Reward effect of flubromazolam and its underlying neural circuit mechanism
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摘要:
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。
Abstract:Flubromazolam (Flub) is a novel psychoactive substance of benzodiazepines and the mechanism underlying its addiction still remains elusive. This study investigated the reward effect of Flub using conditioned place preference (CPP) mouse model. The neuronal activity was evaluated by c-Fos expression, and the neural circuit was tracked by virus tracing. This study also investigated the regulatory effect of neural circuits on Flub-induced reward effects through chemogenetic approach. The results showed that, at the dose of 3 mg/kg, Flub significantly increased CPP score and c-Fos expression in dopaminergic (DA) neurons of ventral tegmental area (VTA). Inhibition of VTA dopaminergic neuron activity dramatically decreased Flub-induced CPP score. Virus tracing verified GABAergic neuronal projection of medial rostrum tegmental nucleus (RMTg) to VTA dopaminergic neurons. Activation of RMTgGABA→VTADA circuit or blockade of benzodiazepine receptors (BZR) in RMTg significantly decreased Flub-induced CPP score. These results indicate that Flub produced reward effect via BZR-mediated RMTgGABA→VTADA circuit.
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Figure 2. Inhibition of ventral tegmental area (VTA) dopaminergic neuronal activity decreased Flub-induced CPP score A: Representative images showing c-Fos-positive cells and co-localization of c-Fos-positive neurons with tyrosine hydroxylase (TH); B: Statistical plot of number of c-Fos-positive neurons($ \mathit{\mathit{\bar{\mathrm{\mathit{x}}}\mathit{\mathit{\mathit{ }}}}} $±s,n=5); C: Statistical plot of co-localization of c-Fos-positive neurons with TH-positive neurons($ \bar{\mathrm{\mathit{x}}} $±s,n=5); D: Schematic diagram of virus injection; E:Expression of TH-hM4Di-mCherry (red) in the VTA; F: CPP score under chemogenetic inhibition of dopaminergic neurons in VTA of mice treated with Flub ($ \bar{\mathrm{\mathit{x}}} $±s,n=10)
*P<0.05, **P<0.01, ***P<0.001,****P<0.0001
Figure 3. Suppression of rostrum tegmental nucleus (RMTg) inhibitory projections to VTA dopaminergic neurons is necessary for Flub-induced CPP A,D: Schematic diagram of virus injection; B: Expression of GAD67-mCherry (red) in the RMTg; C: mCherry-positive neuronal fibers from VTA-projecting RMTg γ-aminobutyric acid (GABA) neurons; E: Expression of EGFP(green) in the VTA; F:Expression of EGFP in the RMTg; G: Schematic diagram of virus injection; H: The expression of DIO-hM3Dq-mCherry (red) in the RMTg; I: CPP score in chemogenetic activation of RMTgGABA→VTA ($ \mathit{\bar{\mathrm{\mathit{x}}}\mathit{\mathit{\mathit{\mathit{ }}}}} $±s,n=10); J: Schematic diagram of virus injection; K: Representative diagram of cannula track in the VTA; L: CPP score in chemogenetic inhibitions of RMTgGABA→VTA and dopaminergic neurons in VTA($ \mathit{\bar{\mathrm{\mathit{x}}}\mathit{\mathit{\mathit{ }}}} $±s,n=12)
**P<0.01
Figure 4. Intra-RMTg infusion of flumazenil (FMZ) significantly reduced Flub-induced CPP score A: Schematic diagram of cannula track in the RMTg; B: Representative diagram of cannula track in the RMTg; C: CPP score in intra-RMTg of FMZ 10 min before administration of Flub (ip)($ \bar{\mathrm{\mathit{x}}} $±s,n= 9)
**P<0.01
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