A short photoperiod alters brain metabolism and cold resistance in Drosophila melanogaster.

To survive, animals need to prepare for winter in advance, and this process begins in the brain in response to the shortening of the photoperiod in fall. Here, we demonstrate that exposing adult flies for just 14 days to a short photoperiod at a constant temperature of 20 °C increases their cold resistance and dramatically alters brain metabolism. Such flies have significantly lower levels of monosaccharides, and a lower ATP/AMP ratio in their brains than flies exposed to a long photoperiod, despite being less active and eating more. The levels of storage and structural lipids (triacylglycerols and phospholipids) as well as the number of lipid droplets in the brain increase, suggesting the utilization of glucose for the synthesis of lipids via the citrate shuttle. In addition, during short days, the ratio between the reduced and oxidized forms of glutathione increase, as do detoxification processes and autophagy. This suggests that the brain of short-term flies is less sensitive to oxidative stress and neurodegeneration, which is essential for survival throughout the winter. Overall, our results show that exposure to a short photoperiod has significant metabolic and physiological consequences in the fly brain that serve to prepare for the coming winter.