Possible pathophysiological mechanisms regulating food intake in seasonal affective disorder

Noradrenaline, estrogen, neuropeptide Y and galanin are all involved in regulation of eating behaviour. Based on a recent case report on seasonal affective disorder (SAD), there is evidence of decreased insulin sensitivity. Reduced insulin sensitivity may increase the transcriptional activity of the neuropeptide Y gene in the medial basal hypothalamus and subsequent ingestion of food. Decreased availability of estrogen may also increase the levels of neuropeptide Y, leading to decreased release of noradrenaline from the ventromedial hypothalamus. The increased noradrenaline content may increase the concentration of galanin, which will decrease the circulating levels of insulin and increase the pace of transcription of the neuropeptide Y gene. Among some SAD patients, it is possible that the sustained ingestion of high-fat diet will rather activate the transcription of the neuropeptide Y gene than deactivate it, indicating a defect in macronutrient selection.