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Sammy Chi Sam Lee, Arndt Meyer, Karin Dedek, Silke Haverkamp; The neurocircuitry of A8 bistratified amacrine cells in the mouse retina. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4175.
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© ARVO (1962-2015); The Authors (2016-present)
There are at least 20 different types of amacrine cells in the mammalian retina and here we describe the morphology, connectivity, and the development of a glycinergic amacrine cell, the A8 amacrine cell, in the mouse retina.
A8 amacrine cells were identified in a transgenic mouse line where green fluorescent protein is expressed under the thy1 promoter. The distinct bistratified morphology first appears at postnatal day 8 and matures to an adult morphology through to postnatal day 15. Adult retinas were triple labeled with bipolar and synaptic markers to determine the synaptic connectivity of A8 amacrine cells. Antibodies to C-terminal binding protein (CtBP2) were used to identify ribbon synapses; antibodies against glycine receptor α (1-4) subunits were used to identity potential postsynaptic partners. In addition, we injected single A8 cells with neurobiotin to determine cell coupling.
We found an average of 276±65 CtBP2 puncta per cell for the ON plexus and 367±84 puncta for the OFF plexus (n=10 cells). 49% of the CtBP2 puncta in the OFF plexus were from t2 cone bipolar axons (n=7 cells). 39% of the CtBP2 puncta in the ON plexus were from t6 bipolar cell axons (n=4 cells) and only few were from rod bipolar axons (7%; n=4 cells). We also found all glycine receptor α subunits associated with A8 amacrine cells in varying numbers with GlyRα1 being the highest in the OFF-plexus. In addition, A8 amacrine cells were coupled to ON cone bipolar cells and provided putative inhibitory feedback via GlyRα1 to OFF cone bipolar cells. Furthermore, we found evidence that A8 cells provide glycinergic output via GlyRα1 onto sustained A-type ganglion cells.
We predict the A8 amacrine cell functions as an ON-OFF crossover-inhibiting cell with an increase in excitation from ON-bipolar cells leading to an increase in inhibition of OFF-bipolar cells. We also predict the A8 cell modulates sustained responses of A-type ganglion cells to enhance the dynamic range through “push-pull” of excitatory and inhibitory inputs.
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