Anatomical and functional connectivity of the transected ulnar nerve after intercostal neurotization in cats

OBJECT: Acute transfer of three intercostal nerves to the ulnar nerve was performed in cats for histological and clinical evaluation of a distal muscle reinnervation. METHODS: Infraclavicular intercostal-ulnar communications were created after dividing the motor branches of the upper intercostal nerves in 14 adult cats. Reinnervation of distal forelimb muscles in the ulnar territory was assessed by electromyographic (EMG) studies and motor function rating each month until 18 months postsurgery. In five of these treated animals, and in tour controls, horseradish peroxidase (HRP) was applied to the ulnar or intercostal nerves to study the amount and distribution of retrograde motor neuron labeling in the spinal cord. Also, samples of reinnervated muscles and neurotized ulnar nerves were processed to assess regeneration. Simple ulnar transection without reconstruction led to permanent atrophy of ulnar muscles, lack of recovery according to EMG or clinical studies, and disappearance of the ulnar motor neuron pool. In contrast, ulnar neurotization with the intercostal nerves led to a high rate of functional recovery, which began 5 months postsurgery, and progressed from muscle activity synchronized with ventilatory movements to spontaneous movements that were independent of respiration. This recovery was accompanied by substantial retrograde labeling of intercostal motor neurons after HRP application in the ulnar nerve. Cell counts showed that practically the whole motor neuron pool of the involved intercostal nerves contributed to reinnervation of the transected ulnar nerve. CONCLUSIONS: These findings demonstrate that the use of intercostal nerves to neurotize long brachial plexus nerves can achieve long-lasting and successful reinnervation of distal forelimb muscles.