Effect Of Electroacupuncture On Pain Memory Behaviors And Synchronous Neural Oscillations In The Rostral Anterior Cingulate Cortex In Unanesthetized Rats

Objective Through extracellular multi-channel recording in vivo,the pain memory behaviors and synchronous local field potentials(LFPs)were used to observe the sensory and emotional dimensions of pain memory,exploring the effect of electroacupuncture on pain memory behavior and synchronous effect of neural oscillations in the rostral anterior cingulate cortex(rACC)in unanesthetized rats.Methods Adult male Sprague-Dawley rats were randomly divided into blank control(Control)group,pain memory model(Model)group,pain memory model+electroacupuncture(EA)group,pain memory model+rACC lesion(rACC lesion)group.The pain memory model was established by sequentially two injecting carrageenan(Carr)into left and right hindpaw in rats.EA group were applied to bilateral "Housanli"(ST 36)(2-100 Hz)from 5 h to 5 d every day.In the rACC lesion group,two stainless steel lesion electrodes were inserted to bilateral rACC and a 1 mA(the 30s)direct current was passed through the electrode.To study electrophysiological properties,one recording microwire array was surgically implanted into rACC area.And by the methods of behavior and synchronous multi-channel recording in vivo,it is observed that the behavioral changes of non-noxious mechanical stimulation and avrsive emotional memory paradiam and synchronous changs of neural oscilations in rACC area.Results(1)We reanalyzed 1220 previous mechanosensitivity measurements on the ipsilateral paws of 244 rats measured 5 times in succession.The scatter and violin plots suggest that during 4 later measurements,the distributions of paw withdrawal thresholds(PWTs)were more robust and volatility was smaller than in the first one.Compared to the first mechanical stimulus,higheramplitude LFP signals were observed during the pre-stimulus period of the subsequent 4 stimuli,yielding a generally higher power spectral densities(PSD)in the longitudinal heat maps.The pre-stimulus total PSD of the last 4 stimuli was significantly higher than that of the first stimulus(P<0.05,P<0.05,P<0.05,P<0.05).Compared to the first pre-stimulus period,post hoc analysis revealed an increase in PSD in the delta frequency band(P<0.05 for the subsequent 4 times).(2)The PWTs of left(ipsilateral)hindpaws were rapidly decreased at 4 h after left hindpaws injected by Carr(P<0.05).At 13 d,all rats’ PWTs of left hindpaws were restored.On 1 d after right(contralateral)hindpaws injected by Carr(ie.15 d after left hindpaws injection),rats’PWTs of model group decreased considerably compared to those in control rats(P<0.05);compared with model group,the PWTs of left hindpaws in EA and rACC lesion group were increased(P<0.05).At the 13 d after left hindpaw injection of Carr,the amplitude of LFPs and PSD in the rACC area did not recover before stimulating(rest state),howerver,the amplitude and PSD in rACC decreased during stimulating.On 1 d after right hindpaw injected by Carr,when the probe of the dynamic plantar aesthesiometer is beganning to stimulate the left plantar,the amplitude and PSD in rACC did not change,however,with the increasing of stimulus intensity,the amplitude of LFPs and PSD decreased.Compared to the pre-stimulating period in the same band,the percentage of PSD in theta and gamma band increased during stimulating at 13 d(Bonferroni test;P<0.05,P<0.05).After EA treated,there was a decrease in the theta band at 15 d after left hindpaw injection(1 d after right hindpaws injection)with respect to the pre-stimulating period(Bonferroni test;P<0.05).(3)The results of pain-related aversion emotional memory paradiam showd that after 1 d of right hindpaws injected by Carr,the score values of four groups were not equal(One-way ANOVA;F[3,29]=5.889,P<0.05).Post hoc analysis indicated that the score value in model group was lower than the control group(Bonferroni test;P<0.05);compared with model group,the score values in EA and the rACC lesion group were significantly increasing(Bonferroni test;P<0.05,P<0.05).Compare to 13 d,the mean PSD of theta band in rACC area increased in the two compartments at 15 d after left hindpaws injected by Carr(ie.1 d after right hindpaws injection)(Bonferroni test;P<0.01,P<0.01).In the case of EA stimulation,the mean PSD in the alpha and beta band increased at 15 d with respect to 13 d after left hindpaws injections(Bonferroni test;P<0.01,P<0.01).Compare with-1d,the theta/gamma ratio of the model group itself at 15 d increased significantly(Paired T test,P<0.05);after EA treated,compared to 15 d in the model group,the theta/gamma ratio of EA group decreased(Independent T test,P<0.05)at the same stage.Conclutions:(1)Under physiological conditions,the increase in neuronal oscillations in the delta-band may be related to the adaptation of rats to continuous stimulation of the plantar.(2)In the state of pain memory,rACC neuronal oscillations are more sensitive to non-painful stimuli,and electroacupuncture may disinhibit the rACC neuronal oscillatory activity to distinguish between non-painful and painful stimuli.(3)The increased PSD of the theta band could be related to the retrieval of aversive emotional memory;EA,through inhibiting the up-regulation of PSD power in the theta band and enhancing the PSD power of alpha and beta band,strengthened the inhibition control of topdown,as to regulate pain momery induced responses on emotional dimensions;EA could suppress the retrieval pain memory induced memory impairment driven by the theta/gamma ratio.