Diffuse Nerve Net of Hydra Revealed by NADPH-Diaphorase Histochemical Labeling

The processing of the information coming from the external environment, including the interactions between molecular and cellular keyplayers involved in, is perhaps the “hard problem” in the cybernetic approach to the nervous system. As a whole, this information shapes the behavioral activity of an organism. The problem is faced considering the information processing flow in action from the lower organisms’ nervous elements to the higher cognitive levels of man. The cnidarian Hydra is the first organism of the zoological scale in which a nervous system is encountered. It is composed by isolated nerve cells scattered throughout the animal body constituting a diffuse nerve net for the input-output activity. In this paper is reported, for the first time in Hydra nerve net, the histochemical indication of a NADPH-diaphorase (NADPH-d) activity as putative marker of nitric oxide synthase (NOS) activity. The identification and the tentative localization of nitric oxide (NO) in Hydra is discussed in the light of the emerging role that such a signaling molecule exerts in sensory (visual especially) and motor neural systems.