Perlman I, Normann R A
Rappaport Family Institute for Research in the Medical Sciences, Haifa, Israel.
Vis Neurosci. 1990 Nov;5(5):469-77. doi: 10.1017/s0952523800000596.
The role of GABA in the outer plexiform layer of the turtle retina has been examined by intracellular recordings from L- and C-type horizontal cells in the isolated retina preparation. GABA (1-5 mM) slightly depolarized the L-type horizontal cells, reduced the amplitude of their photoresponses, and slowed down the rate of hyperpolarization during the ON component of the photoresponse. These effects could not be replicated by either muscimol or baclofen. When synaptic transmission from the photoreceptors had been blocked by either kynurenic acid or cobalt ions, GABA depolarized L-type horizontal cells and augmented the remaining photoresponses. Neither muscimol nor baclofen exerted any effect on L-type horizontal cells under these conditions. Nipecotic acid, a competitive inhibitor of the GABA-uptake system, induced effects on turtle L-type horizontal cells which were similar to those exerted by GABA. Thus, the complex GABA effect on turtle L-type horizontal cells seems to represent the summation of at least two actions; an indirect one mediated by the red cones via GABAa-type receptors and a direct one which probably reflects the activation of an electrogenic GABA-uptake system. GABA (1-5 mM) induced a transient depolarization in C-type horizontal cells but eliminated color opponency in only three cells out of seven studied. This observation is inconsistent with the notion that the only neural mechanism responsible for the chromatic properties of C-type horizontal cells in the turtle retina is a GABAergic negative feedback from the L-type horizontal cells onto the green ones.
通过在分离的视网膜标本中对L型和C型水平细胞进行细胞内记录，研究了γ-氨基丁酸（GABA）在乌龟视网膜外网状层中的作用。GABA（1 - 5 mM）使L型水平细胞轻微去极化，降低其光反应幅度，并减缓光反应ON成分期间的超极化速率。这些效应不能被蝇蕈醇或巴氯芬复制。当感光细胞的突触传递被犬尿氨酸或钴离子阻断时，GABA使L型水平细胞去极化并增强剩余的光反应。在这些条件下，蝇蕈醇和巴氯芬对L型水平细胞均无任何作用。GABA摄取系统的竞争性抑制剂尼克酸对乌龟L型水平细胞产生的效应与GABA相似。因此，GABA对乌龟L型水平细胞的复杂效应似乎代表了至少两种作用的总和；一种是由红锥细胞通过GABAa型受体介导的间接作用，另一种是可能反映生电GABA摄取系统激活的直接作用。GABA（1 - 5 mM）在C型水平细胞中诱导了短暂的去极化，但在所研究的七个细胞中只有三个细胞消除了颜色拮抗。这一观察结果与以下观点不一致，即乌龟视网膜中负责C型水平细胞颜色特性的唯一神经机制是从L型水平细胞到绿色细胞的GABA能负反馈。
