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Fiber optic activation of serotonergic terminals during olfactory discrimination

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Shedding light on the role of serotonin

The 'happy chemical' serotonin is involved in neuromodulation and is therefore implicated heavily in disorders like depression. A European project has devised a new method to regulate serotonin levels in the brain to determine the precise role of serotonin-releasing nerve cells.

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Although it is clear that psychoactive drugs have a profound effect on mood including fear, anxiety and depression, the exact role of the nerve cells that produce serotonin (5-HT) remain unclear. Research so far has been hampered because of limitations in inducing different concentrations of 5-HT in the brain. Previously, pharmaceutical and electrical means were used to vary serotonin levels in the lab. However, the EU-funded 'Fiber optic activation of serotonergic terminals during olfactory discrimination' (FAST) project has refined the use of optogenetics to induce serotonin production in rodents. The main success of the project lies in the development of tools to manipulate serotonin nerve cells. The FAST researchers found that they could promote the production of serotonin with a high degree of neurochemical specificity and accuracy. The scientists used channelrhodopsin-2 (ChR2), a protein that controls movement in algae attracted by light. When delivered by a specially engineered virus vector and expressed in rat 5-HT nerve cells, it prompted them to produce the serotonin. For mice, another viral vector was used known as double-floxed inverted ORF (DiO). Serotonin neurons are found deep in the brain. The FAST researchers used blue light to trigger the nerve cells but this wavelength of light is absorbed by tissue. An optical fibre was therefore used to deliver the light straight to the appropriate region. Tools developed by the project can be used to study in detail changes in behaviour induced by 5-HT. The biochemical causes of psychiatric disorders like anxiety, panic, depression and schizophrenia can be unravelled for the development of appropriate therapies.

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