Connections between postparotid terminal branches of the facial nerve: An immunohistochemistry study

Abstract

It has been assumed that connections between the postparotid terminal branches of the facial nerve are purely motor. However, the nature of their fibers remains unexplored. The aim of this study is to determine whether these connections comprise motor fibers exclusively. In total 17 connections between terminal facial nerve branches were obtained from 13 different facial nerves. Choline acetyltransferase antibody (ChAT) was used to stain the fibers in the connections and determine whether or not all of them were motor. All connections contained ChAT positive and negative fibers. The average number of fibers overall was 287 (84-587) and the average proportion of positive fibers was 63% (37.7%-91.5%). In 29% of the nerves, >75% of the fibers were ChAT+ (strongly positive); in 52.94%, 50%-75% were ChAT+ (intermediately positive); and in 17.65%, <50% were ChAT+ (weakly positive). Fibers traveling inside the postparotid terminal cranial nerve VII branch connections are not exclusively motor.

Keywords: choline acetyltransferase; facial nerve; facial nerve motor disorders; immunohistochemistry; nerve fibers.

FIGURE 1

Example of images used for counting axons. The continuous circle shows a ChAT+ motor fiber. The discontinuous circle shows a ChAT− fiber.

FIGURE 2

Classification of facial nerve connections based on number of motor fibers. (A) Strongly positive connection (>75% of ChAT+); (B) Intermediately positive (50%–75% of ChAT+); (C) Weakly positive (<50% of ChAT+).

FIGURE 3

Different types of terminal facial nerve connections. (A) Temporo‐temporal (strongly +); (B) Temporo‐zygomatic (weakly +); (C) Zygomatic‐zygomatic (intermediately +); (D) Bucco‐buccal (strongly +); (E) Bucco‐mandibular (intermediately +); (F) Mandibulo‐cervical (strongly +).

FIGURE 4

Box plot diagram of ChAT+ fibers by side and sex. The number of ChAT+ fibers was more variable on the left side than the right, and more variable in males than females, but these differences were not statistically significant.