摘要:

AbstractPhysiological studies inmany vertebrates indicate that vestibular primary afferents are not a homogeneous population. Such date raise the question of what structural mechanisms underlie these physiological differeneces and what functional role is played by afferents of each type. We have begun to answer these questions by characterizing the architecture of 110 afferents innervating the posterior canal ofPseudemys scripta.We emphasize their spatial organization because experimental evidence suggests that afferent physiological properties exhibit significant spatial heterogeneity.The sensory surface of the posterior canal comprises paired, triangular hemicristae, which are innervated by two afferent types. Bouton afferents (66% of total afferents) are found over the entire sensory surface. They differ significantly in the shape and size of their collecting areas, number of boutons, soma size, and axon diameter; this morphological variation is systematically related to the afferent's spatial postion. In addition, multivariate analyses suggest that bouton afferents may comprise two subtypes: α afferents have delicate processes and are found throughout the crista; β afferents are more robust and are concentrated preferentially toward the canal center. Calyx‐bearing afferents comprise two morphological subtypes: dimorphs (13% of total afferents) bear calyceal and bouton endings; calyceal afferents (21%) bear calyceal endings only. Both types occur exclusively in an elliptical region near the center of each hemicrista; their morphology varies with radial distance from the center of this elliptical region.Our data provide evidence that inPseudemys:(1) the classical vestibular afferents types (bouton, calyx, dimorph) are structurally heterogeneous, and (2) their spatial sampling characteristic are highly structured and distinctive for each type. These spatial patterns may shed light on regional differences in physiological profiles of vestibular afferents, and they raise questions about the role of this spatial heterogeneity in signaling head movement. © 1994 Wiley‐Lis

ISSN:0092-7317    

DOI:10.1002/cne.903440402

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

年代:1994

数据来源: WILEY

摘要:

AbstractConnections between the thalamus and the cortex are generally regarded as ipsilateral, even though contralateral connections exist as well in several adult mammalian species. It is not known however, whether contralateral thalamocortical projections reach particular cortices or whether they emanate from specific nuclei. In the rhesus monkey different types of cortices, ranging from transitional to eulaminate, vary in their cortical connectional pattern and may also differ in thier thalamic connections. Because olfactory and transitional prefrontal cortices receive widespread projections, we investaged whether they are the target of projections from the contralateral thalamus as well. With the aid of retrograde tracers, we studied the thalamic projections of primary olfactory (olfactory tubercle and prepiriform cortex) and transitional orbital (areas PAPP, Pro 13) and medial (areas 25, 24, 32) areas, and of eulaminate (areas 11, 12, 9) cortices for comparison.To determine the prevalence of neurons in the contralateral thalamus, we compared them with the ipsilateral in each case. The pattern of ipsilateral thalamic projections differed somewhat among orbital, medial, and olfactory cortices. The mediodorsal nucleus was the predominant source of projections to orbital areas, midline nuclei included consistently about 25% of the thalamic neurons directed to medial transitional cortices, and primary olfactory areas were distinguished by receiving thalamic projections predominantly from neurons in midline and intralaminar nuclei.Notwithstanding some broad differences in the ipsilateral thalamofrontal projections, which appeared to depend on cortical location, the pattern of contralateral projections was thalamus were noted in midline, the magnocellular sector of the mediodorsal nucleus, the anterior medial and intralaminar nuclei, and ranged from 0 to 14% of the ipsilateral; they were directed primarily to olfactory and transitional orbital and medical cortices but rarely projected to eulaminate areas. Several thalamic nuclei projected from both sides to olfactory and transitional areas, but issued only ipsilateral projections to eulaminate areas. Though ipsilateral thalamocortical projections predominate in adult mammalian species, crossed projections are a common feature in development. The results suggest differences in the persistence of contralateral thalamocortical interactions between transitional and eulaminate cortices. © 1994 Wiley‐Liss, I

ISSN:0092-7317    

DOI:10.1002/cne.903440403

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

年代:1994

数据来源: WILEY

摘要:

AbstractEarly eye morphogenesis in the zebrafish between 12 and 36 hours postfertilization was studied by light‐ and scanning electron microscopy. Overall, early eye morphogenesis in the zebrafish is similar to that vertebrates even thought the optic primordia evaginate from the forebrain as solid masses of cells. After initial evagination 6–7 somite stage [SS], the optic primordia take on a wing‐like shape (8–9 SS). Subsequently, they bend ventrally and rotate slighlty in an anterior direction (10–12 SS). These changes serve to bring the primordia from a horizontal to a more Vertical orientation in relation to the embryonic neural axis. Invagination commences from the center of each primordium (14 SS) and progresses symmetrically out towards the periphery (14–20 SS). The choroid fissure forms by an involution along the anterior region of the eyecup (18–20 SS). By 24 hours postfertilization (pf), the eyecups are well formed. Between 24 and 36 hours pf, the eyes rotate further in relation to the axis of the embryo, and this repositions the choroid fissue to a typical ventral location by 36 hours pf. Because of the two rotations of the eye during early morphogenesis, particularly the later one, the anterior‐posterior orientation of the emerging optic primordium ultimately becomes the ventral‐dorsal axis of the completed eyecup. © 19

ISSN:0092-7317    

DOI:10.1002/cne.903440404

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn this study, we examined the morphological structure and synaptic physiology of long‐range axon projections among supragranular pyramidal cells in the extrastriate visual cortex of the rat. Intra‐and extracellular recordings form layer II/III pyramidal cells were performed in brain slices of area 18a following extracellular stimulation of either the underlying white matter or within layer II/III. Neurons were injected with biocytin for two‐dimensional reconstruction of their axon arborizations.The conduction velocity of afferent fibers (0.58 m/s) was twice as high as that of intracortical tangential fibers (0.28 m/s). Layer II/III cells were mainly di‐or polysynaptically driven by afferent activation, but predominantly monosynaptically driven from intracortical stimulation sites. The afferent as well as intracortically as well as intracortically evoked postsynaptic potentials showed a very similar time course and shape. From both stimulation sites, suprathreshold action potentials could be elicited. The current threshold for a postsynaptic response and the slope and width of excitatory postsynaptic potentials (EPSPS) increased with the distance of lateral stimulation. The morphological properties of layer II/III pyramidal cell axon collaterals colsely corresponded to the electrophysiological results. Long‐range intraareal axon collaterals could be followed up to 1 mm within the supragranular layers. Their length‐distance distribution showed an inverse relationship to the threshold currents of EPSPs. Pyramidal cells exhibited regularly spaced patches of horizontal axon collaterals with an interpatch distance of about 250 μm.We concluded that the supragranular horizontal network in the extrastriate visual cortex of the rat is qualitatively very similar to that of cats and monkeys. However, quantitative differences exist in its spatial extent and physiological characteristics. © 1994 Wi

ISSN:0092-7317    

DOI:10.1002/cne.903440405

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe large larval sea lamprey is a primitive vertebrate that recovers coordinated swimming following complete spinal transection. An ultrastructural study was performed in order to determine whether morphologic features of regenerating axons and their cellular environment would provide clues to their successful regeneration compared to their mammalian counterparts. Three larvel sea lampreys were studied at 3, 4 and 11 weeks following complete spinal transection and compared with an untransected control. Müller and Mauthner cells or their giant reticulospinal axons (GRAs) were impaled and injected with horseradish peroxidase (HRP). Alternating thick and thin sections were collected for light and electron microscopy. A total of 9 neurites were examined.At all times, growth cones of GRAs differed from those of cultured mammalian neurons in being packed with neurofilaments and in lacking long filopodia, suggesting possible differences in the mechanisms of axon outgrowth. Morphometric analysis suggested that GRA growth cones contact glial fibers disproportionately compared to the representation of glial surface membranes in the immediate environment of these growth cones. No differences were found between glial cells in regenerating spinal cords and those of untransectred control animals with regard to the size of the cell body and nucleus and the packing density of their intermediate filaments. Glial fibers in control animals and glial fibers located far from a transection were oriented transversely. Glial cells adjacent to the transection site sent thickened, longitudinally oriented processes into the blood clot at the transection site. These longitudinal glial processes preceded the regenerating axons. Desmosomes were observed on glia adjacent to the lesion but were scarce in the lesion during the first four weeks post‐transection. These findings suggest that longitudinally oriented glial fibers may serve as a bridge along which axons can regenerate across the lesion. The presence of desmosomes might prevent migration of astrocytes near the transection, thus stabilizing the glial bridge. © 1994 Wiley‐Liss

ISSN:0092-7317    

DOI:10.1002/cne.903440406

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe ability of pre‐ and postsynaptic populations to achieve the proper convergence ratios during development is especially critical in topographically mapped systems such as the retinotectal system. The ratio of retinal ganglion cells to their target cells in the optic tectum can be altered experimentally either by early partial tectal ablation, which results in an orderly compression of near‐normal numbers of retinal projections into a smaller tectal area, or by early monocular enucleation, which results in the expansion of a reduced number of axons in a near‐normal tectal volume. Our previous studies showed that changes in cell death and synaptic density consequent to these manipulations can account for only a minor component of this compensation for the population mismatch.In this study, we examine other mechanisms of population matching in the hamster retinotectal system. We used an in vitro horseradish peroxidase labeling method to trace individual retinal ganglion cell axons in superior colliculi partially ablated on the day of birth, as well as in colliculi contralateral to a monocular enucleation. We found that individual axon arbors within the partially lesioned tectum occupy a smaller area, with fewer branches and fewer terminal boutons, but preserve a normal bouton denstiy. In contrst, ipsilaterally projecting axon arbors in monoculary enucleated animals occupy a greater area than in the normal condition, with a much larger arbor length and greater number of boutons and branches compared with normal ipsilaterally projecting cells. Alteration of axonal arborization of retinalganglion cells is the main factor responsible for matching the retinal and tectal cell populations within the tectum. This process conserves normal electrophysiological function over a wide range of convergence ratios and may occur through strict selectivity of tectal cells for their normal number of inputs. © 1994 Wiley‐L

ISSN:0092-7317    

DOI:10.1002/cne.903440407

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe primary goal of this study was a determine whether the striate cortex (Oc 1) of the guinea pig projects to the pretactal nucleus of the optic tract (NOT), the first postretinal station of the horizontal optokinetic pathway, and, if so, to analyze the anatomical organization of this cortico‐NOT projection. Other goals of this investigation are to identify other pretectal nuclear projections from the visual cortex in the guinea pig, and to determine whether there is any visuotopic organization in this pathway.Axonal tracers (biocytin or3H‐leucine) were injected into the striate cortex (Oc 1), and the tissue processed with histochemical or light autoradiographic techniques. All subcortical terminal labeling is ipsilateral in the basal ganglia and thalamic nuclei. Furthermore, projections are traced to the ipsilateral brainstem, including two areas of the pretectal complex: (1) one in the NOT, extending in some cases to the adjacent lateral portion of the posterior pretectal nucleus (PPN), and (2) one in the pars compacta of the anterior pretectal nucleus (APNc). The terminal fields in the APN are consistently located rostrally in the dorsolateral portion of the nucleus, independently of the injection site in Oc 1, whereas in the NOT the terminal fields shift slightly after injections placed in different locations in the striate cortex. A correlation of the injection sites in Oc 1 and terminal fields in the NOT reveals a loose topographic organization in the cortico‐NOT projection; accordingly, the rostrocaudal axis of the striate cortex projects to the lateromedial axis of the NOT, with a 90° rotation, whereas lateral parts of the striate cortex project diffusely throghout the rostrocaudal extent of the NOT.These data show for the first that the NOT in the guinea pig receives a substantial projection form the visual cortex. Given the fact that in the guinea pig the optokinetic nystagmus shares some of the characteristics found in cat and monkey (i.e., consistent intial fast rise in the slow phase velocity and reduced asymmetry in monocular stimulation), the present findings lend support to the hypothesis that a cortical input to the NOT is a necessary condition for these oculomotor properties to be present. © 1994 Wiley‐

ISSN:0092-7317    

DOI:10.1002/cne.903440408

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

年代:1994

数据来源: WILEY

摘要:

AbstractThis study examined the distribution and localization of the γ‐aminobutyric acid (GABA)Areceptor in the brain cortex of a reptile by light and electron microscopy, to test whether cortical GABA inhibition is mainly mediated through the GABAAreceptro complex. We used preembedding immunocytochemistry and a monoclonal antibody, raised against the receptor complex, that recognizes the β2 and β3 subunits of the receptor. GABAAreceptors were distributed throughout the entire cerebral restricted to the plexiform layers of the cortex as seen by light microscopy. This granular aspect of the immunoreactivity most likely corresponds to the immunopositive dendritic and axonal profiles observed under the electron microscope. Some neurons in the medial and lateral cortices displayed pathches of immunoreactivity along the cell body and processes, and as a result their morphology was outlined. We discuss the possibility that these neurons were GABAergic as well. The immunocytochemical data demonstrate that the distribution and localization of GABAAreceptors in discrete regions of the reptilian cerebral cortex resemble that of parts of the hippocampal formation of humans and rats, suggesting that the basic configuration of the GABA system in these regions is conserved. © 1994 Wiley‐Li

ISSN:0092-7317    

DOI:10.1002/cne.903440409

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe describe a group of neurons with egg‐laying bioactivity in the cerebral ganglia of an opisthobranch mollusc, the nudibranchArchidoris montereyensis.These cells, the intercerebral white cells (IWCs), share morphological, biochemical, and electrophysiological characteristics with the egg‐laying neuroendocrine cells of two other molluscs,Aplysia californica(bag cells) andLymnaea stagnalis(caudodorsal cells). The IWCs, comprising two superficial clusters of about 100 neurons each, were located immediately posterior to the intercerebral commissure in the cerebral ganglia. The somata of these cells were small (<20 μm) and possessed varicose, bifurcating unipolar processes that collectively formed a loop within the commissure and bilateral extensions into the cerebral ganglia. The IWC clusters and commissural processes were enveloped by a large ganglionic vascular sinus, forming a potential neurohemal release site. Homogenates of whole cerebral ganglia or isolated IWC clusters induced egg‐laying behavior within hours of injection into the hemocoel of quiescent animals. The IWCs were immunoreactive for alpha bag‐cell peptide, one of the neuropeptide transmitters encoded by the egg‐laying hormone gene ofAplysia.Electrophysiologically, the IWCs were silent neurons with large resting potentials and appeared to be highly refractory to electrical stimulation. The similarities of the IWCs to the egg‐laying neuroendocrine cells inAplysiaandLymnaeasuggest that they are members of a homologous group of neurons controlling egg‐laying behavior in gastropod molluscs. © 1994

ISSN:0092-7317    

DOI:10.1002/cne.903440410

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

年代:1994

数据来源: WILEY

ISSN:0092-7317    

DOI:10.1002/cne.903440401

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

年代:1994

数据来源: WILEY