Abstract
Sigma receptors (SigRs) have been implicated in behavioral and appetitive effects of psychostimulants and may also modulate the motivating properties of ethanol. The present study tested the hypothesis that SigRs modulate ethanol reinforcement and contribute to excessive ethanol intake. The effects of subcutaneous treatment with the potent, selective Sig-1R antagonist BD-1063 on operant ethanol self-administration were studied in two models of excessive drinking - Sardinian alcohol-preferring (sP) rats and acutely-withdrawn ethanol-dependent Wistar rats – and compared to ethanol self-administration in non-dependent Wistar controls. To assess the specificity of action, the effects of BD-1063 on self-administration of an equally reinforcing saccharin solution were determined in Wistar and sP rats. Gene expression of Sig-1R in reward-related brain areas implicated in ethanol reinforcement was compared between ethanol-naïve sP and Wistar rats and withdrawn ethanol-dependent Wistar rats. BD-1063 dose-dependently reduced ethanol self-administration in sP rats (3.3–11 mg/kg) and withdrawn, dependent Wistar rats (4–11 mg/kg) at doses that did not modify mean ethanol self-administration in non-dependent Wistar controls. BD-1063 did not reduce concurrent water self-administration nor did it comparably suppress saccharin self-administration, suggesting selectivity of action. BD-1063 also reduced the breakpoints of sP rats to work for ethanol under a progressive-ratio reinforcement schedule. Ethanol-naive sP rats and 24-hr withdrawn, dependent Wistar rats showed reduced Sig-1R mRNA expression in the nucleus accumbens. The results suggest that SigR systems may contribute to innate or ethanol-induced increases in susceptibility to self-administer high ethanol levels, identifying a potential neuroadaptive mechanism contributing to excessive drinking and a therapeutic target for alcohol abuse and dependence.
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