Reticular facilitation of visually evoked responses by optic tract stimulation before and after enucleation

Abstract

Reticular facilitation of evoked responses in the lateral geniculate nucleus and visual cortex elicited by ipsilateral optic tract stimulation was studied in cats prepared under diethyl ether-oxygen anesthesia, subsequently locally anesthetized, paralyzed with decamethonium, and placed on artificial respiration. In animals with an intact visual system, single electrical shocks to the reticular formation produced a more marked facilitation of the visually evoked response in primary visual cortex than in the lateral geniculate body. After bilateral enucleation of the eyeballs, the input-output relationship in both lateral geniculate and visual cortex dramatically shifted to the left, suggesting removal of tonic retinal inhibition. Although reticular stimulation still produced a slight facilitation at the neocortex and possibly at the lateral geniculate, it was much less than in intact preparations. The data suggest that reticular disinhibition of inhibitory discharge is still another phenomenon that must be considered in the over-all effects of reticular modulation of the visual system.