Transient, high levels of SNAP-25 expression in cholinergic amacrine cells during postnatal development of the mammalian retina

In the present study, we have examined the development of cholinergic amacrine cells in the retina of the Brazilian opossum, Monodelphis domestica. An antibody directed against choline acetyltransferase (ChAT) revealed that ChAT-like immunoreactivity (ChAT-IR) was first observed at 15 days postnatal (15PN). By 25PN, ChAT-IR identified two matching populations of amacrine cells in the inner nuclear and ganglion cell layer. Bromodeoxyuridine birth-dating analysis coupled with immunolabeling with the anti-ChAT antibody revealed that the cholinergic amacrine cells are born postnatally, between 2PN and 15PN. In addition, we have examined the differentiation of the cholinergic amacrine cells by using an antibody directed against a presynaptic terminal-associated protein, synaptosomal-associated protein of 25 kDa (SNAP-25). Double-labeling analysis revealed that relatively high levels of SNAP-25-IR were selectively present in cholinergic amacrine cells prior to eye opening. However, in the mature retina, high levels of SNAP-25-IR were no longer observed in the ChAT-IR amacrine cells. These results reveal a distinct period in development, prior to eye opening, when high levels of SNAP-25-IR are selectively expressed in cholinergic amacrine cells. The specificity and time course of the high levels of SNAP-25 in cholinergic amacrine cells may be critical in mediating the transient properties of these cells during visual system development.