Comparisons of sizes of pinealocyte nuclei and pinealocytes in young and adult Chinese hamsters (Cricetulus griseus) under different photoperiod conditions.

Semiquantitative electron microscopic observations on pinealocytes of the Chinese hamster (Cricetulus griseus) were made to compare the sizes of pinealocyte nuclei and pinealocytes as a whole, their nuclei and cytoplasm together, over a 24-hr period, between young animals (60-70 days old) and adult animals (120-130 days old) under LD 12:12 and between adults under LD 12:12 and LD 14:10. Under LD 12:12, similar 24-hr rhythms exist in the nuclear area and the area of pinealocytes of young animals, whereas in adults these values exhibit no significant 24-hr rhythm. In adults under LD 14:10, there is no significant 24-hr rhythm in the nuclear area, but the area of pinealocytes shows a statistically significant 24-hr rhythm. Thus, in the Chinese hamster, the relationships between nuclear area and area of pinealocytes with time of day vary, depending on the age of animals as well as different photoperiodic conditions, although they differ only slightly.