Dark-reared cats: responsitivity of cortical cells influenced pharmacologically by an inhibitory antagonist

When studied physiologically, dark-reared kittens exhibit abnormal responses. Specifically, cortical cells respond poorly, if at all, to visual stimulation. In the preceding paper (Ramoa et al. 1986) we showed that iontophoretic application of an excitatory amino acid allows all cells in this preparation to be excited or suppressed by visual stimuli. In the current study, we have pursued this finding by studying additional dark-reared kittens using iontophoretic application of an inhibitory antagonist, bicuculline methiodide (BIC). Responses of most cells studied were affected by application of BIC. Of cells which were originally weak or unresponsive, 76% became clearly responsive with application of BIC. Of cells which responded without BIC and were orientation-selective, only 33% lost selectivity during application of BIC. Considered together, these findings suggest functional inhibitory input in dark-reared animals which appears to differ from that in normal kittens with respect to its role in selectivity for stimulus orientation.