Eating high fat chow and the behavioral effects of direct-acting and indirect-acting dopamine receptor agonists in female rats.

Eating high fat chow increases the sensitivity of male rats to some behavioral effects of the direct-acting dopamine receptor agonist quinpirole; it is not known whether sensitivity to quinpirole is similarly enhanced in female rats eating high fat chow. Female Sprague-Dawley rats had free access to standard chow (5.7% fat) or either free or restricted access (i.e. body weight matched to rats eating standard chow) to high fat (34.3% fat) chow. Quinpirole (0.0032-0.32 mg/kg) produced hypothermia and a low frequency of yawning. Eating high fat chow produced insulin resistance without affecting quinpirole-induced yawning or hypothermia. Pretreatment with the dopamine D2 receptor antagonist L-741,626 failed to increase quinpirole-induced yawning, indicating that the low frequency of yawning was not due to enhanced D2 receptor sensitivity. Compared with younger (postnatal day 75), drug-naive female rats in a previous study, rats in the present study (postnatal day 275) were more sensitive to cocaine-elicited (1-17.8 mg/kg) locomotion and the development of sensitization across 5 weeks; however, eating high fat chow did not further enhance these effects. These results suggest that drug history and age might modulate the effects of diet on sensitivity to drugs acting on dopamine systems.