Neuroadaptations Underlying Drug Conditioning and Sensitization

描述（由申请人提供）：反复间歇性暴露于安非他明会导致其精神运动刺激作用的持久敏化，因此几周到几个月后再次暴露于该药物会产生增强的运动反应和药物的自我给药。这些发现支持了下述建议：安非他明的食欲效应敏化可能是由偶然吸毒过渡到毒品渴求和滥用的基础。这种药物致敏的诱导必然涉及与复杂的环境刺激相关联的药物暴露。药物与环境刺激的反复配对导致两者之间形成联系，这些刺激引起的行为和生化反应与药物本身产生的反应相似。因此，很容易混淆联想条件反射和非联想致敏对重复药物暴露后观察到的增强反应的单独贡献。区分这两个过程的一种方法是比较全身安非他明暴露与直接应用于腹侧被盖区（VTA）的安非他明的影响。已知安非他明在VTA中起致敏作用，但当应用于该部位时不能产生调节作用。因此，通过比较VTA和系统给药安非他明的作用，可以相对孤立地研究反复接触该药物的关联和非关联后果。本研究旨在更好地描述联想条件反射和非联想敏化的神经化学和形态学基础，并将测试两个主要假设。假设1：在药物调节过程中，伏隔核（NAcc）中特定蛋白质的活性对于将药物环境与刺激联系起来的习得关联的形成是必要的。初步研究结果表明，在药物暴露期间，抑制NAcc中的蛋白周期蛋白依赖性激酶5 （cdk5）如何阻断联想条件作用，同时保持非联想致敏。此外，通过比较NAcc中由反复全身或VTA安非他明暴露引起的其他蛋白质变化，我们将能够识别与条件反射或致敏相关的其他蛋白质。假设2：特定的神经元群体经历了与条件相关的神经解剖学可塑性。使用c-Fos作为标记来识别参与联想条件反射的NAcc细胞，我们将给这些神经元注射碳氰神经元示踪剂DiI，以便使用共聚焦双光子显微镜表征它们的树突棘形态。

DESCRIPTION (provided by applicant): Repeated intermittent exposure to amphetamine leads to long-lasting sensitization of its psychomotor stimulant effects, such that re-exposure to the drug weeks to months later produces enhanced locomotor responding and self-administration of the drug. These findings support the proposal that sensitization of the appetitive effects of amphetamine may underlie the transition from casual drug use to drug craving and abuse. The induction of this drug-induced sensitization necessarily involves exposure to the drug in association with a complex of environmental stimuli. Repeated pairings of drugs with environmental stimuli leads to the formation of associations between the two such that these stimuli come to elicit behavioral and biochemical responses similar to those produced by the drug itself. Thus, it can be easy to confound the separate contributions of associative conditioning and non-associative sensitization to the enhanced responding observed following repeated drug exposure. One method for distinguishing between these two processes is to compare the effects of systemic amphetamine exposure to those of amphetamine applied directly to the ventral tegmental area (VTA). Amphetamine is known to act in the VTA to initiate sensitization, but fails to produce conditioning when applied to this site. Thus, by comparing the effects of VTA and systemically administered amphetamine, the associative and non-associative consequences of repeated exposure to the drug can be studied in relative isolation. The experiments in this grant proposal aim to better characterize both the neurochemical and morphological underpinnings of associative conditioning and non-associative sensitization, and will test two main hypotheses. Hypothesis 1: The activity of specific proteins in the nucleus accumbens (NAcc) during drug-conditioning are necessary for the formation of learned associations linking the drug environment to stimuli. Preliminary findings demonstrate, and the proposed experiments will further explore, how inhibition of the protein cyclin-dependent kinase 5 (cdk5) in the NAcc during drug exposure blocks associative conditioning while preserving non-associative sensitization. Furthermore, by comparing other protein changes in the NAcc caused by repeated systemic or VTA amphetamine exposure, we will be able to identify other proteins correlated either with conditioning or sensitization. Hypothesis 2: Specific populations of neurons undergo conditioning-related neuroanatomical plasticity. Using c-Fos as a marker to identify NAcc cells contributing to associative conditioning, we will inject these neurons with the carbocyanine neuronal tracer DiI in order to characterize their dendritic spine morphology using confocal 2-photon microscopy. PUBLIC HEALTH RELEVANCE: Drug addiction is a disease that is uniquely costly to society and affects the health, productivity, and well-being of individuals in various age groups and demographics. Much published research demonstrates how prolonged drug use produces changes in the brain. The proposed experiments extend this approach to study how these changes are regulated at the neuronal level by environmental factors that may encourage drug-seeking. Understanding how drug-paired environments regulate brain processes underlying compulsive drug use may lead to novel therapeutic and pharmacological treatments for the disease.