Sensitization, duration, and pharmacological blockade of anxiety-like behavior following repeated ethanol withdrawal in adolescent and adult rats.

Adolescence is Known to be a time of increased risk-taking behaviors, which includes increased use of alcohol. Recent statistics showed that 73% of high school students had used alcohol by the time they graduated (Johnston et al., 2007). Adolescents are also known to consume alcohol in a “binge-like” pattern and likely experience repeated ethanol withdrawals (Hiller-Sturmhofel and Swartzwelder, 2004/2005). Of considerable concern is the fact that the strongest predictor of alcohol dependence in adulthood is the use of alcohol before the age of 14 (Grant, 1998). Furthermore, the dependency course (time between initial use and dependence) is more rapid in adolescents than adults (Clark et al., 1998). While considerable attention is currently being paid to adolescent alcohol use and abuse, less work is being done on the consequences of chronic ethanol exposure. In particular, further investigations are needed on the consequences of more “naturalistic” or cyclic/repeated patterns of chronic ethanol abuse known to characterize intake and differentially impact on withdrawal in adult humans and rodents. Clinical evidence first suggested that increased alcohol withdrawal symptoms (including seizures) occurred following multiple detoxifications (Ballenger and Post, 1978). Later work illustrated that an increased susceptibility for withdrawal sensitization or “kindling” was also produced after repeated ethanol withdrawals in rodents (Becker and Hale, 1993; Kokka et al., 1993; McCown and Breese, 1990). Further investigations demonstrated that other symptoms of withdrawal (i.e., anxiety) could undergo a kindling-like process in adult rodents (Breese et al., 2004; Overstreet et al., 2002). In these experiments, it was shown that withdrawal from three 5-day cycles of ethanol diet induced anxiety-like behavior, which was not produced by withdrawal from 15 continuous days of ethanol exposure (Overstreet et al., 2002). The production of anxiety-like behavior only following repeated ethanol withdrawals demonstrated that the pattern of ethanol exposure, independent of the amount of ethanol per se, was important in sensitizing anxiety-like behavior (Breese et al., 2005a). Recent work illustrated that adolescent rats have increased anxiety-like behavior and reduced seizure thresholds following exposure to repeated ethanol withdrawals (Wills et al., 2008). While behavioral comparisons indicated an increased vulnerability to these effects in adolescents, increased ethanol intake and differential blood ethanol concentrations (BECs) could have accounted for age-related differences. Nonetheless, these experiments showed that adolescent rats displayed at least as much withdrawal related behaviors as adult rats. This effect was distinct from previous investigations where adolescent rats had either reduced or absent withdrawal-related behaviors compared to adults (Acheson et al., 1999; Doremus et al., 2003; Varlinskaya and Spear, 2004). While a number of experimental differences could account for these differences, including route of ethanol administration, species used, age of behavioral testing, and test used to measure anxiety, a potentially critical factor is the use of cycled chronic ethanol exposure (Wills et al., 2008), a variable not employed in these other investigations. While it has been illustrated that adolescent rats can exhibit anxiety-like behavior following repeated withdrawals, it was not established whether repeated ethanol withdrawals actually sensitized anxiety-like behaviors, as has been shown in adult rats (Overstreet et al., 2002; Wills et al., 2008). In order to illustrate sensitization of anxiety-like behavior in adolescent rats it would need to be shown that neither continuous or a single cycle of ethanol produced anxiety, which was not demonstrated in previous work (Wills et al., 2008). The current studies were performed to evaluate whether repeated withdrawals sensitize anxiety-like behavior in adolescent rats. Additionally, it was evaluated whether there were age-related differences in the sensitivity to the effects of repeated withdrawals between adolescent and adult rats. Further experiments determined the duration (amount of time following the final withdrawal) of anxiety-like behavior in both adolescent and adult rats. In all of these studies, ethanol intake and BECs were measured to make sure behavioral effects were not dependent on differences in BECs. Finally, it was determined whether certain drug pretreatments (benzodiazepine receptor antagonist, CRF1 receptor antagonist, or 5-HT1A receptor agonist) would prevent the development of sensitized anxiety-like behavior in adolescents.