Effect of methotrexate exposure at middle gestation on the inner plate of the ocular cup and lens in the rat fetus

Pregnant rats were treated intraperitoneally with a single dose of methotrexate (MTX) 90 mg/kg on gestation day (GD) 13, and fetal eyeballs were examined time-dependently from GD 13.5 to 15.5. Throughout the experimental period, the inner plate of the ocular cup in the MTX group was significantly thinner than that in the control group. In the inner plate of the ocular cup on GD 15 and 15.5, whereas a developed ganglion cell layer was observed in the control group, the ganglion cell layer in the MTX group was undeveloped and indistinguishable. Disturbance of the arrangement of lens fiber cells, narrowing of the hyaloid cavity of the optic cup, and hypoplasia of optic nerve fibers were observed in the MTX group on GD 15 and 15.5. Increase of pyknosis and decrease of mitosis were induced in the optic cup and the lens epithelium of the MTX group. In the inner plate of the optic cup and the lens epithelium of the MTX group, the cleaved caspase-3- and TUNEL-positive rates increased significantly throughout the experimental period. The phospho-histone H3-positive rate in the inner plate of the optic cup decreased significantly from GD 13.5 to 14.5, and it recovered on GD 15. On the other hand, the phospho-histone H3-positive rate in the lens epithelium decreased significantly throughout the experimental period. These results suggested that optic tissue on GD 13 in rats was sensitive to MTX.