Witkovsky P, Gabriel R, Haycock J W, Meller E
Department of Ophthalmology, New York University School of Medicine, 550 First Avenue, 10016, New York, NY 10016, USA.
J Chem Neuroanat. 2000 Jun;19(2):105-16. doi: 10.1016/s0891-0618(00)00055-7.
Light has been shown to increase dopamine synthesis and release in vertebrate retinas, but the retinal circuits mediating the light signal are unknown. We utilized three antibodies which recognize phosphorylated forms of tyrosine hydroxylase (TH) at serines 19, 31, and 40 to study the effects of light and neuroactive drugs on TH phosphorylation in the rat retina. Phosphorylated TH and total TH immunoreactivities were co-localized exclusively in retinal neurons whose shape and location are characteristic of dopaminergic interplexiform cells. Phosphorylated TH was weak to absent in darkness, but light strongly stimulated phosphorylation in all the three serine residues. Light-induced phosphorylation of TH induction by light was uniformly blocked by a combination of NMDA and AMPA glutamate receptor antagonists. In darkness, the combination of NMDA+AMPA induced phosphosphorylation of TH at serines 19 and 40 but it was weak at serine 31. A GABA(A) antagonist had the same effect. An agonist of depolarizing (ON) bipolar cells, L-(+)-2-amino-4-phosphonobutyric acid, did not prevent light-induced phosphorylated TH formation. Carbachol, a non-specific cholinergic agonist, selectively induced phosphorylation of TH at serine 31 in darkness, an effect which was blocked by the nicotinic antagonist, d-tubocurarine. These results show that retinal circuits involving glutamatergic, GABAergic and cholinergic synapses influence phospho-TH formation at different serine residues in this enzyme. Gamma amino butyric acid (GABA) and glutamate influence TH phosphorylation at serines 19 and 40, whereas cholinergic inputs affect its phosphorylation at serine 31.
研究表明，光可增加脊椎动物视网膜中多巴胺的合成与释放，但介导光信号的视网膜神经回路尚不清楚。我们使用了三种可识别丝氨酸19、31和40位点磷酸化酪氨酸羟化酶（TH）的抗体，来研究光和神经活性药物对大鼠视网膜中TH磷酸化的影响。磷酸化TH和总TH免疫反应性仅共定位于视网膜神经元中，这些神经元的形状和位置具有多巴胺能网间细胞的特征。在黑暗中，磷酸化TH较弱或不存在，但光强烈刺激了所有三个丝氨酸残基的磷酸化。NMDA和AMPA谷氨酸受体拮抗剂的组合可完全阻断光诱导的TH磷酸化。在黑暗中，NMDA+AMPA的组合可诱导TH在丝氨酸19和40位点的磷酸化，但在丝氨酸31位点较弱。GABA(A)拮抗剂也有相同作用。去极化（ON）双极细胞的激动剂L-(+)-2-氨基-4-膦酸丁酸不能阻止光诱导的磷酸化TH形成。非特异性胆碱能激动剂卡巴胆碱在黑暗中选择性诱导TH在丝氨酸31位点的磷酸化，该作用可被烟碱拮抗剂筒箭毒碱阻断。这些结果表明，涉及谷氨酸能、GABA能和胆碱能突触的视网膜神经回路会影响该酶不同丝氨酸残基处的磷酸化TH形成。γ-氨基丁酸（GABA）和谷氨酸影响TH在丝氨酸19和40位点的磷酸化，而胆碱能输入则影响其在丝氨酸31位点的磷酸化。
