Abstract
We recently reported that provocative motion (rotation in a home cage) causes hypothermic responses in rats, similar to the hypothermic responses associated with motion sickness in humans. Many stimuli inducing emesis in species with an emetic reflex also provoke hypothermia in the rat, therefore we hypothesized that a fall in body temperature may reflect a "nausea-like" state in these animals. As rats do not possess an emetic reflex, we employed a pharmacological approach to test this hypothesis. In humans, motion- and chemically-induced nausea have differential sensitivity to anti-emetics. We thus tested whether the hypothermia induced in rats by provocative motion (rotation at 0.7 Hz) and by the emetic LiCl (63 mg/kg i.p.) have a similar differential pharmacological sensitivity. Both provocations caused a comparable robust fall in core body temperature (-1.9 ± 0.3°C and -2.0 ± 0.2°C for chemical and motion provocations, respectively). LiCl(-)induced hypothermia was completely prevented by ondansetron (2mg/kg, i.p., a 5-HT3 receptor antagonist that reduces cancer chemotherapy-induced nausea and vomiting), but was insensitive to promethazine (10 mg/kg, i.p., a predominantly histamine-H1 and muscarinic receptor antagonist that is commonly used to treat motion sickness). Conversely, motion-induced hypothermia was unaffected by ondansetron but promethazine reduced the rate of temperature decline from 0.20 ± 0.02 to 0.11 ± 0.03°C/min (P < 0.05) with a trend to decrease the magnitude. We conclude that this differential pharmacological sensitivity of the hypothermic responses of vestibular vs. chemical etiology in rats mirrors the observations in other pre-clinical models and humans, and thus supports the idea that a "nausea-like" state in rodents is associated with disturbances in thermoregulation.