The innervation pattern of the human patellar tendon is largely unknown. That includes the situation for patients suffering from patellar tendon tendinosis (“jumper’s knee”). Concerning the possible occurrence of a cholinergic system in the human patellar tendon, very little information is available.
In the present study, specimens of pain-free normal (n=16) and chronically painful tendinosis (n=7) tendons were examined by different immunohistochemical and histochemical methods.
It was found that parts of the tenocytes of the tendinosis tendons displayed immunoreactions for choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT). Furthermore, immunoreactions for the M2 muscarinic acetylcholine receptor could be detected in both blood vessel cells and tenocytes, especially in tendinosis specimens. Acetylcholinesterase activity was shown for scarce nerve fibers associated with small blood vessels in both the normal and the tendinosis tendons.
The observations suggest that, besides the occurrence of a scanty nerve related cholinergic system in the human patellar tendon, there is a local non-neuronal cholinergic system as well, at least in tendinosis tendons. As ChAT and VAChT were detected in tenocytes of these tendons, such tenocytes are likely to produce acetylcholine (ACh) locally, and as both tenocytes and blood vessel cells were found to express the M2 receptor, it is likely that both of these cell types may be influenced by ACh.
Thus, in conclusion, there appears to be an upregulation of the cholinergic system, and an occurrence of autocrine/paracrine effects in this system, in the tendinosis patellar tendon. This observation is of importance, not only related to the fact that tendinosis patients exhibit marked pain, but also as stimulation of ACh receptors can lead to cell proliferation, effects on collagen accumulation and angiogenesis, all of which are phenomena that occur in tendinosis.
2nd International Symposium on Non-neuronal Acetylcholine, 2006a