Endogenous Kynurenic Acid Modulates Prefrontal ACh Levels and Cognitive Behavior

描述（由申请人提供）：精神分裂症（SZ）是一种使人衰弱的精神障碍，在前额皮质（PFC）具有显著而复杂的病理生理。这种皮层病理的几个方面与执行功能的缺陷有关，如工作记忆、注意力和认知灵活性。更彻底地了解导致这些认知障碍的神经化学机制是至关重要的，因为传统的抗精神病药物在减轻这些障碍方面并不是特别有效，而且这些缺陷的严重程度预示着患者融入社会的能力。PFC中17个尼古丁受体（17nAChR）的活性与许多测量执行认知功能的行为任务的表现呈正相关。相反，皮质17nachr的失调与SZ的病因有关。Kynurenic acid （KYNA）是一种星形胶质细胞衍生的神经调节剂，在内源性浓度下，可以抑制包括PFC在内的几个大脑区域的17nAChR活性。精神分裂症患者PFC中KYNA水平升高，这种升高不是抗精神病药物引起的。该项目旨在确定KYNA在调节PFC中基础和刺激的谷氨酸和乙酰胆碱（ACh）水平以及调解前额叶介导的认知行为（知觉集转移）中的作用。我们在大鼠身上的初步数据表明，内源性KYNA水平的波动会调节pfc中谷氨酸和乙酰胆碱的水平。拟议的实验将使用互补的生化、药理学和行为学方法，以及两位经验丰富的pi的协同专业知识，来评估KYNA之间的关键化学事件和功能影响。大鼠PFC中的乙酰胆碱和谷氨酸。Aim #1将利用体内微透析来验证PFC内内源性KYNA水平的波动在17nAChR活性基础水平下影响谷氨酸和乙酰胆碱水平的假设。我们还将确定这些影响是否如假设的那样可以追溯到KYNA拮抗17nAChR的能力，以及KYNA相关的乙酰胆碱水平调节是否由局部谷氨酸介导。目标2将确定在激活17nAChR的两种条件下（一种中央给药和一种行为调节范例），KYNA在多大程度上保持调节前额叶谷氨酸和乙酰胆碱释放的能力，作为任务执行大鼠后续目标的前驱。Aim #3将这些神经化学研究扩展到认知行为领域，并将测试皮质KYNA水平的升高选择性地损害大鼠执行感知集转移任务的能力的假设，这取决于pfc中神经传递的完整性。我们还将确定胆碱能和谷氨酸能功能降低在这种KYNA诱导的行为缺陷中的相对作用。这与SZ的病理生理学特别相关，它与PFC中过量的KYNA水平、皮质谷氨酸能和尼古丁能传递异常以及设定转移任务的明显损伤有关。最后，由于在SZ中可以看到皮质KYNA水平的长期升高，我们将在Aim #4中研究脑KYNA水平持续升高的生化和功能后果。这些慢性效应将在对照动物和使用典型（氟哌啶醇）或非典型（氯氮平）抗精神病药物联合使用临床使用的认知增强药物（加兰他明）靶向17nAChR的辅助治疗的大鼠中进行评估。总的来说，提出的实验将验证星形胶质细胞衍生的KYNA水平的波动有效调节皮层神经传递和前额叶介导的认知行为的新假设。我们将利用这些发现来建立一个实验平台，以测试基于kyna的治疗方法在缓解SZ认知缺陷方面的治疗效果。

DESCRIPTION (provided by applicant): Schizophrenia (SZ) is a debilitating mental disorder with significant and complex pathophysiology in the prefrontal cortex (PFC). Several aspects of this cortical pathology have been linked to deficits in executive functions such as working memory, attention, and cognitive flexibility. A more thorough understanding of the neurochemical mechanisms contributing to these cognitive disorders is critical, as conventional antipsychotics are not particularly effective in alleviating these impairments, and since the severity of these deficits is predictive of the patient's ability to integrate into society. The activity of 17 nicotinic receptors (17nAChR) in the PFC has been positively linked to performance in a number of behavioral tasks that measure executive cognitive functions. Conversely, dysregulation of cortical 17nAChRs has been implicated in the etiology of SZ. Kynurenic acid (KYNA) is an astrocyte-derived neuromodulator that, at endogenous concentrations, inhibits 17nAChR activity in several brain regions, including the PFC. KYNA levels are elevated in the PFC of individuals with schizophrenia, and this increase is not secondary to antipsychotic medication. This project is designed to define the role of KYNA in the modulation of basal and stimulated glutamate and acetylcholine (ACh) levels in the PFC and in the mediation of a prefrontally- mediated cognitive behavior (perceptual set-shifting). Our preliminary data in rats demonstrate that fluctuations in the endogenous levels of KYNA modulate levels of glutamate and ACh in the PFC. The proposed experiments will use complementary biochemical, pharmacological and behavioral methods, and the synergistic expertise of two experienced PIs, to evaluate key chemical events and functional implications of this link between KYNA, ACh and glutamate in the rat PFC. Aim #1 will utilize in vivo microdialysis to test the hypothesis that fluctuations in endogenous KYNA levels within the PFC influence glutamate and ACh levels under conditions of basal levels of 17nAChR activity. We will also determine whether these effects, as hypothesized, can be traced to KYNA's ability to antagonize the 17nAChR and whether the KYNA-related modulation of ACh levels is mediated by local glutamate. Aim #2 will determine, as a prelude to subsequent aims in task-performing rats, the extent to which KYNA retains the ability to modulate prefrontal glutamate and ACh release under two conditions that activate the 17nAChR (a centrally-administered drug and a behavioral conditioning paradigm). Aim #3 extends these neurochemical studies to the realm of cognitive behavior and will test the hypothesis that elevations in cortical KYNA levels selectively impair the ability of rats to perform in a perceptual set-shifting task, which is dependent upon the integrity of neurotransmission in the PFC. We will also determine the relative roles of diminished cholinergic and glutamatergic function in this KYNA-induced behavioral deficit. This is especially relevant to the pathophysiology of SZ which is associated with excessive KYNA levels in the PFC, abnormal cortical glutamatergic and nicotinergic transmission, and pronounced impairments in set- shifting tasks. Finally, since prolonged elevations of cortical KYNA levels are seen in SZ, we will, in Aim #4, study the biochemical and functional consequences of persistent increases in brain KYNA levels. These chronic effects will be evaluated both in control animals and in rats treated with typical (haloperidol) or atypical (clozapine) neuroleptic drugs in combination with an adjunctive therapy targeting the 17nAChR with a clinically used cognition-enhancing drug (galantamine). Collectively, the proposed experiments will test the new hypothesis that fluctuations in astrocyte-derived KYNA levels potently modulate cortical neurotransmission and prefrontally-mediated cognitive behavior. We will use these findings to generate an experimental platform for testing the therapeutic efficacy of KYNA-based treatments in alleviating the cognitive deficits seen in SZ.