Disorganization of the facial nucleus after nerve lesioning and regeneration in the rat: Effects of transplanting candidate reparative cells to the site of injury

OBJECTIVE: After the facial nerve has been damaged, functional recovery is impaired by synkinesis: the abnormal movement of part of the face during voluntary movement of another part. This is primarily because of aberrant regenerating axons that fail to reach the correct distal targets. We studied the effects of transplanting Schwann cells, mixed olfactory ensheathing cells, and S-type olfactory ensheathing cells on the histological and functional organization of the connections between the facial nucleus and distal muscles. METHODS: In a control group of adult rats (n = 18), the proximal part of the extracranial facial nerve was completely severed and immediately repaired by suture. In an experimental group (n = 34), a bolus of cultured cells was applied to the cut ends before suture (Schwann cells, n = 10; olfactory ensheathing cells, n = 18; S-type cells, n = 6). A period of regeneration was permitted, after which the animals were assessed functionally by measurement of eye closure in response to a puff of air. The site of lesion and the somatotopic organization of the facial nucleus were assessed histologically, after application of different retrograde fluorescent tracers simultaneously to the buccal and temporal divisions of the facial nerve. RESULTS: The rate of recovery of eye closure was increased by the use of the cell transplants, but the disorganization of the facial nucleus and aberrant nerve branching were unchanged. CONCLUSION: Perhaps regenerating axons become misguided throughout the whole length of the nerve, not only at the site of the lesion, and strategies aimed at improving axon path-finding solely at the lesion site will therefore be inadequate.