GCs, CRF and Stressor-Induced Relapse

描述（由申请人提供）：对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，应激源诱导的可卡因寻求部分是由促肾上腺皮质激素释放因子（CRF）刺激的神经生物学途径介导的，该途径涉及腹侧被盖区（VTA）的多巴胺（DA）神经元，可能投射到伏隔核（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，因此可能与成瘾的发生有关。我们已经证明，每天长时间自我给药（SA）的大鼠（LgA大鼠）在应激源（足电刺激；EFS）或直接给药CRF时，与每天短时间给药的大鼠（ShA大鼠）相比，表现出更强的恢复能力。此外，我们发现应激源诱导的高强度恢复似乎需要在早期LgA SA时糖皮质激素（GCs）的升高，这表明成瘾相关神经可塑性的诱导导致过度使用可卡因后应激源诱导的高强度药物寻求是一个gc依赖的过程。本研究的目的是验证这样一种假设，即可卡因成瘾与从VTA向NA的一个亚区（壳）投射的多巴胺能神经元的紧急或增强的CRF调节有关，这可归因于VTA CRF受体（CRF- r）表达或功能的增加，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升高和GC受体（GR）的激活。这些假设将在本提案的三个具体目标中得到检验。在第一个目标中，我们将通过一系列实验进一步研究增强的VTA CRF敏感性与应激源诱导的恢复之间的关系，这些实验检查了改变的CRF-和efs诱导的恢复的相对时间过程，因为它们与CRF- r表达和贩运的变化有关，并确定VTA中CRF- r亚型通过拮抗剂给药和rna干扰的受体敲低参与应激源诱导的可卡因寻求。在第二个目标中，我们将研究VTA中改变的CRF作用在增强应激源诱导的NA DA调节中的作用，以及它在应激源诱导的可卡因寻找中的作用，使用体内微透析和DA受体拮抗剂进入NA核和壳。在最终目的中，我们将通过外科肾上腺切除术和每日GC替代方法（消除诱发的GC分泌，同时维持血浆GC的正常昼夜模式）以及通过渗透微型泵中央输注GR拮抗剂RU-486，研究LgA SA对应激源诱导的可卡因寻找和NA - DA神经传递以及CRF-R表达/运输的GC依赖性。了解在可卡因成瘾者中建立压力诱发的可卡因使用调节的神经生物学过程，应该有助于开发新的和更有效的治疗方法，特别是对于因压力而使用毒品的可卡因成瘾亚群。

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. PUBLIC HEALTH RELEVANCE: This project examines the neurobiological mechanisms through which susceptibility to drug relapse during periods of stress is heightened in cocaine addiction. The project focuses on neuroplasticity involving the regulation of neural pathways underlying drug use by corticotropin-releasing factor (CRF), a neuropeptide previously implicated in stress and anxiety. The ability of a rat model of excessive drug use to enhance CRF regulation of drug-seeking behavior in a manner that depends on secretion of glucocorticoid hormones will be tested.