Percutaneous electrical nerve field stimulation modulates central pain pathways and attenuates post-inflammatory visceral and somatic hyperalgesia in rats

A non-invasive, auricular percutaneous electrical nerve field stimulation (PENFS) has been suggested to modulate central pain pathways. We investigated the effects of BRIDGE® device on the responses of amygdala and lumbar spinal neurons and the development of post-colitis hyperalgesia. Male Sprague-Dawley rats received intracolonic trinitrobenzene sulfonic acid (TNBS) and PENFS on the same day. Control rats had sham devices. The visceromotor response (VMR) to colon distension and paw withdrawal threshold (PWT) was recorded after 7 days. A different group of rats had VMR and PWT at baseline, after TNBS and following PENFS. Extracellular recordings were made from neurons in central nucleus of the amygdala (CeA) or lumbar spinal cord. Baseline firing and responses to compression of the paw were recorded before and after PENFS. Sham-treated rats exhibited a much higher VMR (>30 mmHg) and lower PWT compared to PENFS-treated rats (p < 0.05). PENFS decreased the VMR to colon distension and increased the PWT compared to pre-stimulation (p < 0.05). PENFS resulted in a 57% decrease in spontaneous firing of the CeA neurons (0.59 ± 0.16 vs control: 1.71 ± 0.32 imp/s). Similarly, the response to somatic stimulation was decreased by 56% (3.6 ± 0.52 vs control: 1.71 ± 0.32 imps/s, p < 0.05). Spinal neurons showed a 47% decrease in mean spontaneous firing (4.05 ± 0.65 vs control: 7.7 ± 0.87 imp/s) and response to somatic stimulation (7.62 ± 1.7 vs control: 14.8 ± 2.28 imp/s, p < 0.05). PENFS attenuated baseline firing of CeA and spinal neurons which may account for the modulation of pain responses in this model of post-inflammatory visceral and somatic hyperalgesia.