Effects of insulin-like growth factor-1 in motor nerve regeneration after nerve transection and repair vs. nerve crushing injury in the rat

Despite highest standards in nerve repair, functional recovery following nerve transection still remains unsatisfactory. Non-specific re-innervation of target organs are regarded as one reason for a poor functional outcome. Insulin-like growth factor-1 (IGF-1) has demonstrated promoting effects on sciatic nerve regeneration after crushing injury. Similarly, IGF-1 has shown a direct inductive effect on motoneuron growth associated protein-43 (GAP-43) which is believed to play a role in axon guidance during development. Based on this fact we have examined the trophic effects of recombinant human IGF-1 on peripheral motor nerve regeneration following transection and epineural repair in rats median nerve. RhIGF-1 (0.5 mg/kg/rat) was administered subcutaneously to the neck of the repaired side for 14 days postoperation. Accuracy of re-innervation of the flexor carpi radialis muscle motoneuron pool was studied by sequential retrograde double labelling technique. Motor recovery was tested with the grasping test. No significant differences between experimental and control animals in accuracy of re-innervation and in recovery of muscle power could be demonstrated. Non-specific re-innervation of the flexor carpi radialis muscle was found in 23.2% in the experimental group and in 24.2% in the control group. These results demonstrate that systemically applied rhIGF-1 failed to improve functional motor recovery after nerve transection and repair in the rat as it was demonstrated after nerve crushing injury in several studies. Furthermore, systemically applied IGF-1 did not improve accuracy of re-innervation after axotomy and repair in adult rats.