Ultrastructural morphology of the aged pineal.

Thirty-four pineals of 18-month-old rats were studied, of which 12 belonged to animals exposed to 7% and 13 to a group exposed to 10% oxygen in breathing gas. Nine pineals were from controls kept under normoxic conditions. For comparison 2 pineals of 6-week-old rats were also examined. No influence of hypoxia on histology of the pineal gland can be stated. In this the pineal behaves like other parts of the rat brain, which in previous experiments has been shown to adapt well to low-oxygen concentrations. Also no important difference between pineals of young and advanced aged rats were found by us. In 8 of 34 pineals striated muscle cells were present. We consider this an important finding, as pineal cells have a unique differentiation potential in cell culture systems and in tumorous lesions of the pineal. As rats exposed to severe hypoxia exhibit body organ changes indicating stress, it would be interesting to measure melatonin secretion and pineal melatonin content under prolonged and increasing hypoxic conditions.