Acute ethanol administration differentially alters enkephalinase and aminopeptidase N activity and mRNA levels in regions of the nigrostriatal pathway.

Opioid peptides play a key role in ethanol reinforcement and may also represent important determinants in brain sensitivity to ethanol through modulation of nigrostriatal dopaminergic activity. Regulation of opioid levels by peptidase-degrading enzymes could be relevant in ethanol's actions. The aim of this work was to study the acute ethanol (2.5 g/kg) effects on the activity and mRNA expression of enkephalinase (NEP) and aminopeptidase N (APN) in the rat substantia nigra (SN) and the anterior-medial (amCP) and medial-posterior (mpCP) regions of the caudate-putamen (CP). Enzymatic activities were measured by fluorometric assays and mRNA expression by reverse transcriptase polymerase chain reaction. Acute ethanol administration differentially altered peptidase activities and mRNA expression with different kinetics. Ethanol increased and decreased NEP mRNA levels in the SN and amCP, respectively, but produced biphasic effects in the mpCP. APN mRNA levels were increased by ethanol in all brain regions. Ethanol induced a transient and long-lasting increase in NEP (mpCP) and APN (amCP) activities, respectively. Peptidase activities were not changed by ethanol in the SN. Our results indicate that striatal NEP and APN are important ethanol targets. Ethanol-induced changes in these neuropeptidases in the CP could contribute to the mechanisms involved in brain sensitivity to ethanol.