Effects of anesthetics on thalamic excitability

描述(由申请人提供)：麻醉药导致安全和可逆的意识丧失的能力是至关重要的，然而新的动物数据表明，激活GABAA受体和/或抑制NMDA通道的全麻药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障碍有关。因此，有必要进一步研究目前可用的麻醉药的细胞机制和开发新的麻醉药，特别是用于儿科麻醉的麻醉药。在过去的十年里，几项研究表明，在暴露于全身麻醉剂的年轻啮齿动物中，包括丘脑核团在内的各个大脑区域都出现了广泛的神经变性。然而，全麻药在导致丘脑皮质功能持续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，未成熟大鼠在P7龄暴露于常用的全身麻醉药后，抑制性突触传递持续减少，伴随而来的是丘脑网状核(NRT)内离子通道的可塑性。我们假设，在发育早期暴露于全身麻醉药会导致NRT中抑制性GABA能传递减少和T通道上调，从而导致丘脑皮质网络的慢性兴奋。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(EEG)记录来追求以下特定目标：目的1：确定在P7暴露于普通挥发性麻醉剂异氟醚或常用静脉麻醉剂异丙酚和氯胺酮是否会抑制NRT神经元的GABA能传递。目的：确定异氟醚暴露于P7的大鼠NRT神经元上的T-通道是否上调，以及这种上调是否会导致这些细胞的爆发式放电模式增强。目的：通过对自由活动动物的脑电记录，确定全麻药引起丘脑突触传递和内源性离子通道的持续改变是否会导致丘脑皮质网络的过度兴奋性。目的：确定丘脑T-电流抑制是否参与了神经活性类固醇3-�-OH的催眠作用，后者是一种T-通道阻滞剂，对突触后GABA和NMDA受体没有任何影响。我们还将测试这一假设，即大鼠幼鼠暴露于3-�-OH将对突触稳态产生最小的影响，因此不会触发丘脑的神经元过度兴奋。这项拟议的工作是创新的，因为将表征麻醉剂诱导的突触和内在神经元可塑性的新机制。它具有重要的医学意义，因为它记录了由于短时间接触广泛使用的临床药物而引起的重要的智力发育变化，并有望帮助确定开发更安全的麻醉药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.