Choline acetyltransferase-immunoreactive neurons in the developing rat retina

The development of cholinergic cells in the rat retina has been examined wi th immunocytochemistry by using antisera against choline acetyltransferase (ChAT). ChAT-immunoreactive (IR) cells were first detected at embryonic day 17 (E17) in the transitional zone between the neuroblastic layer (NBL) and ganglion cell layer (GCL). At E20, ChAT-IR cells are located exclusively i n the GCL. At postnatal day 0 (PO), ChAT immunoreactivity appeared for the first time in cells at the distal margin of the NBL. Two prominent bands of labeled processes were first visible at P3, and by P15, these two bands re sembled those of the adult retina. In addition, ChAT immunoreactivity appea red transiently in horizontal cells from P5 to P10. The number of ChAT-IR c ells increased steadily up to P15. This resulted in a 93.8-fold increase be tween E17 and P15 (680-63,800 cells). However, after P15, the number declin ed by 19% from 63,800 cells at P15 to 51,800 in the adult. At all ages, the spatial density of each ChAT-IR cell population in the central retina was higher than in the periphery. In both central and peripheral regions, the p eak density of ChAT-IR cells in the GCL was attained at E20. However, in th e INL, the peak densities occurred at P3 in the central region and at P5 in the peripheral region. Up to P15, the soma diameter of ChAT-IR cells in th e INL and GCL in each region increased continuously, reaching peak values a t P15. Our results demonstrate that ChAT immunoreactivity is expressed in e arly developmental stages in the rat retina, as in other mammals, and that acetylcholine released from ChAT-IR cells may have neurotrophic functions i n retinal maturation. J. Comp. Neurol. 427:604-616, 2000. (C) 2000 Wiley-Li ss, Inc.