Opioid Control of Identified Midbrain GABAergic Synapses

描述（由申请人提供）：中脑腹侧被盖区（VTA）的多巴胺（DA）神经元在阿片类药物的奖励和强化作用中发挥重要作用。在腹侧被盖区内，作用于μ阿片受体的阿片类物质抑制GABA的释放，导致DA神经元的抑制解除（约翰逊和North，1992 a）。然而，VTA DA神经元上的GABA突触不仅来自局部GABA能神经元，而且来自外源性来源，其中至少一些可能对阿片类药物敏感。对腹侧被盖区神经元的两个主要外部抑制源来自丘脑腹侧核（NAc）和腹侧苍白球（VP），这两者都与阿片类物质奖赏密切相关。这些输入尚未得到很好的定义，主要是由于隔离各个连接的技术挑战。尽管如此，我们对阿片类物质奖赏的神经回路的理解需要对这些腹侧被盖区传入神经的突触特性进行彻底的研究。在这项研究中，我们将利用最近开发的光遗传学工具，结合中脑切片中VTA神经元的全细胞膜片钳电生理学，独立激活NAc或VP产生的轴突终末。这将使我们能够比较和对比这两种输入，并确定它们如何受到急性和慢性阿片类药物暴露的调节。此外，通过将这种强大的技术与来自特定投射目标的VTA神经元的逆行标记相结合，我们将能够确定VTA内这些传入神经的详细微电路。这些研究提供的数据将为边缘系统功能的电路模型的发展提供关键信息。

DESCRIPTION (provided by applicant): Dopamine (DA) neurons in the midbrain ventral tegmental area (VTA) play an important role in the rewarding and reinforcing effects of opioids. Within the VTA, opioids acting at the mu opioid receptor inhibit the release of GABA, which leads to the disinhibition of DA neurons (Johnson and North, 1992a). However, GABA synapses onto VTA DA neurons arise not only from local GABAergic neurons, but also from extrinsic sources, at least some of which are likely to be sensitive to opioids. Two major external sources of inhibition onto VTA neurons arise from the nucleus accumbens (NAc) and the ventral pallidum (VP), both of which have been strongly implicated in opioid reward. These inputs have not been well defined, largely due to the technical challenge of isolating individual connections. Nevertheless, our understanding of the neural circuitry underlying opioid reward requires a thorough investigation of the synaptic properties of these VTA afferents. In this grant, we will make use of recently developed optogenetic tools to independently activate axon terminals arising from either the NAc or the VP in conjunction with whole cell patch-clamp electrophysiology from VTA neurons in midbrain slices. This will allow us to compare and contrast these two inputs and to determine how they are regulated by both acute and chronic exposure to opioids. In addition, by combining this powerful technique with retrograde labeling of VTA neurons from particular projection targets, we will be able to determine the detailed microcircuitry of these afferents within the VTA. The data provided by these studies will provide critical information for the development of circuit based models of limbic system function.