The pineal gland of the aging rat: calcium localization and variation in the number of pinealocytes.

In the present study, we investigated the population of pinealocytes in the pineal gland of aging rats. Dark and light pinealocytes were analyzed as to their calcium content. Calcium localization was realized in dark and light cells by means of cytochemistry and X-ray microanalysis. Calcium was mainly localized in dark pinealocytes characterized by many ultrastructural signs of degeneration. The number of pinealocytes per square surface of aged rats (28 months) was compared to young ones (3-4 months). While there is a significant increase in the number of dark pinealocytes there is a decrease in the total number of pinealocytes in aged rats. This age-related loss of pinealocytes may explain the age-related functional decline of the pineal gland activity (e.g., the decrease of the nocturnal melatonin production).