Role Of Deep Brain Stimulation Of Medial Prefrontal Cortex On Heroin Seeking Behavior In Rats

Objective Deep brain stimulation (DBS) has been widely used in the treatment of refractoryobsessive-compulsive, epilepsy, depression and other psychiatric disorders. When compared toother methods using electrical stimulation and brain surgery, DBS has the advantage of beingreversible, non-destructive and safe. Recent research in both animals and humans has indicated thatDBS may have potential for the treatment of drug dependence and relapse, but few studies of DBSon the treatment of heroin dependence, in particular for relapse to heroin seeking, it is not yetentirely clear which brain and paradigm should be applied. And the mechanisms underlying itsintervention also should be further explored. Therefore, in the present study, we used an animalmodel of heroin self-administration to investigate the role and possible mechanisms of DBStreatment for the two sub-regions(dorsal and ventral) of medial prefrontal cortex(mPFC) in theextinction and reinstatement of heroin seeking behavior.Experiment1: Effects of long-term high frequency or low frequency stimulation ofdorsal medial prefrontal cortex (dmPFC) on heroin seeking behavior of rats duringextinction or reinstatement.Methods Adult male SD rats were catheterized in the right jugular vein and implanted anelectrode in the dmPFC. After7days recovery, all rats were placed in operant chambers for a daily4h self-administration session under fixed ratio reinforcement schedule for consecutive14days.Twenty seven rats were randomly divided into three groups: high frequency stimulation group(H-DBS), low frequency stimulation group(L-DBS) and sham control group(Sham)(n=9). After14days of self-administration, all rats were subjected to daily2-h extinction training for consecutive10days. The rats in DBS groups were given high frequency stimulation(130Hz, pulse width of100μs,0.2mA) or low frequency stimulation(10Hz, pulse width of100μs,0.2mA)1h beforeeach extinction session. And Sham rats were same with DBS group except that the stimulatingcurrent was set to0mA. Cue-induced heroin seeking reinstatement test was conducted24h afterthe last extinction training.Results There was no difference in active nose-pokes between stimulated and sham controlgroups during the extinction sessions; One way ANONA found that the rats H-DBS group hadsignificantly lower active pokes in cue-induced reinstatement of heroin seeking compared withthose of sham stimulation group(F(2,24)=5.304, P <0.05), while there was no difference in active pokes between sham stimulation and L-DBS group in cue-induced reinstatement of heroinseeking(P>0.05).Experiment2: Effects of long-term high frequency or low frequency stimulation of ventralmedial prefrontal cortex (vmPFC) on heroin seeking behavior of rats during extinction orreinstatement.Methods The experimental procedure such as animal model of heroin self-administration,electrode implantation, stimulation paradigms and extinction training were all same withExperiment1except that the electrode were implanted in the vmPFC. The rats were randomlydivided into three groups: high frequency stimulation group(H-DBS), low frequency stimulationgroup(L-DBS) and sham control group(Sham)(n=9).Results Early in the extinction training on days1-3, the number of active pokes in H-DBSgroup have an increasing trend,but there was no difference in active nose-pokes between H-DBSand Sham control groups(P>0.05). While maintenance of extinction on days4-7, the number ofactive pokes in H-DBS group were significantly higher than the control group(P<0.05), but noeffect at the end of sessions(P>0.05). But L-DBS treatment didn,t change extinction behavior; Oneway ANONA found that the active pokes of the H-DBS group were significantly higher than thoseof the sham stimulation group(F(2,24)=8.489, P <0.05), but L-DBS group had no effect(P>0.05).Experiment3: Effects of long-term high frequency stimulation of dmPFC on p-CREB，p-AKt and p-ERK expression in the NAc core and NAc shell.Methods The experimental procedure such as animal model of heroin self-administration,electrode implantation, stimulation paradigms and extinction training were all same withExperiment1. The rats were randomly divided into two groups: high frequency stimulationgroup(H-DBS) and sham control group(Sham)(n=9). Rats were killed immediately after the test ofreinstatement. Western blot was used to detect the expression of p-CREB, p-ERK and p-AKt inthe NAc core and NAc shell. And P-CREB positive neurons in NAc core and NAc shell weredetected by immunohistochemical method.Results Western blot showed that the level of p-CREB in the NAc core significantlyincreased in the rats treated with high frequency stimulation(H-DBS) compared with the shamcontrol (t(6)=9.342, P<0.01). In contrast, the level of p-ERK and p-AKt in the NAc coresignificantly decreased in the rats treated with high frequency stimulation(H-DBS) compared withthe sham control(t(6)=13.347, P<0.01; t(6)=11.678，P<0.01). However, both p-CREB and p-ERKin the NAc shell did not change significantly (P>0.05), but could significantly down-regulate the p-AKt expression (t(6)=3.863, P<0.05). In the immunocytochemical assay for p-CREB, highfrequency stimulation of dmPFC significantly increased the number of P-CREB positive nucleis inNAc core compared with the sham control stimulation (t(6)=12.107，P<0.05), but there is notsignificant difference in the NAc shell among the groups(P>0.05). ConclusionsHigh frequency stimulation of dmPFC can inhibit the reinstatement of heroin-seeking inducedby conditioned cues. And the regulation of phosphorylated CREB, phosphorylated ERK andphosphorylated AKt expression in NAc core may contribute to the behavioral inhibition in cue-induced reinstatement. High frequency stimulation of the vmPFC can impair the extinction ofheroin seeking and facilitate the reinstatement of heroin-seeking induced by conditioned cues;Low frequency stimulation of either dmPFC or vmPFC have no influence on heroin seekingbehavior during extinction and cue-induced reinstatement.