Role Of PFC And NAc 5-HT_2C Receptor On Heroin Relapse Induced By Cues In Rats

Objective:The central serotonin receptor subtype 5-HT_2C is associated with the cocaine relapse, but whether 5-HT_2C mediates the heroin reward and relapse is not still understood. The present study was performed to investigate the role of PFC and NAc 5-HT_2C receptor on heroin relapse elicited by cues or heroin in rat and to assess the effect of microinjection of high selective 5-HT_2C receptor agonists into either PFC or NAc on heroin-seeking triggered by heroin-paired cues.Methods:Male SD rats were trained to nose-poke on a fixed ratio 5(FR5) schedule of sucrose reinforcement in operant chambers during 7 days and acquire sucrose self-administration. The role of acute systemic injection of 5-HT_2C receptor high selective agonist Ro60-0175 was examined on sucrose self-administration was proved.Male SD rats were trained to heroin self-administration under a fixed ratio schedule. After 14 days self-administration session, the rats set up the heroin self-administration model. Acute systemic injection of 5-HT_2C receptor high selective agonists Ro60-0175 and CP809101 were examined on heroin self-administration with FR1 and PR3-4 schedule respectively. Following 14 days of heroin self-administration, the rats underwent non-heroin extinction training. Rats have access to the heroin-associated cues or the heroin self-administration context.After each daily 2 h extinction training session for 14 days consecutive session, the active response was less than 10 % of the response of self-administration .The rats were put back into the training cages and tested for the role of system administration Ro60-0175 and CP809101 on the reinstatement of drug-seeking triggered by heroin-paired cues or heroin. After 14 days of extinction session, rats were placed in stereotaxic apparatus and guided cannulae for microinjections were implanted bilaterally (PFC and NAc). All rats were put into the self-administration chambers after Ro60-0175(3μg/side, 5μg/side) and vehicle (aCSF 0.5μl/side) microinjection 15min.Results:1. We assessed the effect of systemic injection of Ro60-0175 (vehicles, 0.3,1, 3 mg/kg) on the sucrose self-administration. These data were analyzed with a one-way analysis of variance, which indicated 0.3mg/kg (P=0.89) and 1mg/kg (P=0.28) have no significant differences; otherwise 3mg/kg (P<0.01) has opposite effect , Post-hoc test for active responses showed significant differences (F_3,34=19.91,P<0.01).2. Post hoc comparisons showed that Ro60-0175 (vehicles, 0.3,1, 3 mg/kg) significantly inhibited the active responses of heroin self-administration (F (3, 28) =5.15, P=0.007). Compared with saline group, Ro60-0175(1mg/kg) on the heroin self-administration has significant differences (P=0.001). We assessed the effect of systemic injection of CP809101 (vehicles, 1, 3 mg/kg) on the heroin self-administration. The active responses were analyzed with the post hoc test, which indicated significant changes (F (2, 26) =3.71, P=0.04). A one-way analysis of variance for CP809101 (3mg/kg, s.c.) vs. vehicles showed significant changes (P=0.018).3. The total active responses were analyzed with post hoc tests , which revealed that the role of Ro60-0175 on heroin reinforced effect responding under a PR schedule has no significant changes (F_3,28=1.09,P=0.37) and heroin injections have no significant differences (F_3,28=1.31,P=0.29). We assessed the effect of systemic injection of CP809101 (vehicles, 1, 3 mg/kg, s.c.) on the heroin relapse induced conditioned cues. All active responses were analyzed with post hoc test, which revealed significant differences (F (2, 23) =10.45, P=0.001).The results indicated CP809101 dose-dependently decreased heroin relapse induced heroin and conditioned cues.4. We assessed the effect of systemic injection of Ro60-0175 (vehicles, 0.3, 1 mg/kg, i.p.) on the heroin relapse induced conditioned cues. All active responses were analyzed with post hoc test, which revealed significant differences (F (2, 18) =13.64, P<0.001). The active responses between Ro60-0175 (1mg/kg,i.p) and vehicle with ANOVA showed significant changes(P<0.01) A one-way ANOVA analyzed for CP809101 (1mg/kg, s.c.) vs. high selective 5-HT_2C receptor antagonist SB242084 (1mg/kg,i.p.) +CP809101(1mg/kg,s.c.) showed no significant changes of the conditioned cues induced heroin relapse(P=0.066).5. Microinjection of Ro60-0175(3, 5μg/side) into the PFC prior to presenting conditioned cues inhibited the relapse of heroin seeking induced by cues or heroin. Post hoc comparisons showed that PFC total active responses have significant differences (F (2, 20) = 10.26, P = 0.001). Microinjection of Ro60-0175 (5μg/side) into NAc prior to presenting conditioned cues inhibited the relapse of heroin seeking. A one-way ANOVA analyzed revealed significant differences of treatment (5μg/side). Subsequent Post hoc comparisons showed that the NAc total active responses have no significant differences between the Ro60-0175 (3, 5μg/side ) and the vehicle treatment ( F_2,21=3.06, P=0.071). Conclusions:These results demonstrated that 5-HT_2C receptor may mediate the heroin reward, but not heroin motivation, and the activation of 5-HT_2C in either PFC or NAc may play an inhibitory effect in the heroin seeking behavior induced by cues. Both Ro60-0175 and CP809101 could decrease the heroin taking and seeking behavior, which provides the evidence for 5-HT_2C receptor agonists as potential intervention targets on addiction.