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A Wesolowska, RF Nelson, VP Connaughton; Glutamate Mechanisms Involved in the OFF Pathway of Zebrafish Retina . Invest. Ophthalmol. Vis. Sci. 2002;43(13):1826.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose:To determine glutamate receptor types generating light OFF responses in zebrafish retina. Methods:Electroretinograms (ERG’s), evoked by photostimulation from a Xenon source, were recorded in an oxygenated, MEM perfused, in vitro eyecup preparation, before, during, and after treatments with neurotransmitter antagonists. Results:ERG a- b- and d-waves were stably observed over recording periods as long as 10 hours. The d-wave was taken as a measure of excitation in the OFF pathway. CNQX (20-240uM), a blocker of both AMPA and kainate receptors, and GYKI 52466 (50-110uM), which blocks only AMPA receptors, reversibly blocked the d-wave. SYM 2081 (50-100uM), a desensitizing kainate receptor agonist, had no effect on the d-wave. CPP (20-60uM), an NMDA receptor antagonist, also had no effect on the d-wave. DL-AP4 (160-980uM), an agonist activating metabotropic glutamate receptors in the ON pathway, increased d-wave amplitudes, as did picrotoxin (10-70uM) and bicuculline (30-80uM). These increased d-wave responses were blocked by CNQX. Conclusion:The d-wave reflects the massed activity of retinal OFF bipolar cells. While in other species these cells have been reported to use both kainate and AMPA ionotropic receptors, zebrafish OFF bipolar cells, as reflected by ERG d-wave activity, appear to use predominantly AMPA type receptors. The amplitudes of d-wave responses appear to be regulated by GABA-A, GABA-C and ON pathway mechanisms, involving amacrine and ON bipolar cells.
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