells being excluded from the area immediately surrounding other catecholaminergic cells. Further analysis showed that the cellular pattern lacks segmental or other periodic repeats. Ultimately, the location of a cell within a column depends upon the position of its closest catecholaminergic neighbor. © 1993 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903280309

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

年代:1993

数据来源: WILEY

摘要:

AbstractThe internal lateral (IL) subnucleus of the parabrachial nucleus (PB), which is one of the seven lateral subnuclei of the PB, receives information from the spinal cord. The IL subnucleus perhaps relays nociceptive signals to the intralaminar nuclei of the thalamus, apparently being implicated in the motivational‐affective component of pain reaction. However, cells of origin of spinal fibers to the IL subnucleus have not been investigated sufficiently. We intended to clarify these cells by injection of fast blue or wheat germ agglutinin‐conjugated horseradish peroxidase into the IL subnucleus and/or other lateral subnuclei in the rat. When the tracer was injected into the IL subnucleus, many cells were labeled bilaterally in laminae I, V, and VII, and in the dorsolateral and dorsomedial parts of the lateral funiculus throughout the entire length of the spinal cord. A small number of labeled cells appeared ipsilaterally in laminae II–IV and VI in the upper cervical segments and contralaterally in laminae VIII and X throughout the spinal cord. Labeled cells in lamina I were more numerous ipsilaterally than contralaterally in the first two cervical segments but were more numerous contralaterally than ipsilaterally in the remaining spinal segments. Labeled cells were seen with a contralateral predominance in lamina VII, but with an ipsilateral predominance in lamina V and in the dorsolateral and dorsomedial parts of the lateral funiculus. With tracer injected into the lateral subnuclei of the PB, excluding the IL subnucleus, labeled cells were found primarily in lamina I throughout the entire length of the spinal cord. These results show that cells giving rise to spinoparabrachial fibers were more numerous and more widely distributed than previously reported. © 1993 Wiley‐L

ISSN:0092-7317    

DOI:10.1002/cne.903280310

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

年代:1993

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903280301

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

年代:1993

数据来源: WILEY