Science Questions

How can rodents help model addiction?

Mon, 14th Apr 2014

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Peter Steadman asked:

There was an experiment where they isolated the pleasure receptors in the brains of rats and they enabled the rats to stimulate themselves basically by pressing a button. So, I'm wondering if that constituted addiction because the rats just gave up food and basically kept pressing this button until it died.



Hannah - Well yeah, there are a lot of scientists that work on rodents, rats and A house mousemice with this kind of lever pressing paradigm or task and you can for example, stimulate a rat to continue pressing a lever or a button if you give them a nice little reward. That might be a nice food treat for example or it might be a drug of addiction, a drug of choice. And for the rats, they particularly like cocaine and also heroin, and even ethanol alcohol.

Actually, 20% of rats will compulsively continue to press this lever in a way that will then give then deliver these drugs even if the rats will then receive a very mild electric shock. So, even if there's adverse ramifications of pressing this lever, 20% of rats will want to continually get cocaine or heroin or ethanol, in order to stimulate the reward centre of the brain, the nucleus accumbens. It causes this release of dopamine, this flush of dopamine, this flush of reward and pleasure in the brain of the rats.

Chris - I was going to say, why do they find it pleasurable when they put this electrode in this part of the brain? As Peterís saying, why do the rats find that pleasant?

Hannah - Well, itís because weíve all evolved to feel pleasure. I mean, itís part of the things that drive us to success and to succeed as a species, we have to feel pleasure and feel reward, and feel motivation for things. And so, drugs of abuse and also, this kind of electric shock kind of thing that you can do will actually stimulate this reward and pleasure pathway. Interestingly, 20% of humans will actually kind of go towards more of this compulsive behaviour and also, kind of go towards adverse ramifications of drug abuse for example and seeking drugs of abuse. And so, that also taps into that system.

Chris - Ramsey.

Ramsey - So, is this helping us to learn about how to treat addiction in humans?

Hannah - Yes, so, this is why scientists are so interested in it. So, they're actually trying to find the genetic basis for why there's this conserved 20% of both rodents and also human populations that seem to be keen on tapping into this kind of reward motivation pathway in the brain. And there's other animals as well in the world that seem to exhibit this kind of interest in reward and pleasure. For example, I was in New Zealand recently and there was these Tui birds, that are these beautiful iridescent magpie type birds and they like drinking or supping on this flax fermented flower juice and that get them quite tipsy and then they soar around in this tipsy way. So yeah, itís not just rats, itís not just humans. Itís also other birds and animals.


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Peter Steadman asked the Naked Scientists: That experiment when the pleasure receptors in rats' brains were hard-wired to be stimulated when the rat pushed a button: the rat would push the button and completely neglect food and end up dead as a result. Is that a form of addiction? What do you think? Peter Steadman, Sun, 13th Apr 2014

It could be called a behavioural addiction; a recurring compulsion to do some activity despite seriously harmful consequences. It's not so different from certain drug addictions, except that it presumably lacks the severe physiological withdrawal effects of some drugs. dlorde, Mon, 14th Apr 2014

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