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M. J. Rowan, W. Shen; Immunocytochemical Analysis of the On and Off Bipolar Cells of the Salamander Retina. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4593.
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© ARVO (1962-2015); The Authors (2016-present)
To understand the glutamatergic and glycinergic synapses in the On- and Off-pathways.
Immunofluorescence labeling and confocal imaging techniques were performed on retinal vertical sections and flat mounts from tiger salamanders. Several monoclonal and polyclonal antibodies were used to localize neurotransmitter receptors and transporters in BCs.
We found that sEAAT2b, a salamander specific glutamate transporter, labeled both rod- and cone-dominated Off-BCs with axon terminals stratified respectively at the distal margin and central half of the IPL. Many displaced Off-BCs were also labeled by sEAAT2b. sEAAT2b was also represented in a subgroup of dendrites that were labeled by Goα, indicating a presence on On-BC dendrites specifically. In addition, an AMPA receptor subtype,GluR4, was found to be presented in the Off-cone BC dendrites, clustered and invaginated into the cone pedicles. Furthermore, glycine receptor ß subunits (GlyRß) were found in both On- and Off-BC dendrites and the Landolt’s clubs in the distal retina. A GlyRß antibody also stained the somatic membranes and axon terminals of both On- and Off-BCs. Interestingly, we found that BC dendrites were labeled by Cl- uptake cotransporters, NKCC1. The special pattern in the OPL showed that NKCC1 labeling covered about 30-40% of BC dendrites labeled by either Goαor sEAAT2b in flat mount retinas.
sEAAT2b was generally present in both rod- and cone-dominated Off-BCs for glutamate uptake. In addition, some On-BC dendrites also appear to use sEAAT2b. In comparison to the On-pathway that uses metabotropic receptor mGluR6, ionotropic receptor GluR4 was used by the Off-pathway in the retinas. It appeared that BC dendrites were participating in glycinergic synapses of the distal retina in conjunction with landolt's club. The glycinergic synapse may not generate an inhibitory response due to the presense of NKCC1 in the dendrites of BCs, which acts to accumulate Cl- in local regions.
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