Synaptic Transmission: Modulation, Plasticity And Effects Of Drugs Of Abuse

综合神经科学实验室内的研究，突触药理学部分，继续侧重于神经调节和可塑性的机制，以及酒精和其他滥用药物对这些神经元功能的影响。我们的主要兴趣是背侧纹状体（DS）的功能，这是一个涉及动作控制和选择以及动作学习的大脑区域。 阿片类/阿片受体介导的纹状体突触长期抑制。 我们继续我们的研究长时程突触抑制（LTD）在纹状体的突触。实验室先前的工作表明，不同的突触前G蛋白偶联受体（GPCRs）可以启动长期抑制纹状体中棘神经元（MSNs）突触处的谷氨酸释放。 这些受体共有的主要特性是Gi/o型G蛋白的激活。 阿片肽，如脑啡肽和强啡肽，是阿片受体的内源性激动剂。 三种经典的阿片受体是Gi/o偶联的μ、δ和κ亚型（分别为MORs、DORS和KORs）。 这些受体存在于纹状体中，包括在该脑区域的突触前元件上。 阿片肽脑啡肽和强啡肽在纹状体中也很丰富，它们的表达在两种不同的MSN亚型中分离，分别称为直接和间接途径MSN。 阿片肽及其同源受体与奖励的神经机制有关，因此我们有兴趣确定它们如何影响纹状体的突触传递，因为这个大脑区域在奖励相关行为中发挥作用。 当从小鼠或大鼠脑切片中的MSN记录时，我们观察到三个OR中的任何一个的激活都产生对突触能突触传递的抑制。 不同受体的拮抗剂抵消亚型选择性激动剂的作用，因此不同的OR似乎独立地起作用以抑制传递。 我们的研究结果表明，突触抑制主要是由于减少神经递质释放。 令人惊讶的是，OR激动剂诱导的抑郁是持久的，即使在激动剂应用已经终止时也持续长达30分钟。 使用已知降解脑啡肽和强啡肽的特定肽酶的阻断剂揭示了OR介导的持久的突触抑制，表明内源性神经肽可以激活这些反应。 阿片激动剂用于治疗疼痛，因此，重要的是要知道，如果在体内暴露于这样的药物改变阿片介导的纹状体LTD。事实上，阿片LTD是不能诱导的纹状体切片从动物在24小时内的一个单一的体内注射羟考酮，广泛使用的阿片类镇痛药。 我们迄今的研究结果表明，内源性阿片类药物产生的LTD的形式，在多巴胺能纹状体突触，具有类似于其他神经递质，激活Gi/o-耦合GPCR产生的属性。 此外，这种突触可塑性可以在使用OR激动剂的治疗性治疗期间被阻止或闭塞，并且还可以在习惯性药物使用和阿片成瘾的发展中发挥作用。 乙醇对纹状体GABA能突触的作用 我们还在继续研究乙醇（EtOH）对背外侧（DLS）和背内侧纹状体（DMS）GABA能突触传递的影响。 我们的观察，乙醇抑制GABA能突触传递在DLS MSNs通过突触前机制，而增强传输在DMS中，表明不同的机制EtOH的行动在两个纹状体亚区。 我们已经开始使用光遗传学技术来确定这些差异EtOH效应是否发生在MSN的不同传入输入。 纹状体MSN的两种主要GABA能输入来自主要在MSN树突上突触的其他MSN的轴突侧支，以及来自主要在MSN索马附近突触的快速尖峰中间神经元。我们可以通过在两种神经元亚型中选择性地表达通道视紫红质2并用光激活该通道来独立地激活两种GABA能输入。使用这种方法，我们发现，乙醇抑制GABA能输入到MSN从两个神经元亚型的DLS。 我们现在开始在DMS中使用相同的方法。 在DLS和DMS中的相反效果是令人惊讶的，并且可能表明EtOH抑制DMS的输出，这对于目标导向的行为是重要的，同时增强参与习惯形成的DLS的输出。

Research within the Laboratory for Integrative Neuroscience, Section on Synaptic Pharmacology, continues to focus on mechanisms underlying neuromodulation and plasticity and the effects of alcohol and other drugs of abuse on these neuronal functions. Our main interest is the function of the dorsal striatum (DS), a brain region involved in action control and selection, as well as action learning. Opiates/Opiate Receptor-Mediated Long-Term Depression at Striatal Synapses. We have continued our studies of long-term synaptic depression (LTD) at synapses in striatum. Previous work in the laboratory indicated that different presynaptic G-protein-coupled receptors (GPCRs) can initiate long-lasting depression of glutamate release at synapses onto striatal medium spiny neurons (MSNs). The main property shared by these receptors is activation of Gi/o-type G proteins. Opioid peptides, such as enkephalin and dynorphin, are endogenous agonists for the opiate receptors. The three classic opiate receptors are the Gi/o-coupled mu, delta and kappa subtypes (MORs, DORS and KORs respectively). These receptors are present in striatum, including on presynaptic elements in this brain region. The opiate peptides enkephalin and dynorphin are also abundant in striatum, where their expression is segregated in two different MSN-subtypes known as the direct and indirect pathways MSNs, respectively. The opiate peptides and their cognate receptors are implicated in neural mechanisms of reward, and we were thus interested in determining how they affect synaptic transmission in the striatum, as this brain region has roles in reward-related behaviors. When recording from MSNs in brain slices from mouse or rat, we have observed that activation of any of the three ORs produces inhibition of glutamatergic synaptic transmission. Antagonists of the different receptors counteract the effects of subtype-selective agonists, and thus the different ORs appear to act independently to depress transmission. Our findings indicate that synaptic depression is mainly due to decreased neurotransmitter release. Surprisingly, the OR agonist-induced depression is long-lasting, persisting for up to 30 min even when agonist application has been terminated. Using blockers of specific peptidases that are known to degrade enkephalin and dynorphin reveals long-lasting synaptic depression that is OR-mediated, indicating that the endogenous neuropeptides can activate these responses. Opiate agonists are used therapeutically for pain treatment, and thus it is important to know if in vivo exposure to such drugs alters opiate-mediated striatal LTD. Indeed, opiate LTD is not inducible in striatal slices made from animals within 24 hr of a single in vivo injection of oxycodone, a widely-used opiate analgesic. Our findings to date indicate that endogenous opiates produce a form of LTD at glutamatergic striatal synapses that has properties similar to that produced by other neurotransmitters that activate Gi/o-coupled GPCRs. Furthermore, this synaptic plasticity may be prevented or occluded during therapeutic treatment with OR agonists, and could also play roles in habitual drug use and the development of opiate addiction. Ethanol actions at striatal GABAergic synapses We are also continuing our studies of ethanol (EtOH) effects on GABAergic synaptic transmission in dorsolateral (DLS) and dorsomedial striatum (DMS). Our observation that EtOH inhibits GABAergic synaptic transmission in DLS MSNs via a presynaptic mechanism, while potentiating transmission in DMS, suggests differential mechanisms of EtOH action in the two striatal subregions. We have begun using optogenetic techniques to determine if these differential EtOH effects occur at different afferent inputs to MSNs. The two predominant GABAergic inputs to striatal MSNs come from axon collaterals of other MSNs that synapse mainly on the MSN dendrites, and from the fast-spiking interneurons that synapse mainly near the MSN soma. We can activate the two GABAergic inputs independently by expressing channel rhodopsin 2 selectively in the two neuronal subtypes and activating this channel with light. Using this approach, we find that EtOH inhibits GABAergic input to MSNs from both neuronal subtypes in the DLS. We are now beginning to use the same approach in the DMS. The opposing effects in DLS and DMS are surprising, and may indicate that EtOH suppresses the output of the DMS that is important for goal-directed actions, while enhancing the output of DLS which is involved in habit formation.