DRUG ADDICTION: DUAL 5-HT INNERVATION OF LIMBIC SYSTEM

除了多巴胺（DA）在奖赏中的作用外，最近的证据表明伏隔核（NAc）释放的5-羟色胺（5-HT）可能有助于兴奋剂药物的成瘾作用。关于5-HT向NAc投射的解剖组织知之甚少，需要这些数据来了解该系统的功能。为了阐明5-HT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-HT向NAc和其他边缘结构的投射的起源，并关注转运蛋白表达不同的5-HT轴突组。许多精神兴奋剂药物通过单胺转运体起作用，对前脑5-HT和DA轴突亚群具有不同的毒性。为了确定介导兴奋剂药理学和毒性作用的因素，我们将研究5-HT和DA轴突对对氯苯丙胺（PCA）和甲基苯丙胺（Meth）的脆弱性。我们在NAc中发现了两种不同类型的5-HT轴突，其中一种密集支配NAc尾侧壳，缺乏转运蛋白（SERT），具有高度耐药性。在前额叶（PFC）和内嗅皮层类似的双5-HT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-HT轴突的神经元起源；(b)起源细胞体中SERT mRNA和蛋白的表达；(c)相同的5-HT神经元是否向多个边缘靶区发送耐药轴突侧枝。(2) NAc外壳和内嗅皮层将通过EM分析，以确定这些区域是否接收曲张的5-HT轴突（缺乏SERT）的特殊投影，并具有新的突触特性。选择性5-HT神经毒素PCA将用于分离两种5-HT轴突类型进行超微结构分析。本研究有助于了解药物诱导的5-HT释放机制以及5-HT在成瘾中的作用。我们认为5-羟色胺的双重性在成瘾、奖励和情感状态控制中起着重要作用。由冲动传导引起的5-HT的自然、生理性释放独立于SERT，应发生在所有5-HT轴突中，而药物诱导的释放需要转运蛋白，并且更受限制。因此，我们假设中缝神经元的生理性兴奋可能会产生与药物诱导释放不同的5-HT释放区域模式，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.