Functional Assessments of the Rodent Facial Nerve: A Synkinesis Model

Abstract

Rodent whisker movement has been used as a tool, after facial nerve manipulation, to quantify functional recovery. We have recently established a method to study functional correlates of aberrant regeneration of the facial nerve. Our objective was to establish normative parameters for both spontaneous and induced whisking and blinking behavior in a large group of normal rats. Prospective animal study. Eighty animals underwent quantitative facial movement testing to measure simultaneous vibrissal movement and ocular closure for each side independently. Right and left C-1 whisker positions were continuously recorded for 5-minute sessions, and changes in infrared detection corresponding to eye closure were continuously recorded. Whisking and blinking were elicited by delivery of olfactory stimuli (10 s scented airflows) and corneal air puffs. Whisks were counted and analyzed, and eye closures were counted. Whisking amplitude, velocity, and acceleration were consistent with literature values. Air puff delivery elicited an ipsilateral blink 99% of the time, a contralateral blink 18% of the time, and changes in or initiation of bilateral whisking 70% of the time. Olfactory stimulus delivery prompted a change in whisking behavior 83% of the time, and eye closure 20% of the time. This study establishes normative data for assessing cranial nerve VII-controlled facial movement in four separate facial regions. We demonstrate the capability and tendency of animals to move their orbicularis oculi muscles independently of and simultaneously with their midfacial muscles. This model provides an excellent tool for the study of aberrant regeneration after facial nerve injury in the rodent.