Effects of Orexin A on Thermal Behaviour: Substantial Evidences forThermoregulatory Role of Orexin A

Orexin A is a hypothalamic neuropeptide produced in the dorsal and lateral hypothalamus, and orexin-producing cell have widespread anatomical projections within the central nervous system. Orexin A is involved in multiple physiological functions, including eating behavior, thermoregulation, and sleep-regulation. The aim of this work was to study the thermal preference induced by orexin A. A thermal preference task with floor thermal gradient from 16°C to 25°C, divided into 10 equal segments, was designed to evaluate the thermal preferences in rats. Male rats (n=10, divided into two groups of five animals) received an intracerebroventricular injection of 1.5 nmol of orexin A or vehicle and were subsequently tested for thermal preference for 4 h. The results showed that the rats injected with orexin A had increased motor activity compared to the control group, particularly after the second hour of the test. Moreover the group treated with orexin A preferred hotter temperatures ranging from 24 to 25°C compared to the control group that preferred temperature of 22°C, which is near room temperature for rat housing (22 ± 1°C). No significant correlation was seen between thermal preference and time (hours). Since orexin A induces thermal preference, this study indicates that this neuropeptide plays a key role in the thermoregulation.