Quantitative assessment of the ability of collateral sprouting of the motor and primary sensory neurons after the end-to-side neurorrhaphy of the rat musculocutaneous nerve with the ulnar nerve

In view of the lack of theoretical information, end-to-side neurorrhaphy is a frequent object of experimental interest. End-to-side neurorrhaphy is based on collateral sprouting of an intact axon. The quantitative assessment of collateral sprouts sent by an intact motor and sensory axon was the goal of the present study. End-to-side neurorrhaphy of the distal stump of transected musculocutaneous nerve (MCN) with intact ulnar nerve (UN) was performed in a rat model. Collateral sprouts were quantitatively evaluated by counting of motoneurons and DRG neurons following their retrograde labeling by Fluoro-Ruby and Fluoro-Emerald applied to the UN and MCN, respectively. The results suggest a comparable capacity of both intact sensory and motor axons to send collateral sprouts into a denervated nerve stump. The ratio of sensory/motor neurons, the axons of which reinnervated distal MCN stumps, was very similar to that of intact UN (6.500 and 6.747, respectively), but different from intact MCN (5.029). This suggests that the pruning process occurred to balance the collateral sprouts at a ratio of sensory/motor neurons for the donor UN, but not according to the number of sensory and motor bands of Bungner available in the distal stump of the MCN. The present experimental study confirms end-to-side neurorrhaphy as a suitable method of nerve reconstruction.