Doctor of Philosophy
Anatomy & Neurobiology
Hugo R. Seibel
The pineal complex of rodents is made up of a pineal organ which developmentally always originates from the area between the habenular and posterior commissure and a pineal sac which is continuous with the choroid plexus of the third ventricle. This sac appears to be identical to the choroid plexus at both light and electron microscopic levels. The pineal sac abuts the deep and superficial pineal organs of the golden hamster. In the PET mouse, gerbil, kangaroo rat and Chinese hamster, the sac is contiguous with only small areas of pinealocytes. This sac never abuts true pineal parenchyma in the albino rat. The variability of the relationship between this sac and pineal parenchyma indicates that this structure may not be the main physiological route of pineal gland secretion.
The ultrastructure of pinealocytes from normal and blinded PET mice and normal and blinded gerbils indicate s the possibility of secretory activity in pinealocytes. Pinealocytes in the PET mouse have many dense core vesicles which can be found in the perykaryon, processes, and polar terminals of the cells which end in a pericapillary space. This space is near a fenestrated capillary. The possibility exists that these dense cored vesicles may be extruded from the cell terminals and pass into the fenestrated capillaries. Such fenestrated capillaries commonly are found in endocrine organs.
The gerbil pinealocyte has two types of granules. Their nature is unknown, and the relationship between the two is uncertain. Small granules, resembling the small granules in gerbil pinealocytes in size and density, can be found in intercellular and pericapillary spaces. The relationships between these two granules is equally in doubt.
The ultrastructure of pinealocytes of PET mice and gerbils reflects changes with blinding. Pinealocytes of blinded PET mice are more vesiculated and have greater numbers of lipid droplets. The pineal glands of those blinded gerbils, which were known to be highly functional by their physiological effects on the gonads, contained large electron dense structures. They were found in unidentified cell processes, interstitial cells, and pinealocytes. Pineal glands from a greater number of animals will have to be studied and compared with those of the same species reflecting low pineal activity in order to verify the relationship between pineal activity and these large electron dense structures. Histochemical analyses would be essential to identify and to clarify the relationships and activities among these vesicles, granules, and electron dense structures in pinealocytes of PET mice and gerbils.
Blinding of the golden brown hamster and the gerbil resulted in a significant decrease of testis and seminal vesicle weight. This effect in the gerbil occurred during the fall season but when repeated during the winter season resulted only in the decrease of seminal vesicle weight. Female gerbils, however, responded to blinding by a decrease in ovarian and uterine weights during the winter season but only in uterine weight during the fall season. All of these effects of a lack of light on the gonads were prevented if the animals were also pinealectomized. The effects of olfactoriectomy which resulted in a decrease in seminal vesicle weight in one series of gerbils could also be overcome by pinealectomy. The pineal gland then may be responsible for production of an antigonadic substance. with the pineal gland removed the antigonadic source is removed, and the testis and/or seminal vesicle weights remain normal. A lack of light appears to stimulate the pineal gland to function since pinealectomy alone did not effect an increase in reproductive organ size in any of the animals which we studied.
The albino rat and PET mouse did not respond to a lack of light as did the hamster and gerbil. Moreover, in the PET mouse, blindness did not affect prepubertal or postpubertal animals, adults during different seasons of the year, or adults treated neonatally with testosterone propionate. Female PET mice and male wild mice were equally unaffected.
An effect of the pineal gland on the pituitary gland and adrenal gland is doubtful. Animals with or without a pineal gland exhibited no difference in pituitary or adrenal weights. More sensitive techniques will have to be employed to determine pineal-pituitary and pineal-adrenal interactions.
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