摘要:

AbstractWhen the optic nerve in a goldfish is crushed, regenerating fibers can reform a normal retinotopic projection. Two processes are thought to generate this retinotopic order. One is an activity‐independent process, presumed to be some form of substrate‐directed growth, which generates rough retinotopy as seen in the early formed projection. The other is an activity‐dependent process that generates fine retinotopy during a protracted period of refinement.This projection also displays two other behaviors. One is retinotopic plasticity, in which optic fibers can compensate for retinal or tectal ablations by expanding or compressing into the available tectal space while preserving retinotopic order. These plasticities can dramatically alter the scale of the projection. The other behavior is the formation of fixed synaptic sites in tectum. Optic fibers make a characteristic number of synaptic connectionsin tectum, which is not changed by increasing the number of invading optic, fibers. This has been interpreted to mean that fibers compete for limited synaptic sites.How the two processes that generate order, substrate‐directed growth, and activity‐dependent refinement might each be affected by the expression of retinotopic plasticity and altered synaptic competition is largely unknown. In particular, it is not known how fine retinotopic order (activity‐dependent refinement) might be affected by altering the scale of the projection. Would optic fibers from neighboring ganglion cells converge into the same‐sized area of tectum, or would they expand or compress in proportion to the altered scale of the overall map? To explore this issue, the posterior half of tectum of goldfish was removed, and the optic nerve was crushed, thereby forcing regenerating fibers to form a compressed retinotopic projection onto the anterior half of tectum. Under these conditions, optic fibers are also forced to compete for half the normal number of synaptic sites.The effect on retinotopy was monitored at various times during regeneration by making a small spot injection of wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) into nasal retina corresponding to fibers that would normally terminate in the missing posterior half of tectum. To distinguish between activity‐dependent and activity‐independent processes, retinal impulse activity was blocked in some animals by repeated intraocular injections of tetrodotoxin.The initial projection was found to be unaffected by impulse activity. Regardless of activity, nasal fibers failed initially to grow to the most posterior available regions, but instead were the “incorrect” anterior half of tectum at 30 days. Under activity dispersed across much of the blockade, compressed retinotopy was subsequently generated by a progressive improvement of this initially dispersed projection over the next 2 months, but this retinotopy was impaired compared to that formed during regeneration into an intact tectum under activity blockade. Surprisingly, with impulse activity, the amount of refinement was normal in that fibers labelled by the retinal spot injections eventually formed a projection that was the same size and shape as that seen in a normal tectum. Fine retinotopy was not obviously compressed, even though the map as a whole was. This indicates that fine retinotopic order, as measured by the convergence of neighboring retinal ganglion cells, is relatively constant in spite of large changes in the scale of the overall projectio

ISSN:0092-7317    

DOI:10.1002/cne.903470402

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPrevious studies suggest that neurons in the dorsomedial subdivisions of trigeminal nucleus oralis (Vo) may contribute, to reflex control of jaw movements and to modulation of sensory information. The present study has addressed this possibility by the use of intracellular staining with horseradish peroxidase of physiologically identified neurons in Vo to examine functional and morphological properties of these neurons. Of 14 labeled neurons, eight had axon collaterals terminating exclusively in the dorsolateral subdivision of the trigeminal motor nucleus (DL neurons) and four in its ventromedial subdivision (VM neurons); axon collaterals of two neurons were not traced. Both groups of neurons sent terminal arbors into other nuclei of the lower brainstem. The DL neurons were distinguishable from the VM neurons in their receptive field (RF) location, neuronal position, somadendritic architecture, and projections to other brainstem nuclei. All neurons, except for two that were exclusively activated by noxious stimuli applied to the tongue, were responsive to light mechanical stimulation of peri‐ and intraoral structures. The RFs of the DL neurons were located in more posterior oral structures than those of the VM neurons. The RF of nearly all low‐threshold DL neurons was located in the maxillary region, and that of the VM neurons, in contrast, involved the mandibular region. The VM neurons were located medial or ventral to the DL neurons. The soma size of the VM neurons was significantly higher than that of the DL neurons. Dendritic arbors of both groups could be separated into medial and lateral components. The ratio of the dendritic transverse areas in the medial vs. later component was significantly higher in the VM neurons than in the DL neurons. The DL neurons also issued collaterals that terminated in larger brainstem areas than those of the VIM neurons. These observations provide new evidence on the morphological and functional properties of Vo neurons that contribute to reflex control of jaw and facial movements and modulation of sensory information. © 1994 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903470403

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThis light and electron microscopic study sought to localize spinal cord interneurons that contribute to the normal and abnormal physiological regulation of spinal sympathetic preganglionic function. Sympathetic preganglionic neurons in caudal C8 through T4 of rat spinal cord were retrogradely labeled with wheat germ agglutinin (WGA) and/or cholera β subunit (CTβ) following injections into the superior cervical ganglion (SCG). With two exceptions, the observed locations of retrogradely VVGA‐ and CTβ‐labeled sympathetic preganglionic neurons were as expected from previous studies. The exceptions were restricted populations of cells in caudal C8 and rostral T1 spinal segments. These neurons were classified as ventrolateral (vlSPN) and ventromedial (vmSPN) sympathetic preganglionic neurons; their somata and dendrites encircled dorsolateral lamina IX motoneurons. Only WGA was transported transneuronally following the retrograde labeling of sympathetic preganglionic neurons. Transneuronally WGA‐labeled spinal interneurons were located principally in the reticulated division of lamina V and dorsolateral lamina VII. A strict segmental organization was observed. All transneuronally labeled interneurons were ipsilateral to, and coextensive with, retrogradely WGA‐labeled sympathetic preganglionic neurons. Electron microscopic observations suggested that retrograde transsynaptic passage of WGA occurred within the sympathetic preganglionic neuropil and showed further that similar classes of organelles were WGA immunoreactive in retrogradely labeled sympathetic preganglionic neurons and in transneuronally labeled lamina V and lamina VII neurons: (1) cisternae and vesicles at the trans face of the Golgi apparatus, (2) large endosomes/dense bodies, and (3) multivesicular bodies. The data are consistent with two hypotheses: (1) Somatic and visceral primary afferent inputs to thoracic spinal cord modify segmental sympathetic preganglionic function through activation of a disynaptic pathway involving lamina V and/or lamina VII interneurons, and (2) long‐loop propriospinal pathways access sympathetic preganglionic neurons through symmetrical, segmental interneuronal circuitry. © 1994 Wi

ISSN:0092-7317    

DOI:10.1002/cne.903470404

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractPrior investigations in other laboratories have provided convincing evidence that the neurons of the rostral nucleus of the solitary tract (rNST) can be grouped according to their physiological response properties or morphologic features. The present study is based on the premise that the response properties of gustatory neurons are related to, and perhaps governed by, their morphology and, connectivity. In this first phase of our ongoing investigation of structure‐function relationships in the rNST of the rat, we have used intracellular injection of neurobiotin to label individual physiologically characterized gustatory neurons. A total of 63 taste‐sensitive neurons were successfully labeled and subjected to three‐dimensional quantitative and qualitative analysis. A cluster analysis using six morphologic features (total cell volume, soma area, mean segment length, swelling density, spine density, and number of primary dendrites) was used to identify six cell groups. Subsequent analyses of variance and posthoc comparisons verified that each of these six groups differed from all others with respect to at least one variable, so each group was “typified” by at least one of the six morphologic features. Neurons in group A were found to be the smallest neurons in the sample. The cells in group B had small somata and exhibited the highest swelling density of any group. Group C neurons were distinguished by dendrites with long, spine‐free branches. These dendrites were significantly longer than those of any other group except Group F. The neurons in group D had more primary dendrites; than any other group. Group E neurons possessed dendrites with the lowest swelling density but the most spines of any group. The cells in group F were the largest neurons in our sample and possessed the largest somata of any group. Thus, overall cell size and density of dendritic spines and swellings were found to be particularly important variables in this classification scheme. Our preliminary results suggest that the number and density of dendritic spines (as well as other morphologic features) may be related to a given neuron's most effective stimulus, indicating that it will indeed be possible to use the criteria established in the present investigation to derive structure‐function relationships for gustatory neurons in the rNST. © 1994 W

ISSN:0092-7317    

DOI:10.1002/cne.903470405

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractWeakly electric fish generate electric fields for the purposes of electrolocation and communication. These fields are detected by specialized receptor organs: the tuberous organs. In the present study we investigated the effects of denervation upon receptor cell survival and progenitor (basal) cell proliferation rate. The left, infraorbital, anterior lateral line nerve of brown ghosts (Apteronotus leptorhynchus) was sectioned, and the proximal stump was dipped in ricin to prevent regrowth. In groups of four, the animals were given two daily injections of the cell proliferation marker bromodeoxyuridine (BrdU) for 2 days at 1, 2, 3, or 4 weeks following denervation. At the completion of the BrdU injection schedule, a piece of cheek skin, rostroventral to the eye, was removed from the left (denervated) and the right (intact) sides and processed for light microscopy or immunocytochemistry. Our results show: (1) there is progressive receptor cell death and tuberous organ degeneration following denervation; (2) basal cell proliferation increases steadily with time after denervation and tuberous organ degeneration; and (3) despite denervation, some proliferating basal cells differentiate into receptor cells, but these new receptor cells eventually die. These results suggest that innervation is essential for tuberous electroreceptor cell survival and that the rate at which basal cells proliferate is regulated by receptor cell health, locally released factors, or both. © 1994 Wiley‐Liss, I

ISSN:0092-7317    

DOI:10.1002/cne.903470406

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractIt is now commonly accepted that the arthropod nervous system has evolved only once, and so homologies between crustacean and insect nervous systems can be meaningfully sought. To do this, we have examined the distribution of serotonin (5‐hydroxytryptamine)‐like immunoreactive neurons in the central nervous system (CNS) of four common British isopods. Two species of terrestrial woodlouse,Oniscus asellusandArmadillidium vulgare, the littoral sea slater,Ligia oceanica, and the aquatic water hoglouse,Asellus meridianus, all possess approximately 40 pairs of serotonin‐like immunoreactive neurons, distributed throughout the CNS in a very similar pattern. Interspecific homology is clearly suggested. Serotonin‐like immunoreactive neurons in the first (T1) and fourth (T4) thoracic ganglia are particularly prominent in each of the four species studied. Whole‐mount immunohistochemistry shows that the pair of T1 neurons have large dorsolateral cell bodies and prominent neurites that project medially and then anteriorly, whereas the pair of T4 neurons have ventrolateral cell bodies and neurites that bifurcate to form a thin axon projecting anteriorly to terminate in T3 and a thick medial axon that projects posteriorly into the abdominal neuromeres of the terminal ganglion. Intracellular cobalt staining of these neurons reveals more of their arborizations: The T1 neurons send three processes anteriorly, which arborize in the brain and exit from the CNS via peripheral nerves, whereas the T4 neurons contribute considerably to the extensive pattern of serotonin‐like immunoreactive fibres in T3–T6 ganglia.The overall pattern of serotonin‐like immunoreactiveneurons in the isopods is similar to that in decapod crustacea, and a number of putative homologies can be assigned. It is more difficult to homologize the isopod serotonin‐like immunoreactive neurons with those in the insect CNS, but some stained brain and thoracic neurons share common cell body positions and axon trajectories in isopods, decapods, and insects and may therefore be homologous. © 19

ISSN:0092-7317    

DOI:10.1002/cne.903470407

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe occipital cortex of the naturally blind mole rat,Spalax ehrenbergi, is occupied by an area of somatosensory representation. To date, no visual cortex has been identified electrophysiologically. In order to determine whether there are corresponding modifications in the thalamus, thalamocortical connections were studied with neuroanatomical tracing methods. Three different fluorescent tracers were injected under electrophysiological control into distinct cortical areas. Injections into the somatosensory head/face and hindlimb/trunk areas of representation revealed a posteromedial ventral nucleus and a posterolateral ventral nucleus, respectively. Additional somatotopic labeling was found in an area dorsomedial to the two ventral nuclei. This structure may be equivalent to the posterior nuclear complex in the laboratory rat. Injections into the auditory cortex of the mole rat resulted in labeling of the medial geniculate body. In contrast to the situation in the laboratory rat, in which a prominent dorsolateral geniculate body and a ventrolateral geniculate body assume dorsolateral positions, the somatosensory thalamus of the mole rat almost reaches the dorsolateral surface. This finding is corroborated by the results of the architectonic study, which failed to reveal a differentiated lateral geniculate body. Our observations suggest that the thalamocortical visual system in the mole rat is minute, whereas the somatosensory system is expanded. This situation fits the mode of life of this subterranean animal, for which touch is more important than vision. © 1994 Wiley‐Liss, I

ISSN:0092-7317    

DOI:10.1002/cne.903470408

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractImmunohistochemical methods have been used to investigate the distribution of various opioid peptides derived from mammalian proenkephalin in the central nervous system of Scyliorhinus canicula. The results indicate that both Leu‐ and Met‐enkephalin‐immunoreactive peptides are present in the dogfish brain. In contrast, enkephalin forms similar to Met‐enkephalin‐Arg‐Phe or Met‐enkephalin‐Arg‐Gly‐Leu, and mammalian α‐neo‐endorphin, dynorphin A (1–8), dynorphin A (1–13), and dynorphin A (1–17) were not detected.Met‐ and Leu‐enkephalin immunoreactivities were found in distinct neurons of the telencephalon and hypothalamus. In particular, cell bodies reacting only with the Met‐enkephalin antiserum were localized in the preoptic nucleus and in the suprachiasmatic region of the hypothalamus. Conversely, cell bodies reacting only with the Leu‐enkephalin antiserum were localized in the pallium and the nucleus lobi lateralis hypothalami. Several areas of the telencephalon and diencephalon exhibited both Met‐ and Leu‐enkephalin‐like immunoreactivity, but the two immunoreactive peptides were clearly contained in distinct perikarya. The overall distribution of Met‐enkephalin‐immunoreactive elements in the dogfish brain exhibited similarities to the distribution of proenkephalin‐derived peptides previously reported for the brain of tetrapods. The fact that Met‐ and Leu‐enkephalin‐like peptides were detected in distinct neurons, together with the absence of dynorphin‐related peptides, suggests the existence of a novel Leu‐enkephalin‐con

ISSN:0092-7317    

DOI:10.1002/cne.903470409

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe most prevalent peptide in the nervous system, N‐acetylaspartylglutamate (NAAG), specifically activates N‐methyl D‐aspartate (NMDA) receptors and a subclass of metabotropic glutamate receptors. One action of this peptide may be to modulate the release of other neurotransmitters, including gamma‐aminobutyric acid (GABA). The present study describes the cellular distribution of NAAG, relative to GABA, in the cerebellum and precerebellar nuclei as a foundation for further physiological investigations. Numerous cells of origin for mossy fibers, including many of the larger neurons of the pontine nuclei, lateral reticular nuclei, vestibular nuclei, reticulotegmental nuclei, and spinal grey, were moderately to strongly stained for NAAG. Many NAAG‐labeled fibers were clearly visible in the cerebellar peduncles and central white matter. Mossy fibers and mossy endings were among the most prominent NAAG‐immunoreactive elements in the cerebellar cortex. Most neurons in the inferior olive were not stained for NAAG, and only sparse, lightly immunoreactive, climbing fiber‐like endings could be identified in restricted regions of the cortical molecular layer. Purkinje neurons ranged from nonreactive to moderately positive, with the great majority being unstained. Cerebellar granule cells did not exhibit any NAAG immunoreactivity. A population of neurons in the deep cerebellar nuclei was highly immunoreactive for NAAG. Additionally, many neurons of the red nucleus were intensely stained for NAAG. Comparisons with staining for the 67 kD form of glutamic acid decarboxylase in serial sections revealed complementary distributions, with NAAG in excitatory pathways and cell groups, and glutamic acid decarboxylase in inhibitory systems. These findings suggest a significant functional involvement of NAAG in the excitatory afferent and efferent projection systems and provide an anatomical basis for investigations into the interactions of NAAG and GABA in the cerebellum. © 1994 W

ISSN:0092-7317    

DOI:10.1002/cne.903470410

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY

摘要:

AbstractRelatively little is known about the organization of neural input to pelvic viscera in amphibia. In this study, sacral spinal efferent neurons were labeled inXenopus laevisfrogs by application of horseradish peroxidase (HRP) to the tenth spinal nerve, to pelvic musculature, or to the pelvic nerve. DiI was applied to the pelvic nerve with similar results. Labeled spinal neurons were located in the intermediate gray or in the ventral horn. Neurons in the tenth dorsal root ganglion, but not in the spinal cord, were labeled after application of HRP or DiI to the pudendal nerve.The peripheral targets of DiI‐labeled pelvic nerve axons were the compressor cloaca muscle, cloaca, and bladder. DiI‐labeled pudendal nerve axons distributed peripherally to cloacal lip and medial thigh integument. These data suggest that the pudendal nerve in amphibians is purely sensory and that both somatic and autonomic motor axons traverse the pelvic nerve. © 1994 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903470411

出版商:Wiley‐Liss, Inc.    

年代:1994

数据来源: WILEY