Abstract
Purpose: :
To compare spatial and temporal properties of glycinergic and GABAergic inhibition to amacrine and ganglion cells
Methods: :
Excitation and inhibition to amacrine cells was measured in whole mount retina by voltage-clamping at -60mV or 0mV. Light spots and annuli were flashed to measure the spatial properties. Strychnine, SR95531 and TPMPA blocked glycinergic, GABAAergic and GABACergic pathways. APB blocked ON activity. Morphology of cells was measured by filling the cells with biotin and viewing with confocal microscopy after recording.
Results: :
1, Glycinergic inhibition: ganglion cells receive only sustained components, but amacrine cells receive both transient and sustained components. All of glycine inhibition was elicited within the dendritic area. 2, Broad GABA inhibition: This component was always transient and measured in ganglion cells and in narrow but never in the broad dendritic amacrine cells. It was elicited from outside the dendritic area. 3, Local sustained GABA inhibition: this was commonly measured in ganglion cells but never in amacrine cells. It was elicited from regions slightly larger than the dendritic area.
Conclusions: :
Most of the spatial and temporal properties of inhibition to amacrine cells are consistent with those to ganglion cells: glycine inhibition was always elicited locally and transient GABA inhibition is always broad. But there is no local GABA inhibition to amacrine cells commonly found in ganglion cells. Besides sustained glycine, there is also transient glycine inhibition to amacrine cells which was not found in ganglion cells. Our results suggest that narrow glycinergic, narrow GABAergic and broad GABAergic inhibitory inputs represent a fundamental set of inhibitory components in retina, but amacrine cells or ganglion cells may each have their own preferred components. This also suggests that although there are more than 30 morphological types of amacrine cells in rabbit retina, there may be far fewer functional types.
Keywords: retinal connections, networks, circuitry • retina: proximal (bipolar, amacrine, and ganglion cells) • amacrine cells