Food intake is regulated by both central and peripheral mechanisms. In the central nervous, the hypothalamus acts for autonomic and endocrine homeostasis. The paraventricular nucleus(PVN) of hypothalamus is an imprtant site of interaction in central feeding pathways. Neuroepetide Y(NPY)is one of the most powerful neurochemical stimulants of food intake known. Also brain nitric oxide(NO), known as neurotransmitter, is involved in the mechanisms that regulate food intake. In this experiment, 24h fasting mice and anorexia mutant mice have been to examine the expression of NPY, which is the major neuropeptide increasing food intake. Double staining with NPY and nicotinamide-adenine-dinucleotide-phosphate diaphorase(NADPH-d), followed by immunohistochemical method and image analysis, have been used to observe coexisting neurons and the level of expression of each neurons. The results were as follows. 1) NPY-immunoreactivitys reduced immune response of the hypothalamus, particularly paraventricular nucleus(PVN), in anorexia mutant mice. Decreased level of NPY is assumed to be a major pathological factor in anorexia mutant mice. On the other hand, PVN in hypothalamus of fasting mice showed increased immunoreactivity which is in agreement of other researchers. 2) NPY and NADPH-d double staining revealed coexisting neurons in the cerebral cortex. Fasting mice had a tendency to have increased level of coexisting neurons compared to the control group. Compared to the control group, fasting mice express is not increase level of NPY-immunoreactivity, while anorexia mutant mice tended to have a decreased level.