Behavioural effects of selective dopamine D-1 and D-2 agonists and antagonists in guinea-pigs

This study describes specific behaviours in guinea-pigs after dopamine D-1 and D-2 receptor activation which differed to those described in other rodent species. Intraperitoneal (IP) administration of the dopamine D-2 receptor agonist quinpirole (1.5, 3 and 6 mg/kg) to guinea-pigs dose-dependently initiated locomotor activity and other behaviours including rearing, head-down sniffing, chewing, circling, licking and head/body shaking. Locomotor activity induced by quinpirole (3 mg/kg) was reduced by the D-2 receptor antagonists sulpiride, (100 mg/kg IP) and raclopride (10 mg/kg IP). The dopamine D-1 receptor agonist SKF 38393 (8, 16 and 32 mg/kg IP) produced little or no behavioural effect, nor did the D-1 receptor antagonist SCH 23390 (0.2 and 0.4 mg/kg IP). A 16 mg/kg dose of SKF 38393, given in combination with 3 mg/kg quinpirole, produced responses similar to quinpirole alone, whereas 32 mg kg SKF 38393 combined with quinpirole induced vacuous oral chewing, with attenuation of locomotor activity and circling, but not other behaviours produced by this dose of quinpirole. In contrast to previous studies in rats, the responses to quinpirole (3 mg/kg) were not significantly affected by SCH 23390 (0.2 and 0.4 mg/kg). It is concluded that the guinea-pig may be a useful and interesting species for study of the behavioural effects of D-1 and D-2 agonists and antagonists, as its responses appear to differ from those of other rodent species, but are similar to some responses to D-1 agonists observed in primates.