GCs, CRF and Stressor-Induced Relapse

描述(申请人提供)：对于许多可卡因成瘾者来说，吸毒是一种压力驱动的行为。先前的研究表明，应激诱导的可卡因寻求部分是通过促肾上腺皮质激素释放因子(CRF)刺激涉及腹侧被盖区(VTA)中的多巴胺(DA)神经元的神经生物学通路而介导的，该通路可能投射到伏核(NA)。应激源和CRF对这一途径的调节似乎是先前使用可卡因的结果，因此可能与成瘾的开始有关。我们已经证明，每天长时间接触可卡因自我给药(SA)的大鼠(LGA大鼠)在应激源(电足电击；EFS)或直接向VTA内注射CRF时表现出更大的恢复，而每天短时间给药的大鼠(SHA大鼠)则表现出更大的恢复。此外，我们还发现，在LGA SA早期，建立高应激源诱导的恢复似乎需要糖皮质激素(GC)的升高，这表明成瘾相关神经可塑性的诱导导致在过量使用可卡因后应激源诱导的药物寻求增加是一个GC依赖的过程。这一建议的目的是检验一种假说，即可卡因成瘾与VTA CRF受体(CRF-R)的表达或功能增加有关，并导致对应激源诱导的渴望和复发的易感性增加。此外，我们假设CRF调节的增强依赖于早期药物暴露时GC的升高和GC受体(GR)的激活。这些假设将在这项提案中以三个具体目标进行检验。在第一个目标中，我们将通过一系列实验进一步研究VTA CRF敏感性增强和应激源诱导的恢复之间的关系，这些实验检测改变的CRF和EFS诱导的恢复的相对时间过程，因为它们与CRF-R表达和运输的变化有关，并确定CRF-R亚型在VTA通过拮抗剂寻求可卡因和通过RNA干扰抑制受体的过程中的参与。在第二个目标中，我们将研究VTA中CRF作用的改变在应激源诱导的NA DA调节中的作用及其参与应激源诱导的可卡因寻找、使用体内微透析以及在NA核心和外壳内给药DA受体拮抗剂。在最终目标中，我们将通过手术肾上腺切除和全天GC替代方法来研究LGA SA对应激源诱导的可卡因寻找、NA DA神经传递和CRF-R表达/运输的GC依赖性的影响，这种方法可以消除诱发的GC分泌，同时保持正常的血浆GC昼夜模式，并通过渗透压小泵中枢输注GR拮抗剂RU-486。了解在可卡因成瘾者中建立应激源诱导的可卡因使用调节的神经生物学过程应有助于开发新的和更有效的治疗方法，特别是对于药物使用是应激驱动的可卡因成瘾者亚群。

DESCRIPTION (provided by applicant): For many cocaine addicts, drug use is a stress-driven behavior. Previous research has shown that stressor- induced cocaine seeking is mediated in part by corticotropin-releasing factor (CRF) stimulation of a neurobiological pathway involving dopamine (DA) neurons in the ventral tegmental area (VTA) that likely project to nucleus accumbens (NA). The regulation of this pathway by stressors and CRF appears to emerge as a consequence of prior cocaine use and therefore may be relevant to the onset of addiction. We have demonstrated that rats provided long access to cocaine for self-administration (SA) each day (LgA rats) display greater reinstatement in response to a stressor (electric footshock; EFS) or administration of CRF directly into the VTA, compared to rats provided shorter daily drug access (ShA rats). Furthermore, we have found that that the establishment of heightened stressor-induced reinstatement appears to require elevation of glucocorticoids (GCs) at the time of earlier LgA SA, suggesting that the induction of addiction-related neuroplasticity leading to heightened stressor-induced drug seeking following excessive patterns of cocaine use is a GC-dependent process. The goal of this proposal is to test the hypothesis that cocaine addiction is associated with an emergent or augmented CRF regulation of dopaminergic neurons projecting from the VTA to a subregion of the NA, the shell, that is attributable to increased VTA CRF receptor (CRF-R) expression or function and leads to a heightened susceptibility to stressor-induced craving and relapse. Furthermore, we hypothesize that the establishment of heightened CRF regulation is dependent upon elevated GCs and activation of GC receptors (GR) at the time of earlier drug exposure. These hypotheses will be tested in this proposal in three specific aims. In the first aim we will further investigate the relationship between augmented VTA CRF sensitivity and stressor-induced reinstatement through a series of experiments that examine the relative time-courses of altered CRF- and EFS-induced reinstatement as they relate to changes in CRF-R expression and trafficking and determine the involvement of CRF-R subtypes in the VTA in stressor-induced cocaine seeking through antagonist administration and receptor knockdown by RNA-interference. In the second aim we will examine the role of altered CRF actions in the VTA in the augmented stressor-induced regulation of NA DA and its involvement in stressor-induced cocaine seeking using in vivo microdialysis in and administration of DA receptor antagonists into the NA core and shell. In the final aim, we will examine the GC- dependence of the effects of LgA SA on stressor-induced cocaine seeking and NA DA neurotransmission and CRF-R expression/trafficking through a surgical adrenalectomy and diurnal GC replacement approach that eliminates evoked GC secretion while maintaining normal diurnal patterns of plasma GCs and through central infusion of the GR antagonist, RU-486 via osmotic minipump. Understanding the neurobiological processes through which stressor-induced regulation of cocaine use is established in cocaine addicts should facilitate the development of new and more effective treatment approaches, particularly for subpopulations of cocaine addicts whose drug use is stress-driven.