Synaptic ribbon in the human pinealocyte.

An electron microscopic study of a pineal gland which had been obtained from a 3-year-old girl at autopsy revealed the presence of synaptic ribbon in it. Namely, in some parenchymal cells observed, synaptic ribbons, each of which was ca. 700 nm in length and with synaptic vesicles of up to 60 nm in diameter gathering on the surface, were found in the cytoplasmic area adjacent to the cell membrane. The substructure of the synaptic ribbon, i.e., parallel striae running inside along the longitudinal direction, was definitely observed. There is a hypothesis which has been almost accepted that the mammalian pinealocyte is homologous to the photoreceptor cell of the pineal organ in lower animals, and one of the morphological evidences which supports this speculation is the presence of sensory cell elements in both. Since, this kind of work has been hardly done with human materials, the above finding may offer a meaningful information which discloses a part of the real function of the pineal gland in man.