Chronic ethanol disrupts circadian photic entrainment and daily locomotor activity in the mouse

Abstract

Background: Chronic ethanol abuse is associated with disrupted circadian rhythms and sleep. Ethanol administration impairs circadian clock phase-resetting, suggesting a mode for the disruptive effect of alcohol abuse on circadian timing. Here, we extend previous studies to explore the effects of chronic forced ethanol on photic phase-resetting, photic entrainment, and daily locomotor activity patterns in C57BL/6J mice.

Methods: First, microdialysis was used to characterize the circadian patterns of ethanol uptake in the suprachiasmatic (SCN) circadian clock and correlate this with systemic ethanol levels and episodic drinking of 10 or 15% ethanol. Second, the effects of chronic forced ethanol drinking and withdrawal on photic phase-delays of the circadian activity rhythm were assessed. Third, the effects of chronic ethanol drinking on entrainment to a weak photic zeitgeber (1 minute of 25 lux intensity light per day) were assessed. This method was used to minimize any masking actions of light that could mask ethanol effects on clock entrainment.

Results: Peak ethanol levels in the SCN and periphery occurred during the dark phase and coincided with the time when light normally induces phase-delays in mice. These delays were dose-dependently inhibited by chronic ethanol and its withdrawal. Chronic ethanol did not impede re-entrainment to a shifted light cycle but affected entrainment under the weak photic zeitgeber and disrupted the daily pattern of locomotor activity.

Conclusions: These results confirm that chronic ethanol consumption and withdrawal markedly impair circadian clock photic phase-resetting. Ethanol also disturbs the temporal structure of nighttime locomotor activity and photic entrainment. Collectively, these results suggest a direct action of ethanol on the SCN clock.

Figure 1

Histologically verified microdialysis probe tip locations for measuring ethanol levels in the SCN of animals consuming 10% (*) and 15% (+) ethanol. OC, optic chiasm; 3V, third ventricle.

Figure 2

Twenty-four hour pharmacokinetic profiles of SCN and subcutaneous (SYS) ethanol concentrations superimposed with daily drinking episodes in individual mice consuming 10% (A) and 15% (B) ethanol. Averaged daily SCN ethanol profiles for mice drinking 10% and 15% ethanol are shown in C (n’s=6/group). Horizontal black bars represent the dark phase of the LD cycle.

Figure 3

Inhibitory effects of chronic 10% and 15% EtOH drinking (A) or withdrawal (B) on light pulse-induced phase-delays of the circadian locomotor activity rhythm. Bars are the mean±SE. Within a treatment group, bars with different letters are significantly different (p<0.05; n’s=7/group).

Figure 4

Representative double-plotted actograms of general locomotor activity showing the effects of chronic ethanol drinking (A, 10%; B, 15%) and withdrawal (D, 10%; E, 15%) vs. respective water controls (C,F) on light pulse-induced phase-delay responses. The “O” denotes the 30 min light pulse delivered at ZT 14.

Figure 5

A,B; Representative double-plotted actograms showing re-entrainment to a skeleton photoperiod (1 min light pulse designated by the vertical line) delivered daily at ZT 6 of the initial LD photocycle in mice chronically drinking 15% ethanol (shading) or water, respectively (n=7/group). C,D: double-plotted actograms showing the effect of chronic 15% ethanol or water, respectively on entrainment to the 1 min skeleton photoperiod delivered at ZT 11 of the initial LD photocycle (n=10/group). The horizontal black bars represent the dark phase of the initial LD cycle.