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Z. Jiang, W. Shen; The Function of Glycine in Regulation of Rod to Off-Bipolar Cell Synapses in Amphibians. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4559.
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© ARVO (1962-2015); The Authors (2016-present)
This study was to define the effect of glycine feedback in distal glutamate transmission. Glycinergic synapses in the distal retina made by glycinergic interplexiform cells. The function of this group of neurons remains to be decided.
Paired-patch whole cell recording were made on rods and Off-bipolar cells in dark-adapted tiger salamander retinal slides. Rods were depolarized by a brief single voltage step to -10mV to elicit glutamate release from the cells; the glutamatergic currents were recorded form OFF-bipolar cells. Glycine and strychnine were applied at the OPL, as well as in the bath solution. The polyclonal antibodies for glycine receptor subunits were used to localize different subtypes of glycine receptors in retina.
10microM glycine significantly enhanced the glutamatergic currents in Off-bipolar cells. The effect of glycine increased both the amplitude and kinetic of the glutamatergic currents in Off-bipolar cells. These effects could be blocked by 1microM strychnine. We also examined the direct effect of glycine in Off-bipolar cells. 10microM glycine produced a negligible current in OFF-bipolar cell dendrites. Immunolabeling results indicated that a low affinity glycine receptor subunit, GlyR alpha-3, were exclusively present in Off-bipolar cells, suggesting that Off-bipolar cells might be expressed a low affinity glycine receptor. In contrast, 5-10microM glycine could regulate voltage-dependent Ca2+ channels in rods by left shifting Ca2+ activation curve, suggesting that the effect of glycine was due to regulation of glutamate release in rods.
Our results indicate that glycinergic interplexiform cells regulate rod-mediated Off-pathway by enhancing glutamatergic synapses in the distal retina. The effect was most likely through regulation of glutamate release from rods. Moreover, a high and low affinity glycine receptors might be expressed in rods and Off-bipolar cells, respectively. Therefore, 10 microM glycine predominately activated rods and potentiates glutamatergic synapses by activation of Ca2+ channels in rods. These results suggest that a glycine feedback could enhance the synaptic input-output relationship from rods to-Off-bipolar cells.
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