Jan. 11, 2011 Scientists from the Agency of Science, Technology and Research/Duke-NUS Neuroscience Research Partnership (A*STAR/Duke-NUS NRP), A*STAR's Institute of Molecular and Cell Biology, and the National University of Singapore have made a breakthrough concerning how anxiety is regulated in the vertebrate brain. Their work, published in the journal Current Biology, sheds light on how the brain normally shuts off anxiety and also establishes the relevance of zebrafish as a model for human psychiatric disorders.
The team of scientists, led by Dr Suresh Jesuthasan from the A*STAR/Duke-NUS NRP, showed that disrupting a specific set of neurons in the habenula prevents normal response to stressful situations. In their experiments, Dr Jesuthasan's team trained larval zebrafish to swim away from a light in order to avoid a mild electric shock. While normal fish easily learned this task, fish that had a specific set of neurons in the habenula damaged displayed signs of "helplessness."
Although they initially tried to avoid the shock, they soon gave up. What's more, these fish showed indications that they were more anxious than normal fish, such as being startled easily by non-harmful stimuli. Because of the similarity of the zebrafish brain to the mammalian brain, the study suggests that malfunction of the habenula is a possible cause of certain anxiety disorders in humans. This means that it may be possible to use direct stimulation of the habenula as a way of treating some types of anxiety disorders in humans. The zebrafish model which the scientists developed in the course of their work may also be used in future drug discovery efforts for psychiatric medicines.
Dr Jesuthasan said, "Our work deals with fundamental aspects of human experience -- stress and anxiety. We think that the habenula of the brain is associated with the assessment of whether a stress has been overcome. Our study provides one possible explanation as to why the need to control the environment is such a critical component of human behavior -- the feeling of control enables organisms to deal with stress."
 The habenula has been shown to be involved in many functions of the brain, such as pain processing, reproductive behavior, and learning. It also seems to be involved in reward processing, particularly with respect to negative/adverse feedback.
 The habenula is difficult to study in humans and in other mammals because it is located deep in the brain. However, the habenula in the zebrafish is located located near the surface of its brain, and is thus easily accessible for study.
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