摘要:

AbstractThe distribution and morphology of neurons and axonal endings (puncta) were analyzed in auditory brainstem, thalamic, and cortical centers in the mustache bat. The goals of the study were (1) to compare and contrast the location of GABAergic and glycinergic neurons and puncta, (2) to determine whether nuclei containing immunoreactive neurons likewise have a similar concentration of puncta, (3) to assess the uniformity of immunostaining within a nucleus and to consider regional differences that were related to or independent of cytoarchitecture, and (4) to compare the patterns recognized in this bat with those in other mammals.There are nine major conclusions. (1) Glycinergic immunostaining is most pronounced in the hindbrain. (2) In the forebrain, GABA alone is present. (3) Some nuclei have GABAergic or glycinergic neurons exclusively; a few have neither. (4) Although there is sometimes a close relationship between the relative number of immunopositive neurons and the density of the puncta, just as often there is no particular correlation between them; this reflects the fact that many GABAergic and glycinergic neurons project beyond their nucleus of origin. (5) Even nuclei devoid of or with few GABAergic or glycinergic neurons contain relatively abundant numbers of puncta; some neurons receive axosomatic terminals of each type. (6) In a few nuclei there are physiological subregions with specific local patterns of immunostaining. (7) The patterns of immunostaining resemble those in other mammals; the principal exceptions are in nuclei that, in the bat, are hypertrophied (such as those of the lateral lemniscus) amd in the medial geniculate body. (8) Cellular colocalization of GABA and Gly is specific to only a few nuclei. (9) GABA and glutamic acid decarboxylase (GAD) immunostaining have virtually identical distributions in each nucleus.Several implications follow. First, the arrangements of GABA and Gly in the central auditory system represent all possible patterns, ranging from mutually exclusive to overlapping within a nucleus to convergence of both types of synaptic endings on single neurons. Second, although both transmitters are present in the hindbrain, glycine appears to be dominant, and it is often associated with circuitry in which precise temporal control of aspects of neuronal discharge is critical. Third, the auditory system, especially at or below the level of the midbrain, contains significant numbers of GABAergic or glycinergic projection neurons. The latter feature distinguishes it from the central visual and somatic sensory pathways.

ISSN:0092-7317    

DOI:10.1002/cne.903550302

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe present study characterizes gonadotropin‐releasing hormone (GnRH) neuronal groups that are located in several different brain regions by investigating GnRH molecular species and projection patterns in an anabantid fish,Colisa lalia. First, we examined the molecular species of GnRHs in extracts of the brain and the pituitary by reverse‐phase high‐performance liquid chromatography followed by radioimmunoassays. We found salmon GnRH (sGnRH), chicken GnRH‐II (cGnRH‐II), and an unfamiliar GnRH‐like substance.Next, to examine the distribution of each GnRH molecule in different GnRH neuronal groups, we performed immunohistochemistry using four kinds of antisera and an antibody. Furthermore, we performed brain lesioning experiments of terminal nerve (TN) cells, the most conspicuous GnRH‐immunoreactive cells inColisa lalia. Comparisons of immunoreactive structures between TN‐lesioned fish and untreated fish elucidated the projection area of each neuronal group. Three major neuronal groups were observed. TN‐GnRH cells, which are located in the transitional area between the olfactory bulb and the telencephalon, showed strong sGnRH and weaker cGnRH‐II immunoreactivity. TN‐GnRH cells projected to wide areas of the central nervous system from the olfactory bulb to the spinal cord. The second group, located in the preoptic area, showed only sGnRH immunoreactivity and projected only to the pituitary. The third ond, located in the midbrain tegmentum, exhibited strong cGnRH‐II and weaker sGnRH immunoreactivity. This cell group projected mainly to brain regions posterior to the hypothalamus and the spinal cord. These different projection patterns suggest functional differentiation of e

ISSN:0092-7317    

DOI:10.1002/cne.903550303

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

年代:1995

数据来源: WILEY

摘要:

AbstractTo identify proteins involved in the early development of the mammalian cerebral cortex, we previously used two‐dimensional gels to compare proteins synthesized at different stages in corticogenesis in the embryonic rat at embryonic day 14 (E14), E17, and E21. During this period, the cortex develops from a morphologically homogeneous population of proliferative precursor cells into a complex structure containing a diverse array of terminally differentiated neurons. Several proteins are up‐regulated coincident with the generation of postmitotic neurons. Here we describe the purification, partial amino acid sequencing, and characterization of one of these proteins, TOAD‐64 (Turned On After Division; 64 kDa), using polyclonal antisera to two synthetic peptides from the protein. This analysis reveals that TOAD‐64 is a 64,000 Da protein that increases in abundance over the period of corticogenesis and then subsequently decreases to very low levels in the adult. The protein is neural specific and is expressed by postmitotic neurons as they begin their migration out of the ventricular zone into the developing cortical plate. It is expressed in advance of most other neuronal proteins. Progenitor cells do not express TOAD‐64. Therefore, this protein is a marker for postmitotic cells that have made a commitment to a neuronal phenotype. The extremely early expression, the relative abundance in newly born neurons, as well as the restriction in expression to the period of initial neuronal differentiation suggest that TOAD‐64 may be a key structural protein for early neuron

ISSN:0092-7317    

DOI:10.1002/cne.903550304

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe present study was undertaken to examine the morphological bases of local synaptic interactions between dorsal horn interneurons. Seven interneurons responding to innocuous mechanical stimuli were intracellularly recorded in lamina III/IV of an isolated preparation of hamster spinal cord with partially intact innervation from an excised patch of hairy skin. Axonal arborizations were stained with horseradish peroxidase (HRP) and examined with an electron microscope. Five cells had extensive synaptic terminations (375‐1, 785 boutons/axon) with localized distributions (rostrocaudal distance, 425‐1,251 μm) overlapping the dendritic trees. Two cells gave rise to deep stem axons that bifurcated into rostrocaudal daughter branches with collaterals ventral to the parent cell bodies (79‐661 boutons/axon). Axons of local interneurons were thinly myelinated and formed terminal and en passant enlargements (mean [±S. D.] diameter = 0.88 ± 0.24 μm, n = 157) containing clear, round vesicles 20‐60 nm in diameter. Collateral branches of deep axon cells produced round, vesicle‐containing boutons comparable in diameter (0.93 ± 0.22 μm, n = 31) to local axon cells. Both types of interneurons formed asymmetric synaptic contacts with dendritic profiles, but not with cell bodies or axon terminals. Postsynaptic profiles contained sparse ribosomes and had a mean diameter of 1.0 ± 0.5 μm (n = 49), significantly smaller than a population of identified proximal dendrites (2.3 ± 0.9 μm, n = 47). HRP‐labeled boutons were rarely (5/45 or 11%) in synaptic contact with more than one profile. We conclude that lamina III/IV interneurons make axodendritic synapses predominantly with distal dendrites. Thus, terminations of deep dorsal horn interneurons appear to have a postsynaptic distribution overlapping with axodendritic contacts formed by several functional classes of cutaneous sensory fibers signaling innocuous mechanical stimuli. Such overlap suggests that local spinal networks selectively and strongly influence afferent signals at initial stages of soma

ISSN:0092-7317    

DOI:10.1002/cne.903550305

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe morphology and distribution of dopaminergic interplexiform cells in adult rat and monkey retinas were analyzed to determine any correlation with the function of dopamine in the outer retinal layers. The retinas were processed as whole mounts for tyrosine hydroxylase immunohistochemistry. There was a network formed by the sclerally directed processes of interplexiform cells in the inner nuclear, outer plexiform, and outer nuclear layers running throughout the retina. Their density was higher in the superior retina than in the inferior retina of the rat and was especially high in the superior temporal quadrant. The external network in this quadrant was significantly less dense in the monkey than in the rat, as are the interplexiform cells. The somata of interplexiform and other dopaminergic cells were about the same size in both rats and monkeys. Computer‐assisted reconstruction of external arborizations of individual cells showed that external processes lay very close to horizontal and photoreceptor cells and also to blood capillaries. Because they were long, thin, and highly varicose; branched at right angles; and often arose from an axon hillock, the external processes were identified as axons. Therefore, we define the dopaminergic interplexiform cells as multiaxonal neurons, with at least one outwardly directed axon that reaches the outer plexiform layer. The function of the network of external processes from the interplexiform dopaminergic cells is discussed in terms of modulating the release of dopamine to external layer

ISSN:0092-7317    

DOI:10.1002/cne.903550306

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

年代:1995

数据来源: WILEY

摘要:

AbstractIn the vestibular and auditory neurosensory epithelia of poikilothermic vertebrates and of birds, damaged sensory “hair” cells are often deleted by extrusion from the apical surface. In contrast, in the adult mammalian auditory epithelium (the organ of Corti), the bodies of damaged hair cells degenerate within the epithelium. To determine whether this apparent difference is species related or is associated with the differing structural organisation of the epithelia, hair cell deletion in the mammalian vestibular end‐organs was examined. The structural organisation of these tissues is closer to that of the inner ear epithelia of lower vertebrates than to the organ of Corti. Hair cell loss was induced by chronic, systemic treatment of guinea pigs with the ototoxic aminoglycoside antibiotic gentamicin. The vestibular sensory epithelia were examined at various times after treatment via scanning electron microscopy, thin sectioning, and staining f‐actin with fluorescently labelled phalloidin. Two distinct modes of hair cell loss were identified: (1) degeneration of hair cells within the epithelium, which often showed morphological features consistent with those described for apoptosis, and (2) extrusion of intact cells from the apical surface. Neither process caused the formation of obvious lesions through the epithelial surfaces. Expansion of adjacent supporting cells during hair cell deletion resulted in repair that appeared to preserve permeability barriers. There was also no evidence of inflammation accompanying hair cell removal. Thus, with both modes of hair cell loss, it appeared that deletion of hair cells was achieved without disruption of tissue architecture or integrity. This may be important for subsequent repair and regeneration processes to

ISSN:0092-7317    

DOI:10.1002/cne.903550307

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe postsynaptic effects of dopamine in the striatum are mediated mainly by receptors encoded by D1, D2, and D3 dopamine receptor genes. The D1 and D2 genes are the most widely expressed in the caudate‐putamen, the accumbens nucleus, and the olfactory tubercle. Several anatomical studies, including studies using in situ hybridization with oligonucleotide and cDNA probes, have suggested that D1 and D2 receptors are segregated into distinct efferent neuronal populations of the striatum: D1 in substance P striatonigral neurons and D2 in enkephalin striatopallidal neurons. In contrast, on the basis of several in vivo and in vitro studies, other authors have suggested the existence of an extensive colocalization of D1 and D2 in the same striatal neurons. Our study was undertaken in order to analyze in detail the expression of the D1 and D2 receptor genes in the efferent striatal populations, with special reference to the various striatal areas, and to yield insights into the question about D1 and D2 mRNA localization in the striatum. We have, therefore, used highly sensitive digoxigenin‐and35S‐labeled cRNA probes to address this question. The present results demonstrate that the D1 and D2 receptor mRNAs are segregated, respectively, in substance P and enkephalin neurons in the caudate‐putamen and accumbens nucleus (shell and core) and in the olfactory tubercle (for their largest part). A very small percentage of neurons may coexpress both genes. These results confirm that the D1 and D2 receptor genes are expressed in distinct populations of striatal efferent neurons in the normal adult rat. © 1995 Wiley

ISSN:0092-7317    

DOI:10.1002/cne.903550308

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe differentiation of neural crest and ectodermal placodes was examined in the axolotl in order to clarify the contribution of these tissues to the formation of the sensory ganglia of the branchiomeric and lateral line cranial nerves in salamanders. The most rostral branchiomeric nerves, the profundal and trigeminal nerves, appear to arise solely from an ectodermal placode and from neural crest, respectively. The sensory ganglia of the more caudal branchiomeric nerves —the facial, glossopharyngeal, and vagal nerves —are formed by a medial component that differentiates from the dorsomedial surface of migrating bands of neural crest associated with each of the developing branchial arches and with one or more lateral components that arise from epibranchial placodes located immediately dorsal and caudal to each pharyngeal pouch. Neuroblasts destined to form these sensory ganglia begin to differentiate from the epibranchial placodes as early as stage 26, whereas neural crest‐derived neuroblasts can be recognized by stage 30. Centrally directed neurites of both groups of neuroblasts enter the medulla by stage 34, and their peripherally directed neurites form recognizable rami by stage 35. Five cranial lateral line nerves, in addition to the octaval nerve, can be recognized in axolotls. Each of these nerves arises from a separate dorsolateral placode that initially gives rise to the neuroblasts of a sensory ganglion whose peripheral neurites innervate sensory receptors subsequently formed from each placode. The time course of the differentiation of these nerves and receptors is comparable to that of the branchiomeric nerves. The possible roles of rhombomeres and their associated regulatory genes and pharyngeal pouches in the induction and specification of neural crest and ectodermal placodes are exp

ISSN:0092-7317    

DOI:10.1002/cne.903550309

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe receptor mGluR5 is a metabotropic glutamate receptor with messenger RNA abundantly present throughout cortex, hippocampus, and caudate/putamen that is also coupled to phosphatidyl inositide hydrolysis and calcium mobilization. In this study, the distribution of mGluR5 was examined in rat brain by immunocytochemistry. The antibody utilized is highly specific and does not cross react with the most closely related other metabotropic glutamate receptor, as determined by Western blot analysis of nonneuronal cells transfected with metabotropic receptor coding sequences. The receptor mGluR5 is widely expressed with the highest density in olfactory bulb, caudate/putamen, lateral septum, cortex, and hippocampus, as confirmed with both immunocytochemistry and Western blot analysis. Electron microscopic studies in hippocampus and cortex indicate that the labeling is mostly on membranes of dendritic spines and shafts. Light and electron microscopic evidence indicates that some mGluR5 immunoreactivity is located in presynaptic axon terminals, suggesting that mGluR5 may function as a presynaptic receptor.

ISSN:0092-7317    

DOI:10.1002/cne.903550310

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe distribution of two phosphoinositide‐linked metabotropic glutamate receptors (mGluR1α and mGluR5) was studied immunohistochemically in area 17 before, during and after the peak of use‐dependent modification of eye‐specific connections. In the adult, mGluR1α immunoreactivity is high in all layers except layer IV, where mGluR5 immunoreactivity is concentrated. This difference in distribution indicates different functions for these two receptor subtypes. The laminar pattern of mGluR1α immunoreactivity is similar in all three ages, but the overall labeling intensity decreases after the peak (6 weeks of age) of the critical period. The laminar pattern of mGluR5 immunoreactivity changes with age, It is expressed in most layers at 2 days of age and is found mainly in layer IV in the adult. This laminar distribution and developmental pattern match the distribution and the development of the geniculocortical terminals. The change in mGluR1α labeling intensity and mGluR5 laminar distribution over time is consistent with both of these mGluRs being involved in sensory‐dependent plasticity for eye‐specific connections in the

ISSN:0092-7317    

DOI:10.1002/cne.903550311

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

年代:1995

数据来源: WILEY