[Effect of orexin-A and orexin-1 receptor antagonist injected into the fourth ventricle of rats on food-intake and spontaneous physical activity].

The present study was aimed to investigate the effects of orexin-A and orexin-1 receptor (OX1R) antagonist injected into the fourth ventricle of rats on food-intake and spontaneous physical activity (SPA). Obese rat model was induced by high fat diet. Different doses of orexin-A or SB334867, an OX1R antagonist, were injected into the fourth ventricle of obese and normal rats respectively. SPA and food intake were monitored for 4 h after injection in both light and dark environment. In the light measurement cycle, different doses of orexin-A significantly stimulated feeding and SPA in all injected rats, and the animals' responses showed a dose-dependent manner (P < 0.05-0.01), and compared with those of normal rats, the orexin-A induced food intake and SPA were more pronounced in obese rats. In the dark measurement cycle, different doses of orexin-A had no obvious effect on food intake and SPA in both normal and obese rats (P > 0.05). In the light cycle, different doses of SB334867 significantly decreased food intake and SPA in all rats during 0-2 h and 2-4 h after injection (P < 0.05), but the food intake and SPA in obese rats were significantly greater than those of normal rats. In the dark cycle, different doses of SB334867 showed no obvious effect on food intake and SPA of normal and obese rats (P > 0.05). These results suggest that fourth cerebral ventricle nuclei may be one target for orexin-A and light condition may play an important role in orexin-A and OX1R physiological functional processes.