Enhancement by the D1 dopamine agonist SKF 38393 of specific components of stereotypy elicited by the D2 agonists LY 171555 and RU 24213.

Dose-effect curves were obtained for five specific components of stereotyped behavior (locomotor hyperactivity, rearing, sniffing, grooming and oral activity) elicited by the nonselective dopamine agonists N-propylnorapomorphine (NPA; 0.001-4.5 mg/kg) and apomorphine (APO; 0.3-10.0 mg/kg), the selective D2 agonists LY 171555 (0.1-18.0 mg/kg) and RU 24213 (0.7-20.0 mg/kg) and the selective D1 agonist SKF 38393 (0.6-40.0 mg/kg) in male Sprague-Dawley rats. All the agonists except SKF 38393 elicited dose-dependent sniffing. Both NPA and APO produced robust oral activity at high doses, with concomitant reductions in other behaviors. Neither RU 24213 nor SKF 38393 elicited dose-dependent oral behavior, whereas LY 171555 induced a maximal level of oral activity which was much less intense than that produced by NPA or APO. SKF 38393 alone induced only dose-dependent grooming. Co-treatment of Sprague-Dawley rats with SKF 38393 (5-40 mg/kg) and either LY 171555 (0.1-1.6 mg/kg) or RU 24213 (6.7 mg/kg) produced significant enhancement of sniffing but not of oral activity. Significant enhancement of both behavioral components was observed in male Wistar rats. Differences in specific components of behavioral response on treatment with combinations of D1 and D2 agonists may reflect use of animal strains with different ratios of D1/D2 innervation and/or different behavioral criteria.