Light-evoked neural activity in the intermediate lobe of the pituitary of Rana pipiens: Electrophysiological evidence for a neural pathway linking the eyes with the pars intermedia

Neural activity was recorded from the pars intermedia of Rana pipiens whose heads were fastened in a molded plastic holder equipped with fiber optic light guides for the selective illumination of the lateral eyes and the pineal region. The major findings of this study are as follows: (I) Illumination of the eyes influences the discharge of some neurons which terminate in the pars intermedia; (2) Single units which responded to illumination of the lateral eyes were ‘on-type’, i.e. they responded to the onset of illumination with a burst of impulses and discharged at an increased average rate throughout the period of illumination; (3) `On-type’ units were binocular, responding to illumination of either the right eye or the left eye individually; (4) The latencies of responses to light suggest that a neural pathway links the retinae of the lateral eyes with the pars intermedia; and (5) Illumination of the pineal region had no detectable effect upon neural activity in the pars intermedia and no effect of illumination could be detected in blinded animals.  The results of this study indicate that a neural pathway exists connecting the lateral eyes with the intermediate lobe of the frog pituitary. These observations are consistent with the hypothesis of Hogbkn and Slomk [1936] that the lateral eyes provide the photic information which regulates the output of the pars intermedia, and they provide the most compelling evidence yet obtained for a rctinohypophysial neural pathway.