The Photoreceptor Cell of the Pineal Organ of Ayu, Plecoglossus altivelis

Abstract

Since the work of DODT1), attention has been directed to the photosensory function of the pineal organ of fish. This function is also indicated by recent electron microscopic studies using some kinds of fish2-5).In Ayu, light is known as the most important environmental factor in maturation of gonad6). In the fish the photosensitivity of the pineal organ was confirmed electrophys iologically7,8). In the previous paper9), we described the light microscopic structure of the pineal organ of Ayu. The present paper deals with the fine structure of pineal receptor cell in Ayu, with special reference to photosensory function. Materials and MethodsFifteen adult specimens of cultivated Ayu, Plecoglosstus ahivelis were used. These fish were about 20cm in body length and obtained in July and August, 1968.The pineal organs of these fish were fixed for 1.5 to 2.0 hours in the following fixatives adjusted at pH 7.4: 1% OsO4 in MILLONIG'S10) and SORENSEN'S phosphate buffer solutions or 1.3% OsO4 in s-collidine buffer one11). After dehydration with in creasing ethanol series, they were imbedded in Epoxy resin12). Thick and thin sections were made on Porter-Blum MT-l microtome.Thick sections were stained with toluidine blue13) for light microscopy. Thin sections were stained with uranyl acetate14)-lead citrate15) and observed with Hitachi HU-IIA type electron microscope. Results and DiscussionThe pineal organ of Ayu has a wide lumen (pineal lumen) in the central portion and pseudostratified epithelium of the organ is divided into many folds. Under light mi croscopy, the cytoplasmic process protruding into the lumen was detected occasionally9).This process seems to correspond to the inner and outer segments of photoreceptor cell in electron microscopy. In the thick sections, small round processes covered with cap like structure were detected along the edge of fold. (Fig. 1) This cap-like structure * This investigation was supported by a research grant of the Ministry of Education.

Immunocytochemical Localization of Taurine in the Pineal Organ and Retina of an Anadromous Fish, Plecoglossus altivelis.

“…The outer segments of pineal photoreceptors indicate structural features similar to retinal photoreceptors of higher vertebrates, although they dramatically change their appearance within their lifespan of one year (OMURA et al, 1969;OMURA and OGURI, 1971). The supporting cells, exhibiting an electron-dense cytoplasm, possess irregularly extended cytoplasmic processes which surround the perikarya of the photoreceptors and the pineal nerve cells.…”

“…As mentioned elsewhere (OMURA, 1980(OMURA, , 1984OMURA et al, 1969;OMURA andOGURI, 1971, 1991), the pineal parenchyma of the ayu is composed of well-constituted photoreceptors, supporting cells and nerve cells. The outer segments of pineal photoreceptors indicate structural features similar to retinal photoreceptors of higher vertebrates, although they dramatically change their appearance within their lifespan of one year (OMURA et al, 1969;OMURA and OGURI, 1971).…”

The effects of constant light and constant darkness on daily changes in the morphology of the pineal organ in the goldfish,Carassius auratus

“…This relationship suggests that the outer segment membranes are periodically shed during the dark phase, a pattern similar to that of the retinal cone cells, but not the rod cells (Balkema andBun6 1981, O'Day andYoung, 1978). On the basis of fine structure, photoreceptor cells in the pineal organ of fishes have been described as resembling retinal cone cells because of continuity of the outer segment saccules with the plasma membrane (Oksche, 1971;Omura et al, 1969;Rudeberg, 1969;Takahashi, 1969). However, the electrophysiological response and sensitivity of these cells have been described as being more like that of retinal rods (Hanyu et al, 1978;Tabata et al, 1975).…”

Anatomical and histological investigation of the pineal gland in the lake van fish (Alburnus tarichi (Güldenstädt, 1814))

“…The pineal organ is attached to the roof of the diencephalon by a thin stalk. It is located tangentially to the brain at the midline where the telencephalic hemispheres intersect with the optic tectum (Omura et al, 1969).…”