Electroacupuncture at different intensities inhibits nociceptive discharges of wide dynamic range neurons in spinal dorsal horn of rats.

Objectives: To observe the effect of electroacupuncture (EA) at different intensities on nociceptive discharges of wide dynamic range (WDR) neurons in the spinal dorsal horns (DHs) of rats, so as to explore its regulatory characteristics on nociceptive signals at the spinal level.

Methods: A total of 25 male SD rats were used in the present study. A microelectrode array was used to record the discharge activity of WDR neurons in the lumbar spinal DHs of normal rats. After finding the WDR neuron, electrical stimulation (pulse width of 2 ms) was administered to the plantar receptive field (RF) for determining its response component of discharges according to the latency of action potential generation (Aβ ［0 to 20 ms］, Aδ ［20 to 90 ms］, C ［90 to 500 ms］ and post-discharge ［500 to 800 ms］). High-intensity electrical stimulation was continuously applied to the RF at the paw's plantar surface to induce DHs neuronal windup response. Subsequently, EA stimulation at different intensities (1 mA and 2 mA) was applied to the left "Zusanli"(ST36) at a frequency of 2 Hz/15 Hz for 10 min. The induction of WDR neuronal windup was then repeated under the same conditions. The quantity of nociceptive discharge components and the windup response of WDR neurons before and after EA stimulations at different intensities were compared.

Results: Compared to pre-EA, both EA and EA significantly reduced the number of Aδ and C component discharges of WDR neurons during stimulation, as well as post-discharge (<0.01, <0.001). The inhibitory rate of C component by EA was significantly higher than that by EA (<0.05). Meanwhile, both EA and EA attenuated the windup response of WDR neurons (<0.05, <0.01), and the effect of EA was stronger than that of EA (<0.05). Further analysis showed that when EA and EA respectively applied to both non-receptive field (non-RF) and RF, a significant reduction in the number of Aδ component, C component and post-discharge was observed (<0.05, <0.01). EA at the non-RF and RF demonstrated a significant inhibitory effect on the windup response of WDR neurons (<0.01, <0.05), but EA only at the non-RF showed a significant inhibitory effect on the windup response (<0.01).

Conclusions: EA can suppress nociceptive discharges of spinal DHs WDR neurons in rats. The inhibitory impact of EA is strongly correlated with the location and intensity of EA stimulation, and EA has a stronger inhibitory effect than EA.