Parenchyma of the cat pineal body consisted of pinealocytes and glial cells. The pinealocyte, predominant cell type, was characterized by having large mitochondria with pale matrix, abundant polyribosomes, moderately-developed Golgi apparatus, centrioles and occasional cilia. The pinealocyte had one thick and long cytoplasmic process at the one pole of the cell, and slender and shorter processes at the other pole, and in addition occasional short processes from the cell body. These processes contained longitudinally arranged microtubules, and a few mitochondria. Thick processes teminated as bulgings either in the intercellular process-rich area, or in the perivascular border which was formed by glial cell processes. These endings of pinealocyte processes had many small vesicles, mitochondria, and occasional dense bodies. Glial cells with abundant filaments of intermediate type and clear cytoplasmic matrix were fibrous astrocyte. Perikarya of the astrocytes had small and dense mitochondria, moderately developed Golgi apparatus, dense bodies and variable amount of intermediate filaments. Glial cell processes run through the intercellular spaces among the pinealocyte processes. Glial cell of protoplasmic type had no or a few filaments, but it had well-organized rough endoplasmic reticulum, dense mitochondria, well developed Golgi apparatus and many dense granules. Intercellular canaliculi formed by adjacent pinealocytes and glial cell processes were often noted. Within the parenchyma, sympathetic and parasympathetic axons and their endings were noted. These endings were present mostly in the intercellular spaces without having membrane specialization, however, in rare instances, ending with small clear and dense cored vesicles, and large dense cored vesicles formed specialized synapse with a pinealocyte process. Within the perivascular spaces nerve fibers and endings, Schwann cells and pericyte were noted. In rare case pinealocyte process penetrated into the perivascular space through the interuptions of glial border.
These results suggest that pinealocyte of the cat has less significance in secretory function and is rather neural type of cell.
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