Developmental Trajectories of Prefrontal Cortical GABA Neurons and Schizophrenia

描述(由申请人提供)：多条证据表明，精神分裂症(SZ)是一种由遗传脆弱性和环境风险因素共同导致的神经发育障碍。例如，在青春期使用大麻与遗传脆弱的个人中认知功能障碍和SZ的风险增加有关。大麻中的主要精神活性成分β-9-四氢大麻酚(9-THC)激活大麻素1受体(CB1R)，该受体高度集中在灵长类动物背外侧前额叶皮质(DLPFC)的表达胆囊素的篮子细胞(CB1R/CCK细胞)的轴突终末，该区域与SZ的认知功能障碍有关，导致这些终末释放GABA的抑制。在猴子和人类中，DLPFC回路在青春期(猴子为15-42个月，人类为13-19岁)继续成熟，同时认知功能也有所改善。在猴DLPFC中，GABAA受体1亚单位和CB1R免疫反应性在青春期经历了实质性的变化，这表明这些细胞中合成GABA的关键标志也可能在这一时期迅速变化。我们的初步研究表明，在猴DLPFC中，谷氨酸脱羧酶67和65(GAD67和GAD65)的组织水平在出生后整个发育过程中都会增加，其中GAD65mRNA和蛋白质的水平在青春期显著和迅速地增加，GAD67mRNA和蛋白质的增加更早。我们课题组的新数据还表明，在成年猴DLPFC中，CB1R阳性(CB1R+)终末的GAD65：GAD67蛋白比例高于其他类型的GABA终末。因此，将研究CB1R/CCK篮子细胞体中GAD65和GAD67 mRNAs的发育过程(目标1)及其轴突末端同源蛋白的发育过程(目标2)，以确定猴子DLPFC发育的潜在时期，由于它们的快速变化可能对大麻暴露特别敏感。具体地说，我们预测，在青春期CB1R/CCK篮子细胞和终末中GAD65表达的显著增加定义了这些神经元成熟的敏感期。这一想法将在青春期暴露于大麻一年的猴子身上进行概念验证测试，检查这些依赖措施(目标3)。这种关于细胞特异性发育轨迹的性质和时间的知识将为易患精神分裂症的个人提供最合适的早期药物干预类型和时间。因此，本申请直接针对NIMH战略计划战略2.1，确定发展的变化期也可能是风险或症状出现的脆弱性时期。该建议还为申请人提供了一个重要的机会，学习如何进行假设驱动的研究，并使用新的和成熟的分子神经科学技术对结果进行批判性分析。

DESCRIPTION (provided by applicant): Multiple lines of evidence suggest that schizophrenia (SZ) is a disorder of neurodevelopment caused by the combination of genetic vulnerabilities and environmental risk factors. For example, cannabis use during adolescence is associated with an increased risk for cognitive dysfunction and SZ in genetically vulnerable individuals. The principal psychoactive component in cannabis, delta-9-tetrahydrocannabinol (9-THC), activates cannabinoid 1 receptors (CB1r) that are highly concentrated on the axon terminals of cholecystokinin-expressing basket cells (CB1r/CCK cells) in the primate dorsolateral prefrontal cortex (DLPFC), a region implicated in the cognitive dysfunction of SZ, resulting in the suppression of GABA release from these terminals. In monkeys and humans, DLPFC circuitry continues to mature well into adolescence (~15-42 mos in monkeys and ~13-19 years in humans) in parallel with improvements in cognitive function. In monkey DLPFC, GABAA receptor 1 subunits and CB1r immunoreactivity undergo substantial changes during adolescence, suggesting that key markers for GABA synthesis may also change rapidly in these cells during this period. Our preliminary studies indicate that tissue levels of the two GABA-synthesizing enzymes, glutamic acid decarboxylase 67 and 65 (GAD67 and GAD65), increase in monkey DLPFC throughout postnatal development, with GAD65 mRNA and protein levels substantially and rapidly increasing during adolescence and GAD67 mRNA and protein increasing earlier. Emerging data from our group also suggest that the ratio of GAD65:GAD67 protein is greater in CB1r-positive (CB1r+) terminals than in other classes of GABA terminals in the adult monkey DLPFC. Thus, the developmental courses of GAD65 and GAD67 mRNAs in CB1r/CCK basket cell bodies (Aim 1), and of the cognate proteins in their axon terminals (Aim 2), will be examined to identify potential periods in monkey DLPFC development that by virtue of their rapid change may be especially sensitive to cannabis exposure. Specifically, we predict that a marked increase in GAD65 expression in CB1r/CCK basket cells and terminals during adolescence defines a sensitive period in the maturation of these neurons. This idea will be subjected to a proof-of-concept test by examining these same dependent measures in monkeys exposed for one year to cannabis during adolescence (Aim 3). Such knowledge about the nature and timing of cell-specific developmental trajectories will inform the most appropriate type and timing of early pharmacological interventions in individuals vulnerable for schizophrenia. Thus, this application directly addresses NIMH Strategic Plan Strategy 2.1 by determining how periods of change in development may also be periods of vulnerability for the emergence of risk or symptoms. This proposal also provides the applicant with a crucial opportunity to learn how to conduct hypothesis-driven research and critically analyze results using both novel and well-established molecular neuroscience techniques.