DOPAMINE ANTAGONIST EFFECTS ON BEHAVIOR MAINTAINED BY COCAINE AND ALFENTANIL IN RHESUS-MONKEYS

The effects of dopamine (DA) antagonists that act on either the D1 sit e (SCH 39166), the D2 site (eticlopride), or both sites non-selectivel y (cis-flupenthixol) were evaluated for their effects on behavior main tained by cocaine or alfentanil in rhesus monkeys. Each of these drugs suppressed rates of responding maintained by cocaine or alfentanil. L arger doses of each of the DA antagonists were necessary to suppress c ocaine- as opposed to alfentanil-maintained responding, suggesting tha t cocaine but not alfentanil was able to antagonize the rate-suppressi ng effects of the antagonists. There was little evidence, under these conditions of acute administration, that the DA antagonists modified t he reinforcing effects of either cocaine or alfentanil. This would hav e been observed by an antagonist-induced increase in the ED(50) of the reinforcing drugs and, although such an increase was seen occasionall y with cocaine, it was never statistically significant. The effects of rate-suppressing doses of each of the antagonists on directly observa ble behavior indicated a rapid onset and relatively short duration of action of intravenously administered SCH 39166 and eticlopride. cis-Fl upenthixol had a much slower onset of action. Each of the DA antagonis ts produced similar increases in measures of sedation and relaxation. These data suggest very similar behavioral effects of DA antagonists t hat act selectively on D1 or D2 receptors or act non-selectively on bo th DA receptors,