Glycine Receptors of Narrow–Field Amacrine Cells of the Mouse Retina

Abstract

Purpose: : Glycine and GABA are the major inhibitory transmitters of the mammalian retina, and approximately half of the amacrine cells are glycinergic. They comprise between 10 and 20 different morphological types and synapse onto bipolar, ganglion and amacrine cells. The purpose was to reveal the expression of glycine receptors in amacrine cells.

Methods: : Patch–clamp recordings were performed from retinal slices of wildtype, Glrα1(–/–) and Glra3(–/–) mice. Whole cell currents following glycine application and glycinergic inhibitory postsynaptic currents (IPSCs) were measured. During the recordings the cells were filled with neurobiotin and Alexa488 in order to identify the cell types. Results from AII amacrine cells and other narrow–field amacrine cells are compared.

Results: : All amacrine cells showed prominent responses to the exogenous application of glycine. Hence, they all express functional glycine receptors (GlyRs). Spontaneous or potassium–induced inhibitory postsynaptic currents could be recorded from 61 amacrine cells. AII amacrine cells receive faster synaptic input (mean decay time constant: τ_w ∼ 10 ms) than other narrow–field amacrine cells (mean τ_w ∼ 25 ms). The decay time constants of AII amacrine cells and other narrow–field amacrine cells in Glrα1(–/–) mice were not significantly different from those of wildtype mice.

Conclusions: : GlyRs are expressed in all amacrine cells recorded. AII amacrine cells and narrow–field amacrine cells differ significantly in the decay time constants of their glycinergic IPSCs, with faster IPSCs recorded from AII cells. The IPSCs of Glrα1(–/–) mice were not significantly different. GlyRs of amacrine cells are probably composed of several different GlyR subunits.

Keywords: retinal connections, networks, circuitry • inhibitory receptors • amacrine cells