Alcohol drinking during adolescence increases consumptive responses to alcohol in adulthood in Wistar rats

Abstract

Binge drinking and the onset of alcohol-use disorders usually peak during the transition between late adolescence and early adulthood, and early adolescent onset of alcohol consumption has been demonstrated to increase the risk for alcohol dependence in adulthood. In the present study, we describe an animal model of early adolescent alcohol consumption where animals drink unsweetened and unflavored ethanol in high concentrations (20%). Using this model, we investigated the influence of drinking on alcohol-related appetitive behavior and alcohol consumption levels in early adulthood. Further, we also sought to investigate whether differences in alcohol-related drinking behaviors were specific to exposure in adolescence versus exposure in adulthood. Male Wistar rats were given a 2-bottle choice between 20% ethanol and water in one group and between two water bottles in another group during their adolescence (Postnatal Day [PD] 26-59) to model voluntary drinking in adolescent humans. As young adults (PD85), rats were trained in a paradigm that provided free access to 20% alcohol for 25 min after completing up to a fixed-ratio (FR) 16 lever press response. A set of young adult male Wistar rats was exposed to the same paradigm using the same time course, beginning at PD92. The results indicate that adolescent exposure to alcohol increased consumption of alcohol in adulthood. Furthermore, when investigating differences between adolescent high and low drinkers in adulthood, high consumers continued to drink more alcohol, had fewer FR failures, and faster completion of FR schedules in adulthood, whereas the low consumers were no different from controls. Rats exposed to ethanol in young adulthood also increased future intake, but there were no differences in any other components of drinking behavior. Both adolescent- and adult-exposed rats did not exhibit an increase in lever pressing during the appetitive challenge session. These data indicate that adolescent and early adult alcohol exposure can increase consumptive aspects of drinking but that adolescent exposure may preferentially influence the motivation to drink.

Keywords: Adolescence; Alcohol drinking; Appetitive responses; Consumptive responses; Wistar rats.

Figure 1. Ethanol Drinking in Adolescence on Behaviors in Adulthood

(A) The mean (± SEM) amount of ethanol consumed during the first three FR sessions of the self-administration paradigm. Adult rats which were given the opportunity to freely consume ethanol during their adolescence. Adolescent-exposed rats consumed a significantly higher amount of ethanol compared to controls. (B) The mean (± SEM) amount of ethanol consumed during the last five FR sessions of the self-administration paradigm. Rats which were exposed to ethanol during adolescence again drank more ethanol during adulthood than control rats. (C) The overall mean (± SEM) time to reach any given FR criterion was similar for both groups. (D) The mean (± SEM) number of failed criterions was less for adolescent-exposed rats compared to controls (E) The mean (± SEM) number of lever presses during the appetitive challenge was not significantly different between the control and alcohol-exposed animals. (F) The mean (±SEM) ethanol consumed after the challenge lever pressing session. Ethanol-exposed rats consumed significantly more alcohol during this period compared to controls. (* p<0.05 vs. control group)

Figure 2. High and Low Adolescent Ethanol Drinkers on Behaviors in Adulthood

(A) The mean (±SEM) amount of ethanol consumed during the first 30 min of the 2-bottle choice paradigm. Adolescent high drinking animals (High EtOH) had significantly higher consumption of alcohol than low drinking animals (Low EtOH). (B) The mean (±SEM) amount of alcohol consumed during adulthood in the first three FR sessions was compared between high drinkers, low drinkers and controls to determine if an initial preference to alcohol had a long-term effect on alcohol consumption during adulthood. High drinking animals consumed significantly more ethanol than both low drinking animals and control animals. Low drinkers consumed significantly more alcohol than controls. (C) The mean (±SEM) amount of alcohol consumed during all sessions was compared between high drinkers, low drinkers and controls. High drinking animals consumed significantly more ethanol than both low drinking animals and control animals, but no difference between low drinkers and controls. (D) The overall mean (± SEM) time to reach FR criterion was significantly faster for the high drinkers compared to low drinkers and controls. (E) The mean (± SEM) number of failed criterions was less for the high drinkers compared to controls but no difference between controls and low drinkers. (F) The mean (±SEM) number of lever presses during the appetitive challenge session was compared between the high drinkers, low drinkers and control animals and no significant difference was found. (G) The mean (±SEM) amount of alcohol consumed during the challenge session was significantly different, with high consuming animals drinking significantly more than low drinkers and control. (* p<0.05 vs. control group, # p<0.05 vs. Low EtOH group)

Figure 3. Ethanol Drinking in Young Adulthood on Behaviors Later in Adulthood

(A) The mean (± SEM) amount of ethanol consumed during the first three FR sessions of the self-administration paradigm. Adult rats which were given the opportunity to freely consume ethanol during earlier in adulthood consumed significantly more ethanol compared to controls. (B) The mean (± SEM) amount of ethanol consumed during the last five FR schedules of the self-administration paradigm. Rats which were exposed to ethanol during adulthood again drank more ethanol later in adulthood than control rats. (C) The overall mean (± SEM) time to reach FR criterion was similar for both groups. (D) The mean (± SEM) number of failed criterions was not significantly different between ethanol-exposed and control group. (E) The mean (± SEM) number of lever presses during the appetitive challenge was not significantly different between the control and ethanol-exposed animals. (F) The mean (±SEM) amount of ethanol consumed during the challenge session was not significantly different between groups. (* p<0.05 vs. control group)