Behavioral hypersensitivity to apomorphine after chronic methamphetamine--intermittent vs. continuous regimen.

The effects of chronic methamphetamine (MAP) on the behavioral response to apomorphine were examined in rats, treated with saline (control) or MAP for 14 days either intermittently (4 mg/kg/day, once daily) or continuously (subcutaneously implanted osmotic pumps releasing 56 mg/kg/14 days). Following a 7-day interval after discontinuing the MAP treatment, a challenge dose (0.5 mg/kg) of apomorphine was administered. The rats treated with MAP intermittently showed a marked augmentation in behavioral response to apomorphine than the continuous MAP group and control. It is presumed that the intermittent MAP administration may produce greater reactivity in the brain dopaminergic systems than the continuous administration.