Acetylcholinesterase activity as a marker for the development of the ciliary epithelium in the chicken embryo.

Specific histochemical staining for acetylcholinesterase was first visible in the presumptive ciliary epithelium on day 4 of embryonic development. The enzyme did not appear in the neural retina until day 6. The presence or absence of this enzyme activity enabled us to differentiate the presumptive ciliary epithelium from the adjacent presumptive neural retina early in development. In the rat embryo, acetylcholinesterase was not found in the ciliary epithelium at any stage, although its appearance in the neural retina followed a temporal pattern similar to that seen in chicken embryos. Weak AChE staining was seen in the ciliary epithelium of the rat by 15 days after birth. The function of acetylcholinesterase in the developing ciliary epithelium is unknown, but from the data currently available it is unlikely to be involved in the degradation of acetylcholine. Our observations suggest that some previous studies of retinal development may have misinterpreted events occurring in the embryonic ciliary epithelium as characteristics of the peripheral retina.