Localization of choline acetyltransferase in the developing and adult retina of Xenopus laevis.

In the present study the presence of choline acetyltransferase (ChAT) immunoreactive cells in the adult retina of Xenopus laevis was demonstrated and their appearance and maturation during development were examined. Two cholinergic amacrine cell types were identified in the retina. They were located in the deepest row of cells in the inner nuclear layer and in the ganglion cell layer, respectively. Cell processes from these cells organized distinct laminae within the inner plexiform layer. ChAT immunoreactivity was first observed at embryonic stage 35 coinciding with the onset of vision and increased rapidly in premetamorphosis as synaptogenesis and growth proceeded. The development of both ChAT cell populations occurred simultaneously and cells that expressed ChAT transiently were not observed. Our results contrast with previous studies that suggested a late involvement of acetylcholine in the retina of Xenopus and support the notion that, like in mammals, this transmitter is involved in early phases of neurogenesis, cell migration, neuronal growth, and synaptogenesis.