Cimini Beth A, Strang Christianne E, Wotring Virginia E, Keyser Kent T, Eldred William D
Department of Biology, Boston University, Boston, Massachusetts 02215, USA.
J Comp Neurol. 2008 Apr 20;507(6):1952-63. doi: 10.1002/cne.21655.
Although acetylcholine is one of the most widely studied neurotransmitters in the retina, many questions remain about its downstream signaling mechanisms. In this study we initially characterized the cholinergic neurotransmitter system in the salamander retina by localizing a variety of cholinergic markers. We then examined the link between both muscarinic and nicotinic receptor activation and nitric oxide production by using immunocytochemistry for cyclic guanosine monophosphate (cGMP) as an indicator. We found a large increase in cGMP-like immunoreactivity (cGMP-LI) in the inner retina in response to muscarinic (but not nicotinic) receptor activation. Based on the amplification of mRNA transcripts, receptor immunocytochemistry, and the use of selective antagonists, we identified these receptors as M2 muscarinic receptors. Using double-labeling techniques, we established that these increases in cGMP-LI were seen in GABAergic but not cholinergic amacrine cells, and that the increases were blocked by inhibitors of nitric oxide production. The creation of nitric oxide in response to cholinergic receptor activation may provide a mechanism for modulating the well-known mutual interactions of acetylcholine-glycine-GABA in the inner retina. As GABA and glycine are the primary inhibitory neurotransmitters in the retina, signaling pathways that modulate their levels or release will have major implications for the processing of complex stimuli by the retina.
尽管乙酰胆碱是视网膜中研究最为广泛的神经递质之一，但其下游信号传导机制仍存在许多问题。在本研究中，我们首先通过定位多种胆碱能标志物来表征蝾螈视网膜中的胆碱能神经递质系统。然后，我们以环磷酸鸟苷（cGMP）免疫细胞化学作为指标，研究了毒蕈碱型和烟碱型受体激活与一氧化氮产生之间的联系。我们发现，毒蕈碱型（而非烟碱型）受体激活会使视网膜内层的cGMP样免疫反应性（cGMP-LI）大幅增加。基于mRNA转录本的扩增、受体免疫细胞化学以及选择性拮抗剂的使用，我们将这些受体鉴定为M2毒蕈碱型受体。通过双标记技术，我们确定这些cGMP-LI的增加出现在GABA能而非胆碱能无长突细胞中，并且这些增加被一氧化氮产生抑制剂所阻断。胆碱能受体激活后产生一氧化氮可能为调节视网膜内层乙酰胆碱-甘氨酸-GABA之间众所周知的相互作用提供一种机制。由于GABA和甘氨酸是视网膜中的主要抑制性神经递质，调节它们水平或释放的信号通路将对视网膜处理复杂刺激产生重大影响。
