Objective This study aimed to investigate the effects of acupoint mid-frequency pulse electrical stimulation on the surface electromyography and the expression of brain-derived neurotropic factor (BDNF) in the mandibular protrusion of Sprague-Dawley (SD) rats. Methods Sixty male SD rats were randomly divided into three large groups, namely, blank control, conditional control (with functional appliance and without acupoint mid-frequency pulse electrical stimulation therapy) and experimental groups (with functional appliance and acupoint mid-frequ- ency pulse electrical stimulation therapy). Each large group was randomly divided into four groups (3, 7, 14 and 21 days according to the number of experimental observation days), resulting in 12 groups (n=5). In this experiment, acupuncture points were selected on both sides of the rat, and the parame-ters of acupoint mid-frequency pulse electrical stimulation therapy were set as follows: sinusoidal waveform, 0-150 Hz modulation frequency, and 2 000-8 000 Hz intermediate frequency electrical frequency. The BL-420F biological signal acquisition and analysis system was used to record the electromyograms of rats in the resting state at different experimental periods (3, 7, 14, and 21 days). Immunohistochemistry and real-time quantitative polymerase chain reaction were carried out to detect the protein and mRNA expression levels of BDNF in the masseter muscle of rats. Results The electromyo-grams of masseter muscle, the protein and mRNA expression levels of BDNF first increased and then decreased in the experimental and condition control groups. Moreover, the electromyography of masseter muscle, the protein and mRNA expression levels of BDNF in the experimental group were higher than those in the condition control group on day 3 (P<0.05); the electromyography of masseter and the protein and mRNA expression levels of BDNF in the experimental group basically returned to the normal level on day 21, while those in the condition control group remained higher than those in the blank control group (P<0.05). Conclusion Acupoint mid-frequency pulse electrical stimulation therapy can improve the expression of BDNF in the masseter muscle of rats with functional mandibular protrusion in the early stage, accelerate the recovery of the masseter muscle to normal level, and may improve the treatment of functional appliance.
