Thus, the herein-shown fluctuations of circulating leptin and its signaling in ABA rats might contribute to set the stage for the transition to AN via persistent, albeit different, changes in the dHip and vHip LepR/JAK2/STAT3 signaling pathway that cannot be ascribed to a generalized effect of malnutrition or exercise alone. The gene discussed is JAK2; the disease is nutritional deficiency disease.