Substance P innervation of equine synovial membranes: joint differences and neural and nonneural receptor...

Substance P (SP) immunocytochemistry and receptor autoradiography were used to define the innervation of the equine synovial membrane of joints equivalent to the wrist and knuckle of man. SP-immunoreactive fibers were mainly concentrated around blood vessels in the subsynovial layer, although not exclusively, while in the more distal joint, SP fibers were more frequently seen in the synovial surface layer. Iodinated SP receptor autoradiography studies revealed silver grain concentrations in the advential layer of blood vessels associated with the vasa vasorum, on the vascular endothelium and in the synovial surface. These findings suggest that SP has various sites of action within the synovial membrane, each of which may contribute both a sensory function and a different component of the inflammatory process to the joint.