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Ji-Jie Pang, Zhuo Yang, Roy A Jacoby, Samuel M Wu; Cone synapses in mammalian retinal rod bipolar cells. Invest. Ophthalmol. Vis. Sci. 2017;58(8):1034.
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© ARVO (1962-2015); The Authors (2016-present)
A subset of mammalian rod bipolar cells (RBCs) have been found to receive excitatory chemical synaptic inputs from both rods and cones (DBCR/C), but anatomical evidence for mammalian cone-RBC contacts has been sparse. This study examined anatomical cone-RBC contacts in mouse and primate retinas.
We used the neuronal tracer neurobiotin (NB) to visualize individual cones and standard immuno-markers to identify RBCs, cone pedicles and neuronal synapses. The cone-RBC contacts were observed with a confocal microscope.
Mouse cones were positively labeled by an anti-red/green (R/G)-opsin antibody, and peanut agglutinin (PNA) stained the basal membrane of cone pedicles. All synapses in the outer plexiform layer (OPL) were labeled for synaptic vesicle protein 2 (SV2) and PSD (postsynaptic density)-95, and those that coincided with PNA resided closest to bipolar cell somas. Cone-RBC synaptic contacts were identified by: 1) RBC dendrites deeply invaginating into the center of cone pedicles filled with NB (invaginating synapses), 2) RBC dendritic spines intruding into the surface of NB-filled cone pedicles (superficial synapses), and 3) PKCα immunoreactivity coinciding with synaptic marker SV2, PSD-95 or PNA at cone pedicles. RBCs that contacted cones accounted for 20.7%+/-0.03% of the cells (mean+/-se) in the peripheral retina and 38.9%+/-0.04% in the central retina (p=0.009, n=14 samples). The proportion of cones contacting RBC was not significantly different (p=0.07, n=14 samples) between the central (48.5%+/-0.05%) and peripheral retina (34.4%+/-0.05%). We also found that primate retinas (n=2 samples) exhibited similar cone-RBC contacts. 12.2%+/-0.01% of RBCs (n=416 cells) contacted cones and 22.5%+/-0.02% of cones (n=225 cells) contacted RBCs.
A population of RBCs, like AII amacrine cells, serve to integrate rod and cone signals in the mammalian retinal ON pathway.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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