Vlahos Lisa M, Knott Ben, Valter Krisztina, Hemmi Jan M
ARC Centre of Excellence in Vision Science, Australian National University, Canberra, ACT 0200, Australia; Research School of Biology, College of Medicine, Biology and Environment, Australian National University, Canberra, ACT 0200, Australia.
J Comp Neurol. 2014 Oct 15;522(15):3423-36. doi: 10.1002/cne.23610. Epub 2014 Apr 22.
Marsupials are believed to be the only non-primate mammals with both trichromatic and dichromatic color vision. The diversity of color vision systems present in marsupials remains mostly unexplored. Marsupials occupy a diverse range of habitats, which may have led to considerable variation in the presence, density, distribution, and spectral sensitivity of retinal photoreceptors. In this study we analyzed the distribution of photoreceptors in the common brushtail possum (Trichosurus vulpecula). Immunohistochemistry in wholemounts revealed three cone subpopulations recognized within two spectrally distinct cone classes. Long-wavelength sensitive (LWS) single cones were the largest cone subgroup (67-86%), and formed a weak horizontal visual streak (peak density 2,106 ± 435/mm2) across the central retina. LWS double cones were strongly concentrated ventrally (569 ± 66/mm2), and created a "negative" visual streak (134 ± 45/mm2) in the central retina. The strong regionalization between LWS cone topographies suggests differing visual functions. Short-wavelength sensitive (SWS) cones were present in much lower densities (3-10%), mostly located ventrally (179 ± 101/mm2). A minority population of cones (0-2.4%) remained unlabeled by both SWS- and LWS-specific antibodies, and may represent another cone population. Microspectrophotometry of LWS cone and rod visual pigments shows peak spectral sensitivities at 544 nm and 500 nm, respectively. Cone to ganglion cell convergences remain low and constant across the retina, thereby maintaining good visual acuity, but poor contrast sensitivity during photopic vision. Given that brushtail possums are so strongly nocturnal, we hypothesize that their acuity is set by the scotopic visual system, and have minimized the number of cones necessary to serve the ganglion cells for photopic vision.
有袋动物被认为是唯一具有三色和二色视觉的非灵长类哺乳动物。有袋动物中存在的色觉系统多样性大多仍未被探索。有袋动物占据了各种各样的栖息地,这可能导致视网膜光感受器的存在、密度、分布和光谱敏感性出现相当大的差异。在本研究中,我们分析了普通帚尾袋貂(Trichosurus vulpecula)光感受器的分布。整体标本的免疫组织化学显示在两个光谱不同的视锥细胞类别中识别出三个视锥细胞亚群。长波长敏感(LWS)单视锥细胞是最大的视锥细胞亚群(67 - 86%),在中央视网膜上形成一条微弱的水平视觉条纹(峰值密度2,106±435/mm²)。LWS双视锥细胞强烈集中在腹侧(569±66/mm²),并在中央视网膜上形成一条“负”视觉条纹(134±45/mm²)。LWS视锥细胞地形图之间的强烈区域化表明视觉功能不同。短波长敏感(SWS)视锥细胞的密度要低得多(3 - 10%),大多位于腹侧(179±101/mm²)。一小部分视锥细胞(0 - 2.4%)未被SWS和LWS特异性抗体标记,可能代表另一种视锥细胞群体。LWS视锥细胞和视杆细胞视觉色素的显微分光光度法分别显示在544纳米和500纳米处的峰值光谱敏感性。视锥细胞与神经节细胞的汇聚在整个视网膜上保持较低且恒定,从而保持良好的视敏度,但在明视觉期间对比敏感度较差。鉴于帚尾袋貂是如此强烈的夜行性动物,我们推测它们的视敏度由暗视觉系统设定,并已将用于明视觉服务神经节细胞所需的视锥细胞数量减至最少。