摘要:

AbstractRecent neural tracer studies in several mammalian species have demonstrated a similar musculotopic organization of the hypoglossal motoneurons which innervate individual tongue muscles. The distribution of this musculotopic organization in nonmammalian tetrapods, however, has not received detailed investigation. As part of an ongoing study on the comparative organization of the vertebrate hypoglossal nucleus, the musculotopic organization of the hypoglossal nucleus ofRana pipienswas studied by injection of lectin‐conjugated horseradish peroxidase into four distinct tongue muscles and the geniohyoid muscle. Injections into the hyoglossus muscle label neurons in dorsal regions of the hypoglossal nucleus in middle and rostral nucleus levels. Injections into the genioglossus basalis muscle label neurons in ventral and lateral regions of the hypoglossal nucleus in caudal nucleus levels. Injections into the genioglossus medialis muscle label neurons in dorsal regions in caudal levels, throughout the nucleus in middle levels, and in ventral regions in more rostral levels. Injections into the geniohyoid muscle label neurons in the ventral tip of the hypoglossal nucleus and in the ventromedial corner of the medullary gray matter in middle and rostral nucleus levels. These results demonstrate that the organization of the hypoglossal nucleus inRana pipiensis more complex than previous tracer studies indicated. Similarities in the musculotopic organization of the amphibian and mammalian hypoglossal nuclei suggest an evolutionary conservatism of the motor system controlling tongue movemen

ISSN:0092-7317    

DOI:10.1002/cne.903080402

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

年代:1991

数据来源: WILEY

摘要:

AbstractCerebellar climbing fibres react by collateral sprouting after subtotal lesions of the inferior olive, and the newly formed branches are able to reinnervate neighbouring denervated Purkinje cells. In the present paper, we used thePhaseolus vulgarisleucoagglutinin (PHA‐L) tracing technique to label the climbing fibres and study their plasticity in detail at the light microscopical level. The specific objectives were to study the time course and morphological aspects of their sprouting, to estimate their extent of growth, and to compare the newly formed terminal plexuses with normal climbing fibres.Intraperitoneal injection of 3‐acetylpyridine induced degeneration of the majority of the olivary neurones, which terminate as climbing fibres in the cerebellar cortex. Regularly, small numbers of neurones survived in the inferior olive. In the cerebellar cortex scattered surviving climbing fibres were found, which were devoid of any sign of injury. Already 3 days after the lesion, surviving climbing fibres had emitted collateral branches, which elongated for some distance through the molecular layer and ended with a number of varicosities and very fine branchlets. By 7 days, it was possible to recognize new developing arbours which grew in the molecular layer with the same orientation as normal climbing fibres. At longer survival times, extensive terminal arbours had developed and double labelling experiments confirmed that they terminated around the proximal dendrites of Purkinje cells. The newly formed terminal plexuses resembled, in all essential aspects, normal climbing fibres. In addition, from 1 month onward, it was evident that every surviving climbing fibre was able to form several new terminal plexuses reinnervating a number of neighbouring Purkinje cells. The result of this process was the formation of large clusters of newly formed plexuses around the parental arborization. Quantitative estimates indicated that the domain of innervation of single surviving climbing fibres could be increased by more than six times.It is concluded that climbing fibres surviving a subtotal olivary lesion are capable of extensive sprouting, axonal growth, and formation of new terminal plexuses, which resemble normal climbing fibres. Previous electrophysiological evidence indicates that this reinnervation is functional. The high specificity with which sprouting olivary axons reinnervate the proximal Purkinje cell dendrites suggests the existence of precise interactions between the growing fibres and their target. This example of “homotypic” collateral sprouting and reinnervation may thus provide a useful model for the study of nerve–target int

ISSN:0092-7317    

DOI:10.1002/cne.903080403

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

年代:1991

数据来源: WILEY

摘要:

AbstractA salient feature of the cerebellar Purkinje cells is the highly ordered distribution of their excitatory afferents on the dendritic tree. Climbing fibres synapse exclusively on the proximal dendrites, whereas parallel fibres articulate with the distal branches, the so‐called spiny branchlets. This input organization is lost following the removal of climbing fibres. Such denervation results in the formation of a large number of new spines on the proximal dendrites, and these become contacted by sprouting parallel fibres, which thereby extend their domain of innervation. We have previously shown that the climbing fibres surviving a subtotal lesion of the inferior olive sprout and reinnervate neighbouring Purkinje cells. In the present ultrastructural study, we have investigated the features of Purkinje cells reinnervated by sprouting climbing fibres. The objectives were to examine the fine morphology of the newly formed synapses and to determine whether the modifications of Purkinje cell morphology and afferent organization are reversed by this reinnervation.Surviving climbing fibres were labelled by the anterograde tracerPhaseolus vulgarisleucoagglutinin (PHA‐L) and immunohistochemically visualized by means of the gold‐substituted silver peroxidase technique, 2 and 6 months after 3‐acetylpyridine lesions of the inferior olive in adult rats. Sprouting climbing fibres and newly formed arborizations were identified in the light microscope, isolated, and cut in serial ultrathin sections for electron microscopic analysis.The labelled boutons belonging to newly formed terminal plexuses exhibited the typical morphological features of climbing fibre terminals, i.e., a high number of round synaptic vesicles and a few small mitochondria. Most frequently they formed asymmetric synapses on stubby thorns protruding from the proximal Purkinje cell dendrites. In some instances, however, the postsynaptic element consisted of long slender spines or spines showing an atypical morphology. A number of labelled boutons was also in contact with the perikarya of reinnervated Purkinje cells, either articulating with spines or synapsing directly on the smooth somatic surface.The proximal dendrites of denervated Purkinje cells were characterized by large numbers of spines, which were frequently postsynaptic to parallel fibres. By contrast, Purkinje cells reinnervated by the sprouting climbing fibres generally showed a lower number of spines on their proximal dendrites, indicating a reversal of this morphological change. The aberrant parallel fibre input was also decreased on reinnervated dendrites or had completely disappeared. Nevertheless, some reinnervated Purkinje cells showed the persistence of some parallel fibre synapses on their proximal dendrites. On occasion, climbing fibre and parallel fibre boutons synapsed on the same spine.These results show that the sprouting of olivocerebellar axons leads to the formation of new contacts on Purkinje cell dendrites, which are almost identical in morphology and location to the normal climbing fibre input. Moreover, this collateral reinnervation substantially reverses the modifications which affect the denervated Purkinje cell dendrites and restores the normal afferent distribution. It is suggested that the interactions which influence the ontogenetic development of these connections are still active during regenerative phenomena in the adult

ISSN:0092-7317    

DOI:10.1002/cne.903080404

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe present study used the NGFR‐5 monoclonal antibody raised against human nerve growth factor receptor (NGFR) to determine the extent of NGFR immunoreactivity within the embryonic and young adultCebus apellacerebellum as well as the human cerebellum. Immunohistochemically processed tissue revealed NGFR expressing Purkinje cell somata, axons, and dendrites, the latter being observed within the molecular layer of both adult species. Within all regions of the cerebellum we observed both darkly and lightly immunostained Purkinje cells. The proximal axons of these cells, which were visualized for short distances within the granular cell layer, appeared to contain bulbous aggregates of reaction product. In sagittal sections, the full extent of the Purkinje cell dendritic tree was observed in the more lightly stained portions of the cerebellum. In situ hybridization experiments revealed NGFR mRNA within Purkinje cells in a pattern similar to that seen with immunohistochemistry. The distribution of NGFR immunoreactivity within the cerebellum exhibits a general topographic organization with the heaviest and most consistent staining occurring within the archi‐ and neocerebellum and weaker staining within the paleocerebellum. In fetalCebusmonkey cerebellum obtained at gestational day 50 and 70, NGFR immunoreactivity was observed as a band composed of developing Purkinje cell neurites. These profiles were seen in the paleo‐ and neocerebellum, but not the archicerebellum. The present investigation is the first demonstration of NGFR immunoreactive profiles in the adult monkey and human cerebellum. These findings suggest that nerve growth factor may influence locomotor and vestibular behaviors that are mediated by cerebellar circuitry. The precise mode of action for the NGF/NGFR system within the cerebellum remains to be deter

ISSN:0092-7317    

DOI:10.1002/cne.903080405

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe ability to target specific cytoskeletal components in axons for disruption within intact developing embryos would provide a valuable tool for studying neuronal development. Neurofilaments are an attractive target for such an approach, because they are neuron specific and are expressed late in embryogenesis principally beginning during axon outgrowth. No pharmacological agents are currently available that disrupt neurofilaments without also affecting general development. One approach that has been used successfully to affect proteins in vivo is to inject specific antibodies into living cells. We employed this approach inXenopus laevisembryos by injecting two antibodies directed against the middle molecular weight neurofilament protein (NF‐M) into a single blastomere of a two‐cell stage embryo. Injected antibodies could be detected for as long as 3.5 days in cells descended from the injected blastomere. Only cell bodies of neurons descended from anti‐NF‐M‐injected blastomeres contained abnormal accumulations of intermediate filament proteins, and peripheral nerve development was unilaterally retarded in these neurofilament antibody‐injected tadpoles. Such accumulations and peripheral nerve defects were not seen in neurons derived from uninjected blastomeres or from blastomeres injected with control antibodies. These data demonstrate the usefulness of specific antibodies to perturb neuronal development in intact frog embryos and, in addition, suggest a role for neurofilaments in axon

ISSN:0092-7317    

DOI:10.1002/cne.903080406

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe expression of three β subunit (β1, β2, and β3) mRNAs for γ‐aminobutyric acidAreceptor in the postnatal rat forebrain was examined by in situ hybridization h istochemistry with probes synthesized for the respective subunit mRNAs. The developmental expression of these subunit mRNAs conformed to one of three patterns. Pattern I was high expression of the mRNA at birth and a constant or increasing expression thereafter. In contrast, pattern II was no or very low expression of the mRNA at birth, with expression quickly increasing to reach the adult level in the early postnatal period. Pattern III was the transient expression of the subunit mRNA or else a marked decrease of its expression after a peak in the early postnatal period.On the basis of this classification, the expression of β3subunit mRNA followed pattern I in most regions of the forebrain, such as the isocortex, the olfactory bulb and some of its related areas, the hippocampal formation, the amygdala, the septum, the bed nucleus of the stria terminalis, the caudate‐putamen, the nucleus accumbens, the globus pallidus, the ventral pallidum, and the hypothalamus. In some areas, such as the magnocellular preoptic nucleus, the thalamus, and the subthalamic nucleus, pattern III was seen for this subunit. However, none of the regions of the brain showed pattern II expression of β3subunit mRNA. In contrast, the expression of β1and β2subunit mRNAs followed pattern II in most regions of the forebrain. These included the expression of β1subunit mRNA in the isocortex, the olfactory bulb, the hippocampal formation, the amygdala, the septum, the bed nucleus of the stria terminalis, the thalamus, and the hypothalamus, and the expression of β2subunit mRNA in the isocortex, the olfactory bulb and some of its related areas, the amygdala, the nucleus of the diagonal band, the caudate‐putamen, the thalamus, and the hyothalamus. Pattern I was not found for β1subunit mRNA, although it was seen in some areas for β2subunit mRNA, such as the ventral pallidum, the globus pallidus, and the magnocellular preoptic nucleus. On the other hand, pattern III was followed by β1subunit mRNA in the anterior olfactory nucleus, the olfactory tubercle, and the piriform cortex, and the same pattern for the β2subunit was also found in the olfactory tubercle, the hippocampal formation, the septum, the bed nucleus of the stria terminalis, and the nucleus accumbens.These results indicate that all three β subunit mRNAs are under developmental regulation, and that the different mRNAs are differentially regulated in various regions of the forebrain. In addition, the present study also showed that β3subunit mRNA is highly expressed in both the neonatal and adult stages, indicating an important role for this subuni

ISSN:0092-7317    

DOI:10.1002/cne.903080407

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

年代:1991

数据来源: WILEY

摘要:

AbstractTo determine how the basal ganglia in reptiles may influence visuomotor behavior, the connections from the basal ganglia to the tectum of the midbrain were studied in several species of reptiles. Immunohistochemical studies by means of antibodies against Leu‐enkephalin (LENK) as well as experimental hodological studies with anterograde (PHA‐L) and retrograde (HRP, Fluorogold, Cholera toxin) tracers were carried out. The results indicate that within the class of Reptilia, two different patterns occur: one in which information from the basal ganglia is relayed to the tectum via the substantia nigra as well as via a pretectal, enkephalinergic cell group, and another one in which only the ventral route, via the substantia nigra, is present. The former pattern is found in turtles, crocodiles, and the lacertid lizardsPodarcisandGallotia, and the latter pattern in the gekkonid lizardsGekkoandEublepharis, inVaranus, and in the snakesPythonandThamnophis. The presence or absence of the pretectal relay center is reflected in the laminar distribution of LENK immunoreactivity in the tectum.The apparent lack of a pretectal relay in nocturnal gekkonids and in snakes underlines the hypothesis (Reiner et al., '84: T.I.N.S.7:320–325) that a de‐emphasis of visual‐basal ganglia mechanisms has occurred during the evolution of ancestral reptiles to moder

ISSN:0092-7317    

DOI:10.1002/cne.903080408

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

年代:1991

数据来源: WILEY

摘要:

AbstractPrevious studies have been directed at the elucidation of neuron‐specific gene expression in the mammalian central nervous system. In particular, we have identified a series of marker molecules that are expressed in cerebellar Purkinje cells with varying degrees of specificity. Here, we show by light microscopic immunocytochemistry and Northern transfer and hybridization that two of these markers, namely, L7 and PEP19, are expressed in the retina of mouse and rabbit, while a third marker, cerebellin, is absent. Light and electron microscopic immunocytochemistry proves that L7‐like immunoreactivity is restricted to rod bipolar cells, while PEP19‐like immunoreactivity is distributed in both rod and cone bipolars. PEP19 is also expressed by subsets of amacrine and ganglion cells. The density of PEP19‐positive bipolar cells is greater than that of L7‐positive bipolar cells, although the density of each is approximately equal in central and peripheral portions of the retina. An antiserum to a fourth Purkinje cell marker, vitamin D‐dependent calcium‐binding protein‐28 kD (CaBP), reveals primarily axon‐less horizontal cells, but also subsets of rod bipolar, amacrine, and, in the mouse but not in the rabbit, ganglion cells. The processes of immunoreactive cell bodies form discrete bands in the internal plexiform layer, and mixtures of the antisera help distinguish their identity. Thus, these Purkinje cell markers can be used at the electron microscopic level to unravel the extremely complex neuropil of this retinal layer. Furthermore, knowledge of the retinal distribution of this panel of molecules is of general value for future studies of retinal neuronal typology and can serve to map the densities of subsets of bipolar cells throughout the retina. The expression of L7 and PEP19 in bipolar cells and in Purkinje cells suggests a biochemical relationship between these two spatially distant neu

ISSN:0092-7317    

DOI:10.1002/cne.903080409

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

年代:1991

数据来源: WILEY

摘要:

AbstractBlood‐nerve barrier tissues (endoneurial blood vessels and perineurium) of the frog's sciatic nerve were studied during chronic Wallerian degeneration to determine whether barrier function depends on the presence of intact axons. Sciatic nerves of adult frogs were transected in the abdominal cavity; the ends were tied to prevent regeneration and the distal nerve stumps were examined. Vascular permeabilities to horseradish peroxidase and to [14C]sucrose increased to day 14, returned toward normal levels by 6 weeks, and continued at near normal levels to 9 months. Perineurial permeabilities to the tracers increased by day 10 and remained elevated at 9 months. Proliferation of perineurial, endothelial, and mast cells occurred between 3 days and 6 weeks, resulting in an increased vascular space (measured with [3H]dextran) and number of vascular profiles. The perineurium increased in thickness and the mast cells increased in number. This study indicates that during Wallerian degeneration of the frog's sciatic nerve there is (1) a transitory increase in vascular permeability distal to the lesion, that is related to changes within the endoneurium; (2) an irreversible increase in permeability of the perineurium, which begins later than that seen in the endoneurial blood vessels; and (3) proliferation of non‐neuronal components in the absence of regenerating neuronal elements. The results indicate that maintenance of vascular integrity does not require the presence of axons in the frog's peripheral nerve, whereas perineurial integrity and barrier function are affected irreversibly by Wallerian degenerat

ISSN:0092-7317    

DOI:10.1002/cne.903080410

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

年代:1991

数据来源: WILEY

摘要:

AbstractCortical afferents to area V1 were studied in sevenCebusmonkeys by means of retrograde fluorescent tracers. Injections were placed in V1, under electrophysiological guidance, in the regions of representation of both the upper and lower visual quadrants, at eccentricities that ranged from 0.5 to 64 degrees.In all cases retrogradely filled neurons were found in retinotopically corresponding portions of areas V2 and MT, as denned electrophysiologically (Rosa et al: J. Comp. Neurol. 275:326, 1988; Fiorani et al: J Comp Neurol 287:98, 1989). The results also revealed two other visual zones located anterior to V2 here named third and fourth visual areas. A topographical organization of the connections was observed in these areas, with upper quadrant located ventrally and lower quadrant located dorsally. A clear central‐peripheral gradient, from the lateral to the medial cortical surface, was also observed in these areas.Lower field injections revealed crude topographic organization in area DZ and a diffuse projecting zone in the annectent gyrus. Peripheral injections in V1 revealed a clear upper and lower field segregation in areas PO and prostriata as well as a complex topography in MST. In addition, another region of labeling revealed the presence of an area, the temporal ventral posterior region, with an organized topographic representation of the upper field, with a central to peripheral gradient, from the lateral to the medial cortical surface.Three groups of cortical areas were distinguished according to the laminar distribution of neurons labeled from V1. In the first group, which is characterized by dense infra‐ and supragranular labeling, only V2 was included. The second group consists of areas V3, MT, and PO. These areas show dense labeling in the infragranular layers and occasionally sparse labeling in the supragranular layers. Finally, V4 and the other projecting areas, which are characterized by exclusive labeling of the infragranular layers were included in the third gr

ISSN:0092-7317    

DOI:10.1002/cne.903080411

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

年代:1991

数据来源: WILEY