Dopamine receptor trafficking in drug sensitization and behavioral flexibility

 描述(申请人提供)：D2多巴胺受体(D2R)在所有类型的吸毒者中显著下调。然而，D2R下调对药物滥用的功能后果，以及在体内介导药物诱导的D2R丢失的分子机制仍未解决。多巴胺受体介导的信号转导受许多过程的调节。一种方法是通过内吞作用，即激活后从细胞表面移除受体。在内吞作用之后，不同的多巴胺受体被不同地分类：D1R被循环，而D2R被降解。我们已经确定了一种名为GASP1的蛋白质，它负责在内吞作用后靶向降解D2R。我们进一步提出，在药物滥用的重要回路中，D1R-Gs信号和D2R-Gi信号的平衡被破坏，这是由于在高多巴胺张力条件下D2R的下调，从而促进了可塑性和行为的改变。为了支持这一假说，GASP1的基因破坏可以防止可卡因诱导的D2Rs下调，并减弱小鼠对可卡因的运动敏感化发展。在这里，我们将研究改变D2R和D1R信号的平衡如何影响对可卡因的运动(目标1)和奖励(目标2)效应的敏感性。然后，我们将评估伏隔核、腹侧被盖区、杏仁基底外侧核或内侧前额叶皮质中选定神经元中多巴胺受体信号平衡的变化是否必要或足够影响这些行为(目标3)。我们将通过我们创造的新型转基因工具部分实现这一点，包括条件性和非条件性GASP1基因敲除(KO)小鼠，以及表达不结合GASP1的D2R的敲入小鼠。我们还将探讨D2R下调在使用商业上可获得的、具有治疗重要性的多巴胺能配体改变行为中的作用这一问题。虽然这些配体的药理学研究已经有一段时间了，但我们方法的创新之处在于，我们不仅检查了经典的药理性质，如配体的亲和力和选择性，而且还检查了这些配体对内吞和内吞后受体转运的影响。

 DESCRIPTION (provided by applicant): D2 dopamine receptors (D2R) are significantly downregulated in drug abusers of all types. However, both the functional consequences of D2R downregulation for drug abuse, and the molecular mechanisms that mediate drug-induced loss of D2R in vivo remain unresolved. Dopamine receptor-mediated signaling is regulated by numerous processes. One way is by endocytosis, whereby receptors are removed from the cell surface after activation. Following endocytosis, distinct dopamine receptors are sorted differentially: the D1Rs are recycled, while the D2Rs, are degraded. We have identified a protein, GASP1, that is responsible for the targeting of the D2R for degradation after endocytosis. We went on to propose that the balance of D1R-Gs signaling versus D2R-Gi signaling in circuits important to drug abuse becomes disrupted due to downregulation of D2R under conditions of high dopamine tone, and thereby promotes changes in plasticity and behavior. In support of this hypothesis, genetic disruption of GASP1, prevents cocaine induced downregulation of D2Rs and attenuates the development of locomotor sensitization to cocaine in mice. Here, we will examine how altering the balance of D2R and D1R signaling impacts sensitivity to both the locomotor (Aim 1) and rewarding (Aim 2) effects of cocaine. We will then assess whether changes in the balance of dopamine receptor signaling in selected neurons of the nucleus accumbens, ventral tegmental area, basolateral amygdala, or medial pre-frontal cortex are either necessary or sufficient to affect these behaviors (Aim 3). We will accomplish this, in part, with novel transgenic tools we have generated, including conditional and non-conditional GASP1 knock out (KO) mice, and a knock-in mouse expressing a D2R that does not bind GASP1. We will also approach the question of the role of D2R downregulation in altering behavior using commercially available, and therapeutically important, dopaminergic ligands. Although the "pharmacology" of these ligands have been studied for some time, the innovation in our approach lies in our examination of not only classical pharmacological properties, such as ligand affinity and selectivity, but also the effects of these ligands on both endocytic and post-endocytic receptor trafficking.