Cross sensitization between phencyclidine and methamphetamine: I. Repeated administration of methamphetamine at a low dose

We investigated whether the effects of phencyclidine (PCP) were modified by repeated pretreatment with methamphetamine (MAP) at a low (3 mg/kg/day for 12 days) dose in rats. The incidence of turning, head-weaving and backpedalling induced by PCP was increased by pretreatment with MAP. In the rats pretreated with MAP, 1) behavioral responses induced by further MAP (a dopamine releaser)-treatment were enhanced, but not those induced by apomorphine (a direct dopamine agonist), 5-methoxy-N,N-dimethyltryptamine (a direct serotonin agonist) and p-chloroamphetamine (a serotonin releaser); 2) dopamine and serotonin contents did not change but the ratio of 3,4-dihydroxyphenylacetic acid to dopamine was increased in the striatum, nucleus accumbens and frontal cortex. These results suggest that repeated administration of MAP (3 mg/kg) increases a presynaptic dopaminergic neuronal activity, but not a serotonergic one, and that there may be cross sensitization to PCP in the dopaminergic neuronal functions following repeated administration of MAP at low dose.