Development and maintenance of connectivity in the visual system of the frog. I. The effects of eye rotation and visual deprivation

Abstract

Visual deprivation or disparity between the eyes was produced in frog embryos or larvae by occluding one eye with a skin graft or by rotating one eye. After metamorphosis, the projections from each eye to the ipsilateral and contralateral optic tectum were mapped electrophysiologically. After rotation of one eye in embryos or larvae, the projection from each eye to the ipsilateral tectum developed at the normal time during metamorphosis, but the ipsilateral and contralateral projections were incongruent. In some cases, surgical rotation of one eye in embryos resulted in growth of optic nerve fibers from either or both eyes directly to the ipsilateral optic tectum. The pattern of these anomalous retinotectal projections was determined by intrinsic developmental mechanisms and was not modified by visual stimulation. Skin grafts over one or both eyes did not alter the normal development of ipsilateral visuotectal projections during metamorphosis. However, long term monocular deprivation by a skin graft which covered an eye from before metamorphosis until 90–105 days after metamorphosis resulted in abnormally large ipsilateral visuotectal responsive fields of the normal eye as well as of the deprived eye. By contrast, no abnormality developed in monocular deprivation started after the onset of metamorphosis or if both eyes were occluded from before metamorphosis until 258 days after metamorphosis. These results show that neither patterned visual stimulation nor functional correspondence between the eyes is required for the initial development of ipsilatera visuotectal projections (which are subserved by intertectal connections) during metamorphosis. However, the maintenance of the ipsilateral projections requires symmetrical (but not patterned) stimulation of both eyes during the onset of metamorphosis.