Ultrastructure, ZIO-staining and chromaffinity of gerbil pinealocytes.

The ultrastructure and cytochemistry of the gerbil pineal gland were studied by the conventional electron microscopy, zinc iodide-osmium tetroxide (ZIO) staining and chromaffin reaction. Conventional electron microscopy revealed that the ultrastructure of gerbil pinealocytes are similar to other rodents, i.e., irregular cell contour with numerous cytoplasmic processes, round or oval nucleus and prominent nucleoli, elongated mitochondria with flattened and tubular cristae and dense matrix, well-developed Golgi apparatus and its associated structures, abundant elements of endoplasmic reticulum--both smooth and rough varieties, and bundles of microfilament and microtubule in the cytoplasm. Some pinealocyte processes contain numerous small clear and "slightly coated" vesicles. Numerous profiles of varicosities containing small dense-cored and clear vesicles were frequently encountered. After ZIO treatment, ZIO staining was preferentially localized in the cytoplasm of some, but not all, of the gerbil pinealocytes. Numerous small clear vesicles (30-50 nm in diameter) in the process of the pinealocytes or in the varicosities of the nerve fibers showed strong ZIO-philia. After chromaffin reaction treatment, the number and electron density of small clear and dense-cored vesicles in the profiles of nerve varicosities increased and this indicates that some of the small clear and dense-cored vesicles in the varicosities are reactive. It is thus concluded that (1) the vesicles in the pinealocytes may be rich in cystine and/or cysteine and possibly the organelle is involved in the sequestering calcium ion during the calcification of the pineal concretions, and (2) the small dense-cored and clear vesicles in the nerve fibers in the gerbil pineal parenchyma may contain both serotonin and primary biogenic amines.

Permeability of the pineal organ of the golden hamster (Mesocricetus auratus) to HRP with special reference to different types of blood capillaries.

The pineal organ of the golden hamster consists of deep and superficial portions which are connected to each other by a stalk. The permeability of capillaries for horseradish peroxidase (HRP) injected intravenously was examined in sections of entire portions of the gland that cut either along coronal or sagittal planes. Two distinct portions of the parenchyma, i.e., dorsal major and ventral minor ones, were found in the superficial gland. Most of the capillaries in the dorsal portion were of the continuous type of endothelium, whereas those in the ventral portion were fenestrated. In the dorsal portion, HRP readily crossed the endothelium, permeated the basal lamina, flowed into the perivascular connective tissue space and intruded into the intercellular clefts of the parenchyma. In contrast, HRP was not found to penetrate through the endothelium of the capillaries in the ventral portion to reach the perivascular area, thereby leaving the intercellular clefts of the parenchyma free of HRP. In the deep gland the capillaries were exclusively of the nonfenestrated type. Intravenously injected HRP was prevented from crossing the endothelium by the tight junction. In some areas, HRP penetrated through the capillaries in the pia mater, and crossed the outer limiting membrane to reach the intercellular clefts of the parenchyma and the basal lamina of the capillaries in the peripheral region of the deep pineal gland. The junctions between endothelial cells were not penetrated by HRP. The observations indicate that the type of capillary, absence of perivascular spaces, and permeability in the deep pineal are all similar to these factors in the general brain tissue; they differ from these in the superficial pineal gland, in which the dorsal portion shows characteristics found in other endocrine glands, but the ventral zone exhibits a unique situations: the presence of a blood-pineal barrier with a pericapillary connective tissue area.

Small granule-containing (SGC) cells in the hamster adrenal medulla.

In addition to adrenalin (A)- and noradrenaline (NA)-containing cells in the hamster adrenal medulla, a third type of small granule-containing (SGC) cells was identified. These cells were characterized by their small size (about 15 microns in diameter) and location adjacent to A-cells. Numerous pleomorphic dense-cored cytoplasmic granules (306 +/- 44.5 nm x 204.5 +/- 58.3 nm, mean +/- standard error) were present in their cytoplasm. The ultrastructure of these granules were similar to that of NA-containing granules but smaller in size. The granular inclusions of the granules were moderate to high in electrol density. The cytoplasm of the SGC cells contained short profiles of rough endoplasmic reticulum and some free ribosomes.