Effects of repeated cocaine administration on sensory inhibition in rats: preliminary data

We have recently reported that acute administration of cocaine to rats alters their sensory inhibitory capacity as tested in a paired click paradigm (S1/S2). Whether such acutely induced changes are persistent, is not known. In order to shed some light on the degree of spontaneous reversibility of cocaine-induced decreased sensory inhibition, rats were tested immediately after cocaine administration and 9 days after cessation of cocaine exposure. Six rats received cocaine HCl 20 mg/kg intraperitoneally and six rats received normal saline for 5 consecutive days. The amplitudes of the S1 responses were significantly decreased in the cocaine animals during the injection days only, but not 9 days later. Two measures of sensory inhibition were employed, S2/S1 x 100 amplitude ratio and S1-S2 amplitude difference. The ratio measure indicated a significant decrease in inhibitory capacity in the cocaine group during the injection days, and remained significantly decreased 9 days after cessation of cocaine administration. The data suggest that repeated cocaine administration can induce persistent deficit in the ability of the rat's brain to inhibit incoming irrelevant sensory stimuli.