Localization of the presynaptic cytomatrix protein piccolo at ribbon and conventional synapses in the rat retina: Comparison with bassoon

In recent years significant progress has been made in the elucidation of th e molecular assembly of the postsynaptic density at synapses, whereas littl e is known as yet about the components of the presynaptic active zone. Picc olo and Bassoon, two structurally related presynaptic cytomatrix proteins, are highly concentrated at the active zones of both excitatory and inhibito ry synapses in rat brain. In this study we used immunocytochemistry to exam ine the cellular and ultrastructural localization of Piccolo at synapses in the rat retina and compared it with that of Bassoon. Both proteins showed strong punctate immunofluorescence in the outer and the inner plexiform lay ers of the retina. They were found presynaptically at glutamatergic ribbon synapses and at conventional GABAergic and glycinergic synapses. Although t he two proteins were coexpressed at all photoreceptor ribbon synapses and a t some conventional amacrine cell synapses, at bipolar cell ribbon synapses only Piccolo was present. Our data demonstrate similarities but also diffe rences in the molecular composition of the presynaptic apparatuses of the s ynapses in the retina, differences that may account for the functional diff erences observed between the ribbon and the conventional amacrine cell syna pses and between the photoreceptor and the bipolar cell ribbon synapses in the retina. (C) 2001 Wiley-Liss, Inc.