�New research by Aberdeen scientists suggests that Seasonal Affective Disorder (SAD) relates to an ancient timing mechanism in the mind dating back millions of years.
Discoveries by a University of Aberdeen-led team, involving collaborators in Edinburgh and Strasbourg, and published in the latest military issue of Current Biology, pour forth new insights into the mechanisms by which seasonal worker rhythms ar generated.
The researchers studied the primitive Soay breed of sheep, which relies on its strong seasonal biology to survive wild on the N. Atlantic islands of St Kilda.
They identified a new role for a chemic known as thyroid exhilarating hormone (TSH), which is secreted by cells in the hypophysis gland and is already known to control the thyroid secretory organ.
The modern work reveals that a specialised grouping of pituitary gland TSH-secreting cells signal right away to the brain to control the sheep's seasonal behaviour.
This surprising find reverses the "master - slave" relationship between the brain and the pituitary body, found in all vertebrates including humans, in which brain signals control pituitary body hormone secretion.
Dr Hazlerigg, Reader in Zoology at the University of Aberdeen said: "Our research points to an ancient seasonal timing chemical mechanism that survives in new vertebrates. Some humans crataegus laevigata retain remnants of this ancient seasonal worker timing mechanism which would explain wherefore they go through SAD.
It is now hoped that identifying this new role for TSH may lead to better understanding of seasonal or thyroid disorders in human beings.
Dr Hazlerigg continues: "Our next objective is to understand exactly what TSH does when it gets into the brain to cause changes in demeanour and endocrine secretion. By defining these pathways we hope to increase our understanding non only of the control mechanisms in seasonal animals but as well of SAD."
University of Aberdeen
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