COCAINE - EXCITATORY EFFECTS ON SENSORIMOTOR REACTIVITY MEASURED WITH ACOUSTIC STARTLE

Cocaine (2.5-10 mg/kg) caused a dose-related increase in the amplitude of the acoustic startle reflex in rats. Procaine (5-40 mg/kg) caused a dose-related decrease in startle, indicating that the effects of cocaine could not be ascribed to its local anesthetic effects. Cocaine''s excitatory effects were blocked by pretreatment with haloperidol (0.5 mg/kg) but not by cyproheptadine or prazosin. The excitatory effects of cocaine (10 mg/kg) were markedly attenuated by pretreatment with reserpine (5 mg/kg 24 and 18 h earlier) but not by .alpha.-methyl-p-tyrosine (100 mg/kg 1 h earlier). Comparably sized excitatory effects of d-amphetamine were blocked by .alpha.-methyl-p-tyrosine and greatly enhanced by pretreatment with reserpine. Neither pretreatment blocked excitatory effects of apomorphine on startle. Cocaine apparently increases startle by acting through reserpine-sensitive pools of dopamine. Acoustic startle is evidently enhanced by activation of dopamine receptors.