Rodent facial nerve recovery after selected lesions and repair techniques.

BACKGROUND: Measuring rodent facial movements is a reliable method for studying recovery from facial nerve manipulation and for examining the behavioral correlates of aberrant regeneration. The authors quantitatively compared recovery of vibrissal and ocular function following three types of clinically relevant nerve injury. METHODS: One hundred seventy-eight adult rats underwent facial nerve manipulation and testing. In the experimental groups, the left facial nerve was either crushed, transected, and repaired epineurially, or transected and the stumps suture-secured into a tube with a 2-mm gap between them. Facial recovery was measured for the ensuing 1 to 4 months. Data were analyzed for whisking recovery. Previously developed markers of co-contraction of the upper and midfacial zones (possible synkinesis markers) were also examined. RESULTS: Animals in the crush groups recovered nearly normal whisking parameters within 25 days. The distal branch crush group showed improved recovery over the main trunk crush group for several days during early recovery. By week 9, the transection/repair groups showed evidence of recovery that trended further upward throughout the study period. The entubulation groups followed a similar recovery pattern, although they did not maintain significant recovery levels by the study conclusion. Markers of potential synkinesis increased in selected groups following facial nerve injury. CONCLUSIONS: Rodent vibrissal function recovers in a predictable fashion following manipulation. Generalized co-contraction of the upper and midfacial zones emerges following facial nerve manipulation, possibly related to aberrant regeneration, polyterminal axons, or hypersensitivity of the rodent to sensory stimuli following nerve manipulation.

Evidence for facial nerve-independent mechanisms of blinking in the rat.

PURPOSE: The rat facial nerve (CN VII) controls the orbicularis oculi (OO) muscle, which contracts to close the palpebral fissure during blinking. It was recently observed that rats are able to achieve nearly complete eye closure shortly after CN VII lesion, and hypothesized that the retractor bulbi (RB) muscle assumes an important compensatory role after CN VII lesion. This study was undertaken to determine the maintenance of rat corneal health and eye closure capability after lesion of the OO, RB, or both. METHODS: Twenty-two rats underwent RB transection; 12 of them had undergone complete unilateral CN VII transection (OO denervation) 15 weeks earlier. Corneal appearance and ability to blink in response to a corneal air puff was monitored weekly for 9 weeks. An additional 13 rats received CN VII transection and were video recorded (1000 frames/s) during elicited blinks at days 1, 3, 5/6, and 11 after surgery. RESULTS: Rats achieved nearly full or full eye closure after OO paralysis or RB myotomy, respectively. Ninety-two percent of rats maintained good corneal health after OO denervation over 9 weeks, consistent with compensatory eyelid movement served by the RB muscles. In contrast, only 40% of rats with loss of RB function alone and only 17% of rats with concurrent OO and RB paralysis were able to maintain corneal health by week 3. CONCLUSIONS: Like other small mammals, the rat RB musculature can support nearly complete eye closure when CN VII is lesioned, and must be carefully considered when using blink as a functional recovery parameter of facial nerve lesion.

Functional assessments of the rodent facial nerve: a synkinesis model.

OBJECTIVES/HYPOTHESIS: 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. STUDY DESIGN: Prospective animal study. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

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

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.

A novel method of head fixation for the study of rodent facial function.

The rodent vibrissial system offers an excellent model for the study of both sensory and motor function. It has been widely employed to gather data pertaining to sensory and motor function involving the 5th and 7th cranial nerves and the central nervous system. Existing methods of head fixation for precise measurements of ocular and vibrissial function involve exposing the cranium and applying dental cement from which two or more threaded rods emerge. This common approach is suboptimal, requiring a relatively complicated implantation procedure, and results in a large, chronic interface between the scalp and environmentally exposed implant material attached to the skull. Here we describe a head fixation device that is inexpensive, easy to build, less prone to infection, preserves access to the cranial midline, and permits repeated measurements over many months.

Interactions of ribosomal protein S1 with DsrA and rpoS mRNA.

Ribosomal protein S1 is shown to interact with the non-coding RNA DsrA and with rpoS mRNA. DsrA is a non-coding RNA that is important in controlling expression of the rpoS gene product in Escherichia coli. Photochemical crosslinking, quadrupole-time of flight tandem mass spectrometry, and peptide sequencing have identified an interaction between DsrA and S1 in the 30S ribosomal subunit. Purified S1 binds both DsrA (K(obs) approximately 6 x 10(6) M(-1)) and rpoS mRNA (K(obs) approximately 3 x 10(7) M(-1)). Ribonuclease probing experiments indicate that S1 binding has a weak but detectable effect on the secondary structure of DsrA or rpoS mRNA.