Electrophysiological and endocrinological aspects of aging in the rat pineal gland.

Previous morphological and biochemical studies point to an age-dependent loss of pineal gland function. In order to investigate the possible alterations of electrical activity of aged rat pineal glands, electrophysiological recordings in 3- and 18-month-old male Sprague-Dawley rats were undertaken at both daytime and nighttime. Extracellularly recorded action potentials were characterized according to discharge frequency and serum melatonin levels were determined concomitantly. Significant differences in the frequency distributions between young adult and old rats were found to occur at nighttime, with a shift towards lower frequencies in old animals. Serum melatonin levels were reduced significantly in old rats and the characteristic nocturnal peak was attenuated. These results demonstrate a distinct decrease of pineal electrical and secretory activity with advancing age, which may contribute to an age-dependent decline of neuroendocrine capacity.