QUANTITATIVE EXAMINATION OF CALCITONIN-GENE-RELATED PEPTIDE-IMMUNOREACTIVE NERVE-FIBERS IN THE CAT KNEE-JOINT CAPSULE

The knee joint of the cat has been used extensively to study the morph ology and function of primary afferents in a deep somatic tissue. A pr oportion of these neurones synthesizes various neuropeptides, with cal citonin gene-related peptide being the most prominent. In the present study we examined the distribution and density of nerve fibres immunor eactive for calcitonin gene related peptide within the medial articula r capsule. The fibres were predominantly located in the superficial la yer of the capsule. They formed a dense innervation pattern, mainly ac companying blood vessels. Electron microscopy showed that most fibres were in close proximity to small arteries. The highest innervation den sity was found in parts of the capsule that were located over the epic ondyle of the femur with 21+/-12 fibres per mm(2) (mean+/-SD). In the tissue over the joint cleft this density was lower, with 11+/-6 fibres per mm(2). In conclusion, the high innervation density of the knee jo int capsule by nerve fibres containing calcitonin gene-related peptide supports the hypothesis of an important regulatory function of this p eptide in normal tissue.