Differential effects of convulsants on visually evoked responses in the albino rat.

Visually evoked responses (VERs) were recorded from primary visual cortex in unanesthetized albino rats during pharmacological modulation by one of the following convulsant agents: Physostigmine, picrotoxin, strychnine and Metrazol. The data were analyzed in terms of effects on VER components. The rat VER consists of six distinct waves constituted by three positive peaks (P1--P3) and three negative peaks (N1--N3). Results indicate a differential convulsant action on VER components. The administration of picrotoxin, resulted in a suppression of the peak amplitude of P1--N1 and delayed peak latencies of all components. Strychnine reliably shortened P1, N1 and P2 peak latencies, significantly increased N3 peak latency and only suppressed P3--N3 amplitude. Physostigmine essentially suppressed all component amplitudes but only increased peak latencies for P2 and P3 components. Metrazol, in general, was found to be relatively ineffective in the alteration of any VER component in a systematic manner. The data are discussed in terms of differential modes of convulsant action on the visual system. The results are likewise discussed with respect to their implications for convulsant modulation of photically evoked after-discharges.