Differences in glial, synaptic and motoneuron responses in the facial nucleus of the rat brainstem following facial nerve resection and nerve suture reanastomosis.

Transection and reanastomosis of the facial nerve with microsurgical sutures in rats (facial-facial anastomosis) results in the complete regeneration of the facial nucleus, whereas resection of a 10 mm length of the peripheral facial nerve leads to degeneration and loss of neurons in the nucleus. Nerve sutures or resections were performed in 84 female Wistar rats, and the time course and differences between regenerative and degenerative reactions in the facial nuclei were compared after survival times of 4-112 days. The volume of the facial nucleus, number of facial motoneurons and motoneuron density were estimated stereologically by the physical dissector method. Synaptic plasticity, activation of astroglia and microglia were studied cytochemically with anti-synaptophysin, anti-glial fibrillary acidic protein and the isolectin Griffonia simplicifolia I-B4 (GSA I-B4). After facial-facial anastomosis the volume of the facial nucleus and its number of motoneurons remained constant, whereas resection of the facial nerve caused shrinkage of the facial nucleus and loss of one-third of facial motoneurons within 112 days post-operation. Synaptic stripping, activation of microglia and astroglia occurred in the same sequence and were reversible after both operations, but these reactions were more severe and prolonged after resection, i.e. without suture of the facial nerve. It appears to be most important clinically that differences between de- and regeneration become clear within 7 days post-axotomy. Our results strongly support reconstruction of the facial nerve as early as possible after a nerve lesion.