ELECTROPHYSIOLOGY AND INNERVATION OF THE PHOTOSENSITIVE EPISTELLAR BODY IN THE LESSER OCTOPUS ELEDONE-CIRRHOSA

The innervation and responses to light of the cephalopod epistellar bo dy were investigated in preparations isolated from the stellate gangli a of the lesser or northern octopus, Eledone cirrhosa. Extracellular g enerator potentials in response to flashes of Light were recorded from these photosensitive vesicles, with the amplitude of the response bei ng found to be dependent upon the intensity of the flash and the level of ambient illumination. Intracellular recordings from photoreceptor cells of the epistellar body showed that they had resting potentials o f about -49 +/- 7 mV (mean +/- SD, n = 43) and were depolarized by fla shes of white, but not red (>650 nm) light. The evoked depolarization consisted of a transient component, followed by a steady plateau in wh ich the amplitude of the depolarization was well correlated with the l og of the stimulus intensity. The evoked depolarizations induced actio n potentials in the photoreceptor cells, with the frequency of firing being well correlated with the stimulus intensity. The morphologies of individual photoreceptor cells were visualized by intracellular injec tions of the fluorescent dye Lucifer yellow, and the path of the epist ellar nerve across the stellate ganglion, into the pallial nerve, towa rd the brain was traced using the Lipophilic dye Di-I. This pathway wa s confirmed physiologically by recording Light-evoked responses from t he cut end of the pallial nerve.