A system for studying facial nerve function in rats through simultaneous bilateral monitoring of eyelid and whisker movements

Abstract

The occurrence of inappropriate co-contraction (synkinesis) of facially innervated muscles in humans is a common sequela of facial nerve injury and recovery. We have developed a system for studying facial nerve function and synkinesis in restrained rats using non-contact opto-electronic techniques that enable simultaneous bilateral monitoring of eyelid and whisker movements. Whisking is monitored in high spatio-temporal resolution using laser micrometers, and eyelid movements are detected using infrared diode and phototransistor pairs that respond to the increased reflection when the eyelids cover the cornea. To validate the system, 8 rats were tested with multiple 5-min sessions that included corneal air puffs to elicit blink and scented air flows to elicit robust whisking. Four rats then received unilateral facial nerve section and were tested at weeks 3-6. Whisking and eye blink behavior occurred both spontaneously and under stimulus control, with no detectable difference from published whisking data. Proximal facial nerve section caused an immediate ipsilateral loss of whisking and eye blink response, but some ocular closures emerged due to retractor bulbi muscle function. The independence observed between whisker and eyelid control indicates that this system may provide a powerful tool for identifying abnormal co-activation of facial zones resulting from aberrant axonal regeneration.

Evidence for Facial Nerve–Independent Mechanisms of Blinking in the Rat

“…Eyelid movement was measured by determining changes in infrared (IR) light reflection from the eye surface with dual IR emitter/ detector units located in front of each eye. 1,14,15 Animal experimentation adhered to protocols approved by the Massachusetts Eye and Ear Infirmary IRB and the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research.…”

“…Eyelid movement was measured by determining changes in infrared (IR) light reflection from the eye surface with dual IR emitter/ detector units located in front of each eye. 1,14,15 Animal experimentation adhered to protocols approved by the Massachusetts Eye and Ear Infirmary IRB and the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research.Fifteen weeks after CN VII transection, 11 of these rats underwent a second surgical manipulation, in which resection of the ipsilateral RB muscle was performed via a superior orbitotomy in the retrobulbar region, transitioning them to an OO paralysis and RB myotomy state. Eye surgery was performed by a team of two microsurgeons, under microsurgical magnification (40ϫ) with a double-headed microscope (Wild M651; Leitz, Rockleigh, NJ), being careful not to damage the long ciliary nerves responsible for corneal sensation.…”

A system for delivering mechanical stimulation to the rat whisker pad during facial nerve regeneration

“…The apparatus described in this paper can be used in conjunction with our previously published system for measuring whisker function in restrained rats [15], but is capable of delivering robotic movement of the right or left whiskers as a stand-alone system. Rats are placed in a body and head restraint half-pipe (see Figure 2), which is then placed on a modified microscope stage providing x-y-z axis, roll, and rotation adjustment.…”

“…The right/left side correlation was R 2 = .998 in this case. Animals were conditioned to the testing apparatus according to previously described methods [15,18]. Briefly, they were handled on a daily basis for approximately 2 weeks prior to fixation device implantation, and then handled daily starting 2 days after implantation, up to the day of testing.…”

“…Once accustomed to being securely held for 10 minutes, animals began sack training. This involved placing the animals in a fitted cloth sack, where the limbs had minimal ability to move (see reference [15] for thorough description). For the five days prior to testing of whisking function, animals were head-fixed in the testing apparatus for progressively longer periods, beginning for 30 seconds, and progressing to 10 minutes.…”