Psychopharmacological responsiveness to the dopamine agonist quinpirole in normal weanlings and in weanling offspring exposed gestationally to cocaine.

The behavioral responsiveness to challenge doses of the D2 agonist quinpirole was examined in 21-day-old normal offspring (experiment 1) as well as offspring exposed gestationally to cocaine (experiment 2). In both experiments weanling rats received a subcutaneous injection of 0 (0.9% saline), 0.04, 0.08, 0.5, or 1.0 mg/kg/3 cc of the D2 agonist quinpirole and were placed in a divided glass testing apparatus containing either a dish of wet mash plus a food pellet or wood block (experiment 1) or both a food pellet and a wood block (experiment 2). Behaviors were recorded for 5 min via time-sampling at 30 and 60 min post-injection. In experiment 1 the three highest doses of quinpirole increased the amount of forward locomotion, rearing, sniffing and probing, as well as increasing directed oral movements at both the wood block and food pellet; in general these findings are reminiscent of those reported previously in adult animals. In experiment 2, cocaine-exposed weanlings exhibited an increased sensitivity to the stimulating effects of a low dose of the D2 agonist for forward locomotion and rearing as well as an increase in the overall incidence of sniffing behavior and chewing on food pellets. These data provide psychopharmacological evidence that the increase in striatal D2 binding previously observed in weanling offspring exposed gestationally to cocaine (Scalzo et al. 1990) may be associated with an increased behavioral sensitivity to the D2 agonist quinpirole.