Editors' ChoiceAlcohol Consumption

How Much Alcohol Is Too Much?

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Science Translational Medicine  05 Sep 2012:
Vol. 4, Issue 150, pp. 150ec160
DOI: 10.1126/scitranslmed.3004842

By now, it is common knowledge that an addictive relationship with alcohol changes your emotional and physical well-being for the worse. But it is less clear where to draw the line for moderate alcohol intake, which is often considered not to be unhealthy. Although some studies have reported that moderate drinking improves overall cognition, others have come to the opposite conclusion. In addition, it is unclear how other variables such as the drinkers’ sex or exact amount of alcohol intake affect the cognitive process. In this new study, Anderson and colleagues set out to model moderate alcohol consumption in Sprague-Dawley rats and to explore its effects on neuron development in the adult rodent hippocampus.

As a first step, the authors found that in both female and male rats, a liquid diet containing 4% (v/v) ethanol led to average blood alcohol concentrations of slightly higher than 0.08%, a threshold commonly used in humans as a legal limit for operating a motor vehicle. They then injected rats with bromodeoxyuridine (BrdU), which proliferating cells incorporate into their newly synthesized DNA as a thymidine analog, to visualize the development of new neurons in the hippocampus. After 2 weeks on the 4% ethanol diet, BrdU-labeled neurons were markedly decreased compared with those seen in animals on an ethanol-free liquid diet, suggesting that alcohol hampered neurogenesis. The authors also demonstrated that the blood alcohol concentrations attained in their rat experiments did not interfere with the animals’ motor control and associative learning. Here, the “rotarod” test—a treadmill exercise for rodents—assessed their ability to stay balanced on the device without falling off. Electromyography of eye blink responses measured how fast the animals could be conditioned to blink when white noise was presented as a stimulus, a process that requires training and relies on hippocampal function. For male and female rats, performance on both of these tests was unaffected by alcohol content in the diet.

The authors propose that moderate alcohol consumption might harm the plasticity of the brain, a characteristic that seems to rely on lifelong neurogenesis. Surely, many open questions remain. If the loss in neuron development induced by moderate alcohol consumption does not affect motor and learning skills, what are the relevant functional measures to assess alcohol-induced physiological dysfunction? This study marks a provocative step in the quest to define what moderate alcohol consumption does to your brain.

M. L. Anderson et al., Moderate drinking? Alcohol consumption significantly decreases neurogenesis in the adult hippocampus. Neuroscience, 12 August 2012 (10.1016/j.neuroscience.2012.08.018). [Abstract]

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