Acta biologica HungaricaJan 1, 1997

Pinopsin in light-sensing cells of the pineal gland and eyes in different vertebrates

Circadian Biology Weekly Brief ↗PubMed ↗

Updated Feb 4, 2026

Abstract

Pinopsin has a strong immunoreactivity in most pinealocytes of birds and large photoreceptors in reptiles, with an absorption maximum at 470 nm.

Pinopsin is a newly identified opsin found specifically in the pineal gland of birds.
Immunoreactivity to pinopsin was observed in various vertebrates, including birds and reptiles, but was less pronounced or absent in mammals and less differentiated species.
Pineal organs show significant diversity across vertebrates, including additional organs like the parapineal in cyclostomes and fishes, and the parietal eye in reptiles.
The presence of pinopsin may indicate green-blue light sensitivity in the photoreceptors where it is found.
Photoreceptors in the avian retina and a cone in the reptile retina also showed immunoreactivity, suggesting potential functional similarities.

Simplified

Pinopsin is a pineal specific opsin newly identified in the pineal of birds which has an absorption maximum at 470 nm. As the opsin content of photoreceptors in the pineal complex of several species is not yet known, in the present work, we studied their pinopsin immunoreactivity in various vertebrates from cyclostomes to mammals. We also compared the immunoreactivity of pineal photoreceptors to that of retinal cones and rods of each animal. For the immunocytochemistry, we raised antibodies in rabbits against a 14 amino acids containing part of the chicken pinopsin molecule. The immunoreaction was performed at the electron microscopic level. The pineal organs show a great diversity in vertebrates: there is a pineal organ present from cyclostomes to mammals, in addition, there is a parapineal organ in cyclostomes and fishes, a frontal organ in frogs and a parietal eye in several reptiles. We detected a strong pinopsin immunoreaction on most of the pinealocytes of birds and on the large photoreceptor-type of the pineal of reptiles. Rod-type photoreceptors of the avian retina and a cone of the reptile retina was immunoreactive as well. According to the known absorption maximum of pinopsin, the immunoreactivity may indicate a green-blue light-sensitivity for these photoreceptors. The immunoreactivity was less pronounced or absent in mammals as well as in less differentiated species. The pineal organ of snakes and the parietal eye of reptiles equally failed to exhibit pinopsin immunoreactive photoreceptors, presumably, due to the absence of green-blue light-sensitive photoreceptors of pinopsin-type in these species.

Pinopsin in light-sensing cells of the pineal gland and eyes in different vertebrates

Abstract

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