Early receptor potential from the pineal photoreceptor.

Rapid photoresponses were obtained from the pineal organ of Rana catesbeiana and Rana esculenta comparable to the early receptor potential (ERP) of the retina of their lateral eyes. Light source was a xenon filled discharge tube with a maximum energy input of 365 J. The flash duration was 600 mu sec measured at 1/3 peak amplitude. The response pattern of the ERP of the exposed Epiphysis cerbri (intracranial portion of the frog's pineal organ) resembled the ERP of the isolated retina and the R1 deflection of the ERP of the eye-cup. It was greatly diminished during consecutive flashes and was absent during light adaptation. It was confined to the Epiphysis cerbri and was similar in time course and shap to, though smaller as, the ERP of the isolated retina. The photoresistant component of the ERP in the eye-cup was lacking in the Epiphysis cerbri and in the isolated retina. The action spectrum of the ERP of the Epiphysis cerbri closely resembled the photopigment absorption of rhodopsin indicating that the structural cones of the pineal organ contain a photopigment different from the retinal cones of the frog's lateral eye.