VTA Ionotropic Glutamate Receptors in Cocaine Addiction

描述（由申请人提供）：可卡因成瘾被认为与中脑边缘多巴胺神经元的神经可塑性有关。先前的研究发现，反复“被动”服用可卡因会短暂地增加腹侧被盖区（VTA）多巴胺神经元的兴奋性，这种效应可能导致对药物和其他刺激的长期敏感，从而引发渴望和复发。一些研究认为，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GluR1和NR1亚基上调引起的，而另一些研究认为，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了AMPA和NMDA受体插入突触膜，并增强了受体功能。我们的初步结果表明，慢性可卡因“自我”给药在早期（1天）停药时，VTA中GluR1水平上调约90%。因此，Aim I的研究将进一步表征慢性可卡因自我给药后GluR1上调和其他AMPA和NMDA受体亚基，包括PKA-和PKC/ camkii介导的GluR1和NR1磷酸化，以及可卡因戒断时神经适应性变化的持久性。这些研究还将确定被动给药和自我给药是否对AMPA和NMDA受体亚基有不同的调节，以及这些变化是否与“成瘾”vs特别相关。“非成瘾”表型基于个体偏好的可卡因摄入水平差异。鉴于VTA神经元的功能和解剖异质性，Aim II将测量慢性可卡因自我给药后不同VTA亚区、多巴胺能和gaba能细胞类型中GluR1的上调。目的III和IV将确定GuR1和NR1上调在可卡因自我给药成瘾样变化中的功能作用，以及对戒断中寻求恢复可卡因的直接（短期）和间接（长期）影响。在这些研究中，在行为测试之前，将病毒载体注入VTA，在体内产生高度局部的AMPA和NMDA受体亚基过表达。GluR1和NR1显性负突变体将决定下调AMPA和NMDA受体介导的VTA神经元兴奋性输入对自我给药和恢复的影响。同样，磷酸化抗性突变体将研究PKA-和PKC/ camkii介导的GluR1和NR1磷酸化在调节成瘾行为中的作用。综上所述，这些研究将验证这样的假设：可卡因诱导的VTA GluR1和NR1上调有助于可卡因自我给药的成瘾相关变化，以及戒断后可卡因寻求复发的倾向。

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.