Alpha adrenoceptors modulate VTA and PFC in cocaine sensitization

描述(由申请人提供)：可卡因敏化是对随后的可卡因挑战所引起的运动刺激效应的渐进和持久的增强。这项工作的目的是阐明VTA和RFC的α肾上腺素能受体在可卡因敏化的发展和表达中的作用。有三个特定的目的：1)评估VTA或RFC内微量注射去甲肾上腺素受体激动剂和拮抗剂是否调节可卡因的敏化过程。利用可卡因敏化模型，VTA或-RFC内微量注射选择性的α-去甲肾上腺素受体激动剂和拮抗剂，以定位介导这些药物药理作用的解剖结构。2)确定行为敏化引起的VTA和RFC的α-去甲肾上腺素受体的变化。我们将使用激动剂刺激的[35S]GTPyS结合作为功能分析来研究α-1和α-2肾上腺素能受体介导的可卡因致敏大鼠G蛋白的激活。假设可卡因敏化的发展包括VTA和RFC区α-1受体功能敏感性的增加和α-2受体功能敏感性的降低，这将促进可卡因敏化。使用体外受体放射自显影分析，将在每个结构中的受体的数量/亲和力的变化与功能的变化之间建立关联。我们还将通过比较停药7天后的动物来评估这些去甲肾上腺素受体的变化是否在行为敏化的启动或表达中发挥作用。3)确定α-2受体在调节VTA谷氨酸释放中的作用。体外全细胞膜片钳记录将被用来研究α-2受体在调节VTA多巴胺细胞谷氨酸释放中的作用。将评估α-2肾上腺素受体激动剂对谷氨酸诱导的兴奋性突触后电流(EPSCs)的影响。配对脉冲比率和微型EPSC将被用来提供证据，证明EPSC的改变局限于突触前终末。假设是突触前α-2受体控制VTA神经元谷氨酸的释放。一个亚假设是，在可卡因致敏的大鼠中，α-2诱导的谷氨酸释放抑制减少。在停药一段时间后，谷氨酸释放到VTA细胞的α肾上腺素能受体调节的变化也将被确定。了解可卡因敏化过程中α-肾上腺素能受体的调节变化将增加我们对去甲肾上腺素系统在可卡因成瘾中作用的认识，并可能为治疗药物干预提供可能的途径。

DESCRIPTION (provided by applicant): Cocaine sensitization is a progressive and long-lasting enhancement of the motor stimulant effect induced by a subsequent cocaine challenge. The goal of this work is to elucidate the role of alpha adrenergic receptors at the VTA and RFC in the development and expression of cocaine sensitization. There are three specific Aims: 1) Assess whether microinjections of alpha noradrenergic receptor agonists and antagonists into the VTA or RFC modulate the process of cocaine sensitization. Using the model of cocaine sensitization, intra-VTA or -RFC microinjections of selective alpha-noradrenergic receptor agonists and antagonists will be used to localize the anatomical structure mediating the pharmacological actions of these drugs. 2) Identify changes in alpha noradrenergic receptors at the VTA and RFC induced by behavioral sensitization. We will investigate alpha-1 and alpha-2 adrenergic receptor mediated G protein activation in cocaine-sensitized rats using agonist-stimulated [35S] GTPyS binding as a functional assay. The hypothesis is that development of cocaine sensitization involves an increase in alpha-1 and a decrease in alpha-2 receptor functional sensitivity in both VTA and RFC areas, which will promote cocaine sensitization. Correlations will be made between changes in functionality and number/affinities of receptors in each structure using an in vitro receptor autoradiography assay. We will also assess whether changes in these noradrenergic receptors play a role in the initiation or expression of behavioral sensitization by comparing animals after a 7days withdrawal period. 3) Determine the role of alpha-2 receptors in the modulation of glutamate release at .the VTA. In vitro whole cell patch clamp recordings will be employed to study the role of alpha-2 receptors in the modulation of glutamate release onto VTA dopamine cells. The effects of alpha-2 adrenoreceptor agonists on glutamate-induced excitatory postsynaptic currents (EPSCs) will be assessed. Paired-pulse ratios and miniature EPSCs will be employed to provide evidence that the EPSC's alterations are localized at the presynaptic terminal. The hypothesis is that presynaptic alpha-2 receptors control glutamate release onto VTA neurons. A sub-hypothesis is that there is a decreased alpha-2 -induced inhibition of glutamate release in cocaine sensitized rats. Changes in alpha adrenoceptor modulation of glutamate release into VTA cells after a withdrawal period will also be determined. Understanding of alpha adrenoceptor modulatory changes in cocaine sensitization will increase our knowledge of the role of the noradrenergic system in cocaine addiction and might provide possible avenues for therapeutic pharmacological interventions..