Poster sessions–late breaking abstracts

introduction: Torpor is a survival strategy characterised by a transient reduction in body metabolism and temperature, which is used by some mammals to cope with harsh environmental conditions. At present, little is known about the mechanisms underlying the arousal for torpor. The Raphe Pallidus (RPa), a brainstem nucleus that plays a crucial role in relaying thermogenic signals from the hypothalamus to autonomic tar- gets, is likely to be active during arousal. Our study aims to investigate the degree of activation of RPa-projecting areas during arousal in mice. Method: Female C57BL/6J mice, housed at an ambient temperature of 21C, underwent surgery under general anaesthesia for the injec- tion of the retrograde tracer Cholera Toxin b (CTb) within the RPa and the intraperitoneal placement of a temperature probe to record core temperature (Tcore; Anipill, Bodycap). A week after surgery, mice were divided in three groups: (i) Torpor (n = 4), euthanized after at least 3 h of torpor, induced by fasting at ZT12 (mean Tcore = 18.1C); (ii) Arousal (n = 3), euthanized 90 minutes after arousal onset (mean Tcore = 32.9C). (iii) Control (n = 3), mice were fasted but did not enter torpor, and were time-matched with the Arousal group. Following transcardial perfusion, brains were harvested to immunohistochemically detect cFos, a marker of neuronal activity, and CTb localization in known central thermoregulatory areas. Results: Preliminary analysis of the results was focused on the Dor- somedial Hypothalamus (DMH), which is known to drive thermogene- sis through an excitatory input to RPa. DMH exhibit extensive presence of cFos+ and CTb+ cells in both Torpor and Arousal groups, and no statistically significant difference emerged in either the num- ber of cFos+ cells (Welch's t-test, p = 0.67), or double-labelled cells (p = 0.62) when these groups were compared. Conclusion: To the best of our knowledge, this is the first attempt to describe the neural network active at arousal-onset after torpor in mice. The results show that DMH-RPa projecting cells are active dur- ing both torpor and arousal, two seemingly opposite states, suggesting that DMH has a more complex role in the torpor-arousal cycle than expected. Ongoing further analysis will elucidate the role of other brain areas in arousal from torpor in mice. Conflict of Interest: No