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Victoria P Connaughton, Zaid Tanvir, Ralph F Nelson; Retinal Physiology Is Altered In Glucose-Treated Zebrafish Retinas. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6175.
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To determine changes in retinal physiology (ERG a- and b-waves) in zebrafish following 1 month exposure to alternating glucose/hyperglycemic conditions
Adult, wildtype zebrafish were exposed to alternating 2% glucose/0% glucose solution for 24hr. Control fish were alternately exposed to either 0% glucose/0% glucose every 24hr or 2% mannitol/0% glucose every 24hr (osmotic control). After ~4 weeks of exposure, physiological responses in superfused retinal eye cups were examined using ERG. Eye cups were perfused with oxygenated MEM containing 50µm CNQX to allow isolation of a- and b-waves. Stimulating wavelengths, 570, 490, 410, and 370nm, corresponded to the wavelengths closest to maximal stimulation for each of the cone types in zebrafish. Each wavelength was tested at 7 light intensities. The stimulation protocol was run four times with each eye cup, 2x with a blue (418nm) background and 2x with a red (627nm) background to prevent dark adaptation and to better isolate individual cone mechanisms. Traces were analyzed using pCLAMP and Origin software.
ERG a-wave and b-wave components were clearly evident in retinas from all treatment groups. No delay in the onset of either ERG component was evident at any of the stimulating wavelengths. b-wave amplitude was consistently reduced in glucose-treated retinas compared to water-treated controls while b-wave amplitude in mannitol-treated retinas was increased. Similarly, a-wave amplitude in glucose-treated retinas was decreased in response to most stimulating wavelengths (vs. water-treated controls), while a-wave amplitude in mannitol-treated retinas was increased. The percent change in mean b-wave amplitude observed in glucose-treated tissue (30-40%) was consistently larger than the percent change in mean a-wave amplitude (< 20% change).
Glucose-treated zebrafish retinas show a reduction in photoreceptor and on-bipolar cell responses after one month. These results correspond to previous studies showing a thinning of inner retina (INL, IPL) (Gleeson et al., 2006) and a loss of cones (Alvarez et al., 2010) after one month of hyperglycemic conditions. These results suggest that one month of glucose treatment alters physiology in zebrafish retina. These findings are consistent with clinical studies showing physiological changes in retinas of diabetic patients.
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