The effect of dopamine receptor agonist treatment on haloperidol-induced supersensitivity in mice

Mice were pretreated with haloperidol (HP) (3-4 mg/kg/day in drinking water) or vehicle for 21 days. On the 25th day, HP-pretreated mice were supersensitive to the locomotor stimulant effects of apomorphine (after acute premedication with reserpine and alpha-methyl-p-tyrosine). This behavioural supersensitivity was accompanied by a 25-39% increase in the number of [3H]-spiperone binding sites in the striata of HP-pretreated mice. Short-term repeated administration of the dopamine (DA) agonist drugs d-amphetamine and L-DOPA during the HP withdrawal phase (days 22, 23 and 24) had no effect on either measure of DA receptor supersensitivity. In contrast, the administration of apomorphine on days 22, 23 and 24 enhanced the HP-induced behavioural supersensitivity but decreased the HP-induced elevation of the number of [3H]-spiperone binding sites. Apomorphine treatment alone did not alter either measure. The results do not support the hypothesis that supersensitive DA receptors can be down-regulated by short-term treatment with DA agonist drugs and, moreover, indicate that important discrepancies may exist between behavioural and biochemical measures of DA receptor supersensitivity.