Synaptic plasticity in the facial nucleus in rats following infraorbital nerve manipulation after facial nerve injury

Abstract

The aim of this study is to investigate the effect of sensory input on the neural plasticity in the facial nucleus following facial nerve injury. Adult male Wistar rats were randomly assigned to four groups: (1) sham control; (2) facial nerve crush (FNC); (3) nerve crush plus daily manual vibrissal stimulation (FMS); and (4) nerve crush with infraorbital nerve transection plus daily manual stimulation (FIMS). Plasticity related proteins in the facial nucleus were evaluated by western blot at 7, 14, and 28 days postsurgery (n = 6/group per timepoint). Synaptophysin-positive terminals were evaluated by immunohistochemistry in a second set of animals (n = 6/group) at 14 days. Quantitation of synaptophysin immunostaining showed that rats in the FNC group had a significantly lower mean number of pixels compared to control animals (29.1 ± 2.6 × 10⁶ vs. 34.2 ± 2.3 × 10⁶; P < 0.05). Values in the FMS group (33.2 ± 1.7 × 10⁶) were similar to that of the control group, while the mean number in the FIMS group (26.5 ± 2.4 × 10⁶) was significantly lower than in the control group. Synapsin I phosphorylation was reduced to 70–83 % in FNC rats, but increased to 121–132 % in the FMS group (P < 0.05 vs. controls). Phosphorylation of cAMP response element-binding protein was similarly reduced by facial nerve crush, which was delayed in FMS animals (P < 0.05 vs. controls at 28 days). Expression and phosphorylation of all proteins were reduced to the lowest in the FIMS group (all P < 0.05). Sensory input from the IoN have a strong effect on synaptic plasticity within the facial nucleus, which is necessary to achieve the benefit of manual stimulation.

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