[Effect of transcutaneous auricular vagus nerve stimulation on the expression of TLR4、MyD88、IL-18 protein in the prefrontal cortex of depression rats].

Objective: To observe the effect of transcutaneous auricular vagus nerve stimulation (taVNS) on the depressive behavior in depression rats, so as to explore its mechanism underlying improvement of depression.

Methods: A total of 24 male Sprague Dawley rats were randomly divided into normal, depression model, taVNS, tnVNS (transcutaneous auricular none-vagus nerve stimulaton) groups (=6 in each group). The depression model was established by chronic unpredictable mild stimulation combined with solitary raising for 35 consecutive days. After 14 days modeling, transcutaneous electrostimulation (2 mA, 2 Hz/15 Hz) was applied to auricular concha or auricular margin, respectively. Each intervention was conducted for 30 minutes, once daily for 21 days. The depression-like behavior was evaluated by forced swimming immobility time and body weight. The expression levels of Toll-like receptor 4 (TLR4), myeloid differentiation factor 88 (MyD88) and interleukin-18 (IL-18) protein in the prefrontal cortex were detected by Western blot.

Results: Following modeling, the increase amount of body weight was decreased, the forced swimming immobility time and expression TLR4, MyD88 and IL-18 protein in the prefrontal cortex were increased in the model group than those in the normal group (<0.01). Following the treatment and compared with the model group, the increase amount of body weight in the taVNS group was obviously increased (<0.05), the swimming immobility time and the expression of TLR4, MyD88, IL-18 protein in the taVNS and tnVNS groups were significantly decreased (<0.01).

Conclusion: TaVNS is able to improve depression in depression rats, which is probably related to its effect in inhibiting inflammatory response of TLR4/MyD88 signaling pathway in prefrontal cortex.