The Journal of Neuroscience, February 15, 1998, 18(4):1491-1504
Synchronizing Retinal Activity in Both Eyes Disrupts Binocular
Map Development in the Optic Tectum
Stephen G.
Brickley1,
Elizabeth A.
Dawes1,
Michael J.
Keating1 and
Simon
Grant1, 2
1 Division of Neurophysiology, National Institute for
Medical Research, London NW7 1AA, United Kingdom, and
2 Department of Sensorimotor Systems, Division of
Neuroscience, Imperial College School of Medicine, London W6 8RF,
United Kingdom
Spatiotemporal correlations in the pattern of spontaneous and
evoked retinal ganglion cell (RGC) activity are believed to influence
the topographic organization of connections throughout the developing
visual system. We have tested this hypothesis by examining the effects
of interfering with these potential activity cues during development on
the functional organization of binocular maps in the
Xenopus frog optic tectum. Paired recordings combined with cross-correlation analyses demonstrated that exposing normal frogs
to a continuous 1 Hz of stroboscopic illumination synchronized the
firing of all three classes of RGC projecting to the tectum and induced
similar patterns of temporally correlated activity across both lobes of
the nucleus. Embryonic and eye-rotated larval animals were reared until
early adulthood under equivalent stroboscopic conditions. The maps
formed by each RGC class in the contralateral tectum showed normal
topography and stratification after strobe rearing, but with
consistently enlarged multiunit receptive fields. Maps of the
ipsilateral eye, formed by crossed isthmotectal axons, showed
significant disorder and misalignment with direct visual input from the
retina, and in the eye-rotated animals complete compensatory
reorientation of these maps usually induced by this procedure failed to
occur. These findings suggest that refinement of retinal arbors in the
tectum and the ability of crossed isthmotectal arbors to establish
binocular convergence with these retinal afferents are disrupted when
they all fire together. Our data thus provide direct experimental
evidence that spatiotemporal activity patterns within and between the
two eyes regulate the precision of their developing connections.
Key words:
retinal ganglion cell; nucleus isthmi; visual topography; stroboscopic illumination; correlated activity; synaptic plasticity; Xenopus laevis
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