According to the researchers, this helps explain certain complex eating behaviors and may be one of the mechanisms by which obesity develops in people exposed to psychosocial stress. The findings, published in the Journal of Clinical Investigation, are not just abstract and relevant only to mice, but likely are also relevant to humans.

Scientists know that fasting causes ghrelin to be released from the gastrointestinal tract, and that the hormone then plays a role in sending hunger signals to the brain. Previous research has shown that chronic stress also causes elevated ghrelin levels, and that behaviors associated with depression and anxiety are minimized when ghrelin levels rise. In mice, these stress-induced rises in ghrelin lead to overeating and increased body weight, suggesting a mechanism for the increase in weight-related issues observed in humans with chronic stress and depression.

For this investigation, the researchers developed a mouse model to determine which hormones and what parts of the brain may play a role in controlling more complex eating behaviors that occur upon stress, particularly those that lead to the indulgence of comfort foods.

They subjected mice to a standard laboratory technique that induces social stress by exposure to more dominant bully mice. Such animals have been shown to be good models for studying depression and the effects of chronic stress and depression in humans.

Wild-type mice subjected to the stress gravitated toward a chamber where they had been trained to find pleasurable, fatty food - the mouse equivalent of comfort food. However, genetically engineered mice, which were not able to respond to stress-induced increases in ghrelin, showed no preference toward the fatty food-paired chamber, and when exposed to the fatty food, did not eat as much as the wild-type animals.

The findings show that ghrelin signaling is crucial to this particular behavior and that the increase in ghrelin which occurs as a result of chronic stress is probably behind these food-reward behaviors.

The study also showed that these effects of ghrelin are due to direct interaction with a subset of neurons that use catecholamines as a neurotransmitter. These include dopaminergic neurons in the brain’s ventral tegmental area, which is known to be associated with pleasure and reward behaviors.

References
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About the Author

Dr. Randi Fredricks, Ph.D. is a psychotherapist and author specializing in the treatment of mental health using integrative medicine and natural therapies. She works with individuals, couples, and families at her office in San Jose, California. Dr. Fredricks' publications include the landmark book Healing & Wholeness: Complementary and Alternative Therapies for Mental Health. No part of this article may be reproduced in any form or by any electronic or mechanical means, including information storage and retrieval systems. Disclaimer: This article is not intended to provide medical advice, diagnosis or treatment. Views expressed here do not necessarily reflect those of Dr. Randi Fredricks as articles often present the published results of the research of other professionals. Copyright © 2012. To cite this article, please use the following citation: Fredricks, R. (2008). Healing & Wholeness: Complementary and Alternative Therapies for Mental Health. Bloomington, IN: Author House.