Anesthetic Actions at GABA and Glutamate Synapses

回忆（记忆）的丧失是全身麻醉的一个重要组成部分，然而这一重要作用的机制尚不清楚。在麻醉过程中未能阻止召回仍然是一个医疗保健问题——在美国每年报告的召回事件超过40,000起。实验概述在拟议的研究将探讨麻醉对突触传递的长期增强（LTP）的影响，作为一个细胞基础的麻醉诱导的回忆丧失。通过电生理记录和特定的药理学探针来分离三种广泛使用的药物：异氟醚、异丙酚和咪达唑仑的突触和分子靶点，研究导致LTP阻滞的作用机制。实验将使用大鼠海马脑切片和表征良好的ca1锥体神经元突触回路的Schaffer-collateral纤维进行，这是大脑中LTP研究得最好的突触。海马体对人类和动物的学习和记忆至关重要，LTP是海马体皮层中学习的细胞基础的主要候选者。拟进行的研究将有三个具体目标：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在麻醉诱导LTP阻滞中的作用。3)确定NMDA受体或其下游的突触后作用是否参与了麻醉诱导的LTP阻滞。在此之前，进行这种性质的实验是不可能的，因为在体内对阻滞回忆所需的麻醉浓度的研究直到最近才出现在文献中。我们的研究结果将提供阻断LTP所需的麻醉浓度的定量分析，并将确定导致这种阻断的作用机制。了解麻醉药诱导LTP阻滞的机制可以开发出高针对性的药物，以在麻醉过程中产生回忆丧失，这可以最大限度地减少目前使用的麻醉药产生的不良副作用。我们实验室的初步结果表明，异氟醚阻断LTP的浓度与阻断人类回忆的浓度没有区别，远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.