SYSTEMIC COCAINE CHALLENGE AFTER CHRONIC COCAINE TREATMENT REVEALS SENSITIZATION OF EXTRACELLULAR DOPAMINE LEVELS IN NUCLEUS-ACCUMBENS BUT DIRECT COCAINE PERFUSION INTO NUCLEUS-ACCUMBENS DOES NOT - IMPLICATIONS FOR THE NEURAL LOCUS OF COCAINE SENSITIZATION

Rats were treated chronically with 20 mg/kg/day cocaine (by intraperit oneal injection) for 16 days, followed by 7 days of cocaine wash-out. On the next day, rats were challenged with an acute dose of cocaine ad ministered by one of two routes (systemic or intracranial), and extrac ellular dopamine (DA) in the nucleus accumbens (Acb) was measured by i n vivo microdialysis. Rats acutely challenged systemically with 20 mg/ kg cocaine showed enhanced Acb extracellular DA levels (compared to co ntrol rats that had not previously received chronic cocaine). However, rats acutely challenged with intracranial cocaine by perfusion of 10( -5) M cocaine directly into the Acb did not. It is suggested that both the development and triggering of cocaine sensitization, as manifeste d by enhanced Acb DA content to subsequent acute cocaine challenge, ma y involve more than just neural mechanisms occurring locally within th e Acb.