摘要:

AbstractThe biological actions of neurotrophins are mediated by specific neurotrophin receptor tyrosine kinases (Trks). A low‐affinity nerve growth factor (NGF) receptor, p75, appears to modulate sensitivity to neurotrophins in some neuronal populations. It has been recently demonstrated that genes encoding members of the Trk family are expressed in distinct patterns in the dorsal root ganglia DRG; Mu et al. [1993] (J. Neurosci. 13:4029–4041). However, the extent to which different neurotrophin receptor genes are coexpressed by individual DRG neurons is unknown. The question of coexpression is important since the expression of more than one member of the trk family by DRG neurons would suggest the potential for regulation by multiple neurotrophins. To address this question, a combination of isotopic and colorimetric in situ hybridization was performed on rat thoracic DRG using riboprobes specific for trk A, trkB, trkC, and p75. We show here that neurons that express trkA are largely distinct from those that express trkC, although there is a small subpopulation that expresses both of these genes. We also show that there is a distinct population of DRG neurons that expresses trkB and does not coexpress either trkA or trkC. P75 is expressed in almost all neurons that express trkA or trkB, but is coexpress in only 50% of trkC‐expressing neurons. Importantly, p75 is not expressed in DRG neurons independent of trk expression. Finally, a subpopulation of DRG neurons does not express any of the neurotrophin receptor mRNAs.Our results demonstrate that there are distinct populations of DRG neurons that express each member of the neurotrophin receptor tyrosine kinase family. Our findings of extensive colocalization of p75 with trkA and trkB lend support to the idea that p75 is important in mediating the actions of NGF and brain‐derived neurotrophic factor on DRG neurons. Interestingly, however, p75 expression is clearly unimportant for a subpopulation of neurons that require neurotrophin‐3. The fact that p75 is not expressed in the absence of trkA, trkB, or trkC suggests that the function of p75 is closely related to functions of the known neurotrophin receptor tyrosine kinases. Finally, our results suggest that a significant percentage of DRG neurons may be regulated by non‐neurotrophin neuronal growth factors. © 1995 Wil

ISSN:0092-7317    

DOI:10.1002/cne.903510302

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe m2 muscarinic acetylcholine receptor gene is expressed at high levels in basal forbrain, but the paucity of information about localization of the encoded receptor protein has limited the understanding of cellular and subcellular mechanisms involved in cholinergic actions in this region. The present study sought to determine the cellular localization of m2 protein, its relationship to cholinergic neurons, and its pre‐and postsynaptic distribution in the rat medial septum‐diagonal band complex using immunocytochemistry with polyclonal rabbit antibodies and a newly developed rat monoclonal antibody specific to the m2 receptor. Light microscopic colocalization studies demonstrated that m2 was present in a subset of choline acetyltransferase immunoreactive neurons, in choline acetyltransferase‐negative neurons, and in more neuropil elements than was choline acetyltransferase. Intraventricular injections of 192 IgG‐saporin, an immunotoxin directed to the low‐affinity nerve growth factor receptor, resulted in depletion of choline acetyltransferase‐immunoreactive neurons in the medial septum‐diagonal band complex, whereas m2 immunoreactivity in neurons and in the neuropil was unchanged. By electron microscopy, m2 receptor in medial septum‐diagonal band complex was localized to the plasmalemma of a small population of small to medium‐sized neurons, and it was also found in dendrites, axons, and axon terminals in the neuorpil Neurons expressing m2 immunoreactivity recived synaptic contacts from unlabelled axon terminals. A small distinct subpopulation of large neurons, unlabelled by m2 immunoreactivity, received synaptic contacts from m2‐immunoreactive terminals. Thus, m2 receptor is situated to mediate the local effects of acetylcholine on basal forebrain cholinergic and noncholinergic neurons and, also, at both pre‐and postsynaptic sites.

ISSN:0092-7317    

DOI:10.1002/cne.903510303

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

年代:1995

数据来源: WILEY

摘要:

AbstractSerotonin (5‐HT) mediates its effects on neurons in the central nervous system through a number of different receptor types. To gain better insight as to the localization of 5‐HT responsive cells, the distribution of cells expressing mRNAs encoding the three 5‐HT receptor subtypes 1A,1C, and 2 was examined in rat brain with in situ hybridization using cRNA probes. 5‐HT1A receptor mRNA labeling was most pronounced in the olfactory bulb, anterior hippocampal rudiment, septum, hippocampus (dentate gyrus and layers CAI‐3), entorhinal cortex, interpeduncular nucleus, and medullary raphe nuclei. 5‐HT 1C receptor mRNA labeling was the most abundant and widespread of the three 5‐HT receptor subtypes examined. Hybridization signal was denset in the choroid plexus, anterior olfactory nucleus, olfactory tubercle piriform cortex, septum, subiculum, entorhinal cortex, claustrum, accumbens nuclues, striatum, lateral amygdala, paratenial and paracentral thalamic nuclei, subthalamic nucleus, substantia nigra, and reticular cell groups. 5‐HT2 receptor mRNA was localized to the olfactory bulb, anteriorhippocampal rudiment, frontal cortex, piriform cortex, entorhinal cortex, claustrum, pontine nuclei, and cranial nerve motor nuclei including the oculomotor, trigeminal motor, facial, dorsal motor nucleus of the vagus, and hypoglossal nuclei. The distributions of mRNAs for the three different 5‐HT receptor subtypes overlap with regions that bind various 5‐HT receptor‐selective ligands and are present in nearly all areas known to receive serotonergic innervation. The results of this study demonstrate that nervous which express these 5‐HT receptor subtypes are very widespread in the central nervous system, yet possess unique distributions with in the rat brain. Moreover, previously unreported regions of 5‐HT receptor subtype expression were observed, particulary with the 5‐HT receptor riboprobe in the brainstem. Finally, several brain areas contain multiple 5‐HT receptor subtype mRNAs, which leads to the possibility that individual cells may express more than one 5‐HT receptor

ISSN:0092-7317    

DOI:10.1002/cne.903510304

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

年代:1995

数据来源: WILEY

摘要:

AbstractWe studied the expression of glutamate decarboxylase (GAD), GAD65 and GAD67, in cat retina by immunocytochemistry. About 10% of GABAergic amacrime cells express only GAD65 and 30% express only GAD67. Rougly 60% contain both forms of the enzyme, but GAD67 is present only at low levels in the majority of these double‐labeled amacrine cells. The staining pattern in the inner plexiform layer (IPL) for the two GAD forms was also different. GAD65 was restricted to strata 1–4, and GAD67 was apparent throughout the IPL but was strongest in strata 1 and 5. This indicates that soams, as well as their processes, are differentially stained for the two forms of GAD. Cell types expressing only GAD65 include interplexiform cells, one type of cone bipolar cell, and at least one type of serotonin‐accumulating amacrine cell. Cell types expressing only GAD67 include amacrine cells synthesizing dopamine, amacrine cells synthesizing nitric oxide (NO), and amacrine cells accumulating serotonin. Cholinergic amacrine cells express a low level of both GAD forms. Our findings in the retina are consistent with previous observations in the brain that GAD65 expression is greater in terminals than in somas. In addition, in retina most neurons expressing GAD67 also contain a second neurotransmitter as well as GABA, and they tend to be larger than neurons expressing GAD65. We propose that large cells have a greater demand for GABA than small cells, and thus require the constant, relatively unmodulated level of GABA that is provided by GAD67. © 1995 Willy‐L

ISSN:0092-7317    

DOI:10.1002/cne.903510305

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe nervus terminalis is a ganglionated vertebrate cranial nerve of unknown function that connects the brain and the peripheral nasal structures. To investigate its function, we have studied nervus terminalis ganglion morphology and physiology in the bonnethead shark (Sphyrna tiburo), where the nerve is particularly prominent. Immunocytochemistry for gonadotropin‐releasing hormone (GnRH) and Leu‐Pro‐Leu‐Arg‐Phe‐NH2(LPLRFamide) revealed two distinct populations of cells. Both were acetylcholinesterase positive, but LPLR‐Famide‐immunoreactive cells consistently stained more darkly for acetylcholinesterase activity. Tyrosine hydroxylase immunocytochemistry revealed fibers and terminal‐like puncta in the ganglion, primarily in areas containing GnRH‐immunoreactive cells.Consistent with the anatomy, in vitro electrophysiological recordings provided evidence for cholinergic and catecholaminergic actions. In extracellular recordings, acetylcholine had a variable effect on baseline ganglion cell activity, whereas norepinephrine consistently reduced activity. Electrical stimulation of the nerve trunks suppressed ganglion activity, as did impulses from the brain in vivo. During electrical suppression, acetylcholine consistently increased activity, and norepinephrine decreased activity. Muscarinic and, to a lesser extent, α‐adrenergic antagoinsts both increased activity during the electrical suppression, suggesting involvement of both systems. Intracellular recordings revealed two types of ganglion cells that were distinguishable pharmacologically and physiologically. Some cells were hyperpolarized by cholinergic agonists and unaffected by norepinephrine; these cells did not depolarize with peripheral nerve trunk stim stimulation. Another. Another group of cells did depolarize with peripheral trunk stimulation; a representative of this group was depolarized by carbachol and hyperpolarized by norepinephrine.These and other data suggest that the bonnethead nervus terminal is ganglion contains at least two cell populations that respond differently to acetylcholine and norepinephrine. The bonnethead nervus terminals ganglion appears to differ fundamentally from sensory and autonomic ganglia but does share some features with the neural circuits of forebrain GnRH systems.

ISSN:0092-7317    

DOI:10.1002/cne.903510306

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

年代:1995

数据来源: WILEY

摘要:

AbstractSeveral mammalian muscles in the limb and trunk receive topographically organized innervation from spinal cord motor neurons. Some muscles in which topographic innervation has been demonstrated have a sheet‐like architecture; others are compartmentalized and/or have more than one origin. An interesting question is whether topography is related to these anatomical features, or whether it occurs as a general consequence of the development of innervation.To address this question, we examined the pattern of projections to the soleus muscles, which lacks these anatomical features. Intracellular recordings of endplate potentials in early and intermediate age rabbits were used to assess the spinal origin of inputes to two distinct regions of the muscle. Both regions were innervated by both rostral and caudal portions of the motor pool. These experiments also showed that individual muscle fibers frequently receive separate inputs arising from widely separated regions of the motor pool. In another set of experiments, physiological measurements of tension overlap in young, polyinnervated muscles showed that the relative positions of motor neurons in the spinal cord do not correlate with the extent to which motor units share muscle fibers. In a third set of experiments, motor neurons were retrogradely labeled following local injections of tracer into muscle. Small and large local injections resulted in comparably dispersed labeling of motor neurons within the motor pool. Moreover, the rostrocaudal position of labeled neurons was not correlated with the position of the injection site within the muscle. Together, these results provide evidence that the soleus muscle is not topographically innervated. Furthermore, an examination of several age groups suggests that the innervation pattern in this muscle is not altered by postnatal synapse elimination. © 1995 Willy‐Liss,

ISSN:0092-7317    

DOI:10.1002/cne.903510307

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

年代:1995

数据来源: WILEY

摘要:

AbstractAfferent group III and IV nerve fibers of the knee joint markedly differ in their responsiveness to mechanical stimulation, which may be reflected in the structure and location of their terminals. Therefore, in sympathectomized cats, the fine afferent innervation of the knee joint capsule was studied via ultrastructural three‐dimensional reconstructions over distance of up 300 μm. Small peripheral nerves and “free” (noncorpuscular) sensory nerve ending were found in a superficial layer of the outer fibrous part of the capsule, in the patellar retinaculum, and in the outer and inner surface layers of the medial collateral and patellar ligaments. Group III nerve fibers showed a proximal myelinated portion inside the nerve, an intermediate portion that lacks a myelin sheath and is only surrounded by perineurium, and a distal portion outside of the perineurium that forms the sensory ending proper. Group IV fibers showed only two distinct portions, an intraperineurial (proximal) and an extraperineurial (distal) portion without any further morphological differences. Outside of the perineurium, a network formed by Schwann cells (“Schwann cell reticulum”) provides a pathway for the distal portion of the sensory axons. No distinct subgroups of the sensory terminal fibers could be defined according to the configuration of the Schwann cells and the nerve fiber terminals. Sensory terminals were located adjacent to different structures such as venous and lymphatic veesels, fat cells, and collagenous fibers. Distinct parts of the same terminal nerve fiber were found in close contact to a vessel wall; others were surrounded by dense collagenous tissue. Close to sensory endings, mast cells and mast cell‐like cells were frequently found, indicating a functional relationship. © 1995 Wi

ISSN:0092-7317    

DOI:10.1002/cne.903510308

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe ultrastructure and synaptic organization of the nucleus medialis and cerebellar crest of the teleost Chelon labrosus have been investigated. The nucleus medialis receives projections from the anterior and posterior lateral line nerves. This nucleus consists of oval neurons and large crest cells (“Purkinje‐like” cells) whose apical dendrites branch in the overlying molecular layer, the cerebellar crest. In the dorsal region of the nucleus medialis, the perikarya and smooth primary dendrites of the crest cells are interspersed among myelinated fibers and nerve boutons. The ventral layer of the nucleus medialis contains crest cell perikarya and dendrites as well as oval neurons. The cerebellar crest lacks neuronal bodies, but the apical dendrites of crest cells receive synapses from unmyelinated and myelinated fibers. In the cerebellar crest, two types of terminals are presynaptic to the crest cell dendrites: boutons with spherical vesicles that from asymmetric synapses with dendritic spines and boutons containing pleomorphic vesicles that from symmetric synapses with dendritic spines and boutons containing pleomorphic vesicles that from symmetric synapses directly on the dendritic shaft. Most axon terminals found on the somata and primary dedrites of crest cells in the nucleus medialis have pleomorphic vesicles and form symmetric contacts, though asymmetric with spherical vesicles and mixed synapses can be observed; these mixed synapses exhibit gap junctions and contain spherical vesicles. Unlike crest cells, the oval neuron perikarya receive three types of contacts (symmetric, asymmetric, and mixed). The origins and functions of these different bouton types in the nucleus medialis are discussed. © 1995 Willy‐L

ISSN:0092-7317    

DOI:10.1002/cne.903510309

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe spatial organization of human cingulate (areas 24b, 23b, and 31) and pericingulate (areas 7 and 19) cortex was examined by using an image analyzer to measure characteristics of vertically oriented, translaminar columns of neurons in the cerebral cortex. Columns of 30–50 μm in diameter are hypothesized to be a general feature of cortical organization, but no quantitative analysis of different human cortical areas has been performed. Our results prove for the first time that a columnar organization was detectable in every area examined. The average width of cell columns was approximately 40 μm separated by a neuropil‐rich fascile of the same dimension. Because differences in the expression of a columnar organization were seen, the degree of columnization was subsequently expressed by a verticality index (VI) revealing specific changes in its dimension depending on the architectonic area. The VI was calculated by a linear combination of three variables derived from the measurement of cell density profiles in Nissl‐stained sections at right angles to vertically oriented cell columns. Variables included the amplitude of profile peaks, the standard deviation of the width of those profile peaks, and the standard deviation of the distances between profile peaks. The index of verticality describes the deviation of a distinct area and layer from the mean degree of vertical organization of all cortical areas and layers examined. Thus, different degrees of columnar organization can be quantitatively described by the verticality index and can be used as criteria to characterize architectonic areas. © 1995 Willy

ISSN:0092-7317    

DOI:10.1002/cne.903510310

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

年代:1995

数据来源: WILEY

摘要:

AbstractFrom previous lesion studies of the hippocampus it has been reported that axons of the commissural/associational pathway expand their termination zone in the molecular layer of the dentate gyrus by 20–25% in response to loss of input from the entorhinal cortex. However, although much is known about the response of the commissural/associational pathway with regard to extent, latency, and speed of the reinnervation response following an entorhinal cortex lesion, little is known about how the loss of additional afferent systems might modulate this response. To address this issue, we examined at 14, 30, and 45 days postlesion, the sprouting of commissural/associational afferents following either a unilateral fimbria fornix transection, a unilateral entorhinal cortex lesion, or combined lesions of both the entorhinal cortex and the fimbria fornix. Loss of septal innervation to the hippocampus was assessed using the cholinesterase stain, whereas sprouting from the commissural/associational pathway was determined from Holmes fiber‐stained sections. In addition, the Timms stain was used to examine the time course of the loss of terminal fields of the various zinc‐containing afferent systems within the hippocampus.Following the removal of input to the hippocampus via the fimbria fornix transection, there was no evidence of sprouting of the commissural/associational fibers into the deafferented portion of the dentate gyrus. In contrast, rats receiving an entorhinal cortex lesion showed a significant increase (28%) in the width of the commissural/associational fiber plexus that was present by 14 days postlesion. By comparison, the magnitude of the expansion of the commissural/associational fiber plexus was significantly larger after lesioning both the entorhinal cortex and the fimbria than after the entorhinal cortex lesion alone (45% vs. 28%). In addition, the expansion of the commissural/associational fiber plexus that was not increased at 14 days postlesion but was significantly increased at 30 days postlesion. The delay in the sprouting of the commissural/associational pathway coincided with the time course of loss of zinccontaining fibers in the outer molecular layer of the dentate gyrus as assessed with the Timms stain. These results suggest that the magnitude and time course for the sprouting of axons from the commissural/associational pathway into the partially deafferented hippocampus of the adult rat is lesion dependent and that the effect of the loss of input from the entorhinal cortex can be modulated and enhanced by the concomitant depletion of input from the fimbria fornix. © 1995 Willy‐L

ISSN:0092-7317    

DOI:10.1002/cne.903510311

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

年代:1995

数据来源: WILEY