Comparison of local and systemic ethanol effects on extracellular dopamine concentration in rat nucleus accumbens by microdialysis.

To determine the site of action of systemic ethanol on dopaminergic function in the nucleus accumbens, we compared the effect of intraperitoneal (i.p.) and local administration of ethanol on interstitial dopamine concentration using microdialysis in freely moving rats. The i.p. administration of 1 g/kg of ethanol significantly increased the dialysate dopamine (DA) concentrations (approximately 40% above basal), compared with saline treatment. The concentration-time profile of DA and ethanol in dialysates was similar after two ethanol injections 4 hr apart. Local perfusion with several ethanol concentrations showed that 510 and 860 mM of ethanol caused a significant concentration-related increase in extracellular DA concentrations in the nucleus accumbens (510 mM, 28% increase; 860 mM, 62% increase). However, lower ethanol concentrations, 170 mM or below, failed to change basal DA concentrations. Stimulation with high potassium (50 mM) in artificial cerebrospinal fluid preceding local ethanol treatment increased dialysate DA concentrations to 523 +/- 83% of basal levels, confirming that the DA terminals were responsive to pharmacological manipulation. Basal DA levels in dialysates were approximately 70% calcium-dependent when tested at the end of the local perfusion experiments. Stereological examination of the nucleus accumbens revealed probe-induced damage, but did not detect additional damage by local perfusion of ethanol. When ethanol concentrations in the DA sampling area around the probe are taken into account in both systemic and local administration experiments, this study suggests that concentrations of ethanol associated with moderate intoxication do not directly affect the function of DA terminals in the nucleus accumbens. Therefore, the systemic effects of ethanol on nucleus accumbens DAergic function is more likely due to an interaction with sites other than the nucleus accumbens.