UV-visible antagonism in extraocular photosensitive neurons of the anthomedusa, Spirocodon saltatrix (Tilesius).

Attempts were made to identify extraocular photosensitive cells in the subtentacular region (the area between the ocelli and the nerve ring) and around the inner-nerve ring of the anthomedusan Spirocodon saltatrix. Irradiation with ultraviolet light (UV) led to inhibition of spontaneous impulses and after UV-off, an afterinhibition which lasted for a few minutes. This afterinhibition was rapidly overcome by exposure to visible light (VIS). UV-VIS antagonism of this type was identified in six different impulse systems monitored in extracellular recordings. Intracellular recordings from two of the six cell types showed that UV irradiation causes hyperpolarization which inhibits spontaneous activity. The other cell types showed no membrane potential changes during UV irradiation even though the cells' spontaneous outputs were inhibited. It was concluded that the photosensitivity lies in three kinds of nerves which are distributed widely through the subtentacular region and the nerve ring.