A possible feline model for human blepharospasm

'Benign essential blepharospasm' is a human eyelid disorder of unknown aetiology characterized by involuntary, bilateral, and disabling spasmodic contracture of the orbicularis oculi muscle. Treatments are frequently disappointing. Here we report what might be a first step toward developing an animal model for exploring mechanisms of the disorder and potential treatments. We surgically implanted stimulating electrodes into brain areas known to supply input to the lateral division of the facial nerve nucleus to induce blinking by electrical stimulation. Single-pulse stimuli at or near the facial, parabrachial, red, and interstitial nuclei produced consistent stimulus-induced eyelid contractions. Responses were ipsilateral to stimulation, except for the interstitial nucleus where contralateral responses occurred. Little or no other movements of the face, head, or body occurred at eye-blink threshold voltages. When these sites were stimulated with pulse trains, eyelid closures followed stimulus frequency and tended to fuse into constant closure. Thresholds at each stimulus site remained constant during three days of testing. Drug treatments produced no consistent effect on eye-blink threshold from any stimulation site, even when general behaviour was affected. We conclude that these input pathways to the facial nucleus may contribute to blepharospasm and that future neurochemical and electrophysiological study of these pathways may produce a suitable animal model for understanding this disorder.