Palatable solutions during paradoxical sleep deprivation: reduction of hypothalamic-pituitary-adrenal axis activity and lack of effect on energy imbalance.

Paradoxical sleep deprivation (PSD) induces increased energy expenditure in rats, insofar as rats eat more but loose weight throughout the deprivation period. In the present study, rats were offered water, saccharin or sucrose to drink during the deprivation period, since it has been proposed that carbohydrates reduce the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Rats were submitted to the flower pot technique for 96 h. During the PSD period, they were weighed daily and food and fluid intake was assessed twice a day. At the end of the PSD period, rats were killed and plasma concentrations of glucose, adrenocorticotropic hormone (ACTH) and corticosterone were assayed. Compared to their control counterparts, all paradoxical sleep-deprived rats consumed more food, but lost weight. Paradoxical sleep-deprived rats given sucrose drank more than their control counterparts (especially in the light phase of the light/dark cycle). Paradoxical sleep-deprived rats showed increased food intake during all periods throughout the experiment, with peak intake during the dark phase and nadir during the light phase of the light/dark cycle. All paradoxical sleep-deprived rats showed lower glucose plasma levels than control rats and increased relative adrenal weight. However, when given saccharin or sucrose, paradoxical sleep-deprived rats showed lower concentrations of ACTH and corticosterone than their water-provided counterparts, indicating that palatable fluids were capable of lowering HPA axis activation produced by PSD. The fact that PSD induced energy imbalance regardless of the relative attenuation of the HPA axis activity produced by saccharin or sucrose suggests that the HPA axis may play only a secondary role in this phenomenon, and that other mechanisms may account for this effect. The data also suggest that supply of palatable fluids can be an additional modification to reduce the stress of the flower pot method.