Signs of hemifacial spasm created by chronic periodic stimulation of the facial nerve in the rat.
We show in this paper that daily electrical stimulation of the facial nerve near its entrance to the brain stem in rats results in abnormalities in the electromyographic response of the facial muscles that resemble those seen in patients with hemifacial spasm. After about 4 weeks of daily electrical stimulation of the facial nerve for 1 min/day, stimulation of the temporal branch of the facial nerve resulted in an abnormal EMG response from the mentalis/orbicularis oris muscles, consisting of an initial deflection with a latency of about 6 ms, followed by a burst of EMG activity lasting 10 to 50 ms. We found such "lateral spread" of antidromic activity in all 10 rats that were subjected to chronic stimulation, but not in normal rats and not in rats that had electrodes implanted but which had not been stimulated. Measurements of neural conduction times suggest that the location of the cross transmission that gives rise to this lateral spread response is central to the site where the facial nerve exits the brain stem, probably in the facial motor nucleus. We take these results to support the hypothesis that chronic stimulation of the facial nerve can change the facial nucleus in such a way that it becomes hyperactive, and cross transmission between neurons that are innervating different facial muscles is facilitated.
Sen
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Department of Neurological Surgery, University of Pittsburgh School of Medicine, Pennsylvania 15213.
Møller
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D000818:Animals; D004558:Electric Stimulation; D004576:Electromyography; D005152:Facial Muscles; D005154:Facial Nerve / Q000502:physiology*; D005260:Female; D010507:Periodicity; D051381:Rats; D011919:Rats, Inbred Strains; D013035:Spasm / Q000209:etiology* / Q000503:physiopathology; D013997:Time Factors