Neurophysiology of ischemic facial nerve paralysis in an animal model.

The establishment of an animal model for facial nerve paralysis is assuming increasing importance in clinical medicine and also in basic facial nerve research. We previously reported an animal model for ischemic facial nerve paralysis using selective vascular embolization through the internal maxillary and posterior auricular arteries in cats using Avitene which contains bovine microfibril collagen. In this paper, we determined the exact site of the lesion in established facial paralysis. A descending signal produced by direct stimulation to the contralateral motor cortex was able to elicit firing of the motor nucleus of the facial nerve, the extra-temporal portion of the peripheral nerve, and the orbicularis oris muscle. After achieving complete facial nerve paralysis, this descending signal was completely abolished within the temporal bone area, whereas peripheral facial nerve stimulation elicited a normal evoked electromyogram of the orbicularis oris muscle. The present results suggest that the site of the lesion of ischemic facial nerve paralysis produced by embolization in an animal model is within the temporal portion of the seventh nerve, and this animal model may lead to the advancement of future facial nerve research which cannot be conducted in humans.