摘要:

AbstractRetrograde tracing with true blue (TB) and diamidino yellow (DY) and anterograde tracing with either wheatgerm agglutinin–conjugated horseradish peroxidase (WGA‐HRP) orPhaseolus vulgarisleucoagglutinin (PHA‐L) were employed to investigate the projections from trigeminal nucleus principalis (PrV) and trigeminal subnucleus interpolaris (SpI) to their targets in the medial ventral posterior (VPM) and posterior (POm) nuclei of the thalamus. Many more cells in both PrV and SpI were labeled by tracer injections into VPM than into POm. Only a very small number of double‐labeled neurons were observed in either PrV or SpI. However, a significantly higher percentage of SpI cells projected to POm or to both POm and VPM than was the case for PrV. Anterograde tracing with WGA‐HRP showed that the projections from both PrV and SpI to VPM were much denser than those from the same nuclei to POm. Small injections of PHA‐L into either PrV or SpI produced a focus of fairly dense labeling in VPM and much more diffuse terminal labeling in POm. These anatomical data provide evidence for two separate trigeminothalamic pathways, one originating from PrV and the second originating from SpI. Both of these pathways converge and diverge at the thalamic level. That is, information from the PrV pathway and from the SpI pathway are both provided to VPM in a morphologically restricted fashion and to POm in a morphologically widespr

ISSN:0092-7317    

DOI:10.1002/cne.903140202

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

年代:1991

数据来源: WILEY

摘要:

AbstractExtracellular recording, intracellular recording, intracellular horseradish peroxidase injection, and receptive field mapping techniques were employed to evaluate the physiological and morphological properties of medial ventral posterior nucleus (VPM) and posterior nucleus (POm) neurons in normal adult rats. Overall, we physiologically characterized 148 VPM and 121 POm neurons. Over 82% of the VPM cells were excited only by deflection of one or more mystacial vibrissae, 10% were activated by displacement of guard hairs, and the remainder were either excited by indentation of the skin or were unresponsive. Less than 40% of the POm cells were activated by vibrissa deflection, 18% were excited by displacement of guard hairs, and another 17% were unresponsive. Most of the rest of the POm cells were excited by stimulation of skin, mucosa, or activation of muscle‐related afferents. Small percentages of POm cells responded only to noxious stimulation, were classified as having a wide dynamic range, or were inhibited by peripheral stimulation. Electrical stimulation of either PrV or SpI activated most neurons in both VPM and POm. This excitation was almost invariably followed by a long‐lasting hyperpolarization which was generally strong enough to prevent responses to either electrical stimuli delivered in the brainstem or mechanical stimulation of the periphery. The receptive fields of vibrissa‐sensitive cells in POm were generally much larger than those of cells in VPM. Data obtained with extracellular recording indicated that VPM and POm cells responded to an average of 1.4 and 4.0 vibrissae, respectively. Intracellular recording from smaller samples of VPM and POm cells demonstrated the existence of inputs that were insufficient to produce spikes from the cell, but did yield epsp's. When both sub‐ and suprathreshold excitation were considered, the average number of vibrissa in the receptive field of a VPM cell was 2.7 and the value for POm cells became 7.8. HRP‐filled neurons recovered in POm (N = 20) generally had much larger dendritic arbors than neurons in VPM (N = 31). For the former cells, the size of the dendritic tree was significantly correlated with the number of vibrissa to which the cell responded; for the latter neurons, i

ISSN:0092-7317    

DOI:10.1002/cne.903140203

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe somatotopic organization of skin sensory nerve projections to the lumbosacral dorsal horn of hatchling chickens was determined with the aid of transganglionic transport of horseradish peroxidase (HRP) processed with tetramethylbenzidine histochemistry, A total of eight hindlimb nerves were studied, five of which were purely cutaneous. When combined, the innervation fields of these nerves covered most of the hindlimb surface, allowing a nearly complete somatotopic map of the hindlimb to be generated.This report describes a novel pattern of cutaneous nerve projections to the dorsal horn. Unlike other vertebrates, cutaneous nerves of chickens formed two separate, somatotopically organized projections across the mediolateral axis of the dorsal horn; when serially reconstructed and superimposed, these projections produced two nonoverlapping somatotopic maps of the skin surface lying side by side. Each of these separate maps was nearly identical to the other in overall topology. These two separate maps appear to represent distinct modalities of sensory information, as projections composing the medial map were preferentially labeled by choleragenoid‐HRP, whereas those composing the lateral map were preferentially labeled by wheat germ agglutinin‐HRP. In mammals, these HRP ligands selectively label the central projections of myelinated and unmyelinated cutaneous afferents, respectively. The present study, therefore, strongly supports the cytoarchitectonic findings of Brinkman and Martin (Brain Res.56:43–62, ′73) that lamina III lies medial, rather than ventral, to lamina II in the chicken dorsal horn. Further, the present studies also suggest that laminae II and III of chickens are homologous to the homonymous laminae in the dorsal horn of

ISSN:0092-7317    

DOI:10.1002/cne.903140204

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

年代:1991

数据来源: WILEY

摘要:

AbstractSerial section electron microscopy has been used to examine a horseradish peroxidase (HRP)‐labelled group Ia afferent collateral from its entry point in the grey matter to its termination in Clarke's column of the cat spinal cord. A wide range of geometries and myelination patterns were identified along the collateral, including (1) nodes specialized to exhibit a single synaptic bouton, (2) nodes specialized to exhibit two or more synaptic boutons connected by fine, unmyelinated lengths of the collateral, (3) terminal heminodes, along which boutons were separated by unmyelinated branches, and (4) complex arrangements along which myelinated and unmyelinated branches gave rise to one or more boutons. Thirty‐six synaptic boutons of varied shape and size were exhibited by this collateral.Previous studies have shown that the geometry, branching, and myelination pattern of an axon play an important role in determining the amplitude and duration of an action potential propagating along that axon. In turn, the amplitude and duration of a presynaptic action potential influence the efficacy of transmitter release. The varied axonal geometries and myelination patterns observed in the present study provide further evidence in support of our previous proposal that there may be considerable nonuniformity in the efficacy of synaptic transmission among release sites arising from the same primary afferent fi

ISSN:0092-7317    

DOI:10.1002/cne.903140205

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

年代:1991

数据来源: WILEY

摘要:

AbstractOur previous results have shown that KATPchannels play an important role in K+efflux and extracellular K+accumulation in the rat brain, and this role was quantitatively more important in the adult than in the newborn brain. The purpose of this study was to localize by autoradiographic techniques the binding sites of glibenclamide, a potent sulfonylurea ligand that targets KATPchannels, in the adult and newborn fat central nervous system (CNS). Since the adult turtle is resistant to anoxia, we also compared the rat to the turtle brain sulfonylurea receptor distribution. In all three animal groups (newborn rat, adult rat, adult turtle), specific glibenclamide binding was saturable. Scatchard plots were curvilinear in the rat, thus suggesting that glibenclamide binds to two types of sites, i.e., high and low affinity sites. Scatchard analysis on turtle brain tissue showed evidence of one binding site only, We also found that the distribution of glibenclamide binding sites was heterogeneous in the adult rat CNS with a higher density in rostral than in caudal regions. The highest binding densities were seen in the cortex, hippocampus, cerebellum, substantia nigra, and a few thalamic nuclei; intermediate densities were observed in the basal ganglia, septum, thalamus, and the hypoglossal nucleus. There was a low density in most areas of the hypothalamus, midbrain, brainstem, and spinal cord. Compared with the adult rat, the newborn had a very homogeneous distribution of binding sites and densities were very low throughout the CNS; the level of binding density was even lower and in some regions undetectable in the adult turtle. Our results indicate that (1) there are high and low affinity sulfonylurea receptors in the rat CNS, (2) there is a striking heterogeneity in the distribution and density of sulfonylurea receptors in the adult rat CNS and this is in sharp contrast to the homogeneous distribution and low density in both newborn rat and adult turtle; (3) sulfonylurea receptors increase in number postnatally in the rat since binding density increases and the Kdin the newborn rat is similar to that in the adult rat. We speculate that KATPchannels and sulfonylurea receptors are poorly developed in the turtle and develop mostly after birth in the rat, reaching highest density in adulthood.

ISSN:0092-7317    

DOI:10.1002/cne.903140206

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

年代:1991

数据来源: WILEY

摘要:

AbstractPolyclonal antibodies to N‐CAM and L1 and monoclonal antibodies to epitopes of N‐CAM (designated 12F11, 8A2, and 12F8) were used to investigate the spatial and temporal distribution of these neural cell adhesion molecules during the development of mouse cortex and olfactory bulb. The aim of the study was to correlate developmental events such as cell migration, dendritic and axonal outgrowth, and synaptogenesis with the appearance and disappearance of specific molecules involved in cell‐cell interactions. Western transfer studies indicated that 12F8 antibody recognized polysialic acid found on embryonic N‐CAM; 8A2 antibody primarily recognized the 140 kD component of N‐CAM while the 12F11 antibody recognized the 180 and the 140 kD forms. The study demonstrates a high degree of cell surface molecular specialization of different compartments in developing neocortex and olfactory bulb. L1 is found on a variety of unmyelinated fiber tracts including thalamocortical fibers, olfactory nerve, and inner plexiform layer of the olfactory bulb. In contrast, N‐CAM epitope recognized by 12F11 antibody is present on olfactory nerve fibers but appears later and is much weaker than L1 on thalamocortical fibers and is absent from the olfactory lobe inner plexiform layer. Dendritic regions are best labeled by 12F8 antibody; the epitope becomes faint in adult cortex but remains strongly expressed in olfactory bulb. This study reveals that widespread N‐CAM expression in the central nervous system is constituted by a diversity of local expression of different molecular forms of N‐CAM; their different anatomical distributions suggest they may each ha

ISSN:0092-7317    

DOI:10.1002/cne.903140207

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe central projections of the auditory nerve were examined in the barn owl. Each auditory nerve fiber enters the brain and divides to terminate in both the cochlear nucleus angularis and the cochlear nucleus magnocellularis. This division parallels a functional division into intensity and time coding in the auditory system. The lateral branch of the auditory nerve innervates the nucleus angularis and gives rise to a major and a minor terminal field. The terminals range in size and shape from small boutons to large irregular boutons with thorn‐like appendages. The medial branch of the auditory nerve conveys phase information to the cells of the nucleus magnocellularis via large axosomatic endings or end bulbs of Held. Each medial branch divides to form 3–6 end bulbs along the rostrocaudal orientation of a single tonotopic band, and each magnocellular neuron receives 1–4 end bulbs. The end bulb envelops the postsynaptic cell body and forms large numbers of synapses. The auditory nerve profiles contain round clear vesicles and form punctate asymmetric synapses on both somatic spines and the cell

ISSN:0092-7317    

DOI:10.1002/cne.903140208

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

年代:1991

数据来源: WILEY

摘要:

AbstractUltrastructure of the major cerebellar territory of the monkey thalamus, or VL as delineated in sagittal maps by Ilinsky and Kultas‐Ilinsky (J. Comp. Neurol.262:331–364, ′87), was analyzed by using neuroanatomical tracing, immunocytochemical, and quantitative morphometric techniques. The VL nucleus contains nerve cells of two types. Multipolar neurons (PN) retrogradely labeled with wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) from the precentral gyrus display a tufted branching pattern of the proximal dendrites and have a range of soma areas from 200 to 1,000 μm2(mean 535.2 μm2, SD = 159.5). Small glutamic acid decarboxylase (GAD) immunoreactive cells (LCN) exhibit sizes from 65 to 210 μm2(mean 122.5 μm2, SD = 32.8) and remain unlabeled after cortical injections. The two cell types can be further distinguished by ultrastructural features. Unlike PN, LCN display little perikaryal cytoplasm, a small irregularly shaped nucleolus, and synaptic vesicles in proximal dendrites. The ratio of PN to LCN is 3:1. The LCN dendrites establish synaptic contacts on PN somata and all levels of dendritic arbor either singly or as a part of complex synaptic arrangements. They are also presynaptic to other LCN dendrites.Terminals known as LR type, i.e., large boutons containing round vesicles, are the most conspicuous in the neuropil. They form asymmetric contacts on somata and proximal dendrites of PN as well as on distal dendrites of LCN. The areas of these boutons range from 0.7 to 12 μm2and the appositional length on PN dendrites ranges from 1.1 to 14 μm. All LR boutons except the largest ones become anterogradely labeled from large WGA‐HRP injections in the deep cerebellar nuclei. These boutons are also encountered as part of triads and glomeruli, but very infrequently since the latter complex synaptic arrangements are rare.The most numerous axon terminals in the neuropil are the SR type, i.e., small terminals (mean area 0.42 μm2) containing round vesicles. The SR boutons become anterogradely labeled after WGA‐HRP injections in the precentral gyrus. They form distinct asymmetric contacts predominantly on distal PN and LCN dendrites; however, their domain partially overlaps that of LR boutons at intermediate levels of PN dendrites. The SR boutons are components of serial synapses with LCN dendrites which, in turn, contact somata and all levels of dendritic arbors of PN. They also participate in complex arrangements that consist of sequences of LCN dendrites, serial synapses, and occasional boutons with symmetric contacts. These structures termed small glomeruli are much more frequent in the monkey VL than classic glomeruli with LR boutons.The third group is composed of boutons known as F1 type. This is a heterogeneous population containing boutons of varying sizes ranging from 0.4 to 9 μm2. The terminals contain pleomorphic or almost cylindrical vesicles and display symmetric contacts. The F1 boutons form axosomatic and axodendritic synapses on both types of cells, and axoaxonic synapses on initial axon segments of PN. It is these boutons that participate in complex synaptic arrangements with vesicle‐containing LCN dendrites and SR boutons, and they are also encountered as part of triads with three symmetric contacts. Representatives of this bouton population display positive GAD immunoreactivity.For measurements of the membrane and apposing structures, the identified PN dendrites were grouped into three categories. The group of “secondary” dendrites included all consecutive‐order short dendritic segments within approximately a 60 μm radius around the soma where most of the branching occurred. It was found that the ratios of boutons with asymmetric contacts to those with symmetric contacts were 4:1 on primary dendrites, 9:1 on “secondary,” and 55:1 on distal dendrites. The ratios of symmetric dendrodendritic synapses to symmetric contacts formed by axon terminals were 3:1 on primary and “secondary” dendrites and 1:1 on distal dendrites. This suggests the overall predominance of excitatory inputs (LR and SR boutons) on PN dendrites with inhibitory inputs coming mainly from GABAergic LCN dendrites.Comparison of the present findings with earlier data on the cerebellar thelamic territory in the cat and the nigrothalamic territory in the monkey suggests significant interspecies and internuclear differences in the

ISSN:0092-7317    

DOI:10.1002/cne.903140209

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe cat retina contains a number of different classes of ganglion cells, each of which has a unique set of receptive field properties. The mechanisms that underlie the functional differences among classes, however, are not well understood. All of the afferent input to retinal ganglion cells are from bipolar and amacrine cell terminals in the inner plexiform layer, suggesting that the physiological differences among cat retinal ganglion cells might be due to differences in the proportion of input that they receive from these cell types.In this study, we have combined in vivo intracellular recording and labeling with subsequent ultrastructural analysis to determine directly the patterns of synaptic input to physiologically identified X‐cells in the cat retina. Our primary aim in these analyses was to determine whether retinal X‐cells receive a characteristic pattern of bipolar and amacrine cell input, and further, whether the functional properties of this cell type can be related to identifiable patterns of synaptic input in the inner plexiform layer. We reconstructed the entire dendritic arbor of an OFF‐center X‐cell and greater than 75% of the dendritic tree of an ON‐center X‐cell and found that (1) both ON‐ and OFF‐center X‐cells are contacted with approximately the same frequency by bipolar and amacrine cell terminals, (2) each of these input types is distributed widely over their dendritic fields, and (3) there is no significant difference in the pattern of distribution of bipolar and amacrine cell synapses onto the dendrites of either cell type. Comparisons of the inputs to the ON‐ and the OFF‐center cell, however, did reveal differences in the complexity of the synaptic arrangements found in association with the two neurons; a number of complex synaptic arrangements, including serial amacrine cell synapses, were found exclusively in association with the dendrites of the OFF‐center X‐cell.Most models of retinal X‐cell receptive fields, because their visual responses share a number of features with those of bipolar cells, have attributed X‐cell receptive field properties to their bipolar cell inputs. The data presented here, the first obtained from analyzing the inputs to the entire dendritic arbors of retinal X‐cells, demonstrate that these retinal ganglion cells receive nearly one‐half of their input from amacrine cells. These results clearly indicate that further data concerning the functional consequences of amacrine cell input are needed to understand more fully visual

ISSN:0092-7317    

DOI:10.1002/cne.903140210

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

年代:1991

数据来源: WILEY

摘要:

AbstractThe mole rat (Spalax ehrenbergi) burrows throughout its life in subterranean tunnels. Several structural and functional features which adapt the mole rat to its habitat have been discerned. The goal of this study was to elucidate the structural basis for adaptation of the auditory end‐organ to an environment where low‐frequency acoustical signals prevail. For this purpose, cochleae of adult mole rats were studied with light and electron microscopy. Inner hair cells throughout the cochlea, and outer hair cells in the basal (high‐frequency) portion of the cochlea, were similar in structure to those seen in other mammals. In contrast, outer hair cells in the apical (low‐frequency) portion displayed unique structural features. These features resembled the structure of inner hair cells or immature outer hair cells. The innervation of outer hair cells was most uncommon, in that classical medial efferent innervation was not found throughout the cochlear

ISSN:0092-7317    

DOI:10.1002/cne.903140211

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

年代:1991

数据来源: WILEY