A Study Of The Effects And Mechanisms Of Habenula Negative Feedback On Heroin Psychological Dependence

BackgroundThe mesolimbic dopamine system has been proved to be the key neural substrates underlying the rewarding effects of drugs of abuse. Habenula,a major relay station conveying information between the limbic forebrain and midbrain,mediates the negative feedback information transmission from forebrain dopamine-rich and limbic structures onto midbrain dopamine-secreting cells.Previous studies provided evidence that the habenula appears to be vulnerable to damage following chronic administration of most of abused drugs.The role of habenula in mediating the acute rewarding effects of abused drugs is less clear.ObjectiveWith the present experiments,we aim to examine the effects of bilateral electrolytic lesion of the habenula on the acquisition and maintenance ofâ…£heroin self-administration,in order to investigation the possible role of the habenula in heroin reward.MethodsSeventy-two Male Sprague Dawley rats were divided into two parts including acquisition and maintenance ofâ…£heroin self-administration training,and received bilateral electrolytic or sham lesions of the habenula individually(1.0mA,15s).1.Acquisition group:Fourty male Sprague-Dawley(SD)rats were randomly assigned to Hb-lesioned group(n=12),Hb-sham group(n=12) and Normal group(n=16);After three groups were performed simultaneously with indwelling intravenous catheters.For Hb-lesioned group,Bilateral electrolytic lesion of the habenular nuclei was performed with self-made stainless-steel electrodes by passage of a DC current of 1mA for 15s.For the Hb-sham group,the electrode was inserted at the same coordinates for the same amount of time,but no current was passed. Normal group was only performed with indwelling intravenous catheters. All the rats returned to their home cage where they were allowed to recover for at least 1 week.Self-administration training was conducted under a FR₁ schedule in a daily 4h session(10:00—14:00).Each rat received one time heroin self-administration per day for a total of 14 consecutive days,and Each active nose-poke resulted in a 0.05mg/kgâ…£heroin infusion.Once an animal had exhibited a stable pattern of drug intake on the FR₁ schedule (range of less than 20%)on 3 consecutive days,the operant requirements were switched to the progressive ratio(PR_3-4)format.All the rats were trained for a total of 7 consecutive days.Each session and heroin infusions were mentioned above.2.Maintenance group:Thirty-two male Sprague-Dawley(SD)rats were randomly divided into Hb-lesioned group(n=11),Hb-sham group (n=11)and Normal group(n=10);Three groups were performed with indwelling intravenous catheters at the same time.After they were allowed to recover for at least 1 week,Self-administration training was conducted under a FR₁ schedule in a daily 4h session(10:00—14:00). Each rat received one heroin self-administration per day for a total of 14 consecutive days.After a stable pattern of drug intake(range of less than 20%)on 3 consecutive days,Bilateral electrolytic lesion of the habenular nuclei was performed with self-made stainless-steel electrodes.For the Hb-sham group,the electrode was inserted at the same coordinates for the same amount of time,but no current was passed.After surgery,the rats were allowed 1 week to recover.Normal group was not performed with electrolytic lesion.Then the rats were again given daily heroin self-administration sessions under a FR₁ schedule of reinforcement for a total of 4 consecutive days.Once an animal had exhibited a stable pattern of drug intake on 3 consecutive days,the operant requirements were switched to the progressive ratio(PR_3-4)format and each rat again received one heroin self-administration per day for a total of 8 consecutive days.Each session and heroin infusion were mentioned above.A progressive schedule(PR_3-4)was also used to evaluate the relative strength by measuring the "breakpoint". Results1.Acquisition group:Whatever FR₁ or PR_3-4,One-way ANOVA analysis revealed that the total number of heroin infusions have no significantly different among three groups during the acquisition ofâ…£heroin self-administration(all P＞0.05).Except for the 4^thand 5^thday, there were no significant differences either the total number of active or inactive nose poke responses among three groups under FR₁ schedule during the acquisition ofâ…£heroin self-administration(all P＞0.05). However,we did find significantly increased nose poke responses of Hb-lesioned group during the 3^rdday,and gradually decreased baseline level during the(4^th,5^th,6^th)day.One-way ANOVA analysis showed that the total number of active nose poke responses have significantly different among three groups during the 4^thand 5^thday during the acquisition ofâ…£heroin self-administration(all P＜0.05),and Post hoc comparisons indicated that the total number of active nose poke responses was significantly higher in the Hb-lesioned group than the Hb-sham group or Normal group(all P＜0.05),but there were no significant differences between Hb-sham group and Normal group.In the meantime, One-way ANOVA analysis revealed that the total number of inactive nose poke responses have also significantly different among three groups during the(5^th,6^th,7^th,9^th)day during the acquisition ofâ…£heroin self-administration(all P＜0.05),and Post hoc comparisons indicated that the total number of inactive nose poke responses was also significantly higher in the Hb-lesioned group than the Hb-sham and Normal group(all P＜0.05),but there were also no significant differences between Hb-sham group and Normal group.One-way ANOVA analysis showed that the total distance traveled or activities have also no significantly different among three groups under FR₁ schedule during the acquisition ofâ…£heroin self-administration(all P＞0.05).2.Maintenance group:Whatever pre-lesion and post-lesion,there were no significant differences between the total number of active and inactive poke responses among three groups under FR₁ schedule during the maintenance ofâ…£heroin self-administration(P＞0.05).But there were no significant difference within the total number of active or inactive responses and the total number of heroin infusions under FR1 and PR_3-4during the maintenance ofâ…£heroin self-administration(P＞0.05).One-way ANOVA analysis showed that post-training lesions of the habenula also had no effects on the maintenance ofâ…£heroin self-administration under the FR₁ schedule and no effects on the "breakpoint" under the PR_3-4schedule(P＞0.05).Conclusions1.The results of the present study also suggested that increase in responding reflect the appearance of an impulsive mode of behavior during the acquisition ofâ…£heroin self-administration.These findings suggest that the habenula is only involved in the learning or memory system in controlling the acquisition of heroin self-administration.2.The habenula is not critically involved in maintaining the heroin self-administration once the behavior has been acquired. BackgroundRepeated exposure to many drugs of abuse(cocaine,amphetamine, opioids)results in a progressive and enduring enhancement in the motor stimulant effect elicited by a subsequent drug challenge.This phenomenon,termed behavioral sensitization,is thought to underlie certain aspects of drug addiction.Behavioral sensitization is the consequence of drug-induced neuroadaptive changes in a circuit involving dopaminergic and glutamatergic interconnections between the ventral tegmental area,nucleus accumbens,prefrontal cortex and amygdala.There is strong evidence that habenula(Hb),a major relay station conveying information between the limbic forebrain and midbrain and hindbrain,regulates midbrain dopamine neuronal activity.A functional correlate of the effect on dopamine neurotransmission is that Hb appears to be part of circuit involved in negative feedback regulation of dopaminergic,glutamatergic,serotonergic neurons.Previous studies provided evidence that the Hb appears to be vulnerable to damage following chronic administration of most of abused drugs.However,the role of habenula in mediating behavioral sensitization of abused drugs is less clear.ObjectiveThe main goal of present study was to determine effects of bilateral habenula lesions on locomotor response and expression of behavioral sensitization.MethodsThirty-two male Sprague-Dawley(SD)rats were randomly assigned to Hb-lesioned group(n=12),Hb-sham group(n=10)and Normal group (n=10);Hb-lesioned group received bilateral electrolytic lesions(1.0mA, 15s).For Hb-sham group,the electrode was inserted at the same coordinates for the same amount of time,but no current was passed. Normal group was not operated.All the rats returned to their home cage where they were allowed to recover for at least 1 week.After all the rats were tested 1 hour total distance traveled using Animal video tracking analysis software(AVTAS),then a single s.c.saline injection was given to each rat once a day 48 h before the start of the repeated s.c.heroin injection to acclimate the animals to the injection procedure,total distance traveled was again tested for 2 hours.Induction phase(7 days): three group rats were individually administered in a fixed heroin dosing (0.25mg/kg)schedule that consisted of once daily s.c.injections for 7 consecutive days.Development phase(7 days withdrawal):no a single s.c. heroin injection was given each rat.Expression phase(8^thdays after withdrawal):After all the rats were tested 1 hour total distance traveled, and the lowest total distance traveled was taken as baseline.Subsequently, a single s.c.heroin injection was administered to each rat,total distance traveled was again tested for 2 hours.ResultsWhen we tested the total distance traveled for 10 minutes before challenge,we found the lowest total distance traveled(baseline level).So we analysed 10 minitues total distance traveled before and after challenge.Before challenge:One-way ANOVA analysis showed that the activities(total distance traveled)have significantly different among three groups(F(2,22)=5.769,P=0.010),Mean±SEM:1579.01±1026.62 and 699.50±384.44 and 529.08±399.82.The total distance traveled were significantly higher in the Hb-lesioned group than the Hb-sham or Normal group during 10 minutes before challenge.But there were no significant differences between Hb sham group and Normal group.After challenge:One-way ANOVA analysis showed that there were no significant differences among three groups(F(2,22)=1.529,P=0.239), Mean±SEM 1592.89±1246.05å’Œ1485.10±816.65及1609.83±966.65. The total distance traveled of Hb-sham group or Normal group were significantly higher in the pre-challenge than the post-challenge(P=0.022å’ŒP=0.0019).However,the total distance traveled had no significantly different within Hb-lesioned group.When we explore the total distance traveled ratio(post-challenge/pre-challenge×100%)and the reduction ratio of the total distance traveled(post-challenge—pre-challenge /pre-challenge),we did find that the total distance traveled of Hb-lesioned group rats had nearly no change before and after challenge(the ratio was 100.8%).Compared with Hb-sham group or Normal group individually, there also were significant differences(P＜0.05).Subsequently,we continued to study the reduction ratio of the total distance traveled, Hb-lesioned group mostly equal to 1%,and the total distance traveled were completely inhibited after challenge.Compared with Hb-sham group and Normal group,there were significant differences(P＜0.05), but there were no significant differences between Hb-sham group and Normal group.Conclusions1.The result suggested that the Hb nuclei might attentuate the development and expression of behavioral sensitization to the locomotor-activating effects of heroin when administered repeatedly.2.The results also indicated that lesions of the habenular nuclei blocked the early-appearing sedative effects and enhanced the later-appearing locomotor activational effects seen after systemic injections of heroin(0.25 mg/kg,s.c.). BackgroundConditioned environmental stimuli are known to be an important determinants of drug seeking behavior.c-Fos,the protein product of the protooncogene c-Fos,Therefore,its expression could serve as a marker of regional neuronal activation.C-Fos is significantly expressed in neurons when there are drug-associated cue-induced drug-seeking behaviour. However,the role of habenula in mediating cue-induced drug-seeking behaviour is less clear.ObjectiveTo explore expression of c-Fos was examined in the medial part of the lateral habenula(LHb),a region important for conveying information between the limbic forebrain and midbrain,during cue-evoked heroin-seeking behavior in rats..MethodsUsing an extinction/reinstatement paradigm of relapse animal model, we trained Sprague-Dawley(SD)rats to nose-poke for i.v.heroin(0.05 mg/kg/infusion)either daily for 4 h or 25 infusions for 14 consecutive days.We then tested these animals for cue-evoked heroin-seeking behavior after abstinence from self-administration of heroin for 14 days. C-Fos expression was investigated with immunohistochemical technique.ResultsOne-way ANOVA revealed that the total number of active nose-poke responses was significantly higher in the CUE than the EXT rats(P＜0.05),which was significantly higher than that of the SAL rats(P＜0.05). The one-way ANOVA indicated that there were significant differences between-group.Post hoc comparisons indicated that the total number c-Fos positive neurons was significantly higher in the CUE than the EXT rats,and that of both groups was higher than that observed in the SAL rats(all Ps＜0.05).Conclusions1.Discrete conditioned stimulus(CS)previously associated with the availability and subjective effects of heroin could elicit robust heroin-seeking behavior after prolonged abstinence.2.Increased c-fos expression were identified in the medial part of the lateral habenula during cue evoked heroin seeking in the rats.This observation suggested that LHb may be a key brain site in mediating drug cue-induced heroin-seeking behavior after abstinence from selfadministration of heroin.