Horizontal cell feedback without cone type-selective inhibition mediates "red-green" color opponency in midget ganglion cells of the primate retina.
Horizontal cell feedback without cone type-selective inhibition mediates "red-green" color opponency in midget ganglion cells of the primate retina.
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DOI：
10.1523/jneurosci.4385-10.2011
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发表时间：
2011-02-02
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影响因子：
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通讯作者：
Dacey DM
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作者：
Crook JD;Manookin MB;Packer OS;Dacey DM
人和非人灵长类动物颜色知觉的独特红绿维度最近出现在灵长类动物谱系中，出现了不同的长(L)和中(M)波长敏感锥形感光器类型。视网膜的“侏儒”神经节细胞利用中心-周围感受野结构，拮抗地结合L信号和M视锥信号，从而建立一条“红-绿、色-反”的视觉通路。然而，红-绿对抗的突触起源尚不清楚，随机或L与M视锥选择性抑制回路的相互矛盾的证据对三基色视觉的发育和进化起源有不同的暗示。在这里，我们直接测量了选择性刺激L或M视锥在侏儒神经节细胞树突状树中诱发的突触电导，结果表明L和M视锥对抗是由突触前向侏儒细胞产生的，并完全通过兴奋性电导的调制传递。L和M视锥的突触抑制是前馈的，因此两种视锥的兴奋是同相的。阻断GABA能和甘氨酸能受体不能减弱或改变L对M视锥的拮抗作用，不考虑突触前和突触后的抑制作为视锥对抗的来源。与之形成鲜明对比的是，视网膜pH缓冲能力的增强，减弱了水平细胞对L和M视锥输入的线性和无选择性的负反馈，完全消除了侏儒细胞周围和所有的染色对抗性。因此，红绿对抗似乎是通过视网膜外水平细胞反馈产生的，这种反馈不是视锥类型选择性的，而是求助于视网膜内的L VS M视锥抑制通路。
The distinctive red-green dimension of human and non-human primate color perception arose relatively recently in the primate lineage with the appearance of separate long (L) and middle (M) wavelength sensitive cone photoreceptor types. ‘Midget’ ganglion cells of the retina utilize center-surround receptive field structure to combine L and M cone signals antagonistically and thereby establish a ‘red-green, color-opponent’ visual pathway. However the synaptic origin of red-green opponency is unknown and conflicting evidence for either random or L vs M cone-selective inhibitory circuits have divergent implications for the developmental and evolutionary origins of trichromatic color vision. Here we directly measure the synaptic conductances evoked by selective L or M cone stimulation in the midget ganglion cell dendritic tree and show that L vs M cone opponency arises presynaptic to the midget cell and is transmitted entirely by modulation of an excitatory conductance. L and M cone synaptic inhibition is feedforward and thus occurs in-phase with excitation for both cone types. Block of GABAergic and glycinergic receptors does not attenuate or modify L vs M cone antagonism, discounting both pre- and postsynaptic inhibition as sources of cone opponency. In sharp contrast, enrichment of retinal pH buffering capacity, to attenuate negative feedback from horizontal cells that sum L and M cone inputs linearly and without selectivity, completely abolished both the midget cell surround and all chromatic opponency. Thus, red-green opponency appears to arise via outer retinal horizontal cell feedback that is not cone type-selective without recourse to any inner retinal L vs M cone inhibitory pathways.