Seasonal Changes in the Central Nervous System of the Arctic Ground Squirrel

Hibernation is a seasonal adaptive strategy characterized by metabolic suppression and a decrease in body temperature (T b ). The Arctic Ground Squirrel (AGS) is an obligatory hibernator; the onset of hibernation is linked to the circannual rhythm even when AGS are housed at constant environmental conditions. This phenomenon suggests an endogenous circannual clock, which mechanism is unknown. We test the hypothesis that sleep‐awake pathways are differentially activated between summer and winter season. Summer season was defined by the lack of torpor bouts; winter season was defined by the presence of periodic torpor bouts. AGS, implanted with body temperature transmitter, were maintained at constant environmental conditions: 2°C and 4L:20D. Euthermic AGS, in winter and summer, were perfused with 4% paraformaldehyde and brains removed for immunohistochemical analysis. Free‐floating immunohistochemistry was used to localize active nuclei as indicated by cFos‐immunoreactivity (mouse anti‐cFos 1:20,000, Millipore). Data analysis was performed in R. Wake active neurons are localized in the Perifornical Nucleus and the Tuberomamillary Nucleus. Both nuclei show higher activation, measured as higher cFos+ count, in summer than winter. A lower wakefulness activity in winter suggests an increase in sleep propensity, supporting that hibernation is characterized by an increase in sleep. In addition the Raphe Pallidus, a region controlling thermoregulation, shows a lower activation in winter compared to summer. This result correlates with the lower euthermic body temperature of AGS in winter compared to summer. In conclusion, winter AGS are characterized by a seasonal decreased in wakefulness and thermogenic nuclei activity; these changes may underlie the mechanisms of the circannual endogenous clock. Support or Funding Information NIH R03 NS081637 NSF IOS‐1258179 Alaska INBRE P20GM103395 NIH TL4GM118992 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .