Electron microscopic observations on the mouse pineal, with particular emphasis on its secretory nature.

The generally accepted view as to the nature of the mammalian pineal is that this organ has secretory activity, but the evidence available, especially the morphological one, is far from sufficient. Recently the pineal of various animal species has been examined repeatedly by electron microscopy (MILOFSKY 1957, GUSEK and SANTORO 1961, DE ROBERTIS and PELLEGRINO DE IRALDI 1961, ANDERSON 1965, GUSEK, BUSS and WARTENBERG 1965, WARTENBERG and GUSEK 1965, WOLFE 1965, DUNCAN and MICHELETTI 1966, RODIN and TURNER 1966, SANO and MASHIMO 1966, ARSTILA 1967, LIN 1967, LEONHARDT 1967, FUJIE 1968, WARTENBERG 1968), but it still remains to be determined whether or not the organ is really glandular at the ultrastructural level. With the electron microscope DE ROBERTIS and PELLEGRINO DE IRALDI (1961) first demonstrated the secretory structure of the rat pineal. They showed that the secretory material is concentrated as vesicles of various forms in the pineal cell processes extending in the perivascular spaces. These findings, however, were later corrected by DE ROBERTIS (1964), since on re-examination the cell processes which had been interpreted as secretory processes of the pineal cells were judged to be nerve endings. The pineal of the mouse was examined by electron microscopy in the present study, since no description was available on the fine structure for this animal. We could recognize characteristic vesicles both in the pineal cells and in the nerve endings. Especially the presence of vesicles in the pineal cells could be regarded as suggesting a secretory activity of the cells. The present paper, therefore, deals primarily with the glandular nature of the pineal in relation to the possible significance of the vesicles in the pineal cells.