Department of Pharmacology, School of Medicine, Kanazawa Medical University, 1-1 Daigaku, Uchinada, Ishikawa, 920-0293, Japan.
Division of Cellular Signal Transduction, Department of Biochemistry, Asahikawa Medical University, 2-1-1-1, Midorigaoka-Higashi, Asahikawa, Hokkaido, 078-8510, Japan.
Neuroscience. 2019 Apr 15;404:39-47. doi: 10.1016/j.neuroscience.2019.01.042. Epub 2019 Jan 30.
Hippocampal cholinergic activity enhances long-term potentiation (LTP) of synaptic transmission in intrahippocampal circuits and regulates cognitive function. We recently demonstrated intracellular distribution of functional M1-muscarinic acetylcholine receptors (mAChRs) and neuronal uptake of acetylcholine (ACh) in the central nervous system. Here we examined whether endogenous ACh acts on intracellular M1-mAChRs following its uptake and causes cholinergic facilitation of hippocampal LTP. ACh esterase (AChE) activities and [H]ACh uptake was measured in rat hippocampal segments. LTP of evoked field excitatory postsynaptic potentials at CA1 synapses was induced by high frequency stimulation in hippocampal slices. Pretreatment with diisopropylfluorophosphate (DFP) irreversibly inhibited AChE, augmented ACh uptake, and significantly enhanced the LTP. This cholinergic facilitation was inhibited by pirenzepine, a membrane-permeable M1 antagonist, while only the early stage of cholinergic facilitation was inhibited by a membrane-impermeable M1 antagonist, muscarinic toxin 7. Tetraethylammonium (TEA) inhibited ACh uptake in hippocampal segments and selectively suppressed late stage cholinergic facilitation without changing the early stage. In contrast, LTP in DFP-untreated slices was not affected by the muscarinic antagonists and TEA. Carbachol (CCh; an AChE-resistant muscarinic agonist) competed with ACh for its uptake and produced cholinergic facilitation of LTP in DFP-untreated slices. The late stage of CCh-induced facilitation was also selectively inhibited by TEA. Our results suggest that when AChE is inactivated by inhibitors, LTP in hippocampal slices is significantly enhanced by endogenous ACh and that cholinergic facilitation is caused by direct activation of cell-surface M1-mAChRs and subsequent activation of intracellular M1-mAChRs after ACh uptake.
海马胆碱能活性增强海马内回路突触传递的长时程增强（LTP），并调节认知功能。我们最近证明了功能性 M1 毒蕈碱型乙酰胆碱受体（mAChR）在中枢神经系统中的细胞内分布和乙酰胆碱（ACh）的神经元摄取。在这里，我们研究了 ACh 摄取后是否作用于细胞内 M1-mAChR 并引起海马 LTP 的胆碱能易化。在大鼠海马段中测量 ACh 酯酶（AChE）活性和 [H]ACh 摄取。在海马切片中通过高频刺激诱导 CA1 突触的诱发电场兴奋性突触后电位的 LTP。二异丙基氟磷酸酯（DFP）的预处理不可逆地抑制 AChE，增加 ACh 摄取，并显著增强 LTP。这种胆碱能易化被哌仑西平抑制，哌仑西平是一种膜通透性 M1 拮抗剂，而只有早期的胆碱能易化被一种膜非通透性 M1 拮抗剂，毒蕈碱毒素 7 抑制。四乙铵（TEA）抑制海马段中的 ACh 摄取，并选择性地抑制晚期胆碱能易化，而不改变早期胆碱能易化。相比之下，DFP 未处理的切片中的 LTP 不受毒蕈碱拮抗剂和 TEA 的影响。卡巴胆碱（CCh；一种 AChE 抗性毒蕈碱激动剂）与 ACh 竞争摄取，并在 DFP 未处理的切片中产生 LTP 的胆碱能易化。CCh 诱导的易化的晚期也被 TEA 选择性抑制。我们的结果表明，当 AChE 被抑制剂失活时，海马切片中的 LTP 被内源性 ACh 显著增强，并且胆碱能易化是由 ACh 摄取后细胞表面 M1-mAChR 的直接激活和随后的细胞内 M1-mAChR 的激活引起的。
