Abstract
Abstract: :
Purpose: The objective is to understand rod and cone synaptic pathways mediating light responses of ON bipolar cells and AII amacine cells in the mammalian retina. Methods: Light–evoked excitatory cation current (ΔIC) and inhibitory chloride current (ΔICl) of rod and cone depolarizing bipolar cells (DBCRs and DBCCs) and AII amacrine cells (AIIACs) in dark–adapted mouse retinal slices were studied by whole–cell voltage clamp recording techniques, and the cell morphology was revealed by Lucifer yellow fluorescence with a confocal microscope. Results: ΔIC of all DBCRs exhibited high sensitivity to 500 nm light, but two patterns of ΔICl were observed in DBCRs with slightly different axon morphology. At least two types of DBCCs were identified: one with axon terminals ramified in 70–85% of IPL depth and DBCR–like ΔIC sensitivity, where the other with axon terminals ramified in 55–75% of IPL depth and much lower ΔIC sensitivity. The relative rod/cone inputs to DBCs and AIIACs were analyzed by comparing the ΔIC and ΔICl thresholds and dynamic ranges with the corresponding values of rods and cones. On average, the sensitivity of a DBCR to the 500 nm light is about 20 times higher than that of a rod. The sensitivity of an AIIAC is more than 1000 times higher than that of a rod, suggesting that AIIAC responses are pooled through a coupled network of about 40 AIIACs. Interactions of rod and cone signals in dark–adapted mouse retina appear asymmetrical: rod signals spread into the cone system more efficiently than cone signals into the rod system. Conclusions: By analyzing light response threshold and dynamic range of DBCs and AIIACs, our data suggest that rod signals in dark–adapted mouse retina are greatly amplified by the ON synaptic pathway and effectively transmitted to the cone system via the electrical synapses between rods and cones and between AIIACs and DBCCs.
Keywords: amacrine cells • bipolar cells • electrophysiology: non–clinical