Effects of intermittent and continuous haloperidol administration on the dopaminergic system in the rat brain.

The effects of intermittent and continuous treatment with haloperidol (HPD) on dopamine turnover in the rat brain were studied. Each rat was treated with HPD for 14 days by either once daily intraperitoneal injections (2 mg/kg/day) (intermittent HPD group) or continuous infusion by a subcutaneously implanted pump which was adjusted to release 28 mg/kg of HPD over 14 days (continuous HPD group). Seven days after cessation of injections or removal of the pump, the regional changes in DA turnover following an acute dose of HPD (1 mg/kg, intraperitoneally) were examined. The continuous HPD group showed more prominent tolerance to HPD effect of augmenting DA turnover than the intermittent HPD group. It is presumed that continuously administered HPD produces greater tolerance to the acute effect of HPD than intermittently administered HPD.