Motor recovery after cross-reinnervation of a forelimb nerve by the phrenic nerve in cats.

Electromyographic (EMG) activities of forelimb muscles and the diaphragm following cross-reinnervation of the elbow flexor nerve by the phrenic nerve sampled simultaneously with cinematographic recording of forelimb movements, in order to examine whether the respiratory nervous system in adult cats is capable of compensation for movement disorders. The right phrenic and musculocutaneous nerves were cut preparatory to cross-union, the proximal stump of the phrenic nerve being joined to the peripheral stump of the musculocutaneous nerve. Reinnervation of the elbow flexor muscles (m. biceps brachii and m. brachialis) was confirmed in terminal experiments by observing muscular contractions induced by nerve stimulations and/or retrogradely labeled motoneurons in cervical (C5-C7) segments following treatment for horseradish peroxidase (HRP) which had been injected previously into the m. biceps brachii of both sides. Behavioral observations were made in the chronically cross-reinnervated cats. Bipolar EMG recording electrodes were implanted chronically in the right m. biceps brachii, m. triceps brachii and in the left intact diaphragm. In freely moving cats 3-22 months after cross-union surgery, EMG activities in the elbow flexor usually were synchronized with those of the left diaphragm. However, occasionally, in cats cross-reinnervated more than 6 months previously, EMG activities in the right biceps muscle were dissociated from those of the left diaphragm during voluntary movements. During walking, EMG activities in the cross-reinnervated biceps muscle were not coordinated with the walking cycle. By contrast, during voluntary goal directed movements, the cats were capable of reaching their right forepaws to the target in a smooth manner using elbow flexion that was associated with EMG activity of the biceps muscles.(ABSTRACT TRUNCATED AT 250 WORDS)