Aramakis V B, Bandrowski A E, Ashe J H
Department of Neuroscience, University of California, Riverside 92521, USA.
Exp Brain Res. 1997 Mar;113(3):484-96. doi: 10.1007/pl00005601.
The present study examines the ability of muscarinic receptor activation to modulate glutamatergic responses in the in vitro rat auditory cortex. Whole-cell patch-clamp recordings were obtained from layer II-III pyramidal neurons and responses elicited by either stimulation of deep gray matter or iontophoretic application of glutamate receptor agonists. Iontophoresis of the muscarinic agonist acetyl-beta-methylcholine (MCh) produced an atropine-sensitive reduction in the amplitude of glutamate-induced membrane depolarizations that was followed by a long-lasting (at least 20 min) response enhancement. Glutamate depolarizations were enhanced by MCh when elicited in the presence of alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA)/kainate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or 2,3-dihydroxy-6-nitro-7-sulfamoyl, benzo(F)quinoxaline (NBQX) but not the NMDA antagonists D-2-amino-5-phosphonovaleric acid (APV) or MK-801 hydrogen maleate. The magnitude of enhancement was voltage-dependent with the percentage increase greater at more depolarized membrane potentials. An involvement of NMDA receptors in these MCh-mediated effects was tested by using AMPA/kainate receptor antagonists to isolate the NMDA-mediated slow excitatory postsynaptic potential (EPSP) from other synaptic potentials. The slow EPSP and iontophoretic responses to NMDA were similarly modified by MCh, i.e., both being reduced during and enhanced (15-55 min) following MCh application. Cholinergic modulation of NMDA responses involves the engagement of G proteins, as enhancement was prevented by intracellular infusion with the nonhydrolyzable GDP analog guanosine-5'-O-(2-thiodiphosphate) trilithium salt (GDPbetaS). GDPbetaS was without effect on the early MCh-induced response suppression. Our results suggest that acetylcholine, acting at muscarinic receptors, produces a long-lasting enhancement of NMDA-mediated neurotransmission in auditory cortex, and that this modulatory effect is dependent upon a G protein-mediated event.
本研究检测了毒蕈碱受体激活对体外培养的大鼠听觉皮层中谷氨酸能反应的调节能力。采用全细胞膜片钳记录技术，从II-III层锥体神经元记录电流，通过刺激深部灰质或离子电泳施加谷氨酸受体激动剂来引发反应。毒蕈碱激动剂乙酰-β-甲基胆碱（MCh）的离子电泳使谷氨酸诱导的膜去极化幅度产生阿托品敏感的降低，随后是持久的（至少20分钟）反应增强。当在α-氨基-3-羟基-5-甲基-4-异恶唑丙酸（AMPA）/海人藻酸受体拮抗剂6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX）或2,3-二羟基-6-硝基-7-氨磺酰基苯并（F）喹喔啉（NBQX）存在的情况下引发谷氨酸去极化时，MCh可增强其反应，但在NMDA拮抗剂D-2-氨基-5-磷酸戊酸（APV）或马来酸MK-801存在时则不然。增强的幅度呈电压依赖性，在膜电位去极化程度越高时，增加的百分比越大。通过使用AMPA/海人藻酸受体拮抗剂将NMDA介导的慢兴奋性突触后电位（EPSP）与其他突触电位分离，来测试NMDA受体是否参与这些MCh介导的效应。慢EPSP和对NMDA的离子电泳反应同样被MCh修饰，即在MCh应用期间两者均降低，而在应用后增强（15 - 55分钟）。NMDA反应的胆碱能调节涉及G蛋白的参与，因为通过细胞内注入不可水解的GDP类似物鸟苷-5'-O-（2-硫代二磷酸）三锂盐（GDPβS）可阻止增强作用。GDPβS对MCh诱导的早期反应抑制没有影响。我们的结果表明，作用于毒蕈碱受体的乙酰胆碱在听觉皮层中产生NMDA介导的神经传递的持久增强，并且这种调节作用依赖于G蛋白介导的事件。
