DEMONSTRATION OF A DIRECT PROJECTION FROM THE RETINA TO THE HYPOTHALAMIC SUPRAOPTIC NUCLEUS OF THE HAMSTER

Hamsters were injected in the left eye with unconjugated cholera toxin subunit B (CHB) and the tracer was localized using immunohistochemistry. A large number of immunoreactive fibers was found in the suprachiasmatic nuclei and the contralateral lateral hypothalamic area. Labeled fibers coursed around the supraoptic nucleus and nerve terminals accumulated in a zone dorsally and laterally to the nucleus. Single fibers from this plexus penetrated into the supraoptic nucleus, where few fibers arborized into delicate immunoreactive profiles possessing varicosities. Labeled fibers were identified only in the dorsal and lateral parts of the nucleus, and mostly at the caudal level of the optic chiasm. These results show a direct retinal innervation of the magnocellular neurons of the supraoptic nucleus, and indicate a direct photic influence on the hypothalamo-neurohypophysial system.