Alterations in dopamine metabolism by intraperitoneal ethanol in rats selected for high and low ethanol preference: A 3-methoxytyramine study

Effects of an ethanol dose (1 g/kg, IP) on the metabolism of dopamine (DA) in the nucleus accumbens, striatum and hypothalamus of ethanol-naive alcohol-preferring (AA) and alcohol-avoiding (ANA) rats were studied. Rats were sacrificed by focused-beam microwave irradiation of the brain 20 minutes after ethanol administration, and the concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), assumed to reflect DA metabolism, and of 3-methoxytyramine (3-MT), assumed to reflect DA release, were measured using gas chromatography-mass spectrometry. Basal striatal DOPAC and HVA concentrations were higher in the AA rats in comparison with ANA rats. Ethanol increased HVA, but not DOPAC, concentration in the nucleus accumbens and striatum, but not in the hypothalamus. There was a significant rat line × ethanol treatment interaction with respect to HVA concentration in the nucleus accumbens. The increase in HVA was higher in the AA than ANA rats. Basal 3-MT concentration was not changed by ethanol, except in the nucleus accumbens, where a significant rat line × ethanol treatment interaction was found. A decrease in 3-MT concentration was only detected in the ANA rats. After inhibition of monoamine oxidase with pargyline hydrochloride (75 mg/kg, IP, 10 min before sacrifice), 3-MT accumulation was decreased by ethanol, especially in the nucleus accumbens of both AA and ANA rat lines as well as in that of nonselected Wistar rats. The results suggest that 1) DA metabolism to DOPAC and HVA is dissociable from DA release as reflected by 3-MT production, 2) ethanol, if anything, reduces DA release, and that 3) the AA and ANA rats differ in their basal DA metabolism and in the ethanol effects thereupon, but not in ethanol-induced changes in DA release.