STARBURST CHOLINERGIC AMACRINE CELLS IN THE TREE SHREW RETINA

In all mammalian retinae studied to date, starburst cholinergic amacri ne cells are a consistently occurring cell type. Here, we show that th e cone-dominated retina of the tree shrew also has starburst cells wit h the characteristic radially symmetric branching pattern known from o ther species. Dendritic field sizes increase from 150 mu m in the cent ral retina to 300 mu m in the retinal periphery. The characteristic mo rphology is established early during postnatal development. Labelling the starburst cholinergic cells with an antibody against choline acety ltransferase (ChAT) reveals two dendritic strata in the inner plexifor m layer and two corresponding soma populations in the inner nuclear la yer (orthotopic) and ganglion cell layer (displaced). These features a re present in the adult and in early postnatal stages. In the adult, t he density of the orthotopic population as well as the displaced popul ation peaks in the central retina at about 2,200 cells/mm(2) and has a peripheral minimum of 400 cells/mm(2). These properties are qualitati vely similar to those of starburst cells in rod-dominated retinae. In contrast to findings in other mammals, we did not see gamma-aminobutyr ic acid (GABA) or glutamic acid decarboxylase 65 kDa (GAD65) immunorea ctivity in tree shrew starburst cells. These cells also appear to lack synaptophysin, a ubiquitous synaptic vesicle protein detected in the starburst cells of some other mammals. However, synaptoporin, a homolo gous synaptic vesicle protein, appears to be present in tree shrew sta rburst cells. (C) 1997 Wiley-Liss, Inc.