Background: The development of dependence may have significant motivational consequences regarding continued use and abuse of ethanol. We have developed a mouse model of ethanol dependence and repeated withdrawals that demonstrates sensitization of seizures and other symptoms of withdrawal. It is unclear whether such experience influences ethanol drinking behavior. The present series of experiments were designed to examine whether repeated cycles of chronic ethanol exposure and withdrawal has an impact on subsequent motivation to voluntarily self-administer ethanol.
Methods: With the use of a modified sucrose-fading procedure, adult male C57BL/6J mice were trained to drink 15% (v/v) ethanol in a limited access procedure (2 hr/day). The animals were not food or water deprived at any time during the experiments. Once stable baseline intake was established, mice were exposed to four cycles of 16 hr of ethanol vapor (or air) in inhalation chambers separated by 8-hr periods of withdrawal. At 32 hr after the last cycle of ethanol exposure, all mice were tested for ethanol intake under limited access conditions for 5 consecutive days. The animals then received a second series of chronic ethanol exposure and withdrawal followed by another 5-day test period for ethanol drinking.
Results: Stable daily baseline intake was established in mice that drank 15% ethanol combined with 5% sucrose (experiment 1), 15% ethanol alone (experiment 2), 5% sucrose alone (experiment 3), or 15% ethanol when presented as a choice with water (experiment 4). After repeated cycles of chronic ethanol exposure and withdrawal experience, consumption of ethanol solutions increased over baseline levels and in comparison with control (air-exposed) groups. However, sucrose consumption did not change in mice that were trained to drink 5% sucrose. The increase in ethanol consumption after chronic ethanol exposure and withdrawal experience resulted in a significant increase in resultant blood ethanol levels.
Conclusions: Once the positive reinforcing properties of ethanol were established, chronic ethanol exposure and withdrawal experience resulted in a significant increase in voluntary ethanol drinking that yielded a >2-fold increase in resultant blood ethanol levels. This increase in ethanol intake occurred whether ethanol was presented in combination with sucrose, alone (unadulterated), or as a choice with tap water. Furthermore, this effect seems to be selective for ethanol in that animals that were trained to drink a sucrose solution did not exhibit a change in their intake after similar chronic ethanol exposure. As such, this model may be useful in studying the mechanisms and conditions in which chronic ethanol treatment influences motivation to resume drinking after a period of abstinence (relapse).