Hemmi J M, Grünert U
Developmental Neurobiology, Research School of Biological Sciences, Australian National University, Canberra ACT.
Vis Neurosci. 1999 Mar-Apr;16(2):291-302. doi: 10.1017/s0952523899162102.
Mammalian retinae generally contain low numbers of short-wavelength-sensitive cones (S-cones) and higher numbers of middle- to long-wavelength-sensitive cones (M-cones). Some recent studies found topographic differences between the different photoreceptor types and in some instances between photoreceptors and ganglion cells. To investigate this question further, we constructed topographical maps of the different photoreceptors found in an Australian marsupial, the tammar wallaby. We used two polyclonal antibodies that have been shown to label S-cones (JH455) or M-cones (JH492) in a range of mammals. In the tammar wallaby, the antisera clearly distinguish two cone types. JH455 recognizes a small subset of cones (S-cones) with a density of less than 500 cells/mm2 in the ventral retina. Their density increases towards the dorsal retina to about 1600-2000 cells/mm2. JH492 recognizes all remaining cones (M-cones), but also faintly labels most cone cells recognized by JH455. The distribution of M-cones, unlike that of the S-cones, shows a clear horizontal streak of high cell density through the central retina, just like the ganglion cells. Unlike the ganglion cells, however, the M-cones do not peak in the temporal retina but show a very broad peak (12,000-18,000 cells/mm2) in the central or even slightly nasal retina. Based on our findings, the retina of the tammar can be divided into three distinct regions: firstly, the dorsal retina, which has a low ganglion and low cone cell density but a high percentage of S-cones (30%), is thought to provide good spectral sensitivity; secondly, the central horizontal band of retina, which has a high ganglion and high cone cell density and therefore provides good spatial resolution; and thirdly, the ventral retina, which has a low ganglion cell but high cone cell density with few S-cones (5%) and is therefore thought to have a high contrast sensitivity but low acuity.
哺乳动物的视网膜通常含有少量的短波长敏感视锥细胞(S - 视锥细胞)和较多的中长波长敏感视锥细胞(M - 视锥细胞)。最近的一些研究发现了不同光感受器类型之间以及某些情况下光感受器与神经节细胞之间的地形差异。为了进一步研究这个问题,我们构建了澳大利亚有袋动物——帚尾袋鼩视网膜中不同光感受器的地形图。我们使用了两种多克隆抗体,它们已被证明能在一系列哺乳动物中标记S - 视锥细胞(JH455)或M - 视锥细胞(JH492)。在帚尾袋鼩中,抗血清能清楚地区分两种视锥细胞类型。JH455识别一小部分视锥细胞(S - 视锥细胞),其在腹侧视网膜中的密度小于500个细胞/平方毫米。它们的密度朝着背侧视网膜增加至约1600 - 2000个细胞/平方毫米。JH492识别所有其余的视锥细胞(M - 视锥细胞),但也会微弱地标记大多数被JH455识别的视锥细胞。与S - 视锥细胞不同,M - 视锥细胞的分布在中央视网膜处显示出一条清晰的高细胞密度水平条纹,就像神经节细胞一样。然而,与神经节细胞不同的是,M - 视锥细胞在颞侧视网膜中并不形成峰值,而是在中央甚至略偏鼻侧视网膜中显示出一个非常宽的峰值(12,000 - 18,000个细胞/平方毫米)。基于我们的研究结果,帚尾袋鼩的视网膜可分为三个不同区域:首先,背侧视网膜,其神经节和视锥细胞密度低,但S - 视锥细胞比例高(30%),被认为具有良好的光谱敏感性;其次,视网膜中央水平带,其神经节和视锥细胞密度高,因此具有良好的空间分辨率;第三,腹侧视网膜,其神经节细胞密度低但视锥细胞密度高,S - 视锥细胞很少(5%),因此被认为具有高对比度敏感性但低敏锐度。