COADMINISTRATION OF THE D2 ANTAGONIST PIMOZIDE INHIBITS UP-REGULATION OF DOPAMINE RELEASE AND UPTAKE INDUCED BY REPEATED COCAINE

To investigate the hypothesis that the D2 dopamine (DA) receptor regulates DA uptake, as well as release, in the nucleus accumbens (N ACC), rats were pretreated for 10 days with either the selective D2 antagonist pimozide (1.0 mg/kg, i.p.) or vehicle, followed 3 h later by either cocaine (20 mg/kg, i.p.) or saline. On day 11, a microdialysis method was performed in which various DA concentrations (0, 10, and 20 nM DA) were perfused through the dialysis probe to characterize the diffusion of DA through tissue to and from the microdialysis probe (recovery). This diffusion of DA has been shown to be sensitive to changes in release and uptake. Pimozide pretreatment was shown to attenuate significantly a cocaine-induced increase in the in vivo recovery of DA (p < 0.01). The in vivo recovery for the vehicle/cocaine group was 47 +/- 4%, whereas the in vivo recovery for the pimozide/cocaine group was 31 +/- 3%. There was no difference between the pimozide/cocaine and control groups (pimozide/saline, 26 +/- 2%; vehicle/saline, 26 +/- 3%). In vitro probe calibrations indicated no significant difference in probe efficiencies between groups. These data suggest that the D2 receptor is capable of modulating uptake as well as release of DA in the N ACC of the rat.