On the occurrence of a myeloid body in pinealocytes of the white-footed mouse, Peromyscus leucopus. An electron-microscopic study.

The fine-structural features of pinealocytes of the white-footed mouse, Peromyscus leucopus, were examined. A single population of pinealocytes was observed in both superficial and deep components of the gland. Cells in both locations are characterized by the presence of an indented nucleus exhibiting a prominent nucleolus. The usual organelles in the perikaryon are the Golgi complexes, mitochondria, endoplasmic reticulum, polysomes, microtubules and dense-core vesicles. In addition the perikaryonal cytoplasm often contains a single myeloid body. These bodies are usually lenticular in shape, are formed of an array of flattened membranous cisternae, and are not bounded by a limiting membrane. This organelle usually lies in the vicinity of the nucleus and is infrequently associated with lipid bodies. Complex forms were also observed. The cisternae are continuous with elements of the endoplasmic reticulum at points along their expanded rims. The outer surface of the cisternal membrane exhibits a granularity or fuzziness. The cisternae may be fenestrated. Pinealocyte processes with an abundance of clear vesicles, and some dense-core vesicles and vesicle-crowned rodlets are present in the parenchyma.