Dopamine supersensitivity occurs in schizophrenia and other psychoses, and after hippocampal lesions, antipsychotics, ethanol, amphetamine, phencyclidine, gene knockouts ofDbh(dopamine β-hydroxylase),Drd4receptors,Gprk6(G protein-coupled receptor kinase 6),Comt(catechol-O-methyltransferase), orTh^-/-,Dbh^Th/+(tyrosine hydroxylase), and in rats born by Cesarean-section. The functional state of D2, or the high-affinity state for dopamine (D2^High), was measured in these supersensitive animal brain striata. Increased levels and higher proportions (40-900%) for D2^Highwere found in all these tissues. If many types of brain impairment cause dopamine behavioral supersensitivity and a common increase in D2^Highstates, it suggests that there are many pathways to psychosis, any one of which can be disrupted.

Accumulating evidence from clinical and preclinical studies shows that catechol-O-methyltransferase (COMT) plays a significant role in dopamine metabolism in the prefrontal cortex, but not in the striatum. However, to what extent dopamine overflow in the prefrontal cortex and striatum is controlled by enzymatic degradation versus reuptake is unknown. We used COMT deficient mice to investigate the role of COMT in these two brain regions within vivovoltammetry. A real-time analysis of evoked dopamine overflow showed that removal of dopamine was twofold slower in the prefrontal cortex of mice lacking COMT than in wild-type mice, indicating that half of the dopamine decline in this brain region results from COMT-mediated enzymatic degradation. Lack of COMT did not influence dopamine overflow/decline in the dorsal striatum. COMT-deficient mice demonstrated a small (20–25%) but consistent increase in evoked dopamine release in the prefrontal cortex, but not in the dorsal striatum. Cocaine affected equally dopaminergic neurotransmission in the prefrontal cortex in both genotypes by prolonging 3–4 times dopamine elimination from extracellular space. Paradoxically, this happened without increase of the peak levels of evoked dopamine release. The present findings represent the first demonstration of the significant contribution of COMT in modulating the dynamics of dopamine overflow in the prefrontal cortex and underscore the therapeutic potential of manipulating COMT activity to alter dopaminergic neurotransmission in the prefrontal cortex.