Effects of anesthetics on thalamic excitability

描述（由申请人提供）：麻醉药诱导安全且可逆的意识丧失的能力至关重要，然而新的动物数据表明，激活GABAA受体和/或抑制NMDA通道的全身麻醉药对发育中的哺乳动物大脑具有神经毒性，并可能导致以后生活中的认知缺陷。因此，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，特别是儿科麻醉药，是必要的。在过去的十年里，几项研究表明，暴露在全身麻醉剂下的年轻啮齿动物在大脑的各个区域，包括丘脑核，都有广泛的神经变性。然而，全身麻醉剂在引起丘脑皮质功能持久改变中的可能作用尚未得到很好的研究。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丘脑网状核（nRT）固有离子通道的可塑性。我们假设，在发育早期暴露于全麻会导致抑制性gaba能传递减少和nRT中t通道的上调，从而导致丘脑皮质网络的慢性高兴奋性。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）记录来实现以下具体目的：目的1：确定P7暴露于常见挥发性麻醉剂异氟醚或常用静脉麻醉剂异丙酚和氯胺酮的大鼠是否会减少nRT神经元的抑制性gaba能传递。目的2：确定暴露于P7异氟醚的大鼠是否表现出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爆发放电模式的增强。目的3：利用自由运动动物的脑电图记录，确定全身麻醉引起的丘脑突触传递和内在离子通道的持久改变是否可能导致丘脑皮质网络的高兴奋性。目的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受体没有任何影响的t通道阻滞剂。我们还将验证这样一个假设，即大鼠幼仔暴露于3 - OH对突触稳态的影响最小，因此不会引发丘脑神经元的过度兴奋性。这项工作的创新之处在于，麻醉药诱导的突触和内在神经元可塑性的新机制将被表征。它在医学上具有重要意义，因为它记录了短期暴露于广泛使用的临床药物所引起的重要发育变化，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.