Quantitative electrophysiological studies of regenerating visuotopic maps in goldfish--I. Early recovery of dimming sensitivity in tectum and torus longitudinalis.
Refinement and connectivity in the regenerating retinotectal system of goldfish were studied quantitatively by electrophysiological methods. One optic nerve was crushed intraorbitally in fish kept at 25 degrees C. At different postcrush times, visually-evoked multiunit activity was recorded from the superficial layers of tectum, and from the torus longitudinalis. Responses in torus longitudinalis were used as a test of retinotectal connectivity because torus longitudinalis derives a visuotopic map from a tectal projection. The stimulus, effective for both the early retinotectal projection and torus longitudinalis, was a 10 degrees wide vertical black stripe rotated horizontally at 25 degrees/s through both visual fields. Activity from repeated sweeps was averaged to yield receptive field profiles in the horizontal dimension. Normally, profiles from tectum were dual-peaked and 20 degrees wide at half maximum amplitude; torus longitudinalis profiles were bell-shaped and 41 degrees wide. Between 20 and 40 days postcrush, tectum gave broad low-amplitude (25% normal) profiles that were roughly visuotopic. Over the same period, torus longitudinalis gave profiles of relatively high amplitude (69% of normal) that were also broadened but normally visuotopic. The widths of both tectal and torus longitudinalis profiles declined with the same exponential timecourse, reaching normal values by 80-100 days. Torus longitudinalis profiles were on average 21.6 degrees wider than tectal profiles at all stages of regeneration. The results agree with previous anatomical observations showing that optic fibers initially form much enlarged arbors that shrink over time, and suggest that arbors engage in widespread synaptic connections, at least with tecto-torus longitudinalis cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Northmore
D P
DP
Department of Psychology, University of Delaware, Newark 19716.
D000200:Action Potentials; D000818:Animals; D003530:Cyprinidae / Q000502:physiology*; D006054:Goldfish / Q000502:physiology*; D009039:Motion Perception; D009409:Nerve Crush; D009416:Nerve Regeneration; D010775:Photic Stimulation; D012160:Retina / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000502:physiology*; D013477:Superior Colliculi / Q000502:physiology*; D014795:Visual Pathways / Q000502:physiology*