Amphibian retinas are commonly used for electrophysiological studies
on neural function and transduction because they share the same general
properties as higher vertebrate retinas. Glycinergic synapses have been
well described in amphibian retinas. However, the role of glycine
transporters in the synapses is largely unknown. We studied the
distribution and function of glycine transporters in the retinas from
tiger salamanders, mudpuppies, and leopard frogs by immunofluorescence
labeling and whole-cell recording methods. Our results indicated that
GlyT1- and GlyT2-like transporters were present in Müller cells and
neurons, respectively. GlyT1 labeling was present in Müller glial
cells and co-localized with Glial fibrillary acidic protein (GFAP), a
Müller cell marker, whereas the GlyT2 immunoreactivity was present in
the somas of amacrine cells (ACs) and processes in the inner plexiform
layer (IPL) and the outer plexiform layer (OPL). Because the axon
processes of glycinergic interplexiform cells (IPCs) are the only source
of glycine input in the OPL, GlyT2 staining revealed a spatial pattern of
the axon processes of IPCs in the OPL. The function of GlyT2 in the IPCs
was studied in tiger salamander retinal horizontal cells (HCs) by
whole-cell gramicidin perforated recording. The results demonstrated that
inhibition of GlyT2 by a specific inhibitor, amoxapine, increased a tonic
glycine input to HCs. Thus, the GlyT2 transporter is responsible for
uptake of synaptic glycine in the outer retina. We also compared the
distribution of glycine transporters in other amphibian species:
salamander, mudpuppy, and frog. The results are consistent with the
general pattern that GlyT1-like transporters are present in Müller
cells and GlyT2-like transporters in neurons in amphibian retinas.