Morphologic Changes in the Pineal Parenchyma Cells of Rats Exposed to Continuous Light or Darkness

Abstract

Young female rats were maintained for 8 weeks in continuous light or darkness, after which their pineal organs were removed and studied with light microscopy. The pineals from animals kept in light appeared to be functionally inhibited in that the parenchymal cells were smaller in size, contained fewer prominent nucleoli and had much less cytoplasmic basophila than those of the pineals from animals kept in darkness. Taken together with previously reported physiologic data, these findings suggest that the pineal is an important functional part of the neuroendocrine mechanism regulating the gonads with regard to varying conditions of illumination.