The Role of Clock in Ethanol-Related Behaviors

Abstract

Mice with a mutation in the Clock gene (ClockD19) exhibit increased preference for stimulant rewards and sucrose. They also have an increase in dopaminergic activity in the ventral tegmental area (VTA) and a general increase in glutamatergic tone that might underlie these behaviors. However, it is unclear if their phenotype would extend to a very different class of drug (ethanol), and if so, whether these systems might be involved in their response. Continuous access voluntary ethanol intake was evaluated in ClockD19 mutants and wild-type (WT) mice. We found that ClockD19 mice exhibited significantly increased ethanol intake in a two-bottle choice paradigm. Interestingly, this effect was more robust in female mice. Moreover, chronic ethanol experience resulted in a long-lasting decrease in VTA Clock expression. To determine the importance of VTA Clock expression in ethanol intake, we knocked down Clock expression in the VTA of WT mice via RNA interference. We found that reducing Clock expression in the VTA resulted in significantly increased ethanol intake similar to the ClockD19 mice. Interestingly, we also discovered that ClockD19 mice exhibit significantly augmented responses to the sedative effects of ethanol and ketamine, but not pentobarbital. However, their drinking behavior was not affected by acamprosate, an FDA-approved drug for the treatment of alcoholism, suggesting that their increased glutamatergic tone might underlie the increased sensitivity to the sedative/hypnotic properties of ethanol but not the rewarding properties of ethanol. Taken together, we have identified a significant role for Clock in the VTA as a negative regulator of ethanol intake and implicate the VTA dopamine system in this response.

Direct Regulation of Diurnal Drd3 Expression and Cocaine Reward by NPAS2

“…Moreover, when we measured cocaine-induced CPP, we found that NAc infected AAV- Clock shRNA injected mice were indistinguishable from Scramble injected mice at doses in which there is an increase in preference in the Clock mutant mice (16) (Figure 3C). This is in contrast to the hyperactivity and increased alcohol preference which is observed when Clock expression is reduced specifically in the VTA (19, 35). Thus, a knock-down of NPAS2, but not CLOCK in the NAc is sufficient for decreased cocaine preference.…”

“…Although Clock is also expressed in the NAc, it does not appear to have a prominent role in the regulation of cocaine reward in this region. Previous studies have established that CLOCKs actions in the ventral tegmental area (VTA) are important for the regulation of dopaminergic activity, as well as mood, anxiety and reward-related behavior (19, 22, 35). Thus, we propose that Clock regulates drug reward primarily through its actions in the VTA, while NPAS2 primarily acts in the NAc.…”

“…Previous work from our laboratory has shown that mice with a dominant negative mutation (Δ19) in the Clock gene exhibit hyperactivity, decreased anxiety- and depression-like behaviors, as well as increased sensitivity in the rewarding value for cocaine as demonstrated in conditioned place preference, cocaine and alcohol self-administration, and intracranial self-stimulation paradigms (14, 16, 19, 22). Moreover, it has been shown that mice lacking a functional NPAS2 protein have defects in cued and contextual fear conditioning, altered patterns of sleep, and are unable to properly entrain to daytime food restriction (23, 24).…”

From Signaling Pathways to Behavior

“…Knockdown of the Clock gene in the mouse VTA leads to increased alcohol intake (Ozburn et al, 2013), and mice lacking the circadian rhythm gene Period 1 (Per1) exhibit augmented alcohol intake following a social-defeat stressor as compared with WT mice (Dong et al, 2011). However, this signaling pathway seems to be more complex as the inhibition of casein-kinase-I-epsilon/delta (CKI ε/δ), which plays a role in the circadian system, decreases alcohol consumption in an alcohol-deprivation paradigm (Perreau-Lenz et al, 2012).…”

Circadian clock genes: Effects on dopamine, reward and addiction

“…Results of this study indicate that the most differentially expressed genes in the NAc were involved in circadian rhythms (55). Recently, we found that chronic alcohol consumption (in a two bottle choice paradigm) and abstinence resulted in decreased Clock expression in the NAc and VTA (56). Moreover, Chen et al (2004) (57) found that chronic ethanol intake via liquid diet shifted Per1 and Per2 gene expression rhythms in the arcuate nucleus (an area that sends projections to the NAc).…”