Glyoxalase (GLO1) inhibition or genetic overexpression does not alter ethanol’s locomotor effects: implications for GLO1 as a therapeutic target in alcohol use disorders

Background Glyoxalase 1 ( GLO1 ) is an enzyme that metabolizes methylglyoxal ( MG ), which is a competitive partial agonist at GABA A receptors. Inhibition of GLO1 increases concentrations of MG in the brain and decreases binge-like ethanol drinking. The present study assessed whether inhibition of GLO1, or genetic over expression of Glo1 , would also alter the locomotor effects of ethanol, which might explain reduced ethanol consumption following GLO1 inhibition. We used the prototypical GABA A receptor agonist muscimol as a positive control. Methods Male C57BL/6J mice were pretreated with aeither the GLO1 inhibitor S-bromobenzylglutathione cyclopentyl diester ( pBBG ; 7.5 mg/kg; Experiment 1) or muscimol (0.75 mg/kg; Experiment 2), or their corresponding vehicle. We then determined whether locomotor response to a range of ethanol doses (0, 0.5, 1.0, 1.5, 2.0, and 2.5) was altered by either pBBG or muscimol pretreatment. We also examined the locomotor response to a range of ethanol doses in FVB/NJ wild type and transgenic Glo1 over expressing mice (Experiment 3). Anxiety-like behavior (time spent in the center of the open field) was assessed in all three experiments. Results The ethanol dose-response curve was not altered by pretreatment with pBBG or by transgenic overexpression of Glo1 . In contrast, muscimol blunted locomotor stimulation at low ethanol doses, and potentiated locomotor sedation at higher ethanol doses. No drug or genotype differences were seen in anxiety-like behavior after ethanol treatment. Conclusions The dose of pBBG used in this study is within the effective range shown previously to reduce ethanol drinking. Glo1 overexpression has been previously shown to increase ethanol drinking. However, neither manipulation altered the dose response curve for ethanol’s locomotor effects, whereas muscimol appeared to enhance the locomotor sedative effects of ethanol. The present data demonstrate that reduced ethanol drinking caused by GLO1 inhibition is not due to potentiation of ethanol’s stimulant or depressant effects.