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Amount of daylight may impact serotonin programming

Jan. 19, 2017, 8:26 AM

The duration of exposure to daylight, or the “photoperiod,” may affect development of seasonal affective disorder by programming serotonin neurons in the brain, according to Vanderbilt University researchers.

Mice exposed to winter-like short photoperiods demonstrated decreased firing of serotonin neurons in a mid-brain region called the dorsal raphe and increased anxiety and depression-like behaviors, postdoctoral fellow Justin Siemann, Ph.D., a member of the laboratory of Douglas McMahon, Ph.D., Stevenson Professor of Biological Sciences and chair of the department, reported last fall.

Interestingly, mice exposed to summer-like long photoperiods before birth exhibited increased firing of serotonin neurons throughout life, demonstrating a developmental sensitive period for these effects, Siemann reported during the Society for Neuroscience annual meeting in San Diego.

The neurotransmitter serotonin is associated with mood regulation. The effects of photoperiod on serotonin neurons and behavior were dependent on the seasonal hormone melatonin, and were not observed in mice lacking melatonin receptors.

Evaluating the effects of the photoperiod thus may provide novel insights into the etiology and treatment of mood-related disorders, Siemann concluded.

Also contributing to the study were lab director McMahon, Noah Green, Ph.D., and Hideki Iwamoto, Ph.D.

Their findings were included in the Neuroscience 2016 “Hot Topics” book, which highlighted about 170 abstracts out of 20,000 presented at the conference.

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