Intra-accumbal orexin-1 receptor inhibition prevents the anxiolytic-like effect of ethanol and leads to increases in orexin-A content and receptor expression

Abstract

Alcohol use is frequently associated with mood disorders. Similarly, individuals suffering from these disorders have a higher risk of developing alcoholism. Several reports have implicated orexin signaling in different behaviors related to alcohol consumption, whereas antagonists block these actions. However, the involvement of orexin-1-receptor (Orx₁R) in ethanol-induced anxiolysis remains relatively unexplored. The purpose of this study was to investigate whether intra-accumbal inhibition of Orx₁R blocks the anxiolytic-like effect of ethanol and to determine if ethanol administration modifies orexin-A content and Orx₁R expression in the nucleus accumbens (NAc). The elevated-plus-maze test (EPM-test) was used to measure anxiety; orexin-A content and Orx₁R expression were determined by enzyme-immunoassay and western blot, respectively. The results showed that the pretreatment with a selective antagonist of Orx₁R, SB-334867 (SB, 3 μg/side), prevents the anxiolytic-like behavior induced by acute ethanol (2.5 g/kg). SB-334867 per se had no effect on anxiety levels. Pretreatment with SB-334867 followed by ethanol (SB + Et) increased orexin-A content and Orx₁R levels in the NAc in comparison to the groups that only received ethanol (V + Et) or SB-334867 (SB + S). Ethanol treatment significantly augmented Orx₁R expression but not the peptide content. The increase in orexin-A observed in SB + Et animals could be due in part to the inhibition of Orx₁R, since SB-334867 prevents the binding of orexin-A to the receptor. This increase in orexin-A may, in turn, induce an up-regulation of receptor. Other possible explanations were discussed. In general, these findings suggest that orexin-A contributes largely to expression of ethanol-induced anxiolytic-like effect through the signaling of Orx₁R in the NAc.

Keywords: Anxiety; Ethanol; Nucleus accumbens; Orexin-1-receptors; Orexin-A; SB-334867.