Neonatal quinpirole treatment enhances locomotor activation and dopamine release in the nucleus accumbens core in response to amphetamine treatment in adulthood

Neonatal quinpirole treatment to rats produces long‐term increases in D₂ receptor sensitivity that persists throughout the animal's lifetime, a phenomenon referred to as D₂ priming. Male and female Sprague‐dawley rats were administered quinpirole (1 mg kg^?1) or saline from postnatal days (P)1–11. At P60, all animals were given an injection of quinpirole (100 μg kg^?1), and results showed that rats neonatally treated with quinpirole demonstrated enhanced yawning in response to quinprole, verifying D₂ receptor priming because yawning is a D₂ receptor mediated event. Beginning 1–3 days later, locomotor sensitization was tested through administration of d‐amphetamine (1 mg kg^?1) or saline every other day over 14 days, and horizontal activity and turning behavior were analyzed. Findings indicated that D₂‐priming enhanced horizontal activity in response to amphetamine in females compared to males at Days 1 and 4 of locomotor sensitization testing, and D₂‐priming enhanced turning in response to amphetamine. Seven to ten days after sensitization was complete, microdialysis of the NAcc core was performed using a cumulative dosing regimen of amphetamine (0.1–3.0 mg kg^?1). D₂‐primed rats administered amphetamine demonstrated a 500% increase in accumbal DA overflow compared to control rats administered amphetamine. Additionally, amphetamine produced a significant increase in NE overflow compared to controls, but this was unaffected by D₂ priming. These results indicate that D₂ receptor priming as is produced by neonatal quinpirole treatment robustly enhances behavioral activation and accumbal DA overflow in response to amphetamine, which may underlie increases in psychostimulant use and abuse within the psychotic population where increased D₂ receptor sensitivity is a hallmark. Synapse 64:289–300, 2010. © 2009 Wiley‐Liss, Inc.