IMMUNOCYTOCHEMICAL IDENTIFICATION OF PHOTORECEPTOR PROTEINS IN HYPOTHALAMIC CEREBROSPINAL FLUID-CONTACTING NEURONS OF THE LARVAL LAMPREY (PETROMYZON-MARINUS)

Antibodies directed against different visual pigment opsins, and an an tibody raised against the C terminal of the alpha-subunit of retinal G protein (transducin) labelled cerebrospinal fluid-contacting cells lo cated within the hypothalamus (postoptic commissural nucleus and ventr al hypothalamic nucleus) of ammocoete lampreys (Petromyzon marinus). T hese antibodies also labelled photoreceptor cells within the retina an d the pineal and parapineal organs, but no other areas of the brain. D espite considerable behavioural and physiological evidence for the exi stence of deep brain photoreceptors, numerous studies have failed to i dentify photoreceptor proteins within the basal brain. The results pre sented in this paper support our recent results in the lizard Anolis c arolinensis, suggesting that a group of cerebrospinal fluid-contacting neurons within the vertebrate brain have a photosensory capacity. We speculate that these cells mediate extraocular and extrapineal photore ception in nonmammalian vertebrates.