Anesthetic Actions at GABA and Glutamate Synapses

回忆（记忆）丧失是全身麻醉的重要组成部分，但这种重要作用的机制仍然未知。麻醉期间未能阻止回忆仍然是一个医疗保健问题-在美国每年报告超过40，000起回忆事件。在拟议的研究中概述的实验将调查麻醉对突触传递的长时程增强（LTP）的影响，作为麻醉诱导的回忆丧失的细胞基础。将使用电生理记录和特定药理学探针研究导致LTP阻滞的作用机制，以分离三种广泛使用的药物的突触和分子靶点：异氟烷、丙泊酚和咪达唑仑。实验将使用大鼠海马脑片和表征良好的CA 1锥体神经元突触回路的Schaffer侧支纤维进行，该突触回路是脑中LTP研究最好的突触。海马对于人类和动物的学习和记忆是必不可少的，并且LTP是海马皮层中学习的细胞基础的主要候选者。本研究的具体目的有三：1）确定麻醉诱导LTP阻滞的有效浓度范围。2)确定GABA和谷氨酸介导的突触参与麻醉诱导的LTP阻滞。3)确定NMDA受体或其下游的突触后作用是否参与麻醉诱导的LTP阻滞。在此之前还不可能进行这种性质的实验，因为在体内阻断回忆所需的麻醉剂浓度的研究最近才出现在文献中。我们的研究结果将提供阻断LTP所需的麻醉剂浓度的定量分析，并将确定导致这种阻断的作用机制。对麻醉诱导的LTP阻滞机制的理解可能会导致开发高度靶向的药物，用于在麻醉期间产生回忆丧失，这可以最大限度地减少目前使用的麻醉剂产生的不良副作用。我们实验室的初步结果表明，异氟烷阻断LTP的浓度与阻断人类回忆的浓度难以区分，并且大大低于阻断突触传递所需的浓度。

Loss of recall (memory) is an essential component of general anesthesia, yet the mechanisms underlying this important effect remain unknown. Failure to block recall during anesthesia continues to be a health care problem-over 40,000 incidents of recall are reported annually in the United States. Experiments outlined in the proposed research will investigate anesthetic effects on Long Term Potentiation (LTP) of synaptic transmission, as a cellular basis for anesthetic-induced loss of recall. Mechanisms of action leading to a block of LTP will be investigated using electrophysiological recordings and specific pharmacological probes to isolate the synaptic and molecular targets for three widely used agents: isoflurane, propofol and midazolam. Experiments will be conducted using rat hippocampal brain slices and the well characterized Schaffer-collateral fiber to CA 1 pyramidal neuron synaptic circuit-the best studied synapse for LTP in the brain. The hippocampus is essential for learning and memory in humans and animals and LTP is the leading candidate for a cellular basis of learning in hippocampal cortex. Three Specific Aims will be undertaken in the proposed research: 1) To determine the effective concentration range for anesthetic-induced block of LTP. 2) To determine the involvement of GABA and glutamate-mediated synapses in anesthetic-induced block of LTP. 3) To determine whether postsynaptic actions at or downstream from NMDA receptors contribute to the anesthetic-induced block of LTP. It has not been possible to undertake experiments of this nature before now, because studies of anesthetic concentrations required to block recall, in vivo, have only recently appeared in the literature. Results from our research will provide a quantitative analysis of anesthetic concentrations needed to block LTP, and will determine the mechanisms of action which lead to this block. An understanding of the mechanisms of anesthetic-induced block of LTP could lead to the development of highly targeted agents for producing loss of recall during anesthesia-this could minimize undesirable side effects produced by anesthetics in current use. Preliminary results from our laboratory indicate that isoflurane blocks LTP at concentrations which are indistinguishable from those that block recall in humans, and considerably lower than those needed to block synaptic transmission.