Diurnal variation in large granulated vesicles in sympathetic nerve fibers of the mouse pineal--quantitative electron micrsocopic observations.

Quantitative electron microscopic studies of the sympathetic nerve fibers of the mouse pineal demonstrated a marked diurnal rhythm in the number of the large granulated vesicles of 80 to 150 nm diameter. The number of these vesicles showed its minimum at the middle and the end of the dark period and its maximum at the end of the light period, respectively. The large non-granulated spherical and elliptical vesicles were almost constant in number throughout the day.