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  • 1
    Electronic Resource
    Electronic Resource
    Topographic refinement of the goldfish retinotectal projection: sensitivity to stroboscopic light at different periods during optic nerve regeneration (1988)
    Springer
    Experimental brain research 70 (1988), S. 109-116 
    Details
    ISSN: 1432-1106
    Keywords: Retinotectal projection ; Regeneration ; Correlated activity ; Sensitive period ; Goldfish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary When the severed optic nerve of a goldfish regenerates, the restored retinotectal projection is at first only grossly topographic. Refinement occurs later, by a mechanism that is thought to depend on correlation in the electrical activity of neighbouring retinal ganglion cells because it can be blocked by exposure to tetrodotoxin or diffuse stroboscopic (strobe) light. To study the sensitivity of retinotectal map refinement to strobe light at different periods during regeneration, four equivalent groups of goldfish with severed right optic nerves and ablated right lenses were interchanged, at 21 day intervals, between strobe (S) and diurnal (D) light to generate four different exposure sequences. After 84 days, a localized iontophoretic injection of WGA-HRP was made into each left tectum to label retinal ganglion cells with terminal arbors at the injection site, and the degree of clustering of the labelled cells was estimated statistically to assess map refinement. Retinae exposed to the sequences SDDS, SSDD or DSSD were broadly similar to each other and to those seen previously after exposure for similar total periods to diurnal light, constant light or strobe light with the lens in place. However, those kept in diurnal light for the first 42 days and in strobe light thereafter (DDSS) revealed significantly less refinement, equivalent to that seen previously after just 42–44 days in diurnal light. Thus diffuse strobe light itself neither sharpens nor unsharpens the regenerated map: its immediate effect seems only to be the indefinite postponement of whatever refinement would otherwise have occurred. Refinement can still occur when fish are returned from strobe to diurnal light late in regeneration, and may then be faster even than in fish kept in diurnal light throughout.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00271853
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Impaired refinement of the regenerated retinotectal projection of the goldfish in stroboscopic light: a quantitative WGA-HRP study (1986)
    Springer
    Experimental brain research 63 (1986), S. 421-430 
    Details
    ISSN: 1432-1106
    Keywords: Retinotectal projection ; Topography ; Correlated activity ; Goldfish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The retinotectal projection of the goldfish was studied after regeneration of a cut optic nerve in stroboscopic light, constant light or diurnal light, with the lens removed to blur the retinal image. Retrograde transport of wheatgerm agglutinin, conjugated to horseradish peroxidase, from a standard tectal injection site was used to measure the topographic precision of the projection. The dispersion of labelled retinal ganglion cells, which reflects this precision, was assessed by a method based on distance to nearest neighbour. In normal fish treated similarly, these cells are known to be clustered into about 1% of the retinal area. Early in regeneration, however, they are widely dispersed. The projection map then re-acquires its precision over two or three months. In diurnal light, lens ablation had no effect on refinement of the regenerated map. Constant light increased the number of labelled cells but also had no significant effect on the map. But in stroboscopic light with a continuous pseudorandom pattern of flash intervals (average rate 4.8 Hz), much less refinement was seen. Even after 70–98 days of regeneration, labelled cells remained scattered, on average, over 20% of the retinal area. These retinae were indistinguishable by several criteria from those obtained in diurnal light after only 32–39 days. Mislocated axon terminals, which are largely eliminated during the second and third months of regeneration in diurnal light, evidently persist much longer in stroboscopic light that synchronizes ganglion cell activity across the retina. These results, like previous ones obtained by blocking the transmission of activity to the tectum, support a model of map refinement based on correlation in the firing of neighbouring neurons, which may have wide application within the nervous system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00236861
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    A sharp retinal image increases the topographic precision of the goldfish retinotectal projection during optic nerve regeneration in stroboscopic light (1987)
    Springer
    Experimental brain research 68 (1987), S. 319-328 
    Details
    ISSN: 1432-1106
    Keywords: Retinotectal projection ; Topography ; Correlated activity ; Goldfish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Locally-correlated neural activity appears to play a key role in refining topographically mapped projections. The retinotectal projection of the goldfish normally regains a high degree of spatial precision after regeneration of a cut optic nerve, but it fails to do so if retinal ganglion cell activity is blocked by tetrodotoxin, or if local correlations in activity are masked by the synchronizing effect of stroboscopic light. A sharp retinal image is not normally needed for a sharp map because local correlation occurs even in darkness or diffuse light, but the possibility that a sharp image might restore local correlation and sharpen the map in stroboscopic light, though taken into account in earlier experiments, has not previously been tested. The precision of the retinotectal map was therefore studied, by retrograde transport of WGA-HRP from a standard tectal injection site and quantitative analysis of the labelled ganglion cell distribution, after regeneration of a cut optic nerve for 83–84 days in either continuous stroboscopic light or normal diurnal light. The lens of the eye was either ablated to blur the retinal image or sham-operated. Two different strobe flash patterns used in previous experiments were also compared. With the lens ablated, stroboscopic light impaired map refinement significantly, confirming previous results. A rapid, irregular flash pattern averaging about 5 Hz was rather more effective than a regular 1 Hz pattern. With the lens intact, however, neither pattern had any detectable effect. The significant gain in precision resulting from a sharp retinal image in these circumstances suggests that common mechanisms could underlie both the internal refinement of the retinotectal map and such directly experience-sensitive processes as the experimental realignment of binocular maps in the frog Xenopus, and of auditory and visual maps in the barn owl.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00248798
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    Paper (German National Licenses)
    Fulltext
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