Conditioned grooming induced by the dopamine D1-like receptor agonist SKF 38393 in rats

Stimulation of dopamine D1-like receptors reliably increases grooming in rats and mice. The study examined whether the grooming response elicited by the prototypical D1-like agonist SKF 38393 (8 mg/kg s.c.) could be conditioned to the specific environment in which it occurred. Rats in one group (Paired) received SKF 38393 and rats in another group (Unpaired) received saline in observation boxes outside of their housing room; the rats were then scored for duration and frequency of grooming bouts over 25 min. The ordering of injections was reversed the next day in the rats, housing room. The procedure was repeated twice, with at least one intervening drug-free day, to give three conditioning trials. The D1-like agonist significantly increased grooming on each of the three conditioning trials, without obvious tolerance or sensitization, and the effect tended to persist for the duration of each trial. On the test trial for conditioned grooming, mean grooming duration was significantly greater in the Paired than the Unpaired group, suggesting that SKF 38393-induced grooming had been conditioned to the test environment. This is the first time that drug-elicited grooming has been conditioned to environmental cues.