Environmental Modulation of Alcohol Intake in Hamsters: Effects of Wheel Running and Constant Light Exposure

Abstract

BACKGROUND Alcohol abuse leads to marked disruptions of circadian rhythms, and these disturbances in themselves can increase the drive to drink. Circadian clock timing is regulated by light, as well as by nonphotic influences like food, social interactions, and wheel-running. We previously reported that alcohol markedly disrupts photic and nonphotic modes of circadian rhythm regulation in Syrian hamsters. As an extension of this work, we characterize the hedonic interrelationship between wheel-running and ethanol intake and the effects of environmental circadian disruption (long-term exposure to constant light [LL]) on the drive to drink. METHODS First, we tested the effect of wheel running on chronic free-choice consumption of a 20% (v/v) ethanol (EtOH) solution and water. Second, the effect of this alcohol drinking on wheel running in alcohol-naive animals was investigated. Third, we assessed the influence of LL, known to suppress locomotor activity and cause circadian rhythm disruption, on EtOH consumption and wheel-running behavior. RESULTS Inhibitory effects of wheel running on EtOH intake and vice versa were observed. Exposure to LL, while not affecting EtOH intake, induced rhythm splitting in 75% of the animals. Notably, the splitting phenotype was associated with lower levels of EtOH consumption and preference prior to, and throughout, the period of LL exposure. CONCLUSIONS These results are evidence that exercise may offer an efficacious clinical approach to reducing EtOH intake. Also, predisposition for light-induced (or other) forms of circadian disruption may modulate the drive to drink.

Voluntary exercise decreases ethanol preference and consumption in C57BL/6 adolescent mice: Sex differences and hippocampal BDNF expression

“…In this work, we have focused on the effects of concurrent exercise, in the form of voluntary wheel running, on ethanol consumption in adolescent C57BL/6 female and male mice. Our results reproduce the effects of exercise decreasing ethanol consumption and preference previously seen in adult mice [27,29,30], and hamsters [31,32]. As previously reported in other studies [reviewed in 24], exercise increased hippocampal BDNF expression in both female and male mice, suggesting a potential role of this neurotrophin in the adaptive response to wheel running.…”

“…Indeed, our results show an escalated ethanol consumption and preference in all groups of mice tested, and an increase in distance travelled and time on wheel running along experimental days, a characteristic of reinforcing and rewarding stimuli when chronically presented [reviewed in 38]. Therefore, the idea of a hedonic substitution between ethanol consumption and wheel running suggested by some authors in rats [39], mice [40], and hamsters [31] could potentially explain the decrease in ethanol consumption and preference observed in our exercised adolescent C57BL/6 mice. Interestingly, this effect was less robust in male mice, supporting previously reported sex differences in the effects of voluntary exercise decreasing alcohol consumption [27].…”

Photoperiodic modulation of voluntary ethanol intake in C57BL/6 mice

“…A number of previous studies reported that access to running wheels can reduce ethanol consumption in several rodent species [5,15,27,36,38]. In contrast, we did not detect a significant effect of wheel access on either ethanol intake or ethanol preference.…”

“…As already mentioned, while Millard and Dole [37] reported photoperioddependent alterations in ethanol intake in this strain, we failed to replicate this effect in a recent study [45], albeit using different lighting schedules. Since the animals in our study were housed in runningwheel cages, and since access to running wheels has been shown to influence ethanol intake [5,15,27,36,38], in the present study we maintained half the animals with continuous access to running wheels and half with locked running wheels. In addition to testing for possible photoperiod by running wheel interactions on ethanol intake, this also allowed assessment of circadian adaptation to photoperiod in the wheel-access animals.…”

Voluntary wheel running reduces voluntary consumption of ethanol in mice: identification of candidate genes through striatal gene expression profiling

“…The concept of hedonic substitution, replacement of one rewarding behavior with another, is a promising area of research. Exercise has been used in the past to help reduce ethanol intake in heavy drinkers (Correia et al, 2005; Murphy et al, 1986; Weinstock, 2010; Werch et al, 2011), and animal studies have shown consistent interaction effects with ethanol consumption (Darlington et al, 2014; Ehringer et al, 2009; Hammer et al, 2010; McMillan, 1978; McMillan et al, 1995; Ozburn et al, 2008; Werme et al, 2002). However, little is known about the neurobiology of this interaction.…”