Dual Convergence of Facial Nerve Branches Innervating Whisker Pad in Rats.

The precise anatomy of the facial nerve branches innervating rat whisker pad and the distribution of their corresponding motor neurons in facial nucleus area were investigated. The extratemporal facial nerves of 6 rats were anatomically observed under a surgical microscope, and then the nerve specimens of facial nerve branches at 7 anatomical sites were taken and examined for the axons and myelin sheath using Luxol fast blue staining. The distribution of facial motor neurons innervating the facial branches was observed in 12 rats by retrograde labelling. The distal pes, a fusing architecture of the buccal and marginal mandibular branches, was found to furcate into superior, middle and inferior branches to innervate whisker pad. Histologically, the myelin sheath of each branch was morphologically consistent, and the nerve fiber bundles of facial nerve branches became increasingly thinner and scattered, particularly after crossing the distal pes site and innervating the whisker pad. The facial motor neurons innervating the buccal and marginal mandibular branches were clearly distributed in similar regions in facial nucleus. This study confirmed the highly spatial synergy between the buccal and marginal mandibular branches innervating the whisker pad from extratemporal anatomy and distribution of facial motor neurons.