Light- and electron-microscopic demonstration of immunoreactive opsin in the pinealocytes of various vertebrates

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Abstract
Summary An antibody to opsin isolated from rod outer segments of the frog retina was applied in light- and electron-microscopic immunocytochemical studies to the pineal organ of various vertebrates (Cyprinus carpio, Carassius auratus, Rana esculenta, Emys orbicularis, Pseudemys scripta elegans, Lacerta agilis and viridis, Gallus domesticus, Columba livia, Melopsittacus undulatus, Serinus canaria, Taeniopyga punctata, Didelphis virginiana, Erinaceus roumanicus, Myotis myotis, rabbit, rat, cat). A strong immunoreaction was visible in the outer segments of the pinealocytes of one anuran and several teleost species. The outer segments of pinealocytes in the chelonian reptiles and birds also contained immunoreactive opsin. Ultrastructurally, PAP complexes were localized to the photoreceptor membranes of the outer segments. Immunoreactivity for opsin could not be demonstrated in the lacertilian parietal eye and pineal organ. In the opossum (Marsupialia), pinealocytes remain in contact with the intrapineal invaginations of the pineal recess. In insectivores, the cilia of the pinealocytes exhibit a relation to glial cells similar to that between the outer segments of retinal photoreceptors and the pigment cells. The cilia of mammalian pinealocytes did not show a clear-cut immunoreactivity to opsin with the electron-microscopic technique employed.