Physical Activity and Neuronal Plasticity after Tendon Rupture

INTRODUCTION Clinically, it is well known that physical activity promotes tissue regeneration after injury. The exact mechanisms for this mechanobiological transduction are still largely unknown. Accumulating data, however, suggest that a variety of neuronal mediators, so called neuropeptides, besides cytokines and growth factors play an important role of tissue repair [1]. Recently we demonstrated that ruptured tendons exhibit extensive new nerve fibre ingrowth during the early regenerative phase of healing (week 1-4) [2]. This new nerve fibre ingrowth is followed by a specific temporal expression of sensory neuropeptides during healing, which may reflect a role in angiogenesis and/or proliferation/differentiation of different cell types in tissue repair. In a recent study it was shown that mechanical stimuli entails an increased occurrence of neural growth factor (NGF) in vascular smooth muscle cells [3]. Given that neuropeptides mediate trophic effects, it may prove that physical activity, i.e. early mobilisation after injury, can regulate the nerve regenerative capability and/or the neuropeptide occurrence during healing. In the present study of healing Achilles tendon 4 weeks after rupture, we analyzed the occurrence of nerve fibres and a specific sensory transmitter at three different activity levels post injury, i.e. running, free mobility and immobilisation.