Years ago, I blogged about a collaborative study that my lab mate from graduate school, other colleagues, and myself undertook. It investigate the (hedonic) substitution potential of exercise for ethanol in young adult hamsters. Hamsters have an incredibly high preference for ethanol manifest from their diet and lifestyle; these desert-dwelling animals pick up cacti fruit, bury it, let it ferment, uncover it, and then enjoy it. Because of this, they have extremely high levels of alcohol dehydrogenase and per body weight, can drink up to 50x the amount of alcohol as the average human. That being said, the hamster is an excellent model of alcoholism.
This past week, an online version of a follow-up study due to be published in Physiology and Behavior, was made available. In this study, we used very old Syrian hamsters (2 years old!!) and undertook the same hedonic substitution protocol; 1 week of access to a 20% (v/v) alcohol solution (wine), 3 weeks of access to this same solution and a running wheel (or no wheel), and 2 weeks of continued access to the alcohol solution, but no running wheel.
In the young adult hamsters, we found that access to a running wheel suppressed alcohol intake. In old hamsters, it prevented alcohol intake from rising to levels seen in the controls; it is very common for alcohol intake to increase across a protocol of chronic alcohol exposure because of something every college student has—tolerance. In addition, we found that this limiting effect of wheel running on alcohol intake in aging hamsters was residual in that levels remained lower upon removal of the running wheel compared with controls.
There are a few differences to note. The extent of alcohol consumed and the extent of alcohol preferred over water in the aging versus young adult hamsters is significantly less (20% to 50% reduction).
There are several, possible aging-related physiological phenomena to speculate on these results. First, aging is associated with osmotic in balance, resulting in increased water intake. This, in part, explains the decrease in ethanol preference since it is total volume of the alcohol solution consumed over total fluid intake. Secondly, there is a decline in dopaminergic signaling with age, possibly attenuating the reward substitution potential of exercise for alcohol.
At any rate, we were pleased to see this study appear in print because it took a long time to complete these two projects….
Brager, A., & Hammer, S. (2012). Impact of wheel running on chronic ethanol intake in aged Syrian hamsters Physiology & Behavior, 107 (3), 418-423 DOI: 10.1016/j.physbeh.2012.09.011