| Objective: The aims of present studies were not only to investigate effects of optogenetic activation of anterior cingulate cortex(ACC) on heroin self-administration, heroin seeking behavior induced by cues or heroin priming and learning and memory in rats, but also to observe effects of NMDA antogonist memantine on dose-response curve for heroin self-administration and heroin seeking behavior induced by cues or heroin priming in rats.Experiment 1: Effects of optogenetic activation of ACC on learning and memory.Methods: Adult male SD rats were randomly divided into three groups:control group(Control,n=6), sham operation group(HSA,n=4), and ACC optogenetic activation group(CCE,n=4). CCE group were catheterized in the right jugular vein and microinjected with 1μl pAAV-CaMKⅡα-hChR2-EYFP into ACC(AP:+2.7mm,ML:0.5mm,DV:-2.3mm), then implanted optical fiber 0.5mm above the site of microinjection.HSA group were microinjected with AVV-EYFP into ACC and others were the same with CCE.Control group were directly under eight-arms maze test without operation. HSA and CCE groups were placed in operant chambers for a daily 4h self-administration session under fixed ratio reinforcement schedule(FR1) for consecutive 14 days. Then three goups were under eight-arms maze test. HSA and CCE groups were illuminated by light(470 nm,5mW) in the test. Reference memory errors(RME), working memory errors(WME) and time of test were recorded.Results:In five days’ eight-arms test, RME,WME and time of HSA group were significantly higher than those of control group(P<0.05). RME in day3, WME and time in day3,day5 of CCE group were significantly lower compaired with HSA group(P<0.05).Experiment 2: Effects of optogenetic activation of ACC on heroin self-administration and seeking behavior.Methods: Adult male SD rats were randomly divided into two groups: sham operation group(Vehicle,n=4), and ACC optogenetic activation group(CCE,n=4). The treatment of two groups were the same with experiment 1. After 7 days recovery, all rats were placed in operant chambers for a daily 4h self-administration session under FR1 for consecutive 10 days. On day11, two groups were illuminated by light(470 nm,5mW) at 30 mins intervals during training session. On day12, rats were continued for heroin self-administration until the end of training on day14. Then all rats were subjected to daily 2-h extinction training for consecutive 10 days. On day25, seeking behavior induecd by cues or heroin priming was detcted in 2-h and illumination was provided for the entire duration of the 2-h reinstatement session.The other vehicle and CCE group were trained for a daily 4h self-administration session under FR1 for consecutive 14 days and then extinguished for 10 d. On day25, rats were injected(i.p.) with LY341495(1.5mg/kg) 30 mins prior to reinstatment test, illumination was provided for the entire session.Results: There was no difference in active, inactive pokes and the number of infusion between CCE and vehicle group in heroin self-administration. The active pokes of CCE were lower significantly than vehicle group during cue-induced reinstatement(P<0.05), while there was no difference in active pokes between CCE pretreatment with LY341495 and vehicle group during cue-induced reinstatement. The active responses were no difference between CCE and vehicle group during heroin priming reinstatement.Experiment 3: Effects of illumination of NAc core on heroin self-administration and seeking behavior.Methods: Adult male SD rats were randomly divided into two groups: sham operation group(Vehicle,n=4), and NAc core illumination group(NAE,n=4). NAE group were catheterized in the right jugular vein and microinjected with 1μl pAAV-CaMKⅡα-hChR2-EYFP into ACC(AP:+2.7mm,ML:0.5mm,DV:-2.3mm), then implanted optical fiber in NAc core(AP:+1.2mm,ML:±3.2mm,DV:-6.7mm)at 10°angle. Vehicle group were microinjected with AVV-EYFP into ACC and others were the same with NAE. After 7 days recovery, all rats were placed in operant chambers for a daily 4h self-administration session under FR1 for consecutive 10 days. In day11, two group were illuminated by light(470 nm,5mW) at 30 mins intervals during training session. On day12, rats were continued for heroin self-administration until the end of training on day14. Then all rats were subjected to daily 2-h extinction training for consecutive 10 days. On day25, seeking behavior induecd by cues or heroin priming was detcted in 2-h and illumination was provided for the entire duration of the 2-h reinstatement session.The other vehicle and NAE group were trained for a daily 4h self-administration session under FR1 for consecutive 14 days and then extinguished for 10 d. On day25, rats were injected(i.p.) with LY341495(1.5mg/kg) 30 mins prior to reinstatment test, illumination was provided for the entire session.Results: There was no difference in active, inactive pokes and the number of infusion between NAE and vehicle group in heroin self-administration. The active pokes of NAE were lower significantly than vehicle group during cue-induced reinstatement(P<0.05), while there was no difference in active pokes between NAE treatment with LY341495 and vehicle group during cue-induced reinstatement. The active responses were no difference between NAE and vehicle group during heroin priming reinstatement. Experiment 4: Effects of memantine on heroin self-administration and seeking behavior.Methods: Rats were self-administered heroin under a fixed ratio 1(FR1) schedule for 14 d and then extinguished for 10 d. A progressive schedule(PR3-4) was used to evaluate the relative motivational value of heroin reinforcement. After training, the conditioned cue or heroin priming was introduced for the reinstatement of heroin-seeking behavior. The effects of memantine at doses 1-15mg/kg pretreatment on behaviors were examined under these schedules.Results: Memantine at these doses produced a upward shift in the dose-response curve for heroin self-administration, but failed to inhibition the break point(reward value) under the PR3-4 schedule. In addition, memantine at doses 5-15mg/kg inhibited the reinstatement of heroin seeking induced by heroin priming in a dose-dependent manner, while at dose of 15mg/kg inhibited the reinstatement of conditioned cue-induced heroin seeking. Memantine at these doses failed to alter locomotion activity.Conclusions: Optogenetic activation of ACC can not only improve the cognitive dysfunction induced by heroin chronic exposure, but also inhibit the reinstatement of heroin-seeking induced by cues but not heroin priming, which could be reversed partially by pretreatment with LY341495. Projective pathway from ACC to NAc core may be involved in the heroin seeking behavior induced by cues. These data also demonstrate that acute treatment with memantine reduces the reward effect of heroin and inhibites the reinstatement of heroin seeking induced by heroin priming or cues. |
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