Differential Effects of Voluntary Ethanol Consumption on Dopamine Output in the Nucleus Accumbens Shell of Roman High- and Low-Avoidance Rats: A Behavioral and Brain Microdialysis Study

Abstract

The Roman high(RHA)and low-Avoidance (RLA) rats were selectively bred for rapid vs poor acquisitionof two-way active avoidance behavior. These lines differ in numerous behavioraltraits, with RLA rats being more fearful/anxious than RHA rats, and the latterbeing novelty-seekers and showing larger intake of, and preference for,addictive substances including ethanol (ETH). Moreover, several differences incentral dopaminergic, serotonergic, and GABAergic functions have been reportedin these two lines. Since those neural systems are involved in the regulationof ETH consumption, it was considered of interest to investigate: 1) thedifferences in ETH intake and preference between RHA and RLA rats, 2) theeffects of ETH on DA release in the shell of the nucleus accumbens (AcbSh) using brain microdialysis. ETHsolutions of increasing concentrations (2% - 10%) were presented on alternatedays in a free choice with water. To examine ETH intake and preference stability, animals were subsequently switched todaily presentations of 10% ETH for 10 consecutive days. RHA rats consumed significantly largeramounts of ETH and displayed higher ETH preference than did RLA rats throughout the acquisition andmaintenance phases. Following chronic exposure to ETH the animals werehabituated to a restricted access to ETH schedule (2% ETH, 2 h per day × 4days) before surgical implantation of a dialysis probe in the AcbSh. Underthese experimental conditions, voluntary ETH intake (2%, 1 h, p.o.) produced asignificant increase in accumbal DA output in RHA rats but not in their RLAcounterparts. Finally, the i.p. administration of ETH (0.25 g/kg) to na?veRoman rats produced a significant increment in accumbal DA output only in RHArats. These results indicate that the mesolimbic dopaminergic system of RHArats is more responsive to the effects of ETH than that of RLA rats.