VTA Ionotropic Glutamate Receptors in Cocaine Addiction

描述（由申请人提供）：可卡因成瘾被认为涉及中脑边缘多巴胺神经元的神经可塑性。先前的研究发现，重复的“被动”可卡因给药会短暂增加腹侧被盖区（VTA）的多巴胺神经元兴奋性，这种效应可能会诱导对药物和其他刺激的长期敏感，从而引发渴望和复发。一些研究表明，多巴胺神经元兴奋性增加是由可卡因诱导的AMPA和NMDA谷氨酸受体GluR 1和NR 1亚基的上调引起的，而另一些研究表明，这些变化与PKA和PKC/CaMKII介导的磷酸化过程有关，这些磷酸化过程促进AMPA和NMDA受体插入突触膜，并增强受体功能。我们的初步研究结果表明，慢性可卡因“自我”管理产生了约90%的上调GluR 1水平在腹侧被盖区在早期（1天）撤出。因此，目标I中的研究将进一步表征慢性可卡因自我给药后GluR 1上调和其他AMPA和NMDA受体亚单位，包括PKA和PKC/CaMKII介导的GluR 1和NR 1磷酸化，以及可卡因戒断中神经适应性变化的持续性。这些研究还将确定被动和自我管理是否差异调节AMPA和NMDA受体亚基，以及变化是否与基于可卡因摄入量偏好水平的个体差异的“成瘾”与“非成瘾”表型具体相关。考虑到腹侧被盖区神经元的功能和解剖异质性，Aim II将在慢性可卡因自我给药后测量不同腹侧被盖区亚区以及多巴胺能和GABA能细胞类型中的GluR 1上调。目的III和IV将确定GuR 1和NR 1上调在可卡因自我给药成瘾样变化中的功能作用，以及对戒断中可卡因寻求恢复的直接（短期）和间接（长期）影响。在这些研究中，将病毒载体注入VTA中，以在行为测试之前在体内产生AMPA和NMDA受体亚基的高度局部化过表达。显性负性GluR 1和NR 1突变体将决定下调AMPA和NMDA受体介导的腹侧被盖区神经元兴奋性输入对自我给药和恢复的影响。类似地，抗磷酸化突变体将研究PKA和PKC/CaMKII介导的GluR 1和NR 1磷酸化在调节成瘾行为中的作用。总之，这些研究将检验可卡因诱导的VTA中GluR 1和NR 1的上调有助于可卡因自我给药的成瘾相关变化以及戒断中可卡因寻求复发的倾向的假设。

DESCRIPTION (provided by applicant): Cocaine addiction is thought to involve neuroplasticity in mesolimbic dopamine neurons. Previous studies have found that repeated "passive" cocaine administration transiently increases dopamine neuron excitability in the ventral tegmental area (VTA), and this effect may induce long-term sensitization to drugs and other stimuli that trigger craving and relapse. Some studies suggest that increased dopamine neuron excitability is caused by cocaine-induced up-regulation in GluR1 and NR1 subunits of AMPA and NMDA glutamate receptors, while others suggest these changes are related to PKA- and PKC/CaMKII-mediated phosphorylation processes that facilitate AMPA and NMDA receptor insertion into synaptic membranes, and enhance receptor function. Our preliminary results suggest that chronic cocaine "self'-administration produces a ~90% upregulation in GluR1 levels in the VTA at early (1 day) withdrawal. Thus, studies in Aim I will further characterize GluR1 up-regulation and other AMPA and NMDA receptor subunits following chronic cocaine self-administration, including PKA- and PKC/CaMKII-mediated phosphorylation of GluR1 and NR1, and the persistence of neuroadaptive changes in cocaine withdrawal. These studies also will determine whether passive and self-administration differentially regulates AMPA and NMDA receptor subunits, and whether changes are specifically related to "addicted" vs. "non-addicted" phenotypes based on individual differences in preferred levels of cocaine intake. Given functional and anatomical heterogeneity in VTA neurons, Aim II will measure GluR1 up-regulation in distinct VTA subregions, and in dopaminergic and GABAergic cell types, following chronic cocaine self-administration. Aims III and IV will determine the functional role of GuR1 and NR1 up-regulation in addiction-like changes in cocaine self-administration, and both the direct (short-term) and indirect (long-term) effects on reinstatement of cocaine seeking in withdrawal. In these studies, viral vectors will be infused into the VTA to produce highly localized over-expression of AMPA and NMDA receptor subunits in vivo prior to behavioral tests. Dominant negative GluR1 and NR1 mutants will determine the effects of down-regulating AMPA and NMDA receptor-mediated excitatory input to VTA neurons on self-administration and reinstatement. Similarly, phosphorylation-resistant mutants will study the role of PKA- and PKC/CaMKII-mediated phosphorylation of GluR1 and NR1 in regulating addictive behavior. Together, these studies will test the hypothesis that cocaine-induced up-regulation in GluR1 and NR1 in the VTA contributes to addiction-related changes in cocaine self-administration, and the propensity for relapse to cocaine seeking in withdrawal.