UC Irvine

Introduction

The objective of this study was to describe facial myokymia in experimental animals accompanying kainic acid affects on facial motor neurons.

Material & methods

Anesthetized cats were injected with kainic acid into the pons adjacent to the facial nucleus. Facial movements appeared shortly after the injections and facial electromyographic potentials were recorded. Cats were killed up to 4 weeks later, the brainstems were processed histologically, and the number of neurons in the facial nucleus counted.

Results

Cats receiving injection of kainic acid adjacent to facial nucleus all developed spontaneous writhing movements of the face ipsilateral to the injection site, clinically resembling facial myokymia in humans. Transient facial paresis, lasting several weeks, appeared in some of the cats. Facial myokymia occurred independent of histological evidence of neuronal loss in facial nucleus, whereas facial paresis occurred in all but one of the animals with significant neuronal loss in the facial nucleus. Placing a needle into the superior olive without injecting kainic acid or injections of kainic acid into cochlear nucleus was not accompanied by facial myokymia or subsequent facial paresis.

Conclusion

Facial movements in cats similar to myokymia in humans accompanies kainic acid injections adjacent to the nucleus of the facial nerve.