Effects of transcutaneous auricular vagus nerve stimulation on autonomic nervous function in rats with functional dyspepsia

OBJECTIVE To observe the effect of transcutaneous auricular vagus nerve stimulation (taVNS) on the autonomic nerve function in a rat model of functional dyspepsia (FD), so as to explore the mechanism of taVNS underlying regulation of FD. METHODS SD rats were randomly divided into normal control group(n=8) and FD model group(n=26).The FD model was replicated with iodoacetamide gavage. The FD model rats were randomly divided into model, taVNS, sham-taVNS and Zusanli(ST36) groups, with 6 rats in each group. Rats in the taVNS group received electrical stimulation of auricular concha,while the sham-taVNS group received no electrical stimulation and rats in the ST36 group received stimulation at ST36 for 30 min once daily for 14 consecutive days. Cervical trapezius electromyography score and abdominal withdrawal reflex (AWR) score were used to evaluate gastric sensitivity. Histopathological changes of the gastric antrum tissue were observed under microscope after H.E. staining. Autonomic nerve function in rats was recorded and assessed by heart rate variability(HRV). The content of acetylcholine (Ach) and the expression of Ach receptor M3R in gastric antrum was detect by ELISA and Western blot, separately. RESULTS Compared with the normal control group, the cervical trapezius electromyography and AWR scores of the model group increased (P<0.01, P<0.001), and there was no erosion in the gastric antral mucosa and muscle layer. The high-frequency power (HF) in HRV decreased (P<0.05), the ratio of low-frequency power/high-frequency power (LF/HF) increased (P<0.001), and the Ach content and its receptor M3R expression in gastric antrum tissue decreased (P<0.05). Following interventions, the cervical trapezius electromyography and AWR scores decreased (P<0.01,P<0.001, P<0.05), HF in HRV increased and LF/HF decreased(P<0.01，P<0.05,P<0.001), and the content of Ach in gastric antrum tissue and the expression of its receptor M3R increased (P<0.01, P<0.05) in both taVNS and ST36 groups relevant to the model group. CONCLUSION taVNS can increase the activity of the vagus nerve and regulate the balance of the autonomic nerve function, which may be one of the mechanisms of taVNS in reducing the gastric sensitivity of rats with FD. In regulating the vagus nerve function, taVNS and acupuncture at ST36 acupoint have the similar effects.