視運動性眼振と関連する網膜神経細胞の分布について 系統発生学的検討

Abstract

The nucleus of the optic tract (NOT) in the pretectum has been considered to be the interface between the retina and premotor nuclei in the pathway conveying signals responsible for horizontal optokinetic nystagmus (OKN). However, what parts of the retina and which kinds of retinal ganglion cells project their fibers into the NOT have not been conclusively determined.We injected horseradish peroxidase conjugated with wheatgerm agglutinin (WGAHRP) into the NOT of rats, cats, and monkeys, and identified the labeled cells in the retina. Labeled retinal ganglion cells were observed bilaterally in each of these animal systems as follows:1. In rats, labeled retinal ganglion cells were diffusely distributed in the contralateral side, whereas those labeled cells were situated only in the lower temporal crescent in the ipsilateral side.2. In cats, the highest concentration of labeled cells was found in the area centralis and the region adjacent to it in both retinae. These cells were situated only above the horizontal meridian through the optic disk and the area centralis, and they were situated mainly in the temporal crescent involved in the area of the area centralis on both sides. No labeled cells were observed in nasal region of the area centralis on the ipsilateral side. In rats and cats, most of the labeled cells were judged to be small cells, i.e., W cells. However, X-and Y-like cells were also definitely labeled, suggesting that these cells participate in OKN.In the monkey, few labeled retinal ganglion cells were observed above the temporal area of the foveae on both retinae. These were small P γ cells. According to the pattern of cortical development, the distribution of retinal ganglion cells responsible for OKN may be altered so that those in the ipsilateral side in rats are in the lower temporal crescent but those in the cat are in upper temporal crescent at the level of the horizontal meridian. Furthermore, the distribution pattern was changed, and the retinal ganglion cells concentrated in the area centralis.By the time of the appearance of the fovea in the monkey, there are no retinal ganglion cells in the fovea and few small cells above the temporal area in both retinae. Consequently, the pursuit system by the fovea might prevail.