Intrinsic interrelation of lymphatic endothelia with nerve elements in the monkey urinary bladder

Histochemical staining techniques for 5'-nucleotidase (5'-Nase) and acetylcholinesterase (AChE) were undertaken to localize the lymphatic network and nerve plexus in the monkey urinary bladder. Abundant 5'-Nase-positive lymphatic networks were characterized by increased number of valve-like structures and decreased calibre of blind-ends from the subepithelium to the subserosa. AChE-positive nerve fibers were visible throughout the vesical walls as fine plexuses, the densest being the neuromuscular plexus among the detrusor muscle cells or in each muscle bundle. AChE-positive nerve fibers or terminals were more frequently discernible around blood vessels than around lymphatics, and showed more intimate association with the lymphatics in the muscularis than those in the subepithelium. The nerve terminals in the subepithelium were frequently separated from attenuated lymphatic endothelium by the long processes of fibroblasts or some connective tissue cells. An ultrastructural observation revealed that unmyelinated nerve fibers with numerous neurofilaments and neurotubules run in close apposition to the lymphatic endothelium. Noteworthily, fewer terminal varicosities containing numerous small agranular vesicles (30-50 nm) and mitochondria, partially or completely bare of their Schwann cell covering in the vicinity of the lymphatic endothelium, were found in the subendothelium of initial lymphatics than in collecting ones. These terminals were occasionally identified at a distance of 120-350 nm from the subendothelial aspect of valve-originating roots, although no direct innervation of the vascular muscle cells could be found. A loose fibro-elastic connective tissue was usually interlaced between glial cell covering and lymphatic endothelium. The intrinsic interrelation of the lymphatic wall with the nerve plexus implies that the twisted subendothelial nerve terminals might be involved in intramural lymph drainage of the bladder.