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 (S-1/S-2). 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 20mg/kg intraperitoneally and six rats received normal saline for 5 consecutive days. The amplitudes of the S-1 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, S-2/S-1 x 100 amplitude ratio and S-1-S-2 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 induced persistent deficit in the ability of the rat's brain to inhibit incoming irrelevant sensory stimuli. (C) 1997 Society of Biological Psychiatry.