Focal ethanol elevates extracellular dopamine and serotonin concentrations in the rat ventral tegmental area

The present study describes the effects of local perfusion with ethanol on extracellular dopamine and serotonin (5-hydroxytryptamine, 5-HT) concentrations in the ventral tegmental area. Various concentrations of ethanol in artificial cerebrospinal fluid (ACSF) (0.1-10%, v/v) were administered through a microdialysis probe into the ventral tegmental area of freely moving Sprague-Dawley rats. A significant and concentration-dependent increment in dialysate output of both dopamine and serotonin was observed after local infusion of ethanol. Perfusion with Ca(2+)-free medium or tetrodotoxin (1 microM in ACSF) produced a significant reduction in basal extracellular dopamine and serotonin concentration but failed to block dopamine or serotonin release produced by infusion of 10% ethanol. Perfusion with 100 mM K+ before and after infusion of 10% ethanol revealed that the second perfusion with high K+ solution still produced an increase in dopamine and serotonin concentration, similar in magnitude to the first response, indicating that perfusion with 10% ethanol did not cause irreversible damage to either dopamine cell bodies or serotonin terminals in the ventral tegmental area. These results suggest that dopamine and serotonin release from the ventral tegmental area produced by focal application of 10% ethanol is mediated, at least in part, by a non-exocytotic mechanism. Direct stimulation of the ventral tegmental area dopamine neurons by ethanol might be involved in the reinforcing properties of the drug.