Arrese C, Dunlop S A, Harman A M, Braekevelt C R, Ross W M, Shand J, Beazley L D
Department of Zoology, University of Western Australia, Nedlands, Australia.
Brain Behav Evol. 1999;53(3):111-26. doi: 10.1159/000006588.
The visual system of the fat-tailed dunnart (Sminthopsis crassicaudata), a small polyprotodont marsupial, has been examined both anatomically and behaviourally. The ganglion cell layer was examined in cresyl-violet stained wholemounts and found to contain a mean of 81,400 ganglion cells (SD +/- 3,360); the identification of ganglion cells was supported by a correspondence to optic axon counts. Ganglion cells were distributed as a mid-temporally situated area centralis, embedded in a pronounced visual streak. Localised implants of horseradish peroxidase into retinal wholemounts revealed both A-type and B-type horizontal cells. Sections of the outer retina showed it to be rod-dominated, with a rod-to-cone ratio of 40:1 at the area centralis; cones were found to contain oil droplets but double cones were not a prominent feature. The retinal pigment epithelium consisted of squamous cells. Visual acuity, estimated from counts of peak ganglion cell density (8,300/mm2, SD +/- 1,180) and measurements of posterior nodal distance (2.9 mm), was found to be 2.30 cycles per degree. The value was close to that of 2.36 cycles per degree estimated by behavioural tests using a Mitchell jumping stand; values were similar at low, intermediate and high light levels. Our findings are discussed in relation to the lifestyle of the dunnart.
肥尾袋鼩（Sminthopsis crassicaudata）是一种小型多门齿有袋动物，其视觉系统已从解剖学和行为学角度进行了研究。在甲酚紫染色的整装标本中检查了神经节细胞层，发现平均含有81,400个神经节细胞（标准差±3,360）；神经节细胞的鉴定得到了与视神经轴突计数相对应的支持。神经节细胞分布为位于颞中部的中央区，嵌入明显的视觉条纹中。将辣根过氧化物酶局部植入视网膜整装标本中，发现了A型和B型水平细胞。视网膜外层切片显示其以视杆细胞为主，在中央区视杆细胞与视锥细胞的比例为40:1；发现视锥细胞含有油滴，但双视锥细胞不是突出特征。视网膜色素上皮由鳞状细胞组成。根据神经节细胞峰值密度计数（8,300/mm²，标准差±1,180）和后节点距离测量值（2.9毫米）估计，视敏度为每度2.30周。该值接近使用米切尔跳跃台通过行为测试估计的每度2.36周；在低、中、高光水平下的值相似。我们根据袋鼩的生活方式对研究结果进行了讨论。
