Stressed individuals might be particularly prone to binge eating or drug addiction because of high levels of a hormone mechanism in their brain, according to University of Michigan and Georgetown University research. Researchers injected rats with either a high dose (500ng/0.2 ml) or a low dose (250ng/0.2 ml) of CRF, part of the brain's internal stress-signalling system that serves as a brain stress neurotransmitter. They injected the rats in a part of the brain called the nucleus accumbens, which is involved in the mediation of pleasurable rewards and stress signals. They observed the rats' behaviour in response to a cue - a 30-second 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 a lever they expected to release more sugar pellets.
The authors made sure the rats did not experience stress due to CRF itself or to other factors in the experimental set-up. The results show that injection of a high dose of CRF tripled the intensity of bursts of sugar craving, measured by the pressing on the sugar-associated 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 leverpressing activity significantly. The results explain 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.
BMC Biology, April 13 2006 online, doi:10.1186/1741-7007-4-8. Susana Pecina et al.. Department of Psychology, University of Michigan, Ann Arbor, Michig