The innervation of the myometrium of the cynomolgus monkey (Macaca fascicularis). A quantitative electron-microscopic study.

The autonomic innervation of the myometrium of Macaca fascicularis consists of bundles of unmyelinated nerve fibres running between the smooth muscle cells, and is therefore considered to be of the "fascicular (= unitary) type". Close contacts between nerve fibres and smooth muscle fibres were not found. Modification of the chromaffin method according to Tranzer and Richards made it possible to visualize the heterogeneity of the nerve fibres in a single bundle. The following fibre types were found to coexist: (1) noradrenergic fibres containing "synaptic" vesicles with a dense granule, (2) cholinergic fibres containing empty "synaptic vesicles", and (3) non-adrenergic non-cholinergic (NANC) fibres containing only or predominantly large dense-cored vesicles, which do not react with this method. Noradrenergic fibres are the most numerous (around 60%), followed by NANC fibres (30%) and cholinergic elements (around 10%). The distribution of these three types is similar in the cervix, the isthmus and the body of the uterus in pregnant and non-pregnant females.