Effects of continuous lighting or continuous darkness on large granulated vesicles in sympathetic nerve fibers of the mouse pineal--quantitative electron microscopic observations.

The influence of continuous light or darkness on the large granulated vesicles in sympathetic nerve fibers of the mouse pineal was investigated by means of quantitative electron microscopic techniques. Continuous illumination at about 20 lux caused the disappearance of the diurnal rhythm in the number of the large granulated vesicles, followed by an accumulation of these vesicles. The diurnal rhythm of the large granulated vesicles was abolished in mice kept in continuous darkness for 7 days. These results suggest that the diurnal variation of the large granulated vesicles may be controlled directly by environmental light. Based on these findings, the relationships between small and large granulated vesicles were discussed.