Effects of repeated light–dark phase shifts on voluntary ethanol and water intake in male and female Fischer and Lewis rats

Abstract Several lines of evidence implicate reciprocal interactions between excessive alcohol (ethanol) intake and dysregulation of circadian biological rhythms. Thus, chronic alcohol intake leads to widespread circadian disruption in both humans and experimental animals, while in turn, chronobiological disruption has been hypothesized to promote or sustain excessive alcohol intake. Nevertheless, the effects of circadian disruption on voluntary ethanol intake have not been investigated extensively, and prior studies have reported both increased and decreased ethanol intake in rats maintained under “shift-lag” lighting regimens mimicking those experienced by shift workers and transmeridian travelers. In the present study, male and female inbred Fischer and Lewis rats were housed in running wheel cages with continuous free-choice access to both water and 10% (vol/vol) ethanol solution and exposed to repeated 6-h phase advances of the daily light–dark (LD) cycle, whereas controls were kept under standard LD 12:12 conditions. Shift-lag lighting reduced overall ethanol and water intake, and reduced ethanol preference in Fischer rats. Although contrary to the hypothesis that circadian disruption would increase voluntary ethanol intake, these results are consistent with our previous report of reduced ethanol intake in selectively bred high-alcohol-drinking (HAD1) rats housed under a similar lighting regimen. We conclude that chronic circadian disruption is a form of chronobiological stressor that, like other stressors, can either increase or decrease ethanol intake, depending on a variety of poorly understood variables.