Nicotine and Alcohol Co-Dependence

摘要 主流观点认为，多巴胺(DA)在中皮质边缘系统中的传递增强 酒精和尼古丁(NIC)的有益特性。中缘区DA系统由DA组成 中脑腹侧被盖区(VTA)中支配伏核(NAC)的神经元。多巴胺 神经传递是由抑制性VTA GABA神经元调节的，其兴奋性是谷氨酸的净效应 NIC胆碱能受体(NAChRs)对传入神经元谷氨酸和GABA神经传递的调节 终点站。我们已经证明，这些神经元可以被低剂量的乙醇兴奋(Steffensen等人，2009)，但是 被中到高剂量乙醇抑制(Gallegos等人，1999；Ludlow等人，2009；Steffensen等人，2009； Stobbs等人，2004；Yang等人，2010)，以及适应慢性乙醇(Gallegos等人，1999)，表现出明显的 戒断时的过度兴奋。根据我们之前的研究和这里提供的数据，我们提出 VTA GABA神经元是乙醇和NIC急性作用的共同底物。核心论题 这一提议的基础是GABA终末上的6*-nAChRs介导了VTA GABA的急性乙醇抑制 NAc内神经元和DA的释放。此外，VTA GABA神经元在戒断过程中的超兴奋性 慢性乙醇由突触前6*-nAChRs和突触后GABA(A)R介导的适应所致 抑制向这些神经元的突触传递，从而导致中脑边缘多巴胺的调节失调 伴随着对乙醇的依赖和对NIC的共同依赖的动态平衡。我们将研究这一角色 6*-nAChRs在乙醇对VTA-GABA神经元和DA释放的急慢性作用中的作用。我们的 拟议的研究构成了对6*-nAChRs在介导急性酒精中的作用的重点研究 对这些神经元的影响及其对酒精依赖的适应。我们的研究将检验以下几点 具体假设：1)急性乙醇抑制VTA-GABA神经元活性和时相DA释放结果 通过GABA终末上的6*-nAChRs促进GABA的释放；2)缺乏6*-nAChRs导致 酒精消耗和奖赏中断；3)戒断时VTA-GABA神经元的过度兴奋性 慢性乙醇产生的原因是6*-nAChRs的适应和随后DA释放的减少 南汽的终点站。为了验证这些假设，我们提出了三个具体目标，包括 急性和慢性乙醇的电生理、行为、神经化学和分子实验 在GAD GFP基因敲除小鼠、野生型(WT)和6*-nAChR KO小鼠中暴露：1)确定 急性乙醇中的6*-nAChRs对VTA神经元的作用和NAc中的多巴胺释放；2)确定 6*-nAChRs在调节酒精消耗和奖励中的作用；以及3)定义6-nAChRs在调节 戒断大鼠NAc内VTA-GABA神经元的超兴奋性及多巴胺释放的降低 慢性酒精中毒。我们将展示6*-nAChRs介导乙醇增强NIC的初步证据 重组nAChRs表达系统中的电流，乙醇增强GABA对VTA的抑制 GABA神经元和乙醇减少NAc中DA的释放，并影响乙醇奖赏。 NAChR KO小鼠。拟议的研究构成了对VTA作用的彻底和系统的调查 GABA神经元介导乙醇和NIC的急性效应及6~*-nAChR的调节作用 这些神经元的GABA神经传递对中脑边缘的DA神经传递起关键调节作用 与酒精奖赏和依赖有关的系统。这项研究的结果可能为临床前提供 将选择性作用于6*-nAChR的药物视为假定治疗药物的药理学基础 用于治疗酒精依赖和酒精与NIC相互依赖的药物。

ABSTRACT The prevailing view is that enhancement of dopamine (DA) transmission in the mesocorticolimbic system underlies the rewarding properties of alcohol and nicotine (NIC). The mesolimbic DA system consists of DA neurons in the midbrain ventral tegmental area (VTA) that innervate the nucleus accumbens (NAc). Dopamine neurotransmission is regulated by inhibitory VTA GABA neurons, whose excitability is a net effect of glutamate (GLU) and GABA neurotransmission that are modulated by NIC cholinergic receptors (nAChRs) on afferent terminals. We have shown that these neurons are excited by low-dose ethanol (Steffensen et al., 2009), but inhibited by moderate to high-dose ethanol (Gallegos et al., 1999; Ludlow et al., 2009; Steffensen et al., 2009; Stobbs et al., 2004; Yang et al., 2010), and adapt to chronic ethanol (Gallegos et al., 1999), evincing marked hyperexcitability during withdrawal. Based on our previous studies and data presented here, we propose that VTA GABA neurons are a common substrate for the acute actions of ethanol and NIC. The core thesis underlying this proposal is that ¿6*-nAChRs on GABA terminals mediate acute ethanol inhibition of VTA GABA neurons and DA release in the NAc. In addition, VTA GABA neuron hyperexcitability during withdrawal from chronic ethanol results from adaptations in presynaptic ¿6*-nAChRs and postsynaptic GABA(A)R-mediated inhibitory synaptic transmission to these neurons, which contributes to the dysregulation of mesolimbic DA homeostasis that accompanies dependence on ethanol and co-dependence on NIC. We will study of the role of ¿6*-nAChRs in acute and chronic effects of ethanol on VTA GABA neurons and on DA release. Our proposed studies constitute a focused investigation into the role of ¿6*-nAChRs in mediating acute ethanol effects on these neurons and their adaptation with alcohol dependence. Our studies will test the following specific hypotheses: 1) Acute ethanol inhibition of VTA GABA neuron activity and phasic DA release results from enhancement of GABA release via ¿6*-nAChRs on GABA terminals; 2) Lack of ¿6*-nAChRs results in disrupted ethanol consumption and reward; and 3) Hyperexcitability of VTA GABA neurons during withdrawal from chronic ethanol results from adaptation of ¿6*-nAChRs and subsequent reduction of DA release at terminals in the NAc. To test these hypotheses, we propose three Specific Aims, which involve electrophysiological, behavioral, neurochemical and molecular experiments with acute and chronic ethanol exposure in GAD GFP knock-in mice, and in wild type (WT) and ¿6*-nAChR KO mice: 1) Define the role of ¿6*-nAChRs in acute ethanol actions on VTA neurons and dopamine release in the NAc; 2) Define the role of ¿6*-nAChRs in mediating ethanol consumption and reward; and 3) Define the role of ¿6-nAChRs in mediating the hyperexcitability of VTA GABA neurons and lowered dopamine release in the NAc during withdrawal from chronic ethanol. We will show preliminary evidence that ¿6*-nAChRs mediate ethanol enhancement of NIC currents in recombinant nAChRs expression systems,that ethanol enhancement of GABA inhibition to VTA GABA neurons and ethanol reduction in DA release in the NAc, and compromised ethanol reward in ¿6*- nAChR KO mice. The proposed studies constitute a thorough and systematic investigation into the role of VTA GABA neurons in mediating the acute effects of ethanol and NIC and the role of ¿6*-nAChR in modulating GABA neurotransmission to these neurons that critically regulate DA neurotransmission in the mesolimbic system implicated in alcohol reward and dependence. Results from this study could provide a preclinical pharmacologic rationale for considering drugs that act selectively on ¿6*-nAChR as putative therapeutic agents for the treatment of alcohol dependence and alcohol and NIC co-dependence.