Effect of melatonin on ram adrenal gland 1179
Fig. 6. Transmission electron microscope images of the zona reticularis in the control and treated group. a,b: The cells in the control group contained heterochromatic nucleus (N), smooth endoplasmic reticulum (sER), and stacks of rough endoplasmic reticulum (rER), mitochondria (M). Note, distinct desmosome- like attachments delimited intercellular canaliculi with large coated pits or vesicles (square) and these canaliculi were opened into subendothelial space (arrow in b). c,d: The cells in the treated group were closely packed with mitochondria (M). Noticeable proliferation of sER, well-developed Golgi apparatus (G), ribo- somes (R) were recorded in these cells.
stacks or in circular arrays and associated with ribosomes (Fig. 8c). The A-cells were crowded with granules and A- and NA-cell cytoplasm was provided with typical nerve endings (Figs. 8c, 8d).
Exocytosis The control group Exocytosis could not be observed in both A- and NA-storing cells as they might be expressed ultra- structural features suggestive of a slow mode of granule discharge. The treated group Excessive granules discharged from the chromaffin cell membranes to the blood vessels were demonstrated (Fig. 9a). Small localized invaginations of the apical cell surface may represent a point of previous dis- charge of a chromaffin granule or pinocytosis. The apical part of the cytoplasm might be empty, suggesting a recent hormonal secretion, and the granular contents could be observed being discharged in the immediate vicinity of the cell (Fig. 9b). Some granules, which lay in peripheral parts of cells, showed varying degrees of contact and fusion with the plasma membrane of chromaffin cells. The chromaffin granules moved toward the peripheral cytoplasm and aug- ment granule density beneath the plasma membrane, showing a release of granule materials to the perivascular space. Opposite the point of discharge, the adjacent
Fig. 7. Transmission electron microscope images of the chromaffin cells in the control group. a,b: Chromaffin cells contained secretory granules (G) and the desmosomes (square, inserted Fig. in b)were evident and existed along the opposing cell surfaces. Also, their cytoplasm contained mitochondria (M), Golgi apparatus (GA), free ribosomes (R), and rough endoplasmic reticulum (rER). c: The noradrenaline (NA)-cell contained electron-dense granules (arrow- head) and numerous membrane-bound vesicles with electron-lucent content. Note, some vesicles fused with the perigranule membranes in the process of attachment to or budding from the granules (arrows). d: Adrenaline (A)-cell granules were rounded to rod in shape (arrowheads) with highly electron-dense cores.
basement membrane showed a slight invagination or thin- ning. This method of discharge was observed on the free surface of chromaffin cells adjacent to blood vessels and connective tissue spaces, as well as on those surfaces adjacent to the junctional intercellular spaces (Fig. 9c). An alternative mechanism of chromaffin cell secretion is
recognized for the first time in rams in our result, referred to as “kiss-and-run” exocytosis, that was well-distinct in the treated group (Fig. 9d). In this process, chromaffin granules would release their constituents by piecemeal degranulation (PMD). PMD implicated the formation and detachment of small, membrane-bound vesicles (150 nm in diameter) from the surface of chromaffin granules. These vesicles contained little chromaffin materials that transfer them to the extra- cellular space through a process of fusion with the plasma membrane. Thus, the chromaffin granule released its content without any direct opening to the cell exterior. To confirm that, many small, membrane-bound, electron dense or lucent vesicles have been recognized free in the cytoplasm of adre- nal chromaffin cells. Some chromaffin granules displayed irregular profiles with budding or tail-like projections, intermingled with normal, resting granules, which supported a process of vesicle detachment from the granule limiting
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