Structure of the pineal gland in the adult cat.

The ultrastructure of the pineal gland in the adult cat is described and compared with that of other mammals. Connective tissue spaces showed capillaries with nonfenestrated endothelia and numerous unmyelinated nerve fibers. In the proximal region of the gland, myelinated nerve fibers coming from the anterior commissure were also found. Cat pinealocytes showed a nucleus with prominent nucleoli, a well developed Golgi apparatus, centrioles, granular endoplasmic reticulum, ribosomes, abundant microtubuli and enlarged mitochondria. Pinealocytes showed several long processes with bulbous endings filled with clear vesicles and scarce "synaptic" ribbons. Pineal astrocytes and their processes were characterized by the presence of abundant filaments.