Alpha adrenoceptors modulate VTA and PFC in cocaine sensitization

描述（由申请方提供）：可卡因致敏是由随后的可卡因激发诱导的运动兴奋剂作用的进行性和持久增强。这项工作的目的是阐明α肾上腺素能受体在腹侧被盖区和RFC的可卡因致敏的发展和表达的作用。具体目标有三个：1）评估将α去甲肾上腺素能受体激动剂和拮抗剂微量注射到VTA或RFC中是否调节可卡因致敏的过程。使用可卡因致敏模型，选择性α-去甲肾上腺素能受体激动剂和拮抗剂的VTA或RFC内微量注射将用于定位介导这些药物的药理作用的解剖结构。2)确定行为致敏诱导的腹侧被盖区和RFC α去甲肾上腺素能受体的变化。我们将使用激动剂刺激的[35 S] GTP γ S结合作为功能测定来研究可卡因致敏大鼠中α-1和α-2肾上腺素能受体介导的G蛋白活化。假设可卡因致敏的发展涉及VTA和RFC区域中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，这将促进可卡因致敏。将使用体外受体放射自显影试验，在每种结构中受体的功能性变化和数量/亲和力之间建立相关性。我们还将通过比较7天停药期后的动物，评估这些去甲肾上腺素能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受体在腹侧被盖区谷氨酸释放调节中的作用。将采用体外全细胞膜片钳记录来研究α-2受体在调节谷氨酸释放到VTA多巴胺细胞中的作用。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（EPSC）的影响。配对脉冲比和微型EPSC将提供证据，EPSC的改变是本地化的突触前末梢。假设是突触前α-2受体控制谷氨酸释放到腹侧被盖区神经元。一个亚假设是，在可卡因致敏大鼠中，α-2诱导的谷氨酸释放抑制降低。还将确定停药期后α肾上腺素受体调节谷氨酸释放到VTA细胞中的变化。 了解α肾上腺素受体在可卡因致敏中的调节变化将增加我们对去甲肾上腺素能系统在可卡因成瘾中的作用的认识，并可能为治疗性药理学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..