Sex differences in nicotine sensitization and conditioned hyperactivity in adolescent rats neonatally treated with quinpirole: Role of D2 and D3 receptor subtypes.

Neonatal quinpirole treatment in rats produces increased sensitivity of dopamine D2-like receptors throughout the animal's lifetime, referred to as D2 priming. There is little information on the effects of nicotine in adolescent rats, especially in a model that has clinical relevance to psychosis where increased D2 receptor sensitivity is common. Male and female rats were treated with quinpirole (1 mg/kg) or saline from postnatal (P) day 1-P21, given nicotine (0.5 mg/kg) or saline from P33 through P49, and placed into a locomotor arena for behavioral testing. Nicotine or saline treatment was preceded by the D2-like receptor antagonist eticlopride, D3 antagonist nafadotride, or saline. Conditioned hyperactivity was analyzed on P50 in the same context in a drug-free test. In females, D2 priming increased the locomotor response to acute nicotine, but did not affect subsequent nicotine sensitization, and only non-D2-primed females demonstrated conditioned hyperactivity. Eticlopride and nafadotride blocked behavioral sensitization, although nafadotride was more effective at blocking nicotine-conditioned hyperactivity in females. In males, D priming enhanced sensitization to nicotine and produced conditioned hyperactivity, which were blocked by eticlopride and nafadotride. These results have implications for psychosis and comorbidity of nicotine abuse in adolescence.