The pinealocytes of the human pineal gland: A light and electron microscopic study.

The pinealocytes of the pineal gland of children and adults were studied at both light and electron microscopic levels. The pinealocytes were classified into light and dark pinealocytes on the basis of their shape, nuclear infolding, cytoplasmic contents and staining density. The light pinealocytes outnumber the dark pinealocytes and both of them have thin processes. The light pinealocytes have round or oval cell bodies and nuclei and have vesicles and ribbons. The dark pinealocytes showed more variations in their shape. The nuclear membrane of the dark cells showed numerous infoldings with deep invagination of parts of the cytoplasm within the nuclear folds, giving the appearance of nuclear pellets. The dark pinealocytes contain pigment in their cytoplasm. In addition to the light and dark pinealocytes a very small cell type with an extremely thin and elongated cell body and nucleus was found. The cells of this type were almost always associated with vacuoles filled with flocculent material and accumulations of presumptive secretion in the extracellular compartment. The findings of this study were discussed in the light of the published data about the pinealocytes of human and non-human species.