The role of central GLP-1 receptors in animal models of cocaine addiction

描述（由申请人提供）：可卡因成瘾仍然是一个重大的公共卫生问题，目前没有fda批准的有效药物治疗方法。因此，有一个明确的需要，以确定和开发新的药物治疗可卡因的渴望和复发。在某种程度上，药物摄入背后的神经生物学机制与寻找食物的机制是重叠的。我们最近的研究表明，大脑中胰高血糖素样肽-1 （GLP-1）受体的激活会减少高美味食物的摄入。具体来说，刺激中边缘多巴胺系统中的GLP-1受体，包括腹侧被盖区（VTA）和伏隔核（NAc），减少了美味食物的摄入。鉴于大量文献表明VTA和NAc在可卡因成瘾中起关键作用，这些结果表明中枢GLP-1受体的激活也可能阻止大鼠的可卡因摄入和寻找。然而，到目前为止，还没有研究检测中枢GLP-1受体在药物成瘾中的作用。本研究的重点是确定中枢GLP-1受体在可卡因成瘾动物模型中的作用。我们的初步研究结果表明，GLP-1受体激动剂直接进入VTA或NAc可减少可卡因自我给药并恢复可卡因寻求行为，这是一种药物渴望和复发的动物模型。这些令人兴奋的结果表明，GLP-1配体，目前被fda批准用于治疗II型糖尿病，可以用于治疗可卡因依赖。除了使用这两种可卡因成瘾动物模型来筛选GLP-1受体配体对可卡因摄入和寻找的抑制作用（Aim 1）外，我们还将确定内源性VTA和NAc GLP-1信号在可卡因摄入和寻找中的生理相关性。使用GLP-1受体拮抗剂和我们最近开发的shRNA结构，我们将在可卡因自我给药和恢复试验之前减少VTA或NAc中的内源性GLP-1受体信号（目的2）。我们预测，VTA和NAc中GLP-1受体表达的药物抑制和病毒介导的下调将增强可卡因自我给药和可卡因启动诱导的可卡因寻求的恢复。产生glp -1的中枢神经元几乎全部位于尾侧脑干的孤束核（NTS），我们最近发现这些神经元与VTA和NAc有直接的单突触连接。为了确定可卡因暴露是否激活投射到VTA或NAc的NTS glp -1产生神经元，我们将在可卡因自我给药期间和可卡因启动诱导恢复之前向VTA或NAc注射逆行示踪剂fluorgold（目的3）。使用FluoroGold抗体（活性依赖的即时早期基因c-fos）和胰高血糖素前原（PPG）抗体（编码GLP-1的基因），我们将确定可卡因暴露是否激活了NTS表达PPG的神经元，并将其投射到VTA或NAc。可卡因激活NTS ppg表达神经元的机制尚不清楚。可卡因摄入与血浆皮质酮水平升高有关，我们的初步数据表明外周皮质酮摄入增加了NTS中表达ppg的神经元的激活。因此，我们将研究皮质酮直接进入NTS是否足以减弱可卡因的摄入和寻找，以及这些作用是否被VTA或NAc中GLP-1受体的药理抑制所阻断。总之，本研究将为重新利用GLP-1受体配体治疗可卡因成瘾提供强有力的理论依据，并为开发基于大脑中增强的GLP-1信号的有效药物治疗可卡因依赖提供新的框架。

DESCRIPTION (provided by applicant): Cocaine addiction continues to be a significant public health problem for which there are currently no effective FDA-approved pharmacological treatments. Therefore, there is a clear need to identify and develop novel pharmacotherapies for cocaine craving and relapse. The neurobiological mechanisms underlying drug taking overlap, to some degree, with those of food seeking. We have recently shown that intake of highly palatable food is attenuated by glucagon-like peptide-1 (GLP-1) receptor activation in the brain. Specifically, stimulation of GLP-1 receptors in the mesolimbic dopamine system, including the ventral tegmental area (VTA) and nucleus accumbens (NAc), reduced intake of highly palatable food. In light of an extensive literature indicating that the VTA and NAc play a critical role in cocaine addiction, these results suggest that activation of central GLP-1 receptors may also prevent cocaine taking and seeking in rats. However, no studies, to date, have examined the role of central GLP-1 receptors in drug addiction. The proposed research focuses on identifying the role of central GLP-1 receptors in animal models of cocaine addiction. Our preliminary findings indicate that administration of a GLP-1 receptor agonist directly into the VTA or NAc attenuates cocaine self-administration and the reinstatement of cocaine-seeking behavior, an animal model of drug craving and relapse. These exciting results suggest that GLP-1 ligands, which are currently FDA-approved for treating type II diabetes, could be used to treat cocaine dependence. In addition to using these two animal models of cocaine addiction to screen the efficacy of GLP-1 receptor ligands to attenuate cocaine taking and seeking (Aim 1), we will determine the physiological relevance of endogenous VTA and NAc GLP-1 signaling in cocaine taking and seeking. Using a GLP-1 receptor antagonist and our recently developed shRNA construct, we will reduce endogenous GLP-1 receptor signaling in the VTA or NAc prior to cocaine self-administration and reinstatement tests (Aim 2). We predict that pharmacological inhibition and viral-mediated down-regulation of GLP-1 receptor expression in the VTA and NAc will augment cocaine self-administration and cocaine priming-induced reinstatement of cocaine seeking. Central GLP-1-producing neurons are located almost exclusively in the nucleus tractus solitarius (NTS) of the caudal brainstem and we have recently shown that these neurons have direct, monosynaptic connections with the VTA and NAc. In order to determine if cocaine exposure activates NTS GLP-1-producing neurons that project to the VTA or NAc, we will inject the retrograde tracer FluoroGold into the VTA or NAc during cocaine self-administration and prior to cocaine priming-induced reinstatement (Aim 3). Using antibodies for FluoroGold, the activity-dependent immediate early gene c-fos, and preproglucagon (PPG), the gene encoding GLP-1, we will determine whether cocaine exposure activates NTS PPG-expressing neurons that project to the VTA or NAc. The mechanisms by which cocaine activates NTS PPG-expressing neurons are not clear. Cocaine taking is associated with elevated plasma corticosterone levels and our preliminary data indicate that peripheral corticosterone administration increases activation of PPG-expressing neurons in the NTS. Therefore, we will investigate whether corticosterone administration directly into the NTS is sufficient to attenuate cocaine taking and seeking, and whether these effects are blocked by pharmacological inhibition of GLP-1 receptors in the VTA or NAc. Overall, the research proposed in this application will provide strong rationale for re-purposing GLP-1 receptor ligands for the treatment of cocaine addiction and advance a novel framework for the development of efficacious pharmacotherapies for cocaine dependence based on enhanced GLP-1 signaling in the brain.