Innervation of the ligament of the femoral head in the formosan rock monkey: a retrograde HRP tracing and ultrastructural study.

The innervation of the ligament attached to the femoral head of the Formosan rock monkey (Macaca cyclopis, Swinhoe) was investigated by means of the retrograde HRP tracing method and by electron microscopy. WGA/HRP was injected into the ligament of the left femoral head. Numerous neurons labelled with HRP were found in the ipsilateral lumbar sympathetic ganglia, from L1 to L7, with a peak in the L3 to L5 region. Labelled neurons were also found in the ipsilateral spinal dorsal root ganglia, from L1 to L7 and concentrated at L4. Ultrastructurally, the nerve fascicles to the ligament had an average diameter at 32.8 microns. They contained both myelinated and unmyelinated axons and accompanied the blood vessels. Sensory receptors were not found in the ligamentum proprium but free nerve endings were observed in the walls of the blood vessels. The present results indicate that the nerve fibres to the ligament of the femoral head may be involved in regulating blood vessel calibre in addition to having a sensory function.