Enhanced stereotyped response to apomorphine after chronic D-1 blockade with SCH 23390.

Rats were treated for 21 days with the selective D-1 blocker SCH 23390 (0.1 mg/kg SC). Threshold doses of apomorphine for hypermotility (0.15 mg/kg SC) and for stereotyped response (0.25 mg/kg SC) were given 7, 21, 35, and 77 days after discontinuation of the chronic treatment. The rats always showed enhanced stereotyped response to the higher dose of apomorphine but never any change in their motility response to the lower dose of dopamine agonist. This finding may represent a behavioral correlate of the reported supersensitivity of D-1 receptors induced by SCH 23390.