Spatial relationships between sympathetic varicosities and smooth muscle cells in the longitudinal layer of the mouse...

The spatial relationships between nerve varicosities and smooth muscle cells in the longitudinal muscle layer of the mouse vas deferens have been determined from serial section reconstructions of individual varicosities at the ultrastructural level. Bundles of up to five axons, together with single axons, occurred frequently at the surface of the muscle as well as at about 3-6 muscle cell diameters into the muscle. Varicosities within axon bundles at the muscle surface each became partially divested of Schwann cell processes. The smallest distance separating varicosity membrane from muscle cell membrane (apposition distance) was 100 nm (mean 170 nm) for varicosities contained in bundles. Varicosities from six single axons on the muscle surface were reconstructed and 11 of the 12 possessed a mean apposition distance of 48 nm. Varicosities in axon bundles at about 12 microns deep into the muscle came into an apposition distance of 50-90 nm (mean = 67 nm). All varicosities of single axons at this depth came into about 50 nm apposition (mean = 53 nm). These results indicate that the varicosities lie at varying distances from the muscle cells in the longitudinal muscle layer of the vas deferens.