CNS mechanisms of alcohol self-administration

Neurochemical and neuropharmacological studies were undertaken to examine the possible involvement of the ventral tegmental area (VTA) dopamine (DA) system and the dorsal raphe nucleus (DRN) serotonin (5-HT) system in regulating oral alcohol self-administration. In vivo microdialysis studies demonstrated that either i.p. ethanol administration (1.0-2.0 g/kg) or local perfusion with ethanol (100 mM) could enhance the extracellular concentrations of both DA and 5-HT in the nucleus accumbens (ACB). Furthermore, the effects of local perfusion with ethanol on DA release in the ACB could be blocked by co-perfusion with a 5-HT3 antagonist. In the selectively-bred alcohol preferring P line of rats, there appears to be abnormal 5-HT and/or DA systems in certain limbic structures, i.e., ACB, olfactory tubercles (OTU) and medial prefrontal cortex (MPF). This is indicated by (a) lower contents of DA and 5-HT; (b) fewer 5-HT immunostained fibers; (c) lower densities of 5-HT1B, 5-HT2 and D2 receptors; and (d) higher densities of 5-HT1A receptors in the CNS of P rats compared to the alcohol-nonpreferring NP line of rats. Neuropharmacological studies demonstrated that local microinfusion of the D2 antagonist, sulpiride, or, at low doses, the DA releaser, d-amphetamine, could increase alcohol drinking by P rats. Intracranial self-administration (ICSA) studies showed that the P line of rats, but not the NP line, will self-administer 50-150 mg% ethanol directly into the VTA. Overall, these results suggest an innate abnormal functioning of the VTA DA and DRN 5-HT systems may be key factors facilitating the rewarding actions of ethanol in the CNS of P rats.