Neuropeptide Y (NPY) is a hypothalamic appetite-stimulating regulator of food intake that has been suggested to interact with components of stress response, including the release of the stress hormone corticosterone (CORT). Recent work suggests that NPY can interact directly with the adrenal gland to promote CORT secretion, raising the question of whether NPY can stimulate a stress response and whether NPY requires an active stress response to regulate food intake. This interaction has been examined in mammals but the role of NPY has not been explored in reptiles. To answer questions about the relationship between NPY, stress, and food intake in reptiles, Micaela Castro, a student with H. Bobby Fokidis at Rollins College, performed two manipulative experiments, one in the field, and one in the laboratory, on the brown anole (Anolis sagrei). These experiments utilized injections of NPY and dexamethasone (DEX), an agonist that inhibits CORT secretion, to test the hypotheses that NPY promotes CORT secretion and food intake and that CORT secretion is required for NPY to exert its appetite-stimulating effect.
In the field, adult male brown anoles were captured and injected with varying levels of either NPY, DEX, or saline as a control. An hour after injection, blood was collected and CORT levels were measured. From this study, it was found that NPY injections promoted CORT secretion while DEX injections decreased CORT secretion relative to the saline control. In the laboratory, adult male brown anoles were fasted for either 24 hours or 48 hours, injected with either NPY, DEX, DEX followed by NPY after an hour, or saline as a control, and were observed for differences in food intake. From this study, it was found that DEX injections decreased food intake relative to controls while NPY injections increased food intake relative to controls, but only when anoles were fasted for 48 hours. DEX injections followed by NPY injections resulted in similar food intake to control animals. All together, these results suggest that NPY and CORT are codependent, with NPY capable of stimulating CORT secretion and CORT being required by NPY for it to exert its appetite-stimulating effects.