Background

Alcohol use disorder (AUD) affects over 15 million Americans (SAMHSA, 2015), costing the US ~$249 billion annually (Sacks et al., 2015). The progressive development of AUD is characterized by repeated periods of alcohol intoxication and withdrawal, which initiates a series of neuroadaptations and behavioral changes. Individuals with AUD drink excessive quantities of alcohol, partly because alcohol has both positive (i.e., drinking alcohol for its rewarding effects) and negative (i.e., drinking alcohol to remove or avoid aversive feelings) reinforcing effects in those individuals (Koob, 2003). Alcohol-dependent rats withdrawn from alcohol exhibit many of the same behaviors exhibited by alcohol-dependent humans, including increases in alcohol drinking (e.g., Roberts et al., 1996), motivation to obtain alcohol (e.g., Walker and Koob, 2007), anxiety-like behavior (e.g., Kallupi et al., 2014) and nociception (e.g., Egli et al., 2012; Avegno et al., 2018). These behaviors suggest that rat models of alcohol dependence are a useful tool for investigating the neurobiological underpinnings of alcohol dependence in humans.

Various experimental methods are available for achieving the high blood alcohol levels (BALs) needed to induce alcohol dependence in rats, including gavage (Majchrowicz, 1975), diet (Lieber and DeCarli, 1982), intraperitoneal injections (Varlinskaya and Spear, 2004), and vapor exposure (Rogers et al., 1979). Vapor exposure allows the experimenter control over the amount, duration, and pattern of alcohol administration. Alcohol is administered passively through vapor delivered into the homecage air supply, decreasing the frequency of handling and/or restraint required for some other alcohol administration procedures. The experimenter controls the amount of alcohol administered to each cage, allowing for titration of BALs and achieving reasonably uniform intoxication levels among subjects in a given experiment. Rats exhibit physiological and behavioral signs of alcohol dependence after a few weeks. Behavioral testing can occur during acute withdrawal or protracted abstinence from alcohol vapor; the former allowing for repeated testing (e.g., within-subjects drug dose-response) at the same withdrawal time point on different days. In this protocol, we provide detailed, step-by-step methods updated from previous protocols (Gilpin et al., 2008) for induction of alcohol dependence using chronic intermittent exposure (CIE) to alcohol vapor in rats.