Study on the analgesic effect of electroacupuncture at different intensities on the primary input level in mice with inflammatory muscle pain based on in vivo calcium imaging

To observe the differential analgesic effects of electroacupuncture (EA) at different intensities on calcium activity in dorsal root ganglia (DRG) neurons induced by mechanical, thermal, and cold stimuli in a state of muscular inflammatory pain, so as to preliminarily reveal the peripheral integration characteristics of acupuncture analgesia mechanisms.

The inflammatory muscle pain model was established by injection of complete Freund’s adjuvant (CFA) into the right tibialis anterior muscle. EA (0.5 mA or 1 mA, 2 Hz) was applied to “Zusanli” (ST36) on the right side for 10 min. Before and after the EA, mice were given body surface stimulation of brush, clamp and different temperature, while simultaneously recording DRG neuron calcium activity during stimulation. The effects of different stimulation methods before and after EA on the change in fluorescence intensity (ΔF/F0) and the percentage of activated DRG neurons were compared.

In the clamp hind paw stimulation, both 0.5 mA and 1 mA EA could reduce the fluorescence intensity of neurons, and the effect of 1 mA was better than that of 0.5 mA (P<0.001). Specifically, 0.5 mA EA decreased the percentage of medium and large neurons (P<0.05), while 1 mA EA decreased the percentage of small, medium, and large neurons (P<0.05, P<0.01), and the effect of 1 mA was better than that of 0.5 mA in reducing the percentage of small and medium neurons (P<0.01). In the stimulation of clamping tibialis anterior muscle, both EA intensities could reduce the fluorescence intensity of neurons (P<0.05, P<0.0001), and the effect of 1 mA was better than that of 0.5 mA (P<0.0001), and 1 mA EA could reduce the percentage of small and medium neurons (P<0.05). In the brush stimulation, both EA intensities could reduce the fluorescence intensity of neurons (P<0.0001), and the effect of 1 mA was better than that of 0.5 mA (P<0.0001), and 0.5 mA EA decreased the percentage of medium and large neurons (P<0.05), while 1 mA EA decreased the percentage of small, medium and large neurons (P<0.05, P<0.01). However, in the temperature stimulation (43, 51, 4 ℃), there were no obvious changes in the fluorescence intensity and the percentage of activated neurons in different intensities of EA.

Both 0.5 mA and 1 mA EA intervention at ST36 can inhibit the reactivity of DRG neurons to mechanical stimulation, with higher intensity EA showing more significant effects.