Characterization of the light response in the pineal gland of intact and sympathectomized rats.

Electrophysiological recordings were performed in the pineal gland of pigmented rats BD9 to investigate the possible contribution of a direct neural connection of the gland with the central nervous system in the transmission of photic information. Extracellular potentials were recorded during brief photic stimulation of the eyes before and after bilateral sympathectomy. Two types of responses could be distinguished in intact as well as in sympathectomized rats: spontaneously active units which were unresponsive to light flashes and units responding to photic stimulation with ON and ON/OFF discharges. Spectral sensitivity curves recorded from the pineal organ of dark adapted rats showed a maximum at 500 nm. Interruption of the sympathetic innervation by bilateral denervation or removal of the superior cervical ganglia did not alter the spectral properties of pineal units. Additionally, response-intensity curves and response threshold (about 0.0017 microW/cm2) were not changed after sympathectomy. These results suggest that the pineal gland of the rat receives projections from the visual system via a central pinealopetal innervation.