Role of NMDA receptors in awake-state thalamocortical slow waves

描述(申请人提供)：在Delta/theta频率范围内的大幅度、全局性脑电振荡通常是慢波睡眠的特征。然而，精神分裂症患者在清醒时，额叶和中央区域的Delta功率很高。这被称为丘脑皮质节律失常。精神分裂症的许多症状可以由NMDAR拮抗剂诱导；在大鼠身上的研究表明，将NMDAR拮抗剂注射到丘脑可以诱导一种增量频率节律失常。我们工作的第一个目标是了解NMDAR拮抗剂是如何产生这种异常的。我们的初步结果指出了一种细胞机制：丘脑网状核(NRT)细胞被NMDAR拮抗剂超极化；这使T型钙通道失活，然后产生增量频率爆发。我们的第二个目标是了解这种效应的分子机制。我们的初步结果证实了原位杂交的结果，即丘脑细胞含有一种罕见的NMDAR亚单位NR2C。这一亚基在静息电位时被镁离子微弱地阻断，因此在环境谷氨酸的作用下产生显著的内向电流；阻断这一电流会导致超极化，从而产生增量频率猝发。因此，我们的工作指向了心律失常的分子/细胞机制。我们工作的第三个目标是了解多巴胺如何与这些过程相互作用。我们的初步结果表明，D2的作用可能与NMDA功能减退在产生心律失常方面具有协同作用。我们将在体内研究这一过程，以确定D2拮抗剂能否减少NMDA功能低下引起的Delta振荡。R.Llinas提出的节律失常假说的一个关键方面是，丘脑的亚区在相关的皮质亚区产生异常的低频振荡；这会导致局部信息处理缺陷，这是疾病症状的基础。我们工作的最终目标是检验这一假设。我们将使用Cre重组酶方法在NRT的亚区产生NMDAR的发育后敲除。我们将测试NRT前部的NMDAR基因敲除是否可以在不影响枕叶皮质的情况下，在精神分裂症患者的额叶/中央区域产生增强的Delta功率。我们将测试这些区域调节的行为是否选择性地受到这些振荡的影响。由于Cre重组酶方法产生慢性变化，它为识别精神分裂症和药物治疗背后的慢性过程提供了一个模型系统。如果成功，这只小鼠将对精神分裂症的脑电症状进行建模，并提供一个系统，在该系统中，可以根据已知的丘脑药理识别潜在的治疗靶点，然后测试它们逆转脑电症状的能力。

DESCRIPTION (provided by applicant): Large amplitude, global EEG oscillations in the delta/theta frequency range are normally characteristic of slow-wave sleep. In schizophrenia, however, delta power is high during wakefulness in frontal and central regions. This has been termed a thalamocortical dysrhythmia. Many symptoms of schizophrenia can be induced by NMDAR antagonists; work in rats shows that a delta frequency dysrhythmia can be induced by injection of NMDAR antagonist into the thalamus. The first goal of our work is to understand how NMDAR antagonists generate this abnormality. Our preliminary results point to a cellular mechanism: cells of the nucleus reticularis (nRT) of the thalamus are hyperpolarized by NMDAR antagonist; this deinactivates T-type Ca2+ channels which then generate delta frequency bursting. Our second goal is to understand the molecular mechanism of this effect. Our preliminary results confirm in situ hybridization showing that thalamic cells contain a rare form of NMDAR subunit, NR2C. This subunit is weakly blocked by Mg2+ at resting potential and thus generates a significant inward current in response to ambient glutamate; block of this current leads to the hyperpolarization that produces delta- frequency bursting. Thus our work points to a molecular/cellular mechanism for dysrhythmia. The third goal of our work is to understand how dopamine interacts with these processes. Our preliminary results suggest that D2 action may be synergistic with NMDA hypofunction in producing dysrhythmia. We will study this process in vivo to determine whether the delta oscillations induced by NMDA hypofunction can be reduced by D2 antagonist. A critical aspect of the dysrhythmia hypothesis, as proposed by R. Llinas, is that subregions of the thalamus generate abnormal low frequency oscillations in associated subregions of cortex; this produces local deficits in information processing that underlie the symptoms of the disease. A final goal of our work is to test this hypothesis. We will use a CRE-recombinase method to produce postdevelopmental knockout of NMDARs in subregions of the nRT. We will test whether NMDAR knockout in anterior nRT can produce enhancement of delta power in the frontal/central regions affected in schizophrenia, without affecting occipital cortex. We will test whether behaviors mediated by these regions are selectively affected by these oscillations. Because the CRE- recombinase method produces chronic changes, it provides a model system for identifying the chronic processes that underlie schizophrenia and drug therapy. If successful, this mouse will model the EEG symptoms of schizophrenia and provide a system in which potential therapeutic targets can be identified, based on the known pharmacology of the thalamus, and then tested for their ability to reverse the EEG symptoms.