LACK OF SENSITIZATION TO THE EFFECTS OF D-AMPHETAMINE AND APOMORPHINEON SENSORIMOTOR GATING IN RATS

This study assessed whether repeated injections of d-amphetamine or ap omorphine could induce sensitization to the disruptive effects of thes e psychomotor stimulants on sensorimotor gating in rats, In the first experiment, rats were given six pre-exposures to either 2.0 mg/kg d-am phetamine or saline before being tested for the effects of d-amphetami ne (0.0, 0.5, 1.0, 2.0 or 4.0 mg/kg, IF) on prepulse inhibition of aco ustic startle (PPI) and locomotor activity. The tests for PPI confirme d that sensorimotor,eating could be disrupted by a high dose of il-amp hetamine (4.0 mg/kg), However, comparison of the dose-response curves for the drug and saline pre-exposed groups did not reveal evidence for sensitization to this d-amphetamine effect in drug-pre-exposed rats, despite indications that sensitization had developed to the locomotor stimulant effects of LJ-amphetamine. A similar pattern of results was obtained in a second experiment that examined the effects of apomorphi ne (0.0, 0.1, 0.2, 0.4 and 0.8 mg/kg, SC) on PPI and locomotion in rat s pre-exposed to 2.0 mg/kg of this drug or its vehicle, These findings demonstrate that treatments which induce sensitization to the behavio ral activating effects of psychomotor stimulants do not necessarily pr oduce sensitization to the disruptive effects of stimulants on sensori motor gating. The implications of these results for hypotheses linking sensitization-like processes to the etiology of schizophrenia are dis cussed.