VTA Ionotropic Glutamate Receptors in Cocaine Addiction

描述(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，反复被动注射可卡因会短暂增加腹侧被盖区(VTA)的多巴胺神经元的兴奋性，这种效应可能会导致对药物和其他刺激的长期敏感化，从而引发渴望和复发。一些研究认为，多巴胺神经元兴奋性的增加是由于可卡因诱导AMPA和NMDA谷氨酸受体GluR1和NR1亚基的上调，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，该过程促进AMPA和NMDA受体插入突触膜，增强受体功能。我们的初步结果表明，在戒断早期(1天)，慢性可卡因“自我”给药可使VTA内GluR1水平升高约90%。因此，Aim I的研究将进一步表征慢性给药后GluR1上调和其他AMPA和NMDA受体亚基的特征，包括PKA和PKC/CaMKII介导的GluR1和NR1的磷酸化，以及可卡因戒断过程中神经适应性变化的持续性。这些研究还将确定被动给药和自我给药是否对AMPA和NMDA受体亚单位进行了不同的调节，以及基于可卡因摄入量偏好水平的个体差异，变化是否特定地与“上瘾”和“非上瘾”表型有关。鉴于VTA神经元在功能和解剖上的异质性，AIM II将在长期服用可卡因后，测量不同的VTA亚区以及多巴胺和GABA能细胞类型中GluR1的上调。AIMS III和IV将确定GuR1和NR1上调在可卡因自我给药成瘾样改变中的功能作用，以及在戒断过程中恢复寻求可卡因的直接(短期)和间接(长期)影响。在这些研究中，病毒载体将被注入VTA，以在行为测试之前在体内产生高度定位的AMPA和NMDA受体亚基的过度表达。显性阴性的GluR1和NR1突变体将决定下调AMPA和NMDA受体介导的兴奋性输入到VTA神经元对自我给药和恢复的影响。同样，耐磷酸化突变体将研究PKA和PKC/CaMKII介导的GluR1和NR1的磷酸化在调控成瘾行为中的作用。总之，这些研究将检验这一假说，即可卡因诱导的VTA中GluR1和NR1的上调有助于可卡因自我管理的成瘾相关变化，以及在戒断过程中寻求可卡因的复发倾向。

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.