Distribution of substance P and calcitonin gene related peptide immunoreactivity in the normal feline knee.

OBJECTIVE

There is substantial evidence that the intraarticular release of the neuropeptides substance P (SP) and/or calcitonin gene related peptide (CGRP) can contribute to the development and perpetuation of joint inflammation. However, there is a paucity of data examining whether SP and CGRP containing fibers are present in articular tissues other than synovium. Our objective was to comprehensively examine all innervated tissues in the normal feline knee for the presence of these neuropeptides.

METHODS

The normal right knee joints from 5 cats were harvested and dissected into 10 regions. These regions included the cruciate and collateral ligaments, menisci, fat pad and synovium, capsule and popliteus tendon. Each area was examined for the immunocytochemical presence of SP and CGRP.

RESULTS

Nerve fibers immunoreactive (Ir) for SP or CGRP were found in all of the joint tissues examined. In general, Both SP-Ir and CGRP-Ir nerve fibers were most often associated with blood vessels. However, there were "free" SP and CGRP fibers present in all 10 articular structures which were not associated with any vascular profiles.

CONCLUSION

Our data demonstrate that articular SP and CGRP-Ir fibers are not limited to the synovium. Both neuropeptides are widely distributed to all joint tissues except articular cartilage, which is devoid of neural tissue. These findings, in conjunction with an increasing appreciation of the functional interrelationship between SP and CGRP, argue cogently for consideration of the effects generated by nonsynovial sources of SP and CGRP when assessing the role of these neuropeptides in both normal joint function and in articular inflammatory processes.