Morphometric Analyses of the Growth in the Visual Organ and Tectum of the Japanese Quail (<i>Coturnix japonica</i>) after Hatching

Morphometric and histological analyses of the eyes, brain, tectum and retina of the Japanese quail were performed in order to study the relationships between the developmental visual center and each organ. A total of 77 animals, at 0, 5, 10, 15, 20, 30, 40 and 54 days after hatching, was used for the experiment. Each animal was perfused transcardinally with 10% formaldehyde in a phosphate buffer (pH 7.4) under sodium pentobarbital anesthesia. The eyes and brain were removed from the body and weighed, then bilaterally, the tectum was also separated from the brain and weighed. The scleral ring and lens were removed from the eye for morphometric analysis. The retina and the tectum were stained using Hematoxylin-Eosin and Nissl staining methods for the histological analysis. The weight of the eyes and brain showed approximately the same growth curve as the body weight from day 0 to 54 after hatching. Even though the weight of the tectum increased the same as the brain weight after hatching, the ratio of the tectum weight to the whole brain weight drastically declined from day 0 to 10 and remained constant ratio of 13.5% from 30 days after hatching. The growth curve of the scleral ring was similar to the total body weight. The weight of the lens increased until 30 days old and then remained constant. In the histological study, the retina of each hatched quail was divided into pigmented epithelium (PE), rod and cone layer (RC), outer limiting layer (OL), outer nuclear layer (ON), outer plexiform layer (OP), inner nuclear layer (IN), inner plexiform layer (IP), ganglion cell layer (G), nerve fiver layer (NF) and inner limiting layer (IL) as in adult. However the cell densities of the IN and G were low from day 0 to 30 and the retina's thickness trended to be thinner at 30 days after hatching. Notably, the thickness of the IN and IP at 30 days was reduced compared to that at 20 days. Layers of the tectum were divided into the stratum opticum (SO), stratum griseum and fibrosum superficiale (SGFS), stratum griesum centrale (SGC), stratum album centrale (SAC) at hatching, while stratum griseum periventriculare (SGP), stratum fibrosum periventriculare (SFP) were divided after 30 days. Furthermore, sublayers of the SGFS were unclear before day 20. These results showed that the visual system of the quail is completely established nearly 30 days after hatching.