Effect of electroacupuncture on the primary input level of dorsal root ganglion neurons under different stimuli observed by in vivo calcium imaging

To observe the effect of electroacupuncture (EA) on the neuronal activity of primary afferent dorsal root ganglion (DRG) caused by different mechanical stimuli such as brush, clamp [clamping hind paw or "Zusanli" (ST36) acupoint] or stimulation at different temperatures (43 ℃, 51 ℃, 4 ℃), so as to explore the interaction between EA signals and different primary afferent signals at the DRG level.

The strength threshold of activated A fiber was determined by electrophysiological technique. DRG neurons were labeled by intrathecal injection of AAV9 virus, and the response of DRG neurons to different primary afferent stimuli was observed and recorded by calcium imaging. EA (0.5 mA, 0.2 ms, 2 Hz) was applied to "Zusanli" (ST36) on the right side for 10 min. The changes of the number, percentage of neurons of different sizes and fluorescence intensity of DRG neurons activated under different stimulation before and after EA were compared.

Clamping stimulation, brush stimulation, or different temperature stimulation could all activate DRG neurons of large, medium, and small classes. EA at ST36 could significantly decrease the percentage of activated small neurons and large neurons in DRG induced by clamping the hind paw (P<0.05), and reduce the fluorescence intensity of neurons with different diameters (P<0.0001), suggesting that EA could suppress the neuronal activity induced by noxious mechanical stimulation of the hind paw. However, EA at ST36 had no significant effect on the percentage of activated DRG neurons and fluorescence intensity caused by clamping the anterior tibial muscle. Meanwhile, EA at ST36 could significantly reduce the percentage of activated neuron in DRG induced by brush stimulation (P<0.05), and reduce the fluorescence intensity of neurons with different diameters (P<0.0001). In temperature stimulation, EA could significantly inhibit the fluorescence intensity of DRG neurons under 4 ℃ cold stimulation (P<0.01), but had no significant effect on the percentage and fluorescence intensity of DRG neurons activated by 43 ℃ and 51 ℃.

EA at ST36 can inhibit the nociceptive mechanical input of the hind paw and the input of 4 ℃ cold stimulation.