Pinealocyte subsurface cisterns. I: Cytological aspects including three-dimensional structure.

Subsurface cisterns (ssc) in the pineal gland of Meriones unguiculatus have been characterized with transmission electron microscopy, freeze-fracture, morphometry, and three-dimensional reconstruction. Subsurface cisterns (which are observed only in pinealocytes and never in gliocytes) are cisterns of the endoplasmic reticulum (ER) approaching the plasmalemma at a distance of 15-20 nm. Freeze-fracture preparations show that except for some ribosomes at the cytoplasmic face, the cistern membranes as well as the related portions of the plasmalemma are free of special or specifically arranged particles or pores. All ssc have a lumen of 15-20 nm width and underlie 5.6% of the plasmalemma in a single layer; neither collapsed types nor stacks of ssc could be observed. As seen from reconstructions, large ssc are fenestrated and are situated preferentially in regions where the neighboring pinealocyte also bears large ssc. As a consequence, double-sided ssc, which can be observed in sections of (mostly large) ssc, are not a random phenomenon. In regions of the large ssc, adhering junctions are also concentrated. Tubules of 20-nm diameter link ssc with deeper parts of the ER, particularly with the perinuclear cistern and with the tubulo-cisternal network at the trans-side of the Golgi apparatus. Besides ssc proper, a lot of small endplates of ER-tubules are seen close to the plasmalemma. It is suggested that ssc form by the widening and fusing of such ER-tubules and decrease by retraction of ER-tubules from the cell surface.

Pinealocyte subsurface cisterns. II: Influence of time of day, sympathectomy, and castration.

Subsurface cisterns (ssc) of the gerbil pinealocyte were studied by electron microscopic morphometry taking account of different external influences: time of day, sympathetic deafferentation, castration with or without substitution of testosterone. Male individuals of Meriones unguiculatus, aged 150 days, were used. Though ssc number is invariant with respect to the light-dark cycle, ssc size follows a highly significant sinusoid curve. The largest ssc were found in the afternoon, the smallest ones in the early morning. Bilateral resection of the superior cervical ganglia reduces the density of pinealocyte ssc markedly, and their size is maximal or, in relation to the scaled-down cell, unusually large. Castration with or without application of testosterone propionate does not alter pinealocyte ssc, neither with respect to density nor size. From these experimental data it is concluded that pinealocyte ssc may play a supportive role in the regulation of pinealocyte sensitivity, in so far as it depends on receptors located in the cell membrane.

Pinealocyte subsurface cisterns. III: Storage of calcium ions and their probable role in cell stimulation.

Different techniques for the ultrastructural demonstration of calcium have been applied to the pineal gland of Meriones unguiculatus, attention being focussed on the endoplasmic reticulum (ER) and its subsurface cisterns (ssc). By means of a "loading" method [Walz, 1982; Wakasugi et al., 1982] it is shown that the pinealocyte ER-ssc system sequesters calcium with dependency on ATP. Furthermore, a modification of the method of Duce and Keen [1978] is presented which turned out a) to be sensitive enough to demonstrate the cell's own low amounts of calcium as fine granular precipitates, and b) to preserve ultrastructure sufficiently. This method rendered possible comparison of the calcium distribution inside pinealocytes of the following groups: animals fixed during daytime, animals fixed at night, animals fixed at night with prior exposure to bright white light, animals fixed at night but injected at the end of the preceding light period with a pharmacon known to prevent the release of calcium from the ER of muscle fibers (Dantrolen). In contrast to the daytime findings, the pinealocyte ER-ssc system at night is free of precipitable calcium; nocturnal illumination induces reacquisition, Dantrolen hinders nocturnal depletion. From the nocturnal coincidence of pinealocyte activity and calcium release from ssc, and from other cytological and experimental data, it is concluded that the functional significance of ssc refers to the regulation of pinealocyte sensitivity. Vice versa, pinealocyte activity may influence ER expansion and ssc size via the calcium-dependent stability of microtubules.

Meningeal calcification of the rat pineal organ. Finestructural localization of calcium-ions.

The surface of the pineal organ of the rat is covered by a leptomeningeal tissue, the continuation of the corresponding meningeal layers of the diencephalon. The pineal leptomeninx consists of stratified arachnoid and of pia mater cells which follow the vessels into the pineal nervous tissue. The pineal arachnoid contains electron-lucent and electron dense cells differing from each other in their cytoplasmic components. Corpora arenacea of various size and density occur among these arachnoid cells and can grow into the pineal organ alongside pia mater tissue. Acervuli often form groups in circumscribed meningeal "calcification foci". Concrements are absent or rare in the 1- and 2-month-old animal, while they are usually present in the 4- and 6-month-old rats. The electronmicroscopic localization of Ca-ions was studied in 2- and 4-month-old rats by potassium pyroantimonate cytochemistry. In the 4-month-old animals, arachnoid cells containing a varying amount of Ca-pyroantimonate deposits were found first of all around corpora arenacea, but there were also cells free of deposits in the close vicinity of the acervuli. Deposits were preferentially localized to the cytoplasm of electron dense arachnoid cells and to the cell membrane of electron-lucent cells. Most of the precipitates occurred in locally enlarged intercellular spaces. Here, microacervuli were found in 4-month-old animals suggesting that a calcium-rich environment was responsible for the appearance of the concrements. Intermediate stages between the small acervuli and large concentric corpora arenacea may indicate an appositional growth of the acervuli in the calcification foci.(ABSTRACT TRUNCATED AT 250 WORDS)