EFFECTS OF COCAINE ON SENSORY INHIBITION IN RATS - PRELIMINARY DATA

The purpose of this study was to determine the effect of cocaine on in hibitory sensory processing mechanisms in the brain. To accomplish thi s aim, recording electrodes were surgically placed into the vertex reg ion of 12 rats. After recovery from surgery, rats were injected once d aily for 5 days with either cocaine (20 mg/kg, IP) or saline. Immediat ely and 23 hr after each injection, the rats were tested for sensory g ating mechanisms. They were presented with a series of two clicking so unds, a conditioning and testing click delivered 0.5 sec apart, and th e amplitude of the N40 responses to each of these clicks was recorded. The ratios of the amplitude of the N40 response to the testing click over that of the conditioning click (T/C ratio) were calculated for ea ch animal for each testing period. The T/C ratios of the control (Sali ne-injected) animals were less than one, indicating that the condition ing stimulus was able to activate inhibitory neural pathways, producin g a decrease in the response to the testing stimulus. The T/C ratios o f the cocaine-treated animals were significantly greater than those of controls when the tests were conducted either immediately after injec tion or 23 hr later. These observations suggest that cocaine can impai r mechanisms involved in the gating of responses to auditory stimuli. The higher T/C ratio found at 23 hr after cocaine injection suggests t hat an impairment in the gating mechanism may be produced by an arousa l response that is associated with the environment in which the animal s had been injected with cocaine.