Diurnal changes in sympathetic nerve endings in the mouse pineal: Semiquantitative electron microscopic observations

• DOI: 10.1007/bf01245839
• Publication Date: 2005-02-26T03:55:38Z
• Authors: S. Matsushima; T. Ito
• Keywords: Male; Nerve Endings; 0301 basic medicine; Periodicity; Sympathetic Nervous System; Light; Darkness; Cytoplasmic Granules; Pineal Gland; Mice; Microscopy, Electron; 03 medical and health sciences; 0302 clinical medicine; Animals

Sympathetic nerve endings of the mouse pineal were examined by qualitative and semiquantitative electron microscopy at various times of the day under usual lighting conditions (12 hours of light and 12 hours of darkness per day). The nerve endings contained a mixed population of both small granular vesicles and small agranular vesicles. The small granular vesicles, 650 A in mean diameter, were characteristic of adrenergic nerves. They were subdivided, on the basis of the size of the granules, into two types, Types 1 and 2. The Type 1 granular vesicles contained a dense granule which, though varying in size, did not completely fill the vesicle and was often located eccentrically within the vesicle. The Type 2 granular vesicles had a large granule that almost filled the vesicle. The small agranular vesicles were also subdivided, according to their shape, into two types, Types 1 and 2. The Type 1 agranular vesicles were spherical with a mean diameter of 650 A, and the Type 2 agranular vesicles, elliptical or flat, measuring 800×300 A in mean long and short diameters. The proportions of vesicles of the above types, except for the Type 1 agranular vesicles, varied diurnally in correlation with the cycles of day and night. During the light period of the day, both the granular and agranular vesicles were almost constant in proportion. After the onset of darkness, however, all the vesicles except for Type 1 agranular vesicles underwent remarkable changes in the proportion of population. The proportion of Type 1 granular vesicles decreased remarkably until midnight, but at the end of the dark period it was increased again. Simultaneously with a decrease in proportion, the granules appeared to decrease in size. After the onset of the light period the Type 1 granular vesicles increased in proportion. The Type 2 granular vesicles, though less numerous in number, also showed the same tendency in proportion as the Type 1 granular vesicles, and they were almost absent at midnight. The small agranular spherical vesicles of Type 1 remained almost unchanged in proportion throughout the light and dark periods. The Type 2 agranular flat vesicles increased after the onset of darkness. At the end of the dark period they were again reduced in proportion. In addition to the four types of small vesicles, occasional large granular vesicles having a diameter of more than 1000 A were also contained within the nerve endings. They remained unchanged in both proportion and nature throughout the day.