Physiological responses to the opioid neuropeptide enkephalin often involve both mu and delta opioid receptors. To facilitate quantitative studies into opioid signaling, we previously developed a caged [Leu⁵]-enkephalin that responds to ultraviolet irradiation, but its residual activity at delta receptors confounds experiments that involve both receptors. To reduce residual activity, we evaluated side-chain, N-terminus, and backbone caging sites and further incorporated the dimethoxy-nitrobenzyl moiety to improve sensitivity to ultraviolet light-emitting diodes (LEDs). Residual activity was characterized using an in vitro functional assay, and the power dependence and kinetics of the uncaging response to 355 nm laser irradiation were assayed using electrophysiological recordings of mu opioid receptor-mediated potassium currents in brain slices of rat locus coeruleus. These experiments identified N-MNVOC-LE as an optimal compound. Using ultraviolet LED illumination to photoactivate N-MNVOC-LE in the CA1 region of hippocampus, we found that enkephalin engages both mu and delta opioid receptors to suppress inhibitory synaptic transmission.

中文翻译：

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为同步探测Mu和Delta阿片类受体而优化的笼状脑啡肽

对阿片类神经肽脑啡肽的生理反应通常涉及mu和delta类阿片受体。为了促进对阿片类药物信号传导的定量研究，我们先前开发了笼状[Leu ⁵对紫外线照射有反应的]-脑啡肽，但其对δ受体的残留活性使涉及这两种受体的实验混淆了。为了减少残留的活性，我们评估了侧链，N末端和骨架的笼统位点，并进一步掺入了二甲氧基-硝基苄基部分，以提高对紫外发光二极管（LED）的敏感性。使用体外功能测定法表征残余活性，并使用电阿片受体介导的大鼠轨迹蓝斑脑片中的μ阿片样物质受体介导的钾电流，测定对355 nm激光照射的解笼响应的功率依赖性和动力学。这些实验确定了N -MNVOC-LE为最佳化合物。使用紫外线LED照明对N进行光活化-MNVOC-LE在海马CA1区，我们发现脑啡肽同时参与mu和delta类阿片受体，以抑制突触传递抑制。