Jensen R J
Department of Biomedical Sciences, Southern College of Optometry, Memphis, TN 38104.
Vis Neurosci. 1991 Jan;6(1):43-53. doi: 10.1017/s0952523800000894.
Previous studies have reported that the surround responses of retinal ganglion cells weaken or disappear upon dark adaptation. The mechanism(s) by which this occurs is largely unknown, although changes in activity of retinal dopaminergic neurons have been implicated. In the light-adapted rabbit retina, the surround ON responses of OFF-center ganglion cells have been shown to be markedly reduced or abolished by a dopamine antagonist. This effect of a dopamine antagonist was recently shown to be reversed by the glycine antagonist strychnine and by compounds that elevate intracellular cAMP levels. The present study was conducted to determine whether strychnine and cAMP-elevating compounds could bring out the surround ON responses in OFF-center ganglion cells that are diminished upon dark adaptation. Extracellular recordings of OFF-center brisk ganglion cells were made from isolated, superfused retinal preparations. During the course of dark adaptation, the surround ON responses of many cells decreased markedly. Application of low micromolar concentrations of strychnine to the bathing solution brought out the surround ON responses in both brisk-transient and brisk-sustained OFF-center ganglion cells. The center OFF responses of these cells, on the other hand, were not enhanced by strychnine. Of the cAMP-elevating compounds tested, 8-(4-chlorophenylthio) cyclic AMP was the most effective in bringing out the surround ON responses in dark-adapted OFF-center ganglion cells. The effects of bath application of this cAMP analog were very similar to those of strychnine. The findings from this study suggest that under dark-adapted conditions glycinergic neurons inhibit the surround component of OFF-center ganglion cells. The release of glycine from these neurons is suggested to be regulated by a cAMP-dependent mechanism.
以往的研究报道，视网膜神经节细胞的周边反应在暗适应时会减弱或消失。尽管视网膜多巴胺能神经元活动的变化与之有关，但这种现象发生的机制在很大程度上仍不清楚。在光适应的兔视网膜中，多巴胺拮抗剂已被证明可显著降低或消除离中心神经节细胞的周边开反应。最近发现，甘氨酸拮抗剂士的宁和提高细胞内cAMP水平的化合物可逆转多巴胺拮抗剂的这种作用。本研究旨在确定士的宁和提高cAMP水平的化合物是否能使暗适应时减弱的离中心神经节细胞的周边开反应恢复。从分离的、灌注的视网膜标本中对离中心快神经节细胞进行细胞外记录。在暗适应过程中，许多细胞的周边开反应明显降低。向浴液中加入低微摩尔浓度的士的宁可使快瞬态和快持续离中心神经节细胞的周边开反应恢复。另一方面，士的宁并未增强这些细胞的中心关反应。在所测试的提高cAMP水平的化合物中，8-（4-氯苯硫基）环磷酸腺苷在使暗适应的离中心神经节细胞的周边开反应恢复方面最为有效。这种环磷酸腺苷类似物的浴用效果与士的宁非常相似。本研究结果表明，在暗适应条件下，甘氨酸能神经元抑制离中心神经节细胞的周边成分。这些神经元释放甘氨酸的过程可能受cAMP依赖性机制的调节。
