Calcium Signaling in the Reward Circuit & Drug Addiction

描述（由申请人提供）：位于中脑腹侧的多巴胺能神经元，即腹侧被盖区和黑质致密部，被认为在奖励感知和滥用药物成瘾（如精神兴奋剂和阿片类药物）中起关键作用。多巴胺神经元的放电模式受兴奋性和抑制性突触输入的控制，并受到奖励和滥用药物的显著调节。多巴胺神经元放电的调节影响目标结构中的多巴胺释放，从而有助于体内奖励驱动的动机行为，包括药物寻求和药物服用行为。最近的研究表明，对多巴胺神经元的谷氨酸能输入的重复刺激引起了由代谢性谷氨酸受体（mGluRs）激活介导的缓慢抑制性突触后电位。这种超极化是由于钙离子从细胞内储存的钙离子释放后，钙活化的钾离子通道打开造成的。该建议的总体假设是，这种钙介导的抑制在控制多巴胺神经元的兴奋性和精神兴奋剂诱导的多巴胺神经元活动调节中起关键作用。第一个目的是确定mGluRs激活后介导钙释放的细胞内信号通路。这将通过结合全细胞膜片钳记录和共聚焦钙成像技术，使用急性制备的大鼠中脑切片来完成。此外，将进行笼状化合物的闪光光解，以在毫秒时间尺度上检查直接应用于细胞质溶胶的第二信使的影响。这些方法将使详细检查细胞内的事件，跟随激活的质膜受体。第二个目的是确定谷氨酸诱导的超极化对多巴胺神经元放电模式的影响。将努力在体外切片制备中再现在体内观察到的发射模式。第三个目的是研究急性给予精神兴奋剂如何干扰mglur诱导的抑制，以调节多巴胺神经元的放电模式。所获得的信息将为理解药物成瘾发展的神经机制开辟一条新的途径。

DESCRIPTION (provided by applicant): Dopaminergic neurons in the ventral midbrain, i.e., the ventral tegmental area and the substantia nigra pars compacta, are believed to be critically involved in the perception of reward and addiction to drugs of abuse, such as psychostimulants and opioids. The firing pattern of dopamine neurons, which is controlled by excitatory and inhibitory synaptic inputs, is significantly modulated by presentation of rewards and administration of drugs of abuse. Modulation of dopamine neuron firing affects dopamine release in target structures, and hence contributes to reward-driven motivated behaviors in vivo, including drug-seeking and drug-taking behaviors. It has been shown recently that repetitive stimulation of glutamatergic inputs to dopamine neurons evokes a slow inhibitory postsynaptic potential mediated by activation of metabotropic glutamate receptors (mGluRs). This hyperpolarization results from the opening of calcium-activated potassium channels following release of calcium from intracellular stores. The overall hypothesis of the proposal is that this calcium-mediated inhibition plays a key role in controlling the excitability of dopamine neurons and in psychostimulant-induced modulation of dopamine neuronal activity. The first aim is to determine the intracellular signaling pathway mediating the release of calcium following the activation of mGluRs. This will be accomplished by combined whole-cell patch clamp recording and confocal calcium imaging techniques using acutely prepared midbrain slices from rats. Furthermore, flash photolysis of caged compounds will be performed to examine the effects of second messengers applied directly into the cytosol on a millisecond time scale. These methods will enable detailed examination of the intracellular events that follow the activation of plasma membrane receptors. The second aim is to determine the impact of this glutamate-induced hyperpolarization on the firing pattern of dopamine neurons. An effort will be made to reproduce the firing pattern observed in vivo in an in vitro slice preparation. The third aim is to investigate how acute administration of psychostimulants interferes with the mGluR-induced inhibition to modulate the firing pattern of dopamine neurons. The information obtained will open a new avenue toward the understanding of the neural mechanism responsible for the development of drug addiction.