Effects of ambient temperature on cardiovascular control during sleep in narcoleptic mice with genetic ablation of hypocretin neurons

Hypothalamic neurons releasing hypocretin (HCRT) control wake-sleep behavior, cardiovascular system and body temperature and their loss entails narcolepsy. We investigated whether HCRT neurons mediate sleep-dependent cardiovascular adaptations to changes in ambient temperature (Ta). Narcoleptic mice with genetic ablation of HCRT neurons (n=11) and wild-type controls (n=12) were implanted with a telemetric blood pressure transducer and electrodes to discriminate wake-sleep behavior. Recordings were performed in each mouse at ambient temperatures of 25°C (acclimation temperature), 30°C, and 20°C in random order. Mean blood pressure (MBP) and heart rate (HR) were computed in each wake-sleep behavior and analyzed with 3-way analysis of variance and t-tests (significance at P < 0.05). Results revealed a significant interaction between the wake-sleep behavior and Ta on MBP and HR in both mouse strains, with MBP and HR rising at 20 °C, particularly during wakefulness and non-rapid-eye-movement sleep. No effect involving the mouse strain was statistically significant. These results demonstrate that hypothalamic HCRT neurons are not necessary for sleep-dependent cardiovascular adaptations to changes in Ta.