Discrepancy and commonality in histological changes for postnatal retinal growth between mice and cattle

Neonatal organs are divided into those that are functionally complete at birth and those that are still developing. Postnatal retinal development varies depending on animal species, with altricial animals being underdeveloped and precocial animals born with vision. Comparing postnatal retinal growth in animals is predicted to reveal cellular and tissue changes necessary for visual function acquisition. In this study, retinal growth was examined from neonatal to adulthood and compared between mice (altricial) and cattle (precocial). Postnatal eyeballs showed rapid, then slow growth in both animals. The retina had a mature 10-layer structure after postnatal day 14 (P14) in mice. Retinal thickness increased from P0 to P14 and decreased sharply from P14 to P35. In the thickening phase, the elongation of the outer nuclear layer (ONL) and inner nuclear layer (INL) was remarkable, and axonal outgrowth in the rod bipolar cell was observed. In the thinning phase, a linear arrangement of the component cells was observed in the ONL, and cell numbers in the array decreased. In the cattle retina, the 10-layer structure was observed and a peak thickness at P0. Cattle retinas showed only the thinning phase after birth with tissue changes resembling those in the mouse retina. Retinal thinning observed at both newborns in mice and cattle seemed to reflect tissue reconstruction in axon and cellular arrangement, potentially being an important trait for functional visual development.