Neuropeptide Y Increases Both Ingestion of a Self-Selection Macronutrient Diet and Fos Expression in the Medial Amygdala of Rats

The rat posterodorsal medial amygdala (MePD) is responsive to the orexigenic neuropeptide Y (NPY) and is a putative candidate to participate in neural circuits that modulate feeding behavior. Here, we studied the effects of intracerebroventricular (icv) microinjection of NPY on the appetitive and food intake behaviors of rats under the paradigm of the self-selection macronutrient isolated diets [high-carbohydrate (high-CHO), high-protein and high-lipid food pellets]. At the same time, Fos expression was also evaluated in the MePD as a marker of local cellular activation. Adult male rats received icv microinjections of NPY (1mg and10mg/5mL, n = 10 and 8, respectively) whereas the control groups either received icv microinjection of artificial cerebrospinal fluid (5mL, n = 8) or underwent sham procedure (n = 8). The data were obtained after a fasting protocol. Feeding behavior was evaluated during a 2 h test period of free access to the selective diets. Rats in all groups preferred the high-CHO diet. Compared to controls, both doses of NPY increased the appetitive behaviors (searching for food and the frequency of attempts to eat any diet) and the percentage of animals eating high-CHO diet. However, only NPY at a dose of 1 μg led to a significant increase in food intake and showed a strong positive correlation with Fos expression in the MePD (p < 0.05 in all cases). These new data reveal a biphasic effect of NPY on the appetite and food intake behaviors and suggest that the MePD participates in the NPY-induced feeding behavior in rats.