Drunken monkeys reveal how binge-drinking harms the adolescent brain

By Ed Yong | May 31, 2010 3:00 pm

Hangover

Most of us will be all too familiar with the consequences of night of heavy drinking. But alcohol’s effects on our heads go well beyond a mere hangover. The brain suffers too. A penchant for incoherent slurring aside, alcohol abusers tend to show problems with their spatial skills, short-term memory, impulse control and ability to make decisions or prioritise tasks. Many of these skills are heavily influenced by a part of the brain called the hippocampus. Now, Michael Taffe and researchers from the Scripps Research Institute have shown how binge-drinking during adolescence can cause lasting damage to this vital area.

The hippocampus is one of only two parts of the brain that clearly produces new neurons throughout adult life. While other areas must make do with the set they had at birth, the hippocampus continually churns out a fresh supply. This process may be important for learning and memory but it’s seriously hampered by alcohol. Taffe found that not only does heavy boozing kill off the hippocampus’s neurons, it also weakens its ability to produce reinforcements.

Much like natural history documentaries and martial arts, Taffe’s research was inspired by the antics of drunken monkeys. Taffe gave seven adolescent rhesus macaques a tangy citrus alcoholic drink, which increased in strength from 1% to 6% alcohol over 40 days. Having established their alcohol preferences, he allowed four monkeys to stick with the strong cocktail for an hour a day over the next 11 months. The other three went back to a non-alcoholic version of the tangy beverage. For the study’s final two months, all of the monkeys went tee-total.

The blood alcohol limits of the four binge-drinkers clearly showed that they were knocking back their tipples. If they’d been humans, they would probably have been drunk, and certainly well over the legal limit for driving. And their brains revealed more worrying signs of damage.

Chitra Mandyam, who collaborated on the study, found that regular chugs of the demon drink severely slashed the numbers of neural stem cells in the monkeys’ hippocampi. These are the cells responsible for churning out fresh neurons. With alcohol cutting their numbers and compromising their ability to divide into more mature cell types, the monkeys’ production of hippocampal neurons more than halved in the course of 11 months.

Even after two months of complete abstinence, Taffe found that each monkey’s hippocampus had fewer traces of fresh, immature neurons. Worse still, he found signs that the existing supply had started to degenerate. By comparison, the tee-total trio had a healthy turnover of new hippocampal neurons and no detectable sign of neural death.

Studies with rats and mice have hinted at the same effect, but monkeys provide a far deeper understanding of the alcoholic brain. They’re incredibly similar to us, not just in terms of their mental skills, but also in the way that their hippocampuses produce new neurons, their lengthier window of adolescence, and the fact that they’ll happily drink alcohol to the point of drunkenness.

If the same thing happens in humans, it suggests that alcoholism starts to wreak damage in the brain after a relatively short amount of time. It starts to kill off the hippocampus’s neurons while nixing its ability to make more. This double-whammy could explain many of the mental problems that regular binge-drinkers experience. Most intriguingly of all, the turnover of neurons in the hippocampus affects our learning and memory skill, and Taffe suggests that problems with this process could help to explain alcohol’s addictive side.

Reference: PNAS http://dx.doi.org/10.1073/pnas.0912810107

Photo by Pauk

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Comments (9)

  1. A lot of animals seek out fermented fruit, indulge, and so become inebriated.

    I didn’t really ponder this too much but the symptoms are similar when an animal suffers from toxicity.

    So, just wondering where the origins of the self-medicating behavior came from for wild animals.

    I thought we already knew about the impact on the brain but appreciate the link to the article–but sad I get a link error from DOI.

  2. How did the researchers count the neurons? By staining brain slices and using that good old eye and tally marks?
    Counting data can be heavily subject to confirmation bias, so I always look for proper blinding of the subjects studied in studies like this..

    Pity the abstract isn’t even available!

  3. mat

    DOI can take time to go live, the publisher’s link is here http://www.pnas.org/content/early/2010/05/20/0912810107.abstract

  4. beth

    Did we give our hard-earned tax dollars for this study? Is this another NIH idiot grant?

    Why don’t we give money to researchers to figure out how to stop oil spills instead of this idiotic information.

  5. Eleanor

    Hi Beth, I’m struggling to see how you class this as idiot information. It shows that teen drinking is likely to be bad (which we’d guessed already), but it shows very specifically what effect it is likely to have.

    You could give neouroscientists money to study oil spills I suppose, but I’m not sure what use they’d make of the money….

  6. Beth has clearly unearthed one of the biggest scandals in academia. I have it on good authority that the reason this study was funded was that the grants review meeting for the National Institute for Ranking All Of The World’s Problems In Order Based on Public Vote And Then Solving Them Sequentially was cancelled after the members couldn’t work out if they should turn up or solve world hunger first. So instead the money went to the NIH instead. Pity.

  7. becca

    So many questions!
    1) Is there anything that can protect against it? Maybe antidepressants, or exercise? (I’m afraid my knowledge of things that stimulate neurogenesis or prevent degeneration is fairly limited)
    2) When are they gonna look at AUTOPHAGY?! They went and found non-caspase dependent neurodegeneration, and then DIDN’T look for autophagy? If I were reviewer #3 I’d kick their BUTTS. At least stain for HMGB1, people!!!!!
    3) I notice the monkeys were routinely exposed to ketamine- what might this do?
    4) In this context, two months is “long lasting” but how long does it really last?
    5) Most importantly, once this research is completed, will we be able to create SuperMonkeys who can clean oil spills for us? Or at least fetch us burritos?

    Finally, a comment: when you write in a paper ‘we did behavioral testing, which you all really wanna know about, but we broke it up into another manuscript so you can’t find it out, but we’ll tell you it’s gonna be published, so you know we got p<0.05 in some behavioral something, but you don't get to find out yet, HAHAHAHAHAHAHA!' is just plain DIABOLICAL.

  8. Diana

    This sounds more like a prank carried out by some idiotic fraternity with too much alcohol on their hands and (unfortunately) access to animals.

    Yes – teen drinking is bad…it’s amazing that it required liquoring up a bunch of monkeys to find this out. This is government sponsored animal abuse.

  9. Apparently some people can’t comprehend the difference between the words “how” and “that”. Perhaps they’re drunk…

    There does seem to be a strange correlation in this thread between wielding the word “idiotic” and actually being it.

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