Influence of sleep deprivation coupled with administration of melatonin onthe ultrastructure of rat pineal gland

The effects of sleep deprivation with or without melatonin treatment on the pineal morphology in rats were studied. Five days after sleep deprivation and using electron microscopy, many of the pinealocytes exhibited structura l alterations including dilation of the cisternae of the rough/smooth endop lasmic reticulum, Golgi saccules and mitochondria, and an increase in the n umbers of lipid droplets, vacuoles and dense-core vesicles. These features were considered as morphological evidence of increased synthesis or secreti on by the pineal gland. In addition, numerous membranous profiles, consider ed to be degraded cellular organelles, were observed in some pinealocytes a nd sympathetic nerve terminals. It is suggested that the occurrence of dege nerating organelles had resulted from the deleterious effect of sleep depri vation. This may be attributed to an overload of secretory activity of the pineal gland during stress elicited by the long-term sleep deprivation, lea ding to functional exhaustion and irreversible damage of the oxidation-rela ted organelles. In sleep-deprived rats receiving a single injection of mela tonin (10 mg/kg) for 5 consecutive days, the above features indicative of p inealocytic activation were attenuated. In fact, all signs of degeneration of cellular organelles were rarely found. These results suggest that the pi neal gland is itself a target for exogenously administered melatonin. Thus, melatonin when administered systemically may be used as a potential neurop rotective drug against neuronal damage induced by sleep deprivation. (C) 20 01 Elsevier Science BY. All rights reserved.