[The effect of transcutaneous auricular vagus nerve stimulation on fear memory and spleen inflammatory response in fear-conditioned mice].

To investigate the effect of transcutaneous auricular vagus nerve stimulation (taVNS) on fear memory and its regulatory role in splenic inflammatory responses in fear-conditioned mice. Twenty-four 12-week-old healthy, male C57BL/6J mice were randomized into two groups using a random number table: taVNS (=12) and control (=12). Both groups underwent conditioned fear modeling using a fear conditioning chamber. The taVNS group received daily taVNS stimulation (dense-disperse wave, 2 Hz/15 Hz, intensity 2 mA, 30 min) for 6 consecutive days, while the control group received sham taVNS (intensity 0 mA, with other parameters identical to the taVNS group). Following two stimulations, the freezing time percentage of contextual fear memory was assessed, along with total distance and time spent in the center zone of the open-field test. After the 4th and 6th stimulations, the freezing time percentage of auditory-cued fear memory was evaluated. Following all behavioral tests, mice were euthanized to measure the spleen index, and levels of interleukin (IL)-1β and IL-10 were measured in both the serum and spleen tissues. After two stimulations, the freezing time percentage of contextual fear memory in the taVNS group was lower than that of the control group (10.7%±8.0% vs 25.8%±14.3%, =0.004), while the total distance [(363.1±125.8) cm vs (234.1±99.2) cm, =0.011] and total time [(39.0±14.7) s vs (23.4±11.6) s, =0.008] in the center zone of the open-field test were higher in the taVNS group. The freezing time percentage of auditory-cued fear memory was lower in the taVNS group compared to the control group after the 4th (36.4%±18.5% vs 58.4%± 21.5%, =0.013) and 6th (30.3%±20.7% vs 63.2%±26.6%, =0.003) stimulations. Serum and splenic IL-1β levels were lower in the taVNS group compared to the control group (all <0.05), while serum and splenic IL-10 levels were higher in the taVNS group (all <0.05). This study indicates that taVNS reduces fear memory in fear-conditioned mice, accompanied by improvements in systemic and splenic inflammatory respcnses, suggesting that splenic inflammatory response may be associated with the effect of taVNS in reducing fear memory.