Cholinergic amacrine cells in the developing cat retina.

Antiserum directed against the ACh-synthesizing enzyme choline acetyltransferase (ChAT) was used to determine the development of cholinergic amacrine cell distributions in wholemounted kitten retinae. From birth (P0) two populations of cholinergic amacrine cells were immunolabelled; one population was located in the inner nuclear layer (INL) and the other was displaced to the ganglion cell layer (GCL). Dendrites from cholinergic amacrines in the INL stratified in the outer third of the inner plexiform layer (IPL), whilst those from displaced amacrines in the GCL stratified in the centre of the IPL. There was a centroperipheral gradient of development in both populations, and the total number of cholinergic amacrines in the GCL always exceeded that of the INL. The most dramatic increase in the number of amacrines expressing ChAT was between P0 and P5 when the numbers doubled. During the same period there was an increase in the soma size of both populations in the peripheral retina. In the GCL, cholinergic amacrines did not attain adult size until P21 whereas those of the INL reached adult proportions by P5. Overall, between P0 and P21 there was a fivefold increase in the number of immunoreactive cholinergic amacrines in the GCL and a 3.5-fold increase in those of the INL. In general, the distribution, soma size, percentage per layer, and total number of cholinergic amacrines in both populations resembled those of the adult by P21.