EFFECT OF MAGNETIC-FIELD ON PINEAL-GLAND VOLUME AND PINEALOCYTE SIZE IN THE RAT

Light microscopic observations on the superficial pineal gland of Wist ar-King rats were made to examine whether or not pineal volume and pin ealocyte size, expressed as nuclear density, at daytime or nighttime a re affected by long-term exposure to 50 Hz rotating magnetic field (MF ) at 5.0 muT. Determinations of pineal volume and pinealocyte size wer e repeated twice (April and October) during the year. Size of pinealoc ytes in MF-exposed and sham-exposed rats exhibited, in addition to the difference between peripheral and central regions, regional differenc es in a proximodistal direction; pinealocytes in the distal and middle -peripheral regions were usually larger than those in the proximal and middle-central regions at daytime or nighttime. In October, distal an d proximal pinealocytes showed significant day-night changes in size i n sham-exposed rats, but not in MF-exposed animals. The situations in the two groups were almost reversed in April. Significant day-night di fferences were scarcely found in pinealocyte size in the middle region in the two groups. Throughout the study, pineal volume and pinealocyt e size in each region were generally the same between MF-exposed and s ham-exposed rats at daytime or nighttime. The results suggest that pin ealocytes in the distal and proximal regions, but not those in the mid dle region, are affected by MF-exposure; day-night differences in size s of distal and proximal pinealocytes appear in April and disappear in October under the influence of MF. MF may exert an effect on mechanis ms controlling day-night rhythms of pinealocyte size in the rat.