Effects of anesthetics on thalamic excitability

描述（由申请方提供）：麻醉剂诱导安全且可逆的意识丧失的能力至关重要，但新的动物数据表明，激活GABAA受体和/或抑制NMDA通道的全身麻醉剂对发育中的哺乳动物大脑具有神经毒性，并与导致以后生活中的认知缺陷有关。因此，进一步研究目前可用的麻醉剂的细胞机制和开发新的麻醉剂，特别是用于儿科麻醉，是必要的。在过去的十年中，一些研究表明，在暴露于全身麻醉剂的年轻啮齿动物中，包括丘脑核在内的各种大脑区域都发生了广泛的神经变性。然而，全身麻醉药在引起丘脑皮质功能持久改变中的可能作用还没有得到很好的研究。我们的数据表明，在P7岁时暴露于常用全身麻醉剂的未成熟大鼠表现出抑制性突触传递的持续减少和伴随的丘脑网状核（nRT）内在离子通道的可塑性。我们推测，在早期发育过程中暴露于全身麻醉剂会导致抑制性GABA能传递减少和nRT中T通道的上调，导致丘脑皮质网络的慢性过度兴奋。为了验证这一假设，我们将使用来自天然nRT和丘脑皮质（TC）中继神经元的体外膜片钳记录和体内脑电图（EEG）记录来实现以下特定目标：目的1：确定大鼠在P7暴露于常用的挥发性麻醉剂异氟烷或常用的静脉内麻醉剂丙泊酚和氯胺酮是否会表现出nRT神经元的抑制性GABA能传递的减少。目标二：确定在P7暴露于异氟烷的大鼠是否表现出nRT神经元中T通道的上调，以及这种上调是否反过来导致这些细胞中增强的爆发放电模式。目标3：确定全身麻醉剂引起的丘脑突触传递和固有离子通道的持久改变是否可能导致丘脑皮质网络的过度兴奋，如在自由活动动物中使用EEG记录所评估的。目标4：确定丘脑T电流抑制是否有助于神经活性类固醇3-OH的催眠作用，3-OH是一种对突触后GABAA或NMDA受体无任何作用的T通道阻滞剂。我们还将测试以下假设：将大鼠幼崽暴露于3-OH对突触稳态的影响最小，因此不会引发丘脑中的神经元过度兴奋。拟议的工作是创新的，麻醉诱导的突触和内在的神经元可塑性的新机制的特点。它具有医学意义，因为它记录了短期暴露于广泛使用的临床药物引起的重要发育变化，预计将有助于确定开发更安全的麻醉剂和临床麻醉实践的新靶点。

DESCRIPTION (provided by applicant): The ability of the anesthetics to induce safe and reversible loss of consciousness is of paramount importance, yet new animal data suggest that general anesthetics that activate GABAA receptors and/or inhibit NMDA channels are neurotoxic for the developing mammalian brain and have implicated them in causing cognitive deficits later in life. Thus, further research into cellular mechanisms of currently available anesthetics and development of novel anesthetics, particularly for pediatric anesthesia, is warranted. Over the past decade, several studies have shown widespread neurodegeneration in various brain regions, including thalamic nuclei, in young rodents exposed to general anesthetics. However, the possible role of general anesthetics in causing lasting alterations of thalamocortical functioning is not well studied. Our data indicate that immature rats exposed to commonly used general anesthetics at age P7 exhibit lasting reduction in inhibitory synaptic transmission and concomitant plasticity of intrinsic ion channels in the nucleus reticular is thalami (nRT). We hypothesize that exposure to general anesthetics during early development causes reduction of inhibitory GABAergic transmission and up-regulation of T-channels in nRT, leading to chronic hyperexcitability of thalamocortical networks. To test this hypothesis, we will use in vitro patch-clamp recordings from native nRT and thalamocortical (TC) relay neurons and in vivo electroencephalographic (EEG) recordings to pursue the following specific aims: Aim 1: To determine whether rats exposed at P7 to the common volatile anesthetic isoflurane or the commonly used intravenous anesthetics propofol and ketamine will exhibit reduction in inhibitory GABAergic transmission of nRT neurons. Aim 2: To determine whether rats exposed at P7 to isoflurane exhibit up-regulation of T-channels in nRT neurons and whether such up-regulation, in turn, leads to an enhanced burst firing pattern in these cells. Aim 3: To determine whether lasting alterations in synaptic transmission and intrinsic ion channels in the thalamus caused by general anesthetics may lead to hyperexcitability of thalamocortical networks as assessed using EEG recordings in freely moving animals. Aim 4: To determine whether thalamic T-current inhibition contributes to the hypnotic effects of the neuroactive steroid 3�OH, which is a T-channel blocker devoid of any effects on postsynaptic GABAA or NMDA receptors. We also will test the hypothesis that exposure of rat pups to 3�OH will have minimal impact on synaptic homeostasis and, thus, will not trigger neuronal hyperexcitability in the thalamus. The proposed work is innovative in that new mechanisms of anesthetic-induced synaptic and intrinsic neuronal plasticity will be characterized. It is medically significant because it documents important develop- mental alterations induced by short exposures to widely used clinical drugs and is expected to help identify new targets for the development of safer anesthetics and practices in clinical anesthesia.