Photic input to rat pineal gland conveyed by both sympathetic and central afferents

Average photic evoked responses were recorded from the pineal in light and dark adaptation. Permanent semimicroelectrodes were implanted several days before the experiments were begun. Local anesthesia (xylocaine) at the superior cervical ganglion (scg) level was used as a tool to determine whether or not photic responses are transmitted via the scg and/or through another CNS route. The experiments demonstrated that in dark adaptation, photic evoked responses recorded from the pineal exhibited higher amplitude. Moreover, the photic evoked responses are transmitted via two separate routes: one, a faster pathway with a "shorter" latency, via the CNS, i.e. the habenular posterior commissure complex, and the other a "slower" (or longer) pathway via the reticular formation scg to the pineal.