摘要:

AbstractThe regenerating optic nerve of goldfish first reestablishes a rough retinotopic map on the contralateral tectum and then sharpens it. Disruption of visual activity, either by blocking activity with intraocular tetrodotoxin (TTX; Schmidt and Edwards, 1983) or by synchronizing activity with strobe illumination (Schmidt and Eisele, 1985), disrupts the sharpening process: the map is correctly oriented but the multiunit receptive fields at each point average 25–40° in diameter. In order to test whether strobe and TTX interfere with the same mechanism, we have tested whether their sensitive periods are the same, and whether strobe, like TTX treatment, does not affect either ganglion cell receptive field properties or synaptogenesis. In parallel studies, we exposed fish to 2 weeks of either strobe illumination or intraocular TTX beginning at various times after crush and determined via electrophysiological recordings that the periods of sensitivity were nearly identical. There was no effect of either treatment during the first 2 weeks (before the fibers arrive at the tectum), maximal disruption of sharpening between 14 and 50 days (the period of rapid synaptogenesis), decreasing disruption between 50 and 125 days, and no effect beyond that point or in the normal projection. In addition, long strobe exposures of up to 142 days produced no greater disruptions than shorter 2–3‐week exposures, indicating no cumulative effect. The reestablishment of synaptic transmission in tectum, assayed by recording field potentials elicited by optic nerve shock, was not affected by stroboscopic illumination. Finally, individual ganglion cells, recorded intraretinally following long‐term strobe exposure, had receptive fields that were normal both in size and in their characteristic responses to light‐on, to light‐off, or to both on and off. These findings support the hypothesis that strobe‐like TTX prevents retinotopic refinement by preventing the correction of errors initially made by the ingrowing optic axons (Schmidt

ISSN:0022-3034    

DOI:10.1002/neu.480190502

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

年代:1988

数据来源: WILEY

摘要:

AbstractIn the clawed frog (Xenopus laevis), motor neurons in cranial nerve nucleus IX‐X control contraction of laryngeal muscles responsible for sexually dimorphic vocal behaviors. We examined sex differences in dendritic arbors of n.IX‐X cells using the Golgi–Cox method. Three morphological classes of somal types (ovoid, triangular, and elongate) are present in similar frequencies in n.IX‐X of both males and females. The male n.IX‐X neuron is a more complex and hypertrophied version of the female n.IX‐X cell. The number of primary dendrites is the same for both sexes, but males have more total dendritic segments. The overall dendritic length of male n.IX‐X neurons is two to three times that of the female. Males have longer dendritic segments between all branch points.Male and female frogs differ in levels of circulating androgens; neurons of n.IX‐X are targets for androgenic steroids. To determine if androgen can affect dendritic morphology in adult females, we examined Golgi‐impregnated cells in n.IX‐X from ovariectomized females treated with testosterone for 1 month. The total number of dendritic segments was reduced by androgen treatment due to reduction in the number of higher order dendritic segments; the number of primary dendritic segments was unchanged. Androgen treatment may induce resorption of higher order dendritic branches. The overall dendritic length of androgen‐treated female n.IX‐X neurons was unchanged, and dendritic segments were longer. Thus, although androgen can alter dendrites of n.IX‐X cells in adult females, this short‐term treatment does not produce a mascu

ISSN:0022-3034    

DOI:10.1002/neu.480190503

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

年代:1988

数据来源: WILEY

摘要:

AbstractThis study describes regeneration of the neural retina in juvenile goldfish. The retina was destroyed with an intraocular injection of ouabain, a technique introduced by Wolburg and colleagues (Maier and Wolburg, 1979; Kurz‐Isler and Wolburg, 1982). We confirmed their observation that the level of damage produced by the toxin was graded, in that neurons in the inner retinal layers were preferentially destroyed, and only in the more severely affected retinas were cells in the outer nuclear layer (i.e., photoreceptor cells) damaged. Evidence of retinal regeneration could be seen beginning about 2 weeks after the injection of ouabain. In contrast to previous studies (Maier and Wolburg, 1979), we found that regeneration took place only in those retinas in which photoreceptors had been destroyed. In cases in which the outer nuclear layer was spared, no regeneration of inner layers occurred, even after 6 months. Thymidine autoradiography was used to document the regeneration of new retinal neurons and to show that rod precursors, like other dividing cells, were not destroyed by the oubain, but in contrast showed an increased mitotic activity. Regeneration did not proceed uniformly, but was initiated at neurogenic foci scattered across the retina. These foci consisted of clusters of dividing neuroepithelial‐like cells. The evidence is consistent with the proposal that these cells were derived from rod precursors. These results imply that rod precursors are capable of a wider range of developmental fates than they normally expr

ISSN:0022-3034    

DOI:10.1002/neu.480190504

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe elimination of polyneuronal innervation (synapse elimination) that occurs following reinnervation was studied in sartorius muscles of adultRana pipiens. The percentage of neuromuscular junctions that were polyneuronally innervated declined from 47% at 40–80 days after nerve crush to 22% at greater than 250 days after nerve crush. We measured the size, synaptic strength, and position of competing nerve terminals at identified dually innervated neuromuscular junctions at these two different periods of synapse elimination. Our goal was to determine if any of these parameters play a role in the competition between nerve terminals that ultimately results in the elimination of polyneuronal innervation. Our data support the hypothesis that polyneuronal innervation will persist if competing nerve terminals are of similar synaptic efficacies but will be eliminated if the competing terminals are of different synaptic efficacies. We also tested, but failed to find any evidence, that the spatial proximity of competing nerve terminals at the same synaptic site influences the elimination of polyneuronal innervatio

ISSN:0022-3034    

DOI:10.1002/neu.480190505

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

年代:1988

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480190501

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

年代:1988

数据来源: WILEY