DRUG ADDICTION: DUAL 5-HT INNERVATION OF LIMBIC SYSTEM

除了多巴胺(DA)的释放在奖赏中的作用外，最近的证据表明，伏核(NAC)释放的5-羟色胺(5-HT)可能与兴奋剂的成瘾效应有关。对NAC的5-羟色胺投射的解剖组织知之甚少，需要这样的数据来了解该系统的功能。为了阐明5-羟色胺神经元在成瘾和药物诱导的神经递质释放中的作用，本项目将分析5-羟色胺投射到NAC和其他边缘结构的来源，并关注不同转运体表达的5-羟色胺轴突。许多精神刺激性药物通过单胺能转运体发挥作用，对前脑中的5-羟色胺和多巴胺轴突亚群有不同程度的毒性。为了确定影响兴奋剂药理和毒性作用的因素，我们将研究5-羟色胺和多巴胺轴突对对氯苯丙胺(PCA)和甲基苯丙胺(Meth)的易感性。我们已经在NAC中发现了两种不同类型的5-羟色胺轴突，其中一种密集分布在NAC的尾侧外壳，缺乏转运蛋白(SERT)，并且具有高度的耐药性。类似的双5-羟色胺在前额叶(PFC)和内嗅皮层的神经支配也将被分析。(1)本项目将研究(A)支配NAC、PFC和内嗅皮层的5-羟色胺轴突的神经元起源；(B)SERT mRNA和蛋白在起源细胞体中的表达；以及(C)相同的5-羟色胺神经元是否将耐药轴突侧支发送到多个边缘靶区。(2)对NAC壳和内嗅皮层进行EM分析，以确定这些区域是否接受具有新突触特性的曲张5-羟色胺轴突(缺少SERT)的特殊投射。选择性5-羟色胺神经毒素PCA将用于分离两种5-羟色胺轴突类型以进行超微结构分析。本研究有助于了解药物诱导5-羟色胺释放的机制以及5-羟色胺在成瘾中的作用。我们认为5-羟色胺投射的二元性在成瘾、奖赏和情绪状态控制中起重要作用。由脉冲传导引起的5-羟色胺的自然、生理释放不受SERT的影响，应该发生在所有的5-羟色胺轴突中，而药物诱导的释放需要转运体，而且受到更多的限制。因此，我们推测中缝神经元的生理兴奋可能产生不同于药物诱导的5-羟色胺释放的区域模式，这种差异可能是药物成瘾效应的基础。

In addition to the role of dopamine (DA) release in reward, recent evidence suggests that 5-HT released in the nucleus accumbens (NAc) may contribute to the addictive effects of stimulant drugs. Little is known about the anatomic organization of 5-HT projections to the NAc and such data are needed to understand the function of this system. In order to elucidate the role of 5-HT neurons in addiction and in drug- induced release of neuro-transmitter, this project will analyze the origin of 5-HT projections to the NAc and to other limbic structures with attention to sets of 5-HT axons that differ in transporter expression. Many psychostimulant drugs act via monoaminergic transporters and are differentially toxic to subsets of 5-HT and DA axons in forebrain. To identify factors that mediate the pharmacologic and toxic effects of stimulant drugs, we will study the vulnerability of 5-HT and DA axons to p- chloroamphetamine (PCA) and to methamphetamine (Meth). We have identified two separate types of 5-HT axons in the NAc, one of which densely innervates the caudal NAc shell, lacks the transporter (SERT) and is highly drug-resistant. A similar dual 5-HT innervation in prefrontal (PFC) and in entorhinal cortex will also be analyzed. (1) This project will investigate (a) the neuronal origins of 5-HT axons that innervate NAc, PFC and entorhinal cortex; (b) the expression of SERT mRNA and protein in the cell bodies of origin; and (c) whether the same 5-HT neurons send drug-resistant axon collaterals to multiple limbic target areas. (2) The NAc shell and entorhinal cortex will be analyzed by EM to establish whether these regions receive a specialized projection of varicose 5-HT axons (lacking SERT) with novel synaptic properties. The selective 5-HT neurotoxin, PCA, will be used to separate the two 5-HT axon types for ultrastructural analysis. This study should contribute to understanding the mechanisms of drug-induced 5-HT release and the role of 5-HT in addiction. We propose that the duality of 5-HT projections plays an important role in addiction, reward and affective state control. Natural, physiologic release of 5-HT resulting from impulse conduction is independent of SERT and should occur in all 5-HT axons, whereas drug-induced release requires the transporter and is more restricted. Therefore, we postulate that physiologic excitation of raphe neurons is likely to produce a different regional pattern of 5-HT release than does drug-induced release, a difference that may underlie the addictive effects of drugs.