Methods: We analyzed the mRNA expressions of nicotinic acetylcholine receptor (AChR) δ-, γ-, and ε-subunits as indicators of synaptogenesis in the masseter, temporalis, and digastric muscles of 8 week-old mi/mi and control (+/+) mice using quantitative RT-PCR. The AChR δ-subunit is commonly expressed in both the embryonic and adult type of AChR, whereas the γ- and ε-subunits are expressed only in the embryonic and adult type of AChR, respectively.
Results: In the masseter muscle, the mRNA levels of δ- subunit (common type) and γ-subunit (embryonic type) in mi/mi mice were approximately 6 and 18-fold greater than those in the control mice respectively (p<0.05), while no significant difference in the mRNA levels of ε-subunit (adult type) was found between mi/mi and control mice. In the digastric muscle, the mRNA levels of δ-subunit and ε-subunit in mi/mi mice were approximately 3 and 5-fold greater than those in the control mice respectively (p<0.05), while no significant difference in the mRNA levels of γ-subunit was found. In the temporalis muscle, there was no significant difference in the mRNA levels of the 3 subunits studied between mi/mi and control mice.
Conclusions: These results suggest that the contribution of occlusal activity to the synaptogenesis vary among the craniofacial muscles.