Department of Physiology & Biophysics and Program in Neurobiology & Behavior, University of Washington, Seattle, WA, USA.
J Neurophysiol. 2013 Jul;110(2):536-52. doi: 10.1152/jn.00118.2013. Epub 2013 May 1.
Dopamine (DA) is a neuromodulator that in the retina adjusts the circuitry for visual processing in dim and bright light conditions. It is synthesized and released from retinal interneurons called dopaminergic amacrine cells (DACs), whose basic physiology is not yet been fully characterized. To investigate their cellular and input properties as well as light responses, DACs were targeted for whole cell recording in isolated retina using two-photon fluorescence microscopy in a mouse line where the dopamine receptor 2 promoter drives green fluorescent protein (GFP) expression. Differences in membrane properties gave rise to cell-to-cell variation in the pattern of resting spontaneous spike activity ranging from silent to rhythmic to periodic burst discharge. All recorded DACs were light sensitive and generated responses that varied with intensity. The threshold response to light onset was a hyperpolarizing potential change initiated by rod photoreceptors that was blocked by strychnine, indicating a glycinergic amacrine input onto DACs at light onset. With increasing light intensity, the ON response acquired an excitatory component that grew to dominate the response to the strongest stimuli. Responses to bright light (photopic) stimuli also included an inhibitory OFF response mediated by GABAergic amacrine cells driven by the cone OFF pathway. DACs expressed GABA (GABA(A)α1 and GABA(A)α3) and glycine (α2) receptor clusters on soma, axon, and dendrites consistent with the light response being shaped by dual inhibitory inputs that may serve to tune spike discharge for optimal DA release.
多巴胺（DA）是一种神经调质，在视网膜中调节视觉处理在暗光和亮光条件下的电路。它是由视网膜中间神经元（称为多巴胺能无长突细胞（DAC））合成并释放的，其基本生理学尚未完全表征。为了研究它们的细胞和输入特性以及光反应，使用双光子荧光显微镜在一个小鼠系中对分离的视网膜中的 DAC 进行全细胞记录，其中多巴胺受体 2 启动子驱动绿色荧光蛋白（GFP）表达。膜特性的差异导致静息自发尖峰活动模式的细胞间变化，范围从沉默到有节奏到周期性爆发放电。所有记录的 DAC 对光敏感，并产生随强度变化的反应。光起始的阈值反应是由杆状光感受器引发的超极化电位变化，该变化被士的宁阻断，表明在光起始时 DAC 上存在甘氨酸能无长突细胞输入。随着光强度的增加，ON 反应获得了兴奋性成分，该成分增长到主导对最强刺激的反应。对强光（明视）刺激的反应还包括由 GABA 能无长突细胞驱动的锥状 OFF 途径介导的抑制性 OFF 反应。DAC 在体、轴突和树突上表达 GABA（GABA(A)α1 和 GABA(A)α3）和甘氨酸（α2）受体簇，与光反应由双重抑制性输入塑造一致，这可能有助于调整尖峰放电以实现最佳 DA 释放。
