Functional Roles of Action Potentials and Na Currents in Amacrine Cells

Abstract

Amacrine cells are retinal interneurons that play important roles in information processing in the inner plexiform layer. It is known that the major population of amacrine cells are y-aminobutyric acid (GABA)-ergic or glycinergic. However, of over 20 morphological subtypes [1], functional roles are known in only two subtypes: glycinergic A2 amacrine cells and cholinergic starburst amacrine cells. GABAergic cells are thought to be inhibitory and their major roles are thought to send inhibitory feedback to bipolar cells, mutual inhibition to neighboring amacrine cells, and feed-forward inhibition to ganglion cells. Most amacrine cells lack an axon and their dendrites function not only as the input site but also as the output site. Therefore, the strength of inhibition is expected to depend on the magnitude of depolarization and the length of its propagation within dendritic processes. Here, we summarize our recent works on the functional role of the action potential and the sustained depolarization induced by transient and persistent Na currents in the information processing of amacrine cells.