Division of Translational Toxicology, Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, USA.
Division of Translational Toxicology, Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, MD, USA.
Neuropharmacology. 2023 Nov 15;239:109684. doi: 10.1016/j.neuropharm.2023.109684. Epub 2023 Aug 6.
Preclinical studies have reported that, compared to the muscarinic receptor (mAChR) antagonist atropine, (R,S)-trihexyphenidyl (THP) more effectively counters the cholinergic crisis, seizures, and neuropathology triggered by organophosphorus (OP)-induced acetylcholinesterase (AChE) inhibition. The greater effectiveness of THP was attributed to its ability to block mAChRs and N-methyl-d-aspartate-type glutamatergic receptors (NMDARs) in the brain. However, THP also inhibits α7 nicotinic receptors (nAChRs). The present study examined whether THP-induced inhibition of mAChRs, α7 nAChRs, and NMDARs is required to suppress glutamatergic synaptic transmission, whose overstimulation sustains OP-induced seizures. In primary hippocampal cultures, THP (1-30 μM) suppressed the frequency of excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs, respectively) recorded from neurons in nominally Mg-free solution. A single sigmoidal function adequately fit the overlapping concentration-response relationships for THP-induced suppression of IPSC and EPSC frequencies yielding an IC50 of 6.3 ± 1.3 μM. Atropine (1 μM), the NMDAR antagonist d,l-2-amino-5-phosphonopentanoic acid (D,L-AP5, 50 μM), and the α7 nAChR antagonist methyllycaconitine (MLA, 10 nM) did not prevent THP-induced inhibition of synaptic transmission. THP (10 μM) did not affect the probability of transmitter release because it had no effect on the frequency of miniature IPSCs and EPSCs recorded in the presence of tetrodotoxin. Additionally, THP had no effect on the amplitudes and decay-time constants of miniature IPSCs and EPSCs; therefore, it did not affect the activity of postsynaptic GABA and glutamate receptors. This study provides the first demonstration that THP can suppress action potential-dependent synaptic transmission via a mechanism independent of NMDAR, mAChR, and α7 nAChR inhibition.
临床前研究报告称，与毒蕈碱受体 (mAChR) 拮抗剂阿托品相比，(R,S)-三羟苯海因 (THP) 更有效地对抗由有机磷 (OP) 诱导的乙酰胆碱酯酶 (AChE) 抑制引起的胆碱能危机、癫痫发作和神经病理学。THP 的更高功效归因于其阻断大脑中的 mAChRs 和 N-甲基-D-天冬氨酸型谷氨酸能受体 (NMDARs) 的能力。然而，THP 也抑制α7 烟碱型乙酰胆碱受体 (nAChRs)。本研究检查了 THP 诱导的 mAChRs、α7 nAChRs 和 NMDARs 抑制是否需要抑制谷氨酸能突触传递，因为过度刺激维持 OP 诱导的癫痫发作。在原代海马培养物中，THP（1-30μM）抑制了在名义上无镁溶液中记录的神经元的兴奋性和抑制性突触后电流 (EPSC 和 IPSC，分别) 的频率。单个 sigmoidal 函数充分拟合了 THP 诱导的 IPSC 和 EPSC 频率抑制的重叠浓度反应关系，得出 IC50 为 6.3±1.3μM。阿托品 (1μM)、NMDAR 拮抗剂 d,l-2-氨基-5-磷戊酸 (D,L-AP5，50μM) 和 α7 nAChR 拮抗剂甲基金刚烷胺 (MLA，10nM) 均不能阻止 THP 诱导的突触传递抑制。THP（10μM）不会影响递质释放的概率，因为它对在河豚毒素存在下记录的微小 IPSC 和 EPSC 的频率没有影响。此外，THP 对微小 IPSC 和 EPSC 的幅度和衰减时间常数没有影响；因此，它不会影响突触后 GABA 和谷氨酸受体的活性。本研究首次证明 THP 可以通过一种不依赖于 NMDAR、mAChR 和 α7 nAChR 抑制的机制抑制动作电位依赖性突触传递。
