Friday, October 5, 2012

Disgusted rats help us understand nausea

We all know the feeling of nausea, but the mechanisms of the body that induce such sensations are poorly understood. This is in contrast to vomiting, which is a well-understood bodily reflex. Nausea is a bit more complex, because it involves brain functions that induce a generally unpleasant feeling, something that is more sophisticated than the vomit reflex. Scientists have found an animal model capable of simulating nausea, and that has lead to more understanding about how this phenomenon actually works. In turn, this may improve drugs that include nausea in their list of side effects, which means it could be relevant for chemotherapy in cancer patients.

In order to assess what happens to the body when experiencing nausea, the scientists, working at the University of Guelph, set up a rat model. The animals were supposed to simulate human feelings of nausea, something that has not been possible for a long time. However, a new setup simulates nausea by assessing something called gaping: a rat opening its mouth after feelings of disgust. By letting the rat taste 'disgusting' things, the scientists were able to analyze what happens in the brain.
A gaping rat.
According to the brain analysis, an area called the visceral insular cortex is the most important when it comes to generating nausea. Specifically, the researchers found that the release of a neurotransmitter, a chemical messenger, called serotonin in that particular area is the determining factor. The evidence was reinforced by an experiment that depleted the available serotonin, thereby reducing the aforementioned gaping effect which is supposed to substitute for nausea.

The visceral insular cortex normally functions by receiving signals from the gut that indicate something bad, calling for feelings of nausea. Another part of the insular cortex deals with input from taste, which actually seems more likely to be affected in the experiments that the University of Guelph has set up. All in all, it does appear that this brain area plays a pivotal role in inducing nausea, which means it is an important target for further investigation.

One of the most powerful inducers of nausea is chemotherapy, where it is often noted as a side effect. Because this is a particularly uncomfortable side effect, it would be beneficial for the patient if we were able to prevent it. This may be possible by blocking the function of serotonin in the insular cortex. Uncovering the mechanism of how the body induces feelings of nausea is important, as there currently is no proper way to repress this bodily response.

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