Stressed individuals might be particularly prone to binge eating or drug addiction because of the high levels of the stress hormone corticotropin-releasing factor in their brain. A study published today in the open access journal BMC Biology (http://www.biomedcentral.com/bmcbiol/) shows that rats with levels of corticotropin-releasing factor (CRF) in their brain similar to the levels experienced by humans when they are stressed show an exaggerated craving for a reward – a piece of sugar - whenever presented with a cue that had previously been associated with that reward. This result explains why stressed individuals might be more likely to experience strong cravings for rewards and compulsively indulge in pleasurable activities such as eating or taking drugs.
Susana Peciña and Kent Berridge from the University of Michigan in Ann Arbor and Jay Schulkin from Georgetown University, Washington DC, USA, injected rats with either a high dose (500ng/0.2 ml) or a low dose (250ng/ 0.2 ml) of CRF. They injected the rats in a part of the brain called nucleus accumbens, known to be involved in the mediation of both pleasurable rewards and stress signals in humans as well as rats. They observed the behaviour of the rats in response to a cue – a 30-second long tone- that had previously been associated with the release of a reward, in the form of sugar pellets. When they heard the cue, the rats pressed on a lever that they expected to release more sugar pellets. The authors made sure that the rats did not experience stress as a result of CRF itself or of other factors in the experimental set-up.
Peciña et al.’s results show that injection of a high dose of CRF tripled the intensity of bursts of sugar craving, as indicated by the intensity of the lever-pressing activity lever. The lever-pressing activity was only enhanced if the injection of CRF was followed by the cue – it did not increase following the injection alone. The low dose of CRF, or an empty injection, also failed to enhance the lever-pressing activity significantly.
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