Preliminary histochemical and electron microscopic observations on the nervous system of hydra.

: The nervous system of a primitive Coelenterate (Chlorohydra viridissima) has been studied using ultrastructural and histochemical techniques. The authors confirm the ultrastructural pattern of nerve cells described by Lentz and coworkers. Reserpine treatment fails to induce any reduction of catechol- and indoleamine content visible to histochemical observation. In vivo treatment with tetanus toxin does not induce behavioural changes and no specific binding of toxin is revealed by immunocytological analysis. This suggests that neuron tetanus toxin receptor sites are absent in hydra. Hydra nerve cells must therefore be considered as extremely primitive elements, which the Authors consider to support the hypothesis of neurons having originated as a gradual differentiation of myoepithelial cells, as proposed by Pantin (1956) and by Passano (1963).