摘要:

AbstractTo gain insight into the possible molecular mechanisms underlying axonal regeneration of neurons of the adult central nervous system (CNS), we have investigated, by in situ hybridization and by immunocytochemistry, the localization and sites of synthesis of the neurite outgrowth‐promoting cell surface molecules Li, N‐CAM and its highly sialylated form, N‐CAM‐PSA, in and around peripheral nerve grafts implanted into the thalamus of adult rats. Normal unoperated adult rat thalamus contains N‐CAM and L1 but no N‐CAM‐PSA immunoreactive axons. Between 7 days and 13 weeks after graft implantation, L1, N‐CAM and N‐CAM‐PSA were all present at the surface of axonal sprouts in the brain parenchyma close to grafts and in the central parts of Schwann cell columns within grafts. Schwann cell membranes were L1 and N‐CAM positive at all postgraft survival times, more strongly at 2–4 weeks than other times, but were associated with N‐CAM‐PSA reaction product only where they abutted N‐CAM‐PSA positive axons. Schwann cell membranes apposed to basal laminae (which wereavoided by regenerating CNS axons) were L1, N‐CAM and N‐CAM‐PSA negative. Between 3 days and 8 weeks after grafting, N‐CAM and L1 mRNA were generally weakly upregulated in neurons of the ipsilateral thalamus, but, most conspicuously, L1 mRNA was strongly upregulated in the neurons of the thalamic reticular nucleus; these neurons are known to regenerate axons very effectively into peripheral nerve grafts and are the probable source of most of the axons which enter thalamic grafts. N‐CAM and L1 mRNA were also strongly upregulated in presumptive Schwann cells in the graft. These results show that regenerating CNS axons (re)express N‐CAM‐PSA and upregulate L1 and N‐CAM, suggesting that all of these molecules may play a role in cellular interactions during the regeneration of CNS axons. Furthermore L1 synthesis appears to be particularly well correlated with the ability of CNS neurons to regenerate axons into

ISSN:0092-7317    

DOI:10.1002/cne.903610202

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractTenascin‐C is a developmentally regulated extracellular matrix component. There is evidence that it may be involved in axon growth and regeneration in peripheral nerves. We have used in situ hybridization and immunocytochemistry to investigate the association of tenascin‐C with central nervous system axons regenerating through a peripheral nerve autograft inserted into the thalamus of adult rats. Between 3 days and 4 weeks after implantation, tenascin‐C immunoreactivity was increased in the grafts, first at the graft/brain interface, then in the endoneurium of the graft, and finally within the Schwann cell columns of the graft. By electron microscopy, reaction product was present around collagen fibrils and basal laminae in the endoneurium, but the heaviest deposits were found at the surface of regenerating thalamic axons within Schwann cell columns. Schwann cell surfaces were not associated with tenascin‐C reaction product except where they faced the tenascin‐rich basal lamina or were immediately opposite axons surrounded by tenascin‐C. By 8 weeks after graft implantation tenascin‐C in the endoneurium and around axons of the graft was decreased. In the brain parenchyma aroundthe proximal part of the graft, axonal sprouts associated with tenascin‐C could not be identified earlier than 2 weeks after grafting and were sparse at this stage. Larger numbers of such axons were present at 8–13 weeks after grafting and were located predominantly where the glia limitans between brain and graft appeared to be incomplete, suggesting that the tenascin‐C may have penetrated the brain parenchyma from the graft. By in situ hybridization, cells expressing tenascin‐C mRNA (probably Schwann cells) appeared first at the brain/graft interface 3 days after grafting and thereafter were mainly located within the grafts. Lightly labelled cells containing tenascin‐C mRNA (probably glial cells) were scattered in the thalamic parenchyma both ipsilateral and contralateral to the graft and a few heavily labelled cells were located very close to the tip of the graft. These results show that regenerating adult thalamic axons, unlike regenerating peripheral axons, become intimately associated with peripheral nerve graft‐derived tenascin‐C, suggesting that they express a tenascin‐C receptor, as many neurons do during development, and that tenascin‐C derived from Schwann cells may play a role in the regenerative growth of such axons through the

ISSN:0092-7317    

DOI:10.1002/cne.903610203

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe distribution of terminal projections in the brainstem from lamina I neurons in the spinal dorsal horn was investigated with the anterograde tracerPhaseolus vulgaris–leucoagglutinin in the cat and the cynomolgus monkey. Iontophoretic injections made with physiological guidance were restricted to lamina I or to laminae I–III in the cervical (C6–8) or lumbar (L6–7) enlargement. The distribution of terminal labeling was essentially identical in the cat and the monkey, although consistently of greater intensity in the monkey. Terminations were observed in the solitary nucleus, the dorsomedial medullary reticular formation, the entire rostrocaudal extent of the ventrolateral medulla, the locus coeruleus, the subcoerulear region and the Kölliker–Fuse nucleus, the lateral and medial portions of the parabrachial nucleus, the cuneiform nucleus, the ventrolateral and lateral portions of the periaqueductal gray, and the intercollicular nucleus. Lamina I terminations were generally bilateral in the medulla but more dense contralaterally in the pons and mesencephalon. The density and laterality of labeling in the medulla varied between cases independently from that in the pons and mesencephalon, suggesting that the lamina I projections to these regions may originate from different subsets of neurons. A clear topographic organization was observed only in the lateral column of the periaqueductal gray, where lumbar lamina I terminations were found caudal to cervical terminations.These observations indicate that spinal lamina I neurons project to a variety of brainstem sites involved in autonomic (cardiovascular, respiratory) and homeostatic processing and the control of behavioral state. These projections provide an afferent substrate for spino‐bulbo‐spinal somatoautonomic reflex arcs activated by nociceptive, thermoreceptive activity and for a spino‐bulbo‐hypothalamic relay of such activity by cells in the caudal ventrolateral medulla. These observations support the general concept that lamina I projections distribute modality‐selective sensory information relevant to the physiological status and maintenance of the tissues and organs of the entire organism. ©

ISSN:0092-7317    

DOI:10.1002/cne.903610204

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe subventricular zone (SVZ) of the lateral ventricle remains mitotically active in the adult mammalian central nervous system (CNS). Recent studies have suggested that this region may contain neuroñal precursors (neural stem cells) in adult rodents. A variety of neuronal and glial markers as well as three extracellular matrix (ECM) markers were examined with the hope of understanding factors that may affect the growth and migration of neurons from this region throughout development and in the adult. This study has characterized the subventricular zone of late embryonic, postnatal, and adult mice using several neuronal markers [TuJ1, nicotinamide adenine dinucleotide phosphate diaphorase (NADPH‐d), neuron‐ specific enolase (NSE)], glial markers [RC‐2, vimentin, glial fibrillary acidic protein (GFAP), galactocerebroside (Gal‐C)], ECM markers [tenascin‐C (TN‐C), chondroitin sulfate, a chondroi tin sulfate proteoglycan termed dermatan sulfate‐dependent proteoglycan‐1 (DSD‐1‐PG)], stem‐cell marker (nestin), and proliferation‐specific marker [bromodeoxyuridine (BrdU)]. TuJ1+and nestin+cells (neurons and stem cells, respectively) persist in the region into adulthood, although the numbers of these cells become more sparse as the animal develops, and they appear to be immature compared to the cells in surrounding forebrain structures (e. g., not expressing NSE and having few, if any, processes). Likewise, NADPH‐d+cells are found in and around the SVZ during early postnatal development but become more sparse in the prolifera tive zone through maturity, and, by adulthood, only a few labeled cells can be found at the border between the SVZ and surrounding forebrain structures (e. g., the striatum), and even smaller numbers of positive cells can be found within the adult SVZ proper. BrdU labeling also seems to decrease significantly after the first postnatal week, but it still persists in the SVZ of adult animals. The disappearance of RC‐2+(radial) glia during postnatal development and the persistence of glial‐derived ECM molecules such as tenascin and chondroitin sulfate proteoglycans (as well as other “boundary” molecules) in the adult SVZ may be associated with a persistence of immaturity, cell death, and a lack of cell emigration from the SVZ in

ISSN:0092-7317    

DOI:10.1002/cne.903610205

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn insects, head movements are mediated by neck muscles supplied by nerves originating in the brain and prothoracic ganglion. Extracellular recordings of the nerves demonstrate units that respond to visual stimulation of the compound eyes and to mechanosensory stimulation of the halteres. The number of neck muscles required for optokinetic eye movements in flies is not known, although in other taxa, eye movements can involve as few as three pairs of muscles. This study investigates which neck motor neurons are likely to be involved in head movements by examining the relationships between neck muscle motor neurons and the terminals visiting them from approximately 50 pairs of descending neurons. Many of these descending neurons have dendrites in neuropils that are associated with modalities other than vision, and recordings show that visual stimuli activate only a few neck motor neurons, such as the sclerite depressor neurons, which respond to local or wide‐field, directionally specific motion, as do a subset of descending neurons coupled to them. The results suggest that, like in the vertebrate eye or the retinas of jumping spiders, optokinetic head movements of flies require only a few muscles. In addition to the importance of visual inputs, a major supply to neck muscle centers by nonvisual descending neurons suggests a role for tactile, gustatory, and olfactory signals in controlling head position. © 1995 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903610206

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn tethered flying flies, moving contrast gratings or small spots elicit head movements which are suited to track retinal images moving at velocities up to 3,000°/sec (about 50 Hz contrast frequency for gratings of spatial wavelength 15°). To investigate the neural basis of these movements we have combined videomicroscopy with electrophysiological stimulation and recording to demonstrate that excitation of prothoracic motor neurons projecting in the anterodorsal (ADN) and frontal nerves (FN), respectively, generates the yaw and roll head movements measured behaviorally. Electrical stimulation of the ADN produces head yaw. The visual stimuli which excite the two ADN motor neurons (ADN MNs) are horizontal motion of gratings or spots moving clockwise around the yaw axis in the case of the right ADN (counterclockwise for left ADN). Activity is inhibited by motion in the opposite direction. Spatial sensitivity varies in the yaw plane with a maximum between 0° and 40° ipsilaterally, but both excitation and inhibition are elicited out to 80° in the ipsilateral and contralateral fields. ADN MNs respond to contrast frequencies up to 15–20 Hz, with a peak around 2–4 Hz forgrating motion in the excitatory or inhibitory directions. Electrical stimulation of the FN primarily elicits roll down to the ipsilateral side. The one FN MN consistently driven by visual stimulation is excited by downward motion and inhibited by upward motion at 80° azimuth in the ipsilateral visual field. At −80° contralateral, visual motion has the opposite effect: Upward is excitatory and downward is inhibitory. The FN MN is tuned to contrast frequencies in the same range as the ADN MNs, with peak sensitivity around 4 Hz. The functional organization of inputs to the ADN and FN is discussed with respect to identified visual interneurons and parallel pathways controlling motor output. © 1995 Wi

ISSN:0092-7317    

DOI:10.1002/cne.903610207

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractIn calliphorid Diptera, motor neurons mediating visually evoked head movements can be excited or inhibited by visual stimuli, depending on the directionality of the stimulus and whether it is in the ipsi‐ or contralateral visual field. The level at which inhibition occurs is of special interest because binocular activation of homolateral tangential neurons in the lobula plate demonstrates that excitatory interaction must occur between the left and right optic lobes. Recordings and dye fillings demonstrate a variety of motion‐sensitive heterolateral pathways between the lobula plates, or between them and contralateral deutocerebral neuropil, which provides descending pathways to neck motor centers. The profiles of heterolateral tangential cells correspond to neurons stained by an antibody against γ‐aminobutyric acid (GABA). Other GABA‐immunoreactive interneurons linking each side of the brain correspond to uniquely identified motion‐sensitive neurons linking the deutocerebra. Additional inhibitory pathways include heterolateral GABAergic descending and ascending neurons, as well as heterolateral GABAergic neurons in the thoracic ganglia. The functional significance of heterolateral GABAergic pathways was tested surgically by making selective microlesions and monitoring the oculoniotor output. The results demonstrate an important new attribute of theinsect visual system. Although lesions can initially abolish an excitatory or inhibitory response, this response is reestablished through alternative pathways that provide inhibitory and excitatory information to the same motor neurons. © 1995 Wile

ISSN:0092-7317    

DOI:10.1002/cne.903610208

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe protein collapsin was purified from chick brain on the basis of its ability to inhibit sensory neuron growth cones, implicating this molecule in sensory axon guidance (Luo et al. [1993] Cell 75:217–227). To examine the relationship between collapsin and sensory axon growth, we examined the pattern of mRNA expression of collapsin's mammalian paralogue, Semaphorin III (Sema III), and compared it to dorsal root ganglion (DRG) axon pathways in the developing rat embryo. Centrally, DRG axons enter the spinal cord by embryonic (E) 11 and branch into the gray matter by E 15 in brachial and thoracic regions. Laminar specific targets are reached by E17. Between E13 and E17, Sema III mRNA is expressed at high levels in the entire ventral half of the spinal cord except the floor plate. This pattern suggests that Sema III may inhibit non‐proprioceptive sensory axons from penetrating the ventral spinal cord. Peripherally, sensory axons have entered the anterior sclerotome by E 11 at all rostrocaudal levels. At this age, Sema III mRNA is already expressed in the dermamyotome and ventral aspect of the posterior sclerotome, areas which axons pass between but do not penetrate en route to their peripheral targets. From E12 to E15, the axons lengthen and branch into smaller fascicles which extend toward peripheral targets. During this time, Sema III mRNA isexpressed by many mesodermal structures surrounding the axon fascicles, with highest levels observed in the dermamyotome, perinotochordal mesenchyme, pelvic girdle, and limb. As development proceeds, Sema III mRNA expression is quickly downregulated before disappear ing by birth. Taken together, our results demonstrate that the gene for Sema III is expressed in central and peripheral regions which are avoided by growing DRG axons. These findings are consistent with the idea tha Sema III inhibits growth and branching of axons into inappropri ate areas during development. © 1995 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903610209

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractProjections from the spinal cord to the vestibular nuclei were examined following injections ofPhaseolus vulgaris–leucoagglutinin, cholera toxin subunit B, or biotinylated dextran at various levels of the spinal cord in the rat. Labeled terminals were abundant after injections of the tracers into the C2 and C3 segments containing the central cervical nucleus. Labeled terminals were seen in the descending vestibular nucleus and the parvocellular, magnocellular, and caudal parts of the medial vestibular nucleus throughout its rostrocaudal extent. Labeled terminals were most numerous in the lateral vestibular nucleus throughout its rostrocaudal extent. The projections from the central cervical nucleus to the vestibular nuclei were exclusively contralateral to the cells of origin because the axons of the central cervical nucleus neurons cross in the spinal cord. Following tracer injections in the cervical enlargement, many labeled terminals were seen in the magnocellular part of the medial vestibular nucleus, but a few were seen in the lateral and the descending vestibular nucleus. Injections into more caudal segments resulted in sporadic terminal labeling in the magnocellular part of the medial vestibular nucleus, the descending vestibular nucleus, and the caudal part of the lateral vestibular nucleus.The results indicate that primary neck afferent input relayed at the central cervical nucleus is mediated directly to the contralateral vestibular nuclei. It is suggested that this projection serves as an important linkage from the upper cervical segments to the lateral vestibulospinal tract in the tonic neck reflex. © 1995 Wiley‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903610210

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY

摘要:

AbstractThe amygdaloid complex is involved in associational processes, such as the formation of emotional memories about sensory stimuli. However, the anatomical connections through which the different amygdaloid nuclei process incoming information and communicate with the other amygdaloid nuclei, is poorly understood. As part of an ongoing project aimed at elucidating the intrinsic connections of the rat amygdaloid complex, we injected the antero grade tracer PHA‐L (Phaseolus vulgaris‐leucoagglutinin) into different rostrocaudal levels of the basal nucleus of the amygdala in 21 rats and analyzed the distribution of labeled fibers and terminals throughout the amygdaloid complex. The connectional analysis, together with cytoarchitectonic observations, suggested that contrary to previous notions the basal nucleus in the rat has three divisions: magnocellular, intermediate, and parvicellular. The magnocellular division has heavy reciprocal connections with the lateral portion of the parvicellular division and the intermediate division projects weakly to the parvicellular division, whereas the projection from the medial: portion of the parvicellular division to the intermediate division is heavy and the lateral and medial portions of the parvicellular division are only weakly interconnected, as are the magnocellular and intermediate divisions. The main intraamygdaloid targets of the basal nucleus projections are the nucleus of the lateral olfactory tract, the anterior amygdaloid area, the medial and capsular divisions of the central nucleus, the anterior cortical nucleus, and the amygdalohippocampal area. Our findings provide the most detailed understanding of the intra‐amygdala connections of the basal nucleus to date and show that the connections within the basal nucleus and between the basal nucleus and other amygdaloid areas are more widespread and topographically organized than previously recognized. © 1995 Wiley‐L

ISSN:0092-7317    

DOI:10.1002/cne.903610211

出版商:Wiley‐Liss, Inc.    

年代:1995

数据来源: WILEY