TRANSGENIC MICE FOR STUDYING DRUGS OF ABUSE

滥用药物如海洛因和可卡因的一个共同特点是， 人类的使用倾向于形成习惯。类似的行为也 在大鼠和小鼠中观察到， 如果有机会，他会反复服用可卡因。重复的自我- 这些药物的施用被认为主要是由于它们的 强的正增强性能。努力查明 神经解剖学基质，可能涉及在动物的重复 海洛因或可卡因的施用集中在特定的 脑核、微透析和神经药理学研究。 的 目前对这一文献的解释是， 多巴胺神经元负责介导正强化 这些药物的特性。起源于腹侧被盖区 (VTA)，这些神经元主要投射到额叶皮层，嗅觉 结节、杏仁核、隔核和丘脑核。虽然每一个 大脑区域对于药物作用的某些方面可能是重要的， 是腹侧被盖区多巴胺能输入到延髓核， 吸引了最多的注意力。这种兴趣是建立在深刻的 损伤和神经药理学操作的影响 多巴胺对动物行为的影响 对鸦片和可卡因的反应由于多巴胺的作用被认为 由G蛋白偶联受体家族介导， 称为D1样和D2样，多巴胺转运蛋白， 是相当大的兴趣在阐明的作用，每一个这些 蛋白质可能在药物奖励中起作用。不幸的是，我们对 三种D2样受体，D2， D3和D4对动物的整体行为有影响。因此，为了检查 三种D2样受体中的每一种的相对参与， 与药物滥用相关的行为，我们建议开发一种体内模型， 系统通过使用同源重组的基因靶向， 胚胎干细胞和转基因小鼠技术 来培育多巴胺D2和D4受体缺陷的小鼠。一旦这些 已经建立了菌株，它们将被杂交， 产生仅表达D3受体（D2 rec-/D4 rec-）的第三株。 多巴胺D2和D4受体基因的成功靶向， 最初将相对于野生型评价转基因小鼠 老鼠，四种方法。首先，D2和D4的原位杂交分析 受体mRNA的表达将在出生前和出生后进行， 小鼠第二，将对脑进行竞争结合测定， 来自D2和D4 rec-小鼠的膜。接下来，从这些细胞中提取的组织 动物将用于第二信使测定。最后，刻板 行为，条件性位置偏爱和运动活动的rec， 将在药物处理后相对于对照组评估动物 和损伤。这些老鼠的可用性将是一个宝贵的资源 对于许多不同的D2样受体参与的体内研究， 药物敏感和依赖。

A common feature of abused drugs such as heroin and cocaine is that their use by humans tends to become habit forming. Similar behavior has also been observed in rats and mice, who will self-administer opiates or cocaine repeatedly if given the opportunity. The repeated self- administration of these drugs is thought to be primarily due to their strong positive reinforcing properties. Efforts to identify the neuroanatomical substrates that may be involved in an animal's repeated administration of heroin or cocaine has focused on lesioning of specific brain nuclei, microdialysis and neuropharmacological studies. The current interpretation of this literature is that mesocortical-mesolimbic dopamine neurons are responsible for mediating the positive reinforcing properties of these drugs. Originating in the ventral tegmental area (VTA), these neurons project primarily to the frontal cortex, olfactory tubercle, amygdala, septum and nucleus accumbens. Although each of these brain areas may be important with respect to some aspect of drug action, it is the VTA's dopaminergic input to the nucleus accumbens that has attracted the most attention. This interest is founded in the profound effects that both lesioning and neuropharmacological manipulations of dopamine in the nucleus accumbens which have on the animal's behavioral response to opiates and cocaine. Since dopamine's effects are thought to be mediated by a family of G protein-coupled receptors, collectively referred to as D1-like and D2-like, and the dopamine transporter, there is considerable interest in elucidating the role that each of these proteins may play in drug reward. Unfortunately, nothing is known about the relative contributions that each of the three D2-like receptors, D2, D3 and D4 make to an animal's overall behavior. Therefore, to examine the relative participation of each of the three D2-like receptors in behaviors related to drug abuse we propose to develop an in vivo model system. Through the use of gene targeting by homologous recombination in embryonic stem cells and transgenic mouse technology we are attempting to develop mice deficient in dopamine D2 and D4 receptors. Once these strains have been established they will be crossed in an attempt to generate a third strain expressing only D3 receptors (D2rec-/ D4rec-). The successful targeting of the dopamine D2 and D4 receptor genes in the transgenic mice will initially be evaluated, with respect to wild type mice, four ways. First, in situ hybridization analysis of D2 and D4 receptor mRNA expression will be performed on pre- and postnatal rec- mice. Second, competition binding assays will be performed on brain membranes from the D2 and D4 rec- mice. Next, tissues derived from these animals will be used in second messenger assays. Finally, stereotypic behavior, conditioned place preference and locomotor activity of the rec- animals will be assessed relative to controls following drug treatment and lesioning. The availability of these mice will be a valuable resource for many different in vivo studies of D2-like receptor involvement in drug sensitivity and dependence.