Arnarsson A, Eysteinsson T
Department of Physiology, University of Iceland, Reykjavik, Iceland.
Vis Neurosci. 1997 Nov-Dec;14(6):1143-52. doi: 10.1017/s0952523800011834.
We have recorded the electroretinogram (ERG) from the superfused eyecup of the Xenopus retina in order to assess the effects of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), and its agonists and antagonists, on individual ERG components. We found that GABA (0.5-10 mM) reduced the amplitudes of both the b- and d-waves of the Xenopus ERG. The GABA uptake blocker nipecotic acid (1 mM) had similar effects on b- and d-waves. GABA at 5 mM and 10 mM also caused an increase in the a-wave. The GABA antagonist picrotoxin (0.1-2 mM) and the GABA/a antagonist bicuculline (0.2 mM) both increased the amplitude of the b- and d-waves of the ERG. The GABA/b agonist baclofen (0.3 mM) reduced the amplitude of the ERG b-wave, enhanced the amplitude of the a-wave, and slightly reduced the amplitude and increased the peak time of the d-wave. The GABA/b antagonists phaclofen and saclofen had no reliable effects on the Xenopus ERG. Glutamate analogs known to affect specific types of retinal neurons were applied to modify the retinal circuitry and then the effects of GABA and its antagonists were examined under these modified conditions. 2-amino-4-phosphonobutyric acid (APB) increased the d-wave, and blocked the b-wave and the effect of GABA on the ERG, but not the antagonist-induced increase in the d-wave. KYN blocked the antagonist-induced increase in the b-wave, while GABA increases the amplitude of the b-wave if the d-wave has been removed by prior superfusion with kynurenic acid (KYN). N-methyl-DL-aspartate (NMDLA), which acts only in the proximal retina, reduced the amplitude of the ERG and blocked the effect of GABA and the antagonist-induced increase in ERG b- and d-waves amplitude. These results suggest that GABAergic mechanisms related to both A and B receptor types can influence the amplitude and light sensitivity of all the components of the Xenopus ERG. Since GABA is found in greatest abundance in the proximal retina, and B type of receptors are present almost exclusively there, the data suggests that most of the effects of GABA agonists and antagonists observed are dependent on proximal retinal mechanisms, and that there are separate mechanisms in the proximal retina related to the b- and the d-waves.
我们记录了非洲爪蟾视网膜灌注眼杯的视网膜电图（ERG），以评估抑制性神经递质γ-氨基丁酸（GABA）及其激动剂和拮抗剂对单个ERG成分的影响。我们发现，GABA（0.5 - 10 mM）降低了非洲爪蟾ERG的b波和d波振幅。GABA摄取阻滞剂尼克酸（1 mM）对b波和d波有类似影响。5 mM和10 mM的GABA还导致a波增加。GABA拮抗剂荷包牡丹碱（0.1 - 2 mM）和GABA/A拮抗剂荷包牡丹碱（0.2 mM）均增加了ERG的b波和d波振幅。GABA/B激动剂巴氯芬（0.3 mM）降低了ERG的b波振幅，增强了a波振幅，并略微降低了d波振幅并增加了其峰值时间。GABA/B拮抗剂法氯芬和沙氯芬对非洲爪蟾ERG没有可靠影响。应用已知会影响特定类型视网膜神经元的谷氨酸类似物来改变视网膜回路，然后在这些改变的条件下检查GABA及其拮抗剂的作用。2-氨基-4-膦酰丁酸（APB）增加了d波，并阻断了b波以及GABA对ERG的作用，但未阻断拮抗剂诱导的d波增加。犬尿氨酸（KYN）阻断了拮抗剂诱导的b波增加，而如果先用犬尿烯酸（KYN）灌注去除d波，则GABA会增加b波振幅。仅作用于近端视网膜的N-甲基-DL-天冬氨酸（NMDLA）降低了ERG振幅，并阻断了GABA的作用以及拮抗剂诱导的ERG b波和d波振幅增加。这些结果表明，与A和B受体类型相关的GABA能机制可以影响非洲爪蟾ERG所有成分的振幅和光敏感性。由于GABA在近端视网膜中含量最高，并且B型受体几乎仅存在于近端视网膜中，数据表明观察到的GABA激动剂和拮抗剂的大多数作用取决于近端视网膜机制，并且近端视网膜中存在与b波和d波相关的独立机制。
