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

Abstract

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. A total of 24 male Sprague Dawley rats were randomly divided into normal, depression model, taVNS, tnVNS (transcutaneous auricular none-vagus nerve stimulaton) groups (n=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. 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 (P<0.01). Following the treatment and compared with the model group, the increase amount of body weight in the taVNS group was obviously increased (P<0.05), the swimming immobility time and the expression of TLR4, MyD88, IL-18 protein in the taVNS and tnVNS groups were significantly decreased (P<0.01). 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.