Rodent Facial Nerve Recovery after Selected Lesions and Repair Techniques

Abstract

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. We quantitatively compared recovery of vibrissal and ocular function following three types of clinically relevant nerve injury. Methods 178 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 1–4 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, though 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 vibrissial 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.

Long-Term Functional Recovery after Facial Nerve Transection and Repair in the Rat

“…Assays of functional recovery were performed for up to 4 months postoperatively. 14,16 As expected, recovery data following crush injury showed near complete recovery. In contrast, recovery after transection and repair injury demonstrated poor function, disorganized whisking, and amplitudes that were scarcely elevated from the baseline.…”

“…11–14 The testing apparatus monitors whisking behavior, an indicator of functional recovery, utilizing laser micrometers that detect vibrissae position across a scan line. During data acquisition, a head-fixation device is crucial to minimize motion artifact and to obtain precise measurements.…”

Deficient functional recovery after facial nerve crush in rats is associated with restricted rearrangements of synaptic terminals in the facial nucleus

“…the structural aberrations were disproportional to the severity of nerve injury (axonotmesis versus neurotmesis). This finding is unusual since most functional and structural consequences of nerve injury show a clear dependence on lesion severity (Søreide, 1981a;Moran and Graeber, 2004;Wolthers et al, 2005;de Ruiter et al, 2008;Hadlock et al, 2010). However, the acute glial and synaptic responses in the facial nucleus of rats do not seem to differ quantitatively after facial nerve crush and transection (Søreide, 1981b) suggesting similar degree of post-traumatic deafferentation.…”

“…The trunk of the right facial nerve was exposed under an operation microscope and injured close to its emergence from the stylomastoid foramen. Two types of injury were performed: (1) nerve crush produced by manual pressing of the nerve between the tips of Dumont forceps #2 (Fine Science Tools, Heidelberg, Germany) for 30 s (Fey et al, 2010;Hadlock et al, 2010) or (2) freezing of approximately 8-mm long segment of the nerve trunk by applying, for 7 s, a metal cryode precooled in liquid nitrogen (Irintchev et al, 1990(Irintchev et al, , 1991. The metal cryode was made out of a copper rod (70 mm long, 4 mm in diameter) and had a flattened tip (4  4  1 mm, length  width  thickness) which was attached to the nerve trunk during freezing.…”

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

“…All rats underwent left facial nerve transection and repair using procedures described previously [19]. Briefly, the facial nerve main trunk was exposed through an incision near the stylomastoid foramen, cut transversely with microsurgical scissors, and repaired with two or three 10-0 nylon epineurial sutures.…”