In vivo microdialysis was used to investigate the effects of acute injections of norharman on extraneuronal concentrations of dopamine (DA) in the nucleus accumbens of rats. Administration of norharman (2. 44 and 43. 97 umol/kg, i.p.) elicited an increase of the DA efflux by 70 % and 160 % respectively which returned to basal levels after 120 and 160 min respectively. In contrast, administration of an intermediate dose of norharman (7. 33 umol/kg, i. p.) elicited a significant decrease to 72 % of basal level. These findings indicate that norharman alters the activity of mesolimbic dopaminergic neurons in an U-shape manner. The observations further suggest several receptor mechanisms mediating the effects of norharman.
