Microinjection of Ghrelin into the Ventral Tegmental Area Potentiates Cocaine-Induced Conditioned Place Preference

Prior work has shown that systemic cocaine pretreatment augments cocaine conditioned place preference (CPP) in rats. In contrast, ghrelin receptor antagonism attenuates cocaine and amphetamine-induced CPP. In order to further investigate ghrelin’s role in dopamine-mediated reward, the present report examined whether pretreament with ghrelin, administered directly into the ventral tegmental area (VTA) of the midbrain, would potentiate the rewarding properties of cocaine as measured by CPP. Adult male Sprague-Dawley rats were given access to either side of the CPP chamber in order to determine initial side preferences. The rats were then restricted to either their non-preferred or preferred side over the course of conditioning which lasted for a total of 16 consecutive days. This was followed by a final test day to then reassess preference. On days where rats were confined to their non-preferred side, ghrelin (30-300 pmol) and cocaine (0.625-10 mg/kg IP) were administered immediately prior to the conditioning trial. On alternate days rats were treated with vehicle and placed into what was initially determined to be their preferred side. CPP was calculated as the difference in percentage of total time spent in the treatment-paired compartment during the post-conditioning session and the pre-conditioning session. Our results indicated that both cocaine and ghrelin elicited CPP and that ghrelin pretreatment potentiated the effect of cocaine on place preference. Overall, these findings provide additional support for the argument that ghrelin signaling within the VTA enhances the rewarding effects of psychostimulant compounds.

Local infusion of low, but not high, doses of alcohol into the anterior ventral tegmental area causes release of accumbal dopamine

The mesolimbic dopamine system consisting of dopaminergic neurons projecting from the ventral tegmental area (VTA) to the nucleus accumbens (N.Acc.) mediates the reinforcing effects of addictive drugs including alcohol. Given that VTA is a heterogeneous area and that alcohol, in rather low doses, interacts directly with ligand-gated ion channels, we hypothesised that low, rather than high, doses of alcohol into the VTA activate the mesolimbic dopamine system and that alcohol may have different effects in the anterior and posterior parts of the VTA. The present study was undertaken to investigate this hypothesis. The present series of experiment show that infusion of a low dose of alcohol (20 mM) into the anterior, but not posterior, part of the VTA increases accumbal dopamine release in rats. In addition, higher doses of alcohol (100 or 300 mM) into the anterior or posterior part of the VTA do not affect the release of dopamine in the N.Acc., suggesting that low doses of alcohol can activate the mesolimbic dopamine system via mechanisms in the VTA. These data contribute to understanding the neuronal mechanisms underlying the dependence-producing properties of alcohol and could tentatively contribute to that new treatment strategies for alcohol use disorder can be developed.

Effect of crocin carotenoid on BDNF and CREB gene expression in brain ventral tegmental area of morphine treated rats

Objective: To investigate the effect of crocin carotenoid on BNDF and CREB gene expression in the brain ventral tegmental area(VTA) and the serum level of BDNF in morphine-treated rats compared to control. Methods: In this study, 40 male Wistar rats(200-250 g) were used in 5 experimental groups: 1) non morphine treat rats(control); 2) non morphine-treated rats with 25 mg/kg crocin carotenoid(i.p., for 21 d); 3) morphine treated rats(10 mg/kg twice a day, s.c., 21 d); 4 and 5) morphine-treated rats with 12.5 and 25 mg/kg crocin carotenoid, respectively. By the end of research, BDNF and CREB expression was determined by real-time-PCR method. ELISA analysis was also applied for assessing the serum BDNF level. Results: The data indicated that morphine treatment could cause a significant decrease in BDNF and CREB gene expression(P<0.01 and P<0.001, respectively) in brain VTA as well as serum level of BDNF(P<0.01) in comparison to control group. Treatment with 25 mg/kg crocin carotenoid caused a significant enhancement in BDNF and CREF gene expression(P<0.01 and P<0.05, respectively) and serum level of BDNF(P<0.01) in morphine-treated rats in comparison to morphine-treated group. Conclusions: Regarding to obtained results, crocin carotenoid can inhibit unfavorable effects of morphine on the neural system to some extent through enhancing BDNF and CREB gene expression in brain VTA and serum level of BDNF.

Potentiation of the lateral habenula-ventral tegmental area pathway underlines the susceptibility to depression in mice with chronic pain

Chronic pain often develops severe mood changes such as depression.However,how chronic pain leads to depression remains elusive and the mechanisms determining individuals’responses to depression are largely unexplored.Here we found that depression-like behaviors could only be observed in 67.9%of mice with chronic neuropathic pain,leaving 32.1%of mice with depression resilience.We determined that the spike discharges of the ventral tegmental area(VTA)-projecting lateral habenula(LHb)glutamatergic(Glu)neurons were sequentially increased in sham,resilient and susceptible mice,which consequently inhibited VTA dopaminergic(DA)neurons through a LHbGlu-VTAGABA-VTADA circuit.Furthermore,the LHbGlu-VTADA excitatory inputs were dampened via GABAB receptors in a pre-synaptic manner.Regulation of LHb-VTA pathway largely affected the development of depressive symptoms caused by chronic pain.Our study thus identifies a pivotal role of the LHb-VTA pathway in coupling chronic pain with depression and highlights the activity-dependent contribution of LHbGlu-to-VTADA inhibition in depressive behavioral regulation.

Brain region-specific roles of brain-derived neurotrophic factor in social stress-induced depressive-like behavior

Brain-derived neurotrophic factor is a key factor in stress adaptation and avoidance of a social stress behavioral response.Recent studies have shown that brain-derived neurotrophic factor expression in stressed mice is brain region–specific,particularly involving the corticolimbic system,including the ventral tegmental area,nucleus accumbens,prefrontal cortex,amygdala,and hippocampus.Determining how brain-derived neurotrophic factor participates in stress processing in different brain regions will deepen our understanding of social stress psychopathology.In this review,we discuss the expression and regulation of brain-derived neurotrophic factor in stress-sensitive brain regions closely related to the pathophysiology of depression.We focused on associated molecular pathways and neural circuits,with special attention to the brain-derived neurotrophic factor–tropomyosin receptor kinase B signaling pathway and the ventral tegmental area–nucleus accumbens dopamine circuit.We determined that stress-induced alterations in brain-derived neurotrophic factor levels are likely related to the nature,severity,and duration of stress,especially in the above-mentioned brain regions of the corticolimbic system.Therefore,BDNF might be a biological indicator regulating stress-related processes in various brain regions.

Ventral Tegmental Area Neuronal Activity Correlates to Animals’ Behavioral Response to Chronic Methylphenidate Recorded from Adolescent SD Male Rats

Methylphenidate (MPD) is considered as the first-line pharmacotherapy to treat ADHD. More recently, MPD has also been used as a cognitive enhancement recreationally. Its therapeutic effects are not fully understood, nor are the long term effects of the drug on brain development. The ventral tegmental area (VTA) neuronal activity was recorded from freely behaving adolescent rats using a wireless recording system. Five groups were used: saline, 0.6, 2.5, 5.0 and 10.0 mg/kg MPD. The experiment lasted for 10 days. This study demonstrated that VTA neurons respond to MPD in a dose response characteristic and the same dose of MPD can cause both behavioral sensitization and behavioral tolerance. The neuronal unit activity was evaluated based on the animals’ behavioral activity following chronic MPD administration. The study showed that the animals’ behavioral response to different acute MPD of 0.6, 2.5 and 10.0 mg/kg doses responded in a dose response characteristics. Moreover, the same chronic dose of 0.6, 2.5, and 10.0 mg/kg MPD elicits in some animals’ behavioral sensitization and in some others behavioral tolerance. Therefore, the neuronal activity recorded from animals expressing behavioral sensitization was analyzed separately from the neuronal activity recorded from of behaviorally tolerant animals and it was found that the VTA units of the behaviorally sensitization animals responded significantly different to the drug than those VTA units recorded from animals expressing behavioral tolerance.

D-Cell Hypothesis: Pathogenesis of Mesolimbic Dopamine Hyperactivity of Schizophrenia

In the present article, the author proposes a new “D-cell hypothesis” for mesolimbic dopamine (DA) hyperactivity of schizophrenia, of which relevant molecular mechanism has not yet been known. The “D-cell” is defined as “the non-monoaminergic aromatic L-amino acid decarboxylase (AADC)-containing cell”. The D-cell contains AADC but not dopaminergic nor serotonergic. D-cells produce trace amines, and also take up amine precursors and convert them to amines by decarboxylation. The author reported “dopa-decarboxylating neurons specific to the human striatum”, that is, “D-neurons” in the human striatum, and preliminarily the number reduction of D-neurons in the striatum and nucleus accumbens of postmortem brains of patients with schizophrenia. Trace amine-associated receptor, type 1 (TAAR1), a subtype of trace amine receptors, having a large number of ligands, including tyramine, β-phenylethylamine (PEA), and methamphetamine, is a target receptor for the latest neuroleptic discovery. Recent studies have shown that the decreased stimulation of TAAR1 on cell membranes or nerve terminals of DA neurons in the midbrain ventral tegmental area (VTA) increased firing frequency of VTA DA neurons. In brains of schizophrenia, dysfunction of neural stem cells in the subventricular zone of lateral ventricle may cause reduction of the number of D-neurons in the striatum and nucleus accumbens, and may result in decrease of trace amine synthesis. The decrease of stimulation of TAAR1 on terminals of VTA DA neurons caused by trace amine reduction may increase firing frequency of VTA DA neurons, and may finally cause mesolimbic DA hyperactivity. This innovative theory, “D-cell hypothesis” might explain mesolimbic DA hyperactivity in pathogenesis of schizophrenia.

Lateral habenula neurocircuits mediate the maternal disruptive effect of maternal stress: A hypothesis

Up to 20%of women experience stress-related disorders during the postpartum period;however,little is known about the specific neural circuitry by which maternal stress exerts its negative impacts on mental health and maternal caregiving behavior.Theoretically,such a circuitry should serve as an interface between the stress response system and maternal neural network,transmitting stress signals to the neural circuitry that mediates maternal behavior.In this paper,I propose that the lateral habenula(LHb)serves this interface function.Evidence shows that the LHb plays a key role in encoding stress-induced effects and in the pathophysiology of major depression and stressrelated anxiety,and thus may play a role in maternal behavior as part of the maternal brain network.I hypothesize that maternal stress acts upon the LHb and two of its major downstream targets,i.e.,ventral tegmental area(VTA)and dorsal raphe nucleus(DRN),compromising the maternal care and contributing to postpartum mental disorders.This hypothesis makes three predictions:(1)maternal stress enhances LHb neuronal activity;(2)activation of DRN-and VTA-projecting neurons in the LHb mimics the detrimental effects of maternal stress on maternal behavior;and(3)suppression of DRN-and VTA-projecting neurons in the LHb attenuates the detrimental effects of maternal stress on maternal care in stressed mothers.Confirmation of this hypothesis is expected to enhance our understanding of the neurocircuit mechanisms mediating stress effects on maternal behavior.

“D-cell hypothesis” of schizophrenia: possible theory for mesolimbic dopamine hyperactivity

The author proposes a new “D-cell hypothesis” for mesolimbic dopamine (DA) hyperactivity of schizophrenia. The “D-cell” is defined as “non-monoaminergic aromatic L-amino acid decarboxylase (AADC)-containing cell”. D-cells produce trace amines, such as tyramine and β-phenylethylamine, and may also take up amine precursors and convert them to amines by decarboxylation. Trace amine-associated receptor, type 1 (TAAR1), a subtype of trace amine receptors, has a large number of ligands, including tyramine, β-phenylethylamine and methamphetamine, that influence on human mental states, and is now regarded to be a target receptor for novel neuroleptics. Recent studies revealed that the reduced stimulation of TAAR1 on DA neurons in the midbrain ventral tegmental area (VTA) increased firing frequency of VTA DA neurons. The author and her colleagues reported the decrease of D-neurons in the striatum and nucleus accumbens of postmortem brains of patients with schizophrenia. This may imply the decrease of trace amine synthesis, resulting the reduced stimulation of TAAR1 on terminals of midbrain VTA DA neurons, and may lead to mesolimbic DA hyperactivity in schizophrenia. The decrease of striatal D-neurons of postmortem brains of schizophrenia is supposed to be due to neural stem cell dysfunction in the subventricular zone of lateral ventricle. The decrease of striatal D-neurons and acts of TAAR1 signals on DA neurons-might explain mesolimbic DA hyperactivity of schizophrenia.

光激活大鼠中脑腹侧被盖核投射至臂旁核多巴胺能通路促进全麻苏醒

目的本研究通过光遗传学技术特异性激活雄性Sprague-Dawley(SD)大鼠中脑腹侧被盖核投射至臂旁核多巴胺能通路(VTA DA-PBN),探究该通路在丙泊酚麻醉苏醒中的作用。方法将32只雄性SD大鼠随机分为ChR2+Light on组、ChR2+Light off组、mCherry+Light on组和mCherry+Light off组,每组8只。各组大鼠经尾静脉以11 mg·kg^(-1)剂量进行丙泊酚麻醉诱导,以48 mg·kg^(-1)·h^(-1)剂量麻醉维持30 min,记录翻正反射消失(LORR)和翻正反射恢复(RORR)时间;通过免疫荧光染色验证病毒注射部位;通过在体脑电(EEG)记录麻醉诱导和苏醒期间的皮层脑电变化。结果光遗传学激活VTA DA-PBN通路,LORR时间无统计学差异(P>0.05),RORR时间缩短(P<0.001);与mCherry组相比,ChR2组VTA中c-Fos蛋白表达明显更高(P<0.001);EEG结果显示:RORR期间,光激活组β波功率百分比高于光对照组(P<0.05),而δ波功率百分比低于光对照组(P<0.01)。结论VTA DA-PBN通路参与调控丙泊酚麻醉苏醒阶段,激活这一通路起到促觉醒作用。

氟溴唑仑的奖赏效应及其神经环路机制研究

氟溴唑仑(Flub)是一种新型苯二氮䓬类精神活性物质,其成瘾性及其机制尚不清楚。本研究采用小鼠条件位置偏爱(CPP)模型,研究Flub的奖赏效应,以c-Fos表达评定神经元活性,采用病毒示踪技术追踪神经环路,通过化学遗传技术研究神经环路对奖赏效应的调控作用。结果显示,Flub(ip 3 mg/kg)显著增加小鼠CPP评分,增加腹侧被盖区(VTA)多巴胺(DA)能神经元c-Fos表达。抑制VTA多巴胺能神经元活性,Flub小鼠CPP评分显著降低。病毒示踪显示,VTA多巴胺能神经元接受喙内侧被盖核(RMTg)γ氨基丁酸(GABA)能神经元投射。激活RMTgGABA→VTADA环路或阻断RMTg脑区苯二氮䓬受体,Flub小鼠的CPP评分显著降低。这些结果表明,Flub通过激活RMTg脑区GABA神经元中的苯二氮䓬受体,抑制RMTgGABA→VTADA环路,产生奖赏效应。

多巴胺奖赏系统参与抑郁环路机制及中医药干预研究思考与展望

在寻找提升抗抑郁疗效新策略的过程中,中医药干预逐渐展露出其独特的防治优势。多巴胺奖赏系统密切参与了抑郁症的病理发生发展过程,现今研究多聚焦于多巴胺奖赏系统中某一特定核团的功能机制,而着眼于神经环路功能机制所开展的研究较少。当前奖赏环路的微观研究中,奖赏环路异常和焦虑、抑郁等负面情绪的关联性已获得广泛认可,中医药干预可通过影响奖赏环路发挥抗抑郁作用。该文围绕多巴胺奖赏系统参与抑郁症的环路机制以及中医药干预研究做一综述。

运动改善甲基苯丙胺戒断者抑制控制和药物渴求的机制

背景:抑制控制和药物渴求是评估甲基苯丙胺成瘾者药物戒断的核心要素,备受学界关注。众所周知,要彻底实现对药物成瘾的戒断,恢复吸毒者受损的抑制控制功能,有效降低对药物的渴求是关键。目的:旨在通过系统分析运动与甲基苯丙胺戒断者抑制控制和药物渴求的关系,找出促进甲基苯丙胺成瘾戒断的有效运动干预方案,并进一步探究运动作用的内在机制,以期为未来运动运用于毒品戒断提供理论上的支持和应用上的参考。方法:通过检索中国知网、万方、维普、Web of Science及PubMed数据库,中文检索词为“运动,体育锻炼,甲基苯丙胺,抑制功能,渴求度,成瘾”等,英文检索词为“Sport*,Exercise,Methamphetamine,Drug craving,Executive function,Addiction”等,依据纳入和排除标准对文献进行筛选,最终获得目标文献65篇进行综述分析。结果与结论:①运动对甲基苯丙胺戒断者抑制控制方面,急性和长期中等强度有氧运动或急性中高强度间歇训练均能够显著提升甲基苯丙胺戒断者抑制控制能力,对于长期有氧运动而言,有氧操课练习或全身性的综合练习效果更佳,若运动形式为功率自行车,建议增加运动干预频次。②运动对甲基苯丙戒断者药物渴求度方面,急性中等强度有氧运动和抗阻力训练或长期中等强度、高强度或递增负荷的有氧及抗阻力训练均能够有效降低甲基苯丙胺戒断者的药物渴求度。③运动对甲基苯丙胺介导的机体成瘾具有内在调控作用,首先,运动可通过影响大脑腹侧被盖区酪氨酸羟化酶的表达,进而刺激多巴胺受体偶联蛋白的表达,促进大脑奖赏区域多巴胺的合成,弥补由于甲基苯丙胺成瘾导致的多巴胺耗竭;其次,运动也可通过调控蛋白激酶A抑制剂,影响多巴胺D1受体介导的蛋白激酶A信号通路,通过抑制蛋白激酶A从而影响环磷酸腺苷反应结合蛋白,实现对甲基苯丙胺成瘾的调控;最后,运动也可在基因水平上通过影响大脑红核区细胞c-fos基因的表达,激活该区域谷氨酸神经元亚群,产生奖赏效应,实现对甲基苯丙胺成瘾的改善。④虽然目前研究已证实运动与甲基苯丙胺成瘾的关系,且已明晰运动作用的脑内机制,但是否还存在运动作用的其他脑内调控途径有待通过设计更为科学、严谨的动物或人体实验,从细胞或分子学水平出发进行深入探究。

食物成瘾及其神经环路调控机制

食物成瘾是指人们对某些特定食物(高度加工、可口、高热量的食物)的依赖性达到难以控制的程度,并表现出一系列成瘾样的行为学变化,具有强迫性、长期性和反复性的特点。食物成瘾可引起肥胖症,而且是大部分人不能维持减肥效果或坚持限制性饮食以保持健康体重的核心因素。深入理解食物成瘾及其神经生物学机制,将为干预食物成瘾以改善肥胖提供准确的靶点。食物成瘾的诊断标准是耶鲁大学食物成瘾量表,而食物成瘾的动物模型为小鼠食物自我管理模型。外侧下丘脑-腹侧被盖区-伏隔核神经环路、腹侧被盖区-前边缘皮质-伏隔核神经环路和外侧隔核-结节核神经环路是调控食物成瘾的关键神经环路机制。

大鼠基底前脑Nestin阳性神经元纤维投射的分布

目的探讨基底前脑Nestin阳性神经元是否投射到内侧缰核、基底外侧杏仁核、腹侧被盖区和中脑脚间核及其规律。方法将36只SD大鼠编号后使用随机数字表分为4组,每组9只,分别在内侧缰核(MHb)、基底外侧杏仁核(BLA)、腹侧被盖区(VTA)和中脑脚间核(IP)注射逆行示踪剂快蓝(FB),5 d后取材,用免疫荧光染色观察基底前脑处Nestin、ChAT阳性神经元的投射情况。结果基底前脑可投射至内侧缰核、基底外侧杏仁核,但与腹侧被盖区、中脑脚间核并无投射环路,其中基底前脑-内侧缰核投射环路中约有14.5%由Nestin阳性神经元发出,这两个脑区之间的胆碱能环路中约有26.9%为Nestin亚型;基底前脑-基底外侧杏仁核投射环路中约有5.19%为Nestin阳性神经元,两脑区之间的胆碱能环路中有16.7%为Nestin亚型。结论除已有报道的脑区外,Nestin阳性神经元主要与内侧缰核形成神经环路,也少量投射至基底外侧杏仁核,可能与恐惧记忆、情绪等的调控有关。

腹侧被盖区-内侧前额叶皮质神经环路在觉醒调控过程中作用的研究进展

腹侧被盖区(VTA)与内侧前额叶皮层(mPFC)之间存在相互神经投射,并形成环路,近年来的研究显示该环路在睡眠与全身麻醉的觉醒调控中发挥着重要的作用。本文通过对VTA与mPFC的解剖结构、二者中的各种神经元及投射通路在觉醒调控过程中的作用进行综述,期望为睡眠觉醒与全身麻醉机制研究提供新的思路。

Dopaminergic Neurons in the Ventral Tegmental–Prelimbic Pathway Promote the Emergence of Rats from Sevoflurane Anesthesia

Dopaminergic neurons in the ventral tegmental area(VTA)play an important role in cognition,emergence from anesthesia,reward,and aversion,and their projection to the cortex is a crucial part of the"bottom-up"ascending activating system.The prelimbic cortex(PrL)is one of the important projection regions of the VTA.However,the roles of dopaminergic neurons in the VTA and the VTADA–PrL pathway under sevoflurane anesthesia in rats remain unclear.In this study,we found that intraperitoneal injection and local microinjection of a dopamine D1 receptor agonist(Chloro-APB)into the PrL had an emergence-promoting effect on sevoflurane anesthesia in rats,while injection of a dopamine D1 receptor antagonist(SCH23390)deepened anesthesia.The results of chemogenetics combined with microinjection and optogenetics showed that activating the VTADA–PrL pathway prolonged the induction time and shortened the emergence time of anesthesia.These results demonstrate that the dopaminergic system in the VTA has an emergence-promoting effect and that the bottom-up VTADA–PrL pathway facilitates emergence from sevoflurane anesthesia.

NSC-induced D-neurons are decreased in striatum of schizophrenia: Possible cause of mesolimbic dopamine hyperactivity

Neural stem cell (NSC) hypofunction is an etiological hypothesis of schizophrenia. Although dopamine (DA) dysfunction is also a widely accepted hypothesis, molecular background of mesolimbic DA hyperactivity has not yet been well known. Here, the author proposes “D-cell hypothesis”, accounting for molecular basis of mesolimbic DA hyperactivity of schizophrenia, by NSC hypofunction and decrease of putative NSC-induced D-cells. The “D-cell” is defined as “non-monoaminergic aromatic L-amino acid decarboxylase (AADC)-containing cell”. D-cells produce trace amines, and also take up amine precursors and convert them to amines by decarboxylation. The author reported “dopa-decarboxylating neurons specific to the human striatum”, that is, “D-neurons” in the human striatum, and decrease of striatal D-neurons in patients with schizophrenia. Trace amine-associated receptor, type 1 (TAAR1), a subtype of trace amine receptors, having a quite number of ligands such as tyramine, β-phenylethylamine (PEA) and methamphetamine, has modulating functions on monoamine neurons. It has been known that reduced binding of ligands to TAAR1 receptors on DA terminal of DA neurons of the midbrain ventral tegmental area (VTA) increased firing frequency of VTA DA neurons. In brains of schizophrenia, NSC hypofunction in the subventricular zone of lateral ventricle may cause decrease of D-neurons in the striatum and nucleus accumbens, and may result in decrease of trace amine signals. Decrease of trace amine signals to TAAR1 on VTA DA neurons may increase firing frequency of VTA DA neurons, and may finally cause mesolimbic DA hyperactivity. Increased stimulation to DA D2 receptors of NSCs might suppress NSC proliferation, and may induce additional mesolimbic DA hyperactivity as well as D-cell decrease. This novel theory, “D-cell hypothesis”, possibly explains mesolimbic DA hyperactivity in pathogenesis of schizophrenia.

Role of mesocorticolimbic DA system in reinstatement induced by cue

OBJECTIVE Dopamine(DA)plays important roles in Pavlovian conditioning by mediating reward,learning and motivation.While the conditioning stimulation(CS) is the most important inducement for reinstatement in addiction.The present study investigated the specific role of the DA projections to nucleus accumbens(NAc) and medial prefrontal cortices(mPFC) from ventral tegmental area(VTA) in reinstatement induced by cue.METHODS(1)Optogenetic intracranial self-stimulation and reinstatement.DAT-Cre transgenic mice received an injection of adeno-associated viral vectors encoding channelrhodopsin2(ChR2) or control vector into the VTA resulting in the selective expression of these opsins in DA neurons.Then,we stimulated the VTA,NAc(core and shel) or mP FC [prelimbic cortex(PL) and infralimbic cortex(IL)] via an optical fiber.In the reinforcement test,the mice with ChR2 learned instrumental responses corresponding to the delivery of photostimulation into the VTA with multiple frequencies and during time;in the reinstatement phase,stimulation of the DA projections to NAc(core or shell) or mPFC(IL and PL) from VTA to induce reinstatement after 2 weeks of extinction of self-stimulation.(2)Reinstatement in cocaine self-administration.Virus encoding ChR2 or hM4 Di were injected into VTA of DAT-Cre transgenic mice.The mice with ChR2 and hM4 Di in DA neurons were trained to establish self-administration of cocaine.After 2 weeks of extinction,laser stimulation of the DA projections to NAc(core or shel) or mP FC(IL and PL) was conducted to induce reinstatement.After that,Clozapine was injected in NAc core to test the impacts of VTA-NAc core depression on the reinstatement induced by cue.(3) Photometry of VTA DA neurons in reinstatement.DAT-Cre transgenic mice were received an injection of AAV-DIO-Gcamp6 m into VTA.After cocaine self-administration and extinction,mice with Gcamp6 m were challenged by cue(paired with cocaine previously) and the photometry of VTA DA neurons was conducted during the reinstatement.RESULTS(1)The enhanced self-stimulation behavior was positive correlation with the stimulation of DA neurons in VTA according to the increasing frequency of stimulation and extent stimulation duration time.Furthermore,DA receptor antagonists significantly depressed the frequency curve.(2) Only stimulation of the projections to the NAc core from the VTA significantly induced reinstatement after extinction of self-stimulation,neither shell nor mPFC(PL or IL).(3) Depression of VTA-NAc core projection significantly inhibited the reinstatement induced by cue.(4) DA neurons in VTA were activated when the cue appeared during the period of reinstatement test.CONCLUSION Mesocorticolimbic DA system directly modulate the reinforcement dependant on DA receptor.The activity of DA neurons in VTA is necessary for cue induced relapse.Importantly,projections to NAc core from VTA perform the unique effects in reinstatement.

Brain regional changes of guanine nucleotide binding protein-inhabitant 2 in acute and chronic morphine-tolerant and-dependent rats

BACKGROUND： Drug addiction involves two main central nervous systems, namely the dopamine and noradrenaline systems. These systems are primarily distributed in five brain regions： the ventral tegmental area, the nucleus accumbens, the prefrontal cortex, the hippocampus, and the locus coeruleus. OBJECTIVE： To investigate regional changes of guanine nucleotide binding protein-inhabitant 2 （Gi2） in dopaminergic and noradrenergic neurons in brains of morphine-tolerant and -dependent rats. DESIGN, TIME, AND SETTING： A randomized control study was performed at the Department of Neurobiology in the Second Military Medical University of Chinese PLA （Shanghai, China） between September 2002 and March 2004. MATERIALS： Thirty-six, healthy, male, Sprague-Dawley （SD） rats were used to establish morphine-dependent models. Morphine hydrochloride was a product of Shenyang First Pharmaceutical Factory （China）; naloxone hydrochloride was a product of Beijing Four-Ring Pharmaceutical Factory （China）; and α subunit of Gi2 antibody was offered by Santa Cruz Biotechnology, lnc （USA）. METHODS： Thirty-six SD rats were randomly divided into six groups （n = 6）： （1） acute morphine-dependent group, （2） acute abstinent group, （3） acute control group, （4） chronic morphine-dependent group, （5） chronic abstinent group, and （6） chronic control group. Rats in the acute morphine-dependent and the acute groups were injected with morphine （5 mg/kg）, one injection every two hours, for a total of eight injections. In the acute and chronic morphine-dependent rat models, morphine withdrawal syndrome was precipitated by an injection of naloxone （5 mg/kg）. Rats in the acute control group were given a peritoneal injection of physiological saline at the same administration time as the above two groups. Rats in the chronic morphine-dependent and chronic abstinent groups were injected with morphine three times per day. The administration dose on day 1 was initially 5 mg/kg at 20：00, which increased by 5 mg/kg at 8：00, 12：00, and 20：00 until day 7. On day 13, the dose continuously increased by 10 mg/kg until a chronic morphine-dependent rat model was successfully induced. Afterwards, the rats presented with withdrawal syndromes on naloxone （5 mg/kg） at 8：00 on the same day. Rats in the chronic control group were injected with physiological saline at the same time of the two chronic groups. MAIN OUTCOME MEASURES： The concentration of Gi2 protein in the five brain regions （ventral tegmental area, nucleus accumbens, prefrontal cortex, locus coeruleus, and hippocampus） was detected by immunohistochemistry. RESULTS： In the acute morphine-dependent and acute abstinent groups, Gi2 protein concentration was significantly decreased in the nucleus accumbens, compared to the acute control group （P 〈 0.01）, while no obvious changes were detected in other brain regions. In the chronic morphine-dependent and chronic abstinent groups, Gi2 protein concentration was significantly decreased in the nucleus accumbens, but significantly increased in the locus coeruleus （P 〈 0.01 ） compared to the chronic control group. CONCLUSION： Morphine dependence and tolerance may induce obvious reductions of Gi2 protein levels in the nucleus accumbens of rats. Chronic morphine dependence desensitizes the homologous neurons.