OPSIN-LIKE IMMUNOREACTIVITY IN THE CIRCADIAN PACEMAKER NEURONS AND PHOTORECEPTORS OF THE EYE OF THE OPISTHOBRANCH MOLLUSK BULLA-GOULDIANA

Circadian pacemaker cells in the eyes of the opisthobranch mollusc Bul la gouldiana generate a near 24-h rhythm in the frequency of optic ner ve impulses. Previous electrophysiological studies suggest that these basal retinal neurons are intrinsically photosensitive and transduce l ight signals that shift the phase of their pacemaker mechanism. To tes t whether the pacemaker neurons contain opsin-like proteins, several p olyclonal antibodies that recognize opsins of vertebrate photoreceptor s have been tested on histological sections of the eye and on the neur ons in primary cell culture. The antibodies label both the pacemaker c ells and the large distal photoreceptors that surround the lens. Immun oblot analyses of the proteins of the eye have identified a single ban d at 62 +/- 4 kDa. These opsin antibodies may label the photopigment u sed in the entrainment of the circadian pacemaker.