Abstract
Abstract: :
Purpose: To study the convergence and/or segregation of signals carried by the multiple rod pathways in the mouse retina. Methods: A retinal–scleral eyecup preparation was used to obtain extracellular recordings from ganglion cells in dark–adapted wild type (WT) and connexin36 knockout (Cx36 KO) mice. Results: Off–center ganglion cells in the dark–adapted WT mouse retina could be divided into 4 groups based on their response thresholds and intensity–response functions. Three of the groups, named high– , intermediate–, and low–intermediate sensitivity responded within the scotopic range, whereas the low sensitivity group showed only cone–mediated responses. Selective blockage of the primary rod bipolar–AII cell pathway with L–AP4 application and/or blockade of the secondary rod–cone coupling pathway using the Cx36 KO mouse was used to determine the pathway(s) subserving rod signaling to off–center cells. Our results indicate that, under well dark–adapted conditions, the primary rod pathway forms the predominant input to high sensitivity cells, whereas the secondary pathway predominantly innervates intermediate sensitivity cells and the tertiary rod–to–off bipolar cell pathway forms the dominant rod signaling pathway to low–intermediate cells. Thus, under dark–adapted conditions, the rod pathways appear to operate under largely different scotopic operating ranges. Analysis of the shifts in the intensity–response functions of ganglion cells in both WT and KO mouse retinas following AP4 application indicated that about one–half of our population of off–center cells (total population of 106 cells) showed segregated scotopic input from only one rod pathway, with the remaining cells receiving convergent inputs from at least 2 of the pathways. Conclusions: Three rod pathways with different sensitivities subserve scotopic signaling to off–center ganglion cells in the mouse retina. Whereas our results indicate that these pathways converge onto certain ganglion cells, others appear to receive segregated inputs. Surprisingly, we encountered a small number of off–center cells that showed only cone–mediated responses.
Keywords: retinal connections, networks, circuitry • ganglion cells • retina: proximal (bipolar, amacrine, and ganglion cells)