Dendritic Integration and Visual Computation in Retinal Amacrine Cells

Amacrine cells are a diverse population of interneurons in the inner retina that perform complex visual signal processing. Most amacrine cells, by definition, lack axons and use their dendrites (or neurites) for both synaptic input and output. Amacrine cells synthesize and release a wide variety of neurotransmitters and neuromodulators and form intricate synaptic circuits with retinal bipolar, amacine, and ganglion cell types. Much of the computation by amacrine cells occur in the dendrites, which may integrate signals globally or locally. While several amacrine cell types have been studied in detail, the great majority of amacrine cell types remains poorly understood in terms of dendritic integration, synaptic connectivity, and circuit function. Recent studies have identified a unique type of amacrine cell, which expresses the vesicular glutamate transporter type 3 (vGluT3) and co-releases an excitatory (glutamate) and an inhibitory (glycine) transmitter. Experiments using electrophysiology, optogenetics, and two-photon imaging discovered intriguing synaptic, dendritic, and cellular properties of vGluT3 amacrine cells, revealing a novel form of local dendritic processing in this small-field amacrine cell type. Mechanisms of dendritic integration by vGluT3 amacrine cells will be discussed.