SYNAPTIC RIBBON IN THE HUMAN PINEALOCYTE

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Abstract
An EM study of a pineal gland which had been obtained from a 3 yr old girl at autopsy revealed the presence of a synaptic ribbon. In some parenchymal cells observed, synaptic ribbons, each of which was about 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 that the mammalian pinealocyte is homologous to the photoreceptor cell of the pineal organ in lower animals, and one of the pieces of morphological evidence which supports this speculation is the presence of sensory cell elements in both.