We investigated about the kisspeptin neurons, which is known as the center of reproductive regulation and integrate the several information in the brain to relay to the HPG axis. Actually, we clearly investigated 1) the subcellular localization of kisspepin, NKB, and dynorphin in the KNDy neuronos, which are coexpressed kisspepin, NKB, and dynorphin in the arcute nucleus by immunoelectron microscopy, 2) the interrelationship between the change of kisspetpin neurons and athe change of reproductive function with aging, 3) the mapping of kisspeptin receptor expression in the rat brain, and 4) the change of expression of kisspepin of certain kind of model animals suc as PCOS an/or hypothyroidism.