Circadian and acamprosate modulation of elevated ethanol drinking in mPer2 clock gene mutant mice

The PER2 clock gene modulates ethanol consumption, such that mutant mice not expressing functional mPer2 have altered circadian behavior that promotes higher ethanol intake and preference. Experiments were undertaken to characterize circadian-related behavioral effects of mPer2 deletion on ethanol intake and to explore how acamprosate (used to reduce alcohol dependence) alters diurnal patterns of ethanol intake. Male mPer2 mutant and WT (wild-type) mice were entrained to a 12:12 h light-dark (12L:12D) photocycle, and their locomotor and drinking activities were recorded. Circadian locomotor measurements confirmed that mPer2 mutants had an advanced onset of nocturnal activity of about 2 h relative to WTs, and an increased duration of nocturnal activity (p < .01). Also, mPer2 mutants preferred and consumed more ethanol and had more daily ethanol drinking episodes vs. WTs. Measurements of systemic ethanol using subcutaneous microdialysis confirmed the advanced rise in ethanol intake in the mPer2 mutants, with 24-h averages being ∼60 vs. ∼25 mM for WTs (p < .01). A 6-day regimen of single intraperitoneal (i.p.) acamprosate injections (300 mg/kg) at zeitgeber time (ZT) 10 did not alter the earlier onset of nocturnal ethanol drinking in the mPer2 mutants, but reduced the overall amplitude of drinking and preference (both p < .01). Acamprosate also reduced these parameters in WTs. These results suggest that elevated ethanol intake in mPer2 mutants may be a partial consequence of an earlier nighttime activity onset and increase in nocturnal drinking activity. The suppressive action of acamprosate on ethanol intake is not due to an altered diurnal pattern of drinking, but rather a decrease in the number of daily drinking bouts and amount of drinking per bout.