Rationale: Rats avidly consume standard off-the-shelf beer; however, the behavioural consequences of beer consumption in rodents have hardly been studied.
Objectives: The present study examined the acute anxiolytic and ataxic effects of beer consumption in rats and the anxiogenic effects of withdrawal from free access to beer.
Method: In experiment 1, male Wistar rats received 30 min access to "near-beer" each day (a malt beverage that looks and tastes like beer but which contains <0.5% ethanol). On the test day, for some rats, ethanol (either 2% or 4% v/v) was added to the near-beer to make it resemble standard (ethanol-containing) beer of "light" (2.5% beer) or full strength (4.5% beer). Immediately after this, rats were tested on their response to a predatory cue (a fabric collar that had been worn by a cat) and on an accelerating rotarod. In experiment 2, rats were trained in the same drinking paradigm as above and then tested on a further battery of anxiety tests. In experiment 3, rats were given continuous home cage access to either 4.5% beer or near-beer for 35 days. Half of the rats were then denied access to beer or near-beer for 24 h and then tested on the same anxiety test battery as in experiment 2.
Results: Rats drinking 4.5% beer approached a predatory cue significantly more than those given near-beer, indicating an anxiolytic effect. In experiment 2, rats drinking 4.5% beer displayed less anxiety-like behaviour in the elevated plus maze and emergence tests but not in the social interaction test. Rats given 4.5% beer fell off the rotarod significantly faster than rats given near-beer, indicating an ataxic effect. Rats previously given 4.5% beer drank significantly less near-beer the following day, suggesting a moderate aversion the day after beer consumption. In experiment 3, rats denied access to 4.5% beer showed significantly less social interaction and took longer to emerge into an open field than controls.
Conclusion: These results are the first to our knowledge to show that rats will consume beer at levels that produce clear effects on anxiety and on motor co-ordination, and that will eventually produce behavioural signs of withdrawal.