Cunningham J R, Neal M J
J Physiol. 1985 Sep;366:47-62. doi: 10.1113/jphysiol.1985.sp015784.
The pharmacology of cholinergic amacrine cells has been further studied by examining the effects of excitatory amino acids and antagonists on [3H]acetylcholine (ACh) release from the retinas of anaesthetized rabbits. Exposure of the retina to glutamate (5 mM), aspartate (5 mM), kainate (8 microM) and quisqualate (8 microM) abolished the light-evoked release of [3H]ACh but increased the spontaneous resting release four- to fivefold. N-methyl-D-aspartate (NMDA) (5 mM) in normal Krebs bicarbonate medium abolished the light-evoked release of [3H]ACh but did not affect the resting release. However, in Mg-free medium, NMDA (0.5 mM) abolished the light-evoked release of [3H]ACh and increased the resting release fivefold. The effects of other agonists were not altered in Mg-free medium. The amplitude of the electroretinogram (e.r.g.) b-wave was not significantly reduced by glutamate, aspartate or NMDA (in normal or Mg-free medium). Kainate and quisqualate reduced the b-wave amplitude to approximately 50 and 30% of controls respectively. The general excitatory amino acid antagonist, cis-2,3-piperidine dicarboxylic acid (PDA) (2 mM) blocked the light-evoked release of [3H]ACh, but had no significant effect on the e.r.g. b-wave amplitude or on the resting release of [3H]ACh. L(+)-2-amino-4-phosphonobutyrate (L(+)-APB) decreased the light-evoked release of [3H]ACh and the amplitude of the e.r.g. b-wave in parallel (correlation coefficient 0.995). D(-)-APB had similar effects but was fifteen times less potent. Since the L(+)-compound is known to mimic the photoreceptor transmitter on the depolarizing, but not hyperpolarizing, bipolar cells, these results strongly suggest that the [3H]ACh released in response to light originates mainly from the 'on' (displaced) cholinergic amacrine cells. Our experiments give no information on the origin of the spontaneously released [3H]ACh. PDA (2-5 mM) blocked the effects of glutamate, aspartate, kainate, quisqualate and NMDA on the resting release of [3H]ACh. In contrast, D(-)-APB (5 mM), which is a relatively non-specific excitatory amino acid antagonist in the spinal cord, blocked only the actions of kainate and had no blocking effect on the actions of glutamate or aspartate (the putative bipolar cell transmitters) or NMDA. D(-)-2-amino-5-phosphonovalerate (APV) which is a relatively selective NMDA antagonist in the spinal cord failed to discriminate between the effects of kainate and NMDA on the resting release of [3H]ACh. D-alpha-aminoadipate at concentrations up to 5 mM had no effect on any of the agonists.(ABSTRACT TRUNCATED AT 400 WORDS)
通过检测兴奋性氨基酸及其拮抗剂对麻醉兔视网膜释放[3H]乙酰胆碱（ACh）的影响，对胆碱能无长突细胞的药理学进行了进一步研究。将视网膜暴露于谷氨酸（5 mM）、天冬氨酸（5 mM）、海人藻酸（8 μM）和quisqualate（8 μM）中，可消除光诱发的[3H]ACh释放，但使自发静息释放增加4至5倍。在正常的 Krebs 碳酸氢盐培养基中，N-甲基-D-天冬氨酸（NMDA）（5 mM）可消除光诱发的[3H]ACh释放，但不影响静息释放。然而，在无镁培养基中，NMDA（0.5 mM）可消除光诱发的[3H]ACh释放，并使静息释放增加5倍。在无镁培养基中，其他激动剂的作用未发生改变。视网膜电图（e.r.g.）b波的振幅未被谷氨酸、天冬氨酸或NMDA（在正常或无镁培养基中）显著降低。海人藻酸和 quisqualate分别将b波振幅降低至对照的约50%和30%。一般兴奋性氨基酸拮抗剂顺式-2,3-哌啶二羧酸（PDA）（2 mM）可阻断光诱发的[3H]ACh释放，但对e.r.g. b波振幅或[3H]ACh的静息释放无显著影响。L(+)-2-氨基-4-膦酰丁酸（L(+)-APB）可平行降低光诱发的[3H]ACh释放和e.r.g. b波的振幅（相关系数0.995）。D(-)-APB有类似作用，但效力低15倍。由于已知L(+)化合物可模拟光感受器递质对去极化双极细胞的作用，而不是超极化双极细胞的作用，这些结果强烈表明，光诱发释放的[3H]ACh主要来自“开”（移位）胆碱能无长突细胞。我们的实验未提供关于自发释放的[3H]ACh来源的信息。PDA（2 - 5 mM）可阻断谷氨酸、天冬氨酸、海人藻酸、quisqualate和NMDA对[3H]ACh静息释放的影响。相比之下，D(-)-APB（5 mM）在脊髓中是一种相对非特异性的兴奋性氨基酸拮抗剂，仅阻断海人藻酸的作用，对谷氨酸或天冬氨酸（假定的双极细胞递质）或NMDA的作用无阻断作用。D(-)-2-氨基-5-膦酰戊酸（APV）在脊髓中是一种相对选择性的NMDA拮抗剂，未能区分海人藻酸和NMDA对[3H]ACh静息释放的影响。浓度高达5 mM的D-α-氨基己二酸对任何一种激动剂均无作用。（摘要截短于400字）
