Abstract
Autonomic nervous system (ANS) plays a crucial role for the viability of animals by regulating physiological activity of organs. Since ANS is located in the brainstem, the most ancient part of the brain, it has been a general understanding that ANS originated early in vertebrate evolution or even earlier. However, no attempts have been made to determine how far we can trace the ANS back in evolution. In this presentation, based upon a series of physiological studies carried out in Hydra, we present a hypothesis that the ANS originated in its primitive form very early in metazoan evolution, as early as in phylum Cnidaria or in Plathyhelminths which had gastrovascular cavity. [Jpn J Physiol 54 Suppl:S203 (2004)]
