effects of aging and vincamine administration on the structure of the rat pineal gland

ABSTRACT

The pineal tissue was studied in four groups of male albino rats a group of adult rats, a second group of senile rats, the third and fourth groups consisted of senile rats which were injected with the vehicle of vincamine drug and the drug itself respectively in their old adult stage of life. The investigations showed that the adult pineal gland was characterized by high cellularity, and two types of cells were observed; the pinealocytes and the glial cells. The pinealocytes constituted the majority of cells and were of two types; light and dark, while the glial cells were fewer, smaller with ramifying thin processes. Using electron microscopy, the cytoplasm of light pinealocytes was noted to be rich in secretory organelles, containing euchromatic nuclei and with prominent nucleoli. On the other hand, the dark pinealocytes appeared more electron dense with less amount of organelles and heterochromatic nuclei in their cytoplasm. Glial cells appeared as small cells of high electron density with thin ramifying processes full of filaments and large dark heterochromatic nuclei. Senile pineal glands of both the second and third groups showed marked decrease in the cellularity, irregularity and in folding of the nuclei were a prominent feature. By electron microscopy, the light pinealocytes showed marked decrease in the amount of secretory organelles together with the appearance of lipid droplets, lysosmes, and dense bodies. In addition, the nuclei of this type showed deep indentations. The cytoplasm of dark pinealocytes showed abundant multivesicular bodies and deeply indented heterochromatic nuclei. The glial cells had to same structure as in the adult glands. The study of the pineal tissue in senile animals which were previously treated with vincamine showed marked increase in the cellularity, and the majority of cells were of the light variety. By electron microscopy, the cells had the picture of highly active cells. The light pinealocytes were rich in mitochondria and secretory organelles such as dilated cisterns of endoplasmic reticulum, and Golgi apparatus. On the other hand, lysosomes, lipid droplets and dense bodies were hardly observed. The nuclei of these cells were either oval or irregular and of the euchromatic appearance. The dark pinealocytes showed secretory organelles in their cytoplasm but less abundant than those observed in the cytoplasm of the light cells. The nuclei, although of high electron density, yet they were of the euchromatic appearance. According to the present investigation, it could be concluded that the currently discussed drop in melatonin synthesis in old age is due to regressive changes in the morphology of the gland. Moreover, the use of vincamine may prevent or delay the appearance of such degenerative changes. This may preserve the melatonin synthesis in the body and consequently delays the aging process