Dissociation between the time course of ethanol and extracellular dopamine concentrations in the nucleus accumbens after a single intraperitoneal injection.

BACKGROUND: Dopamine release in the nucleus accumbens has been linked to the reinforcing effects of ethanol, but the time course or relationship of this response to ethanol concentrations in the brain has not been studied.
METHODS: Various doses of ethanol (0-2.0 g/kg) were administered intraperitoneally to male Sprague Dawley rats, and dopamine and ethanol were simultaneously analyzed in dialysate samples from the nucleus accumbens. A separate study to compare the ethanol-induced dopamine response in male and female rats was carried out by using a 1 g/kg intraperitoneal dose of ethanol.
RESULTS: In male rats, 1 and 2 g/kg ethanol significantly increased dialysate dopamine by 40% over basal, whereas 0.25 and 0.5 g/kg ethanol produced a nonsignificant 20% increase. Dialysate ethanol concentrations exhibited a curvilinear decline after reaching peak levels for the lower doses but showed a linear decrease after 1 and 2 g/kg. There was a dissociation between the time courses of extracellular dopamine and ethanol after 1 and 2 g/kg ethanol treatment. The dopamine response returned to basal within 90 min, whereas the ethanol concentrations remained elevated. In a separate study that compared male and female rats, the ratio of the dopamine response over basal to the dialysate ethanol concentrations was significantly decreased at 60 min after an injection of 1 g/kg. However, there were no differences between males and females.
CONCLUSIONS: The dissociation between dopamine and ethanol levels may reflect the development of acute tolerance to ethanol-induced dopamine release in the nucleus accumbens within the time course of a single acute injection. Given the strong links between dopamine and ethanol reinforcement, our findings may be relevant for understanding the time course of ethanol's reinforcing effects in vivo.