Activation of anterior cingulate cortex produces inhibitory effects on noxious mechanical and electrical stimuli-evoked responses in rat spinal WDR neurons

In present study, in vivo electrophysiological techniques were applied to examine the effects of anterior cingulate cortex (ACC) activation on mechanical and electrical stimuli-evoked responses in rat spinal cord wide-dynamic-range (WDR) neurons. We found that bilateral ACC electrical stimulation (100 Hz, 20 V, 20 s) had different effects on neuronal responses to brush, pressure and pinch stimuli (10 s). The brush-evoked neuronal responses at baseline, post 1 min and post 5 min were 60.8 ± 15.0, 59.2 ± 15.4 and 60.0 ± 19.3 spikes/10 s, respectively (n = 10, P > 0.05 vs. baseline). The pressure-evoked neuronal responses at baseline, post 1 min and post 5 min were 77.8 ± 11.9, 38.0 ± 7.8 and 45.8 ± 7.6 spikes/10 s, respectively (n = 10, P < 0.05 vs. baseline). The pinch-evoked neuronal responses at baseline, post 1 min and post 5 min were 137.6 ± 16.7, 62.6 ± 17.5 and 68.8 ± 15.0 spikes/10 s, respectively (n = 10, P < 0.05 vs. baseline). Furthermore, ACC stimulation generated distinct effects on the different components of wind-up response. The total numbers of late response (LR) and after-discharge (AD), but not early response (ER), significantly decreased. Collectively, the present study demonstrated that short-term ACC activation could generate long-term inhibitory effects on the responses of WDR neurons to noxious mechanical (pressure and pinch) and electrical stimuli. The results indicated that ACC activation could negatively regulate noxious information ascending from spinal cord with long-term effect, providing potential neuronal substrate for the modulation of ACC activation on nociception.