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Michael Flood, Erika D Eggers, Andrea Wellington, Luis Cruz; Impaired light adaptation in early diabetes is not accompanied by major cell death or dopamine receptor insensitivity. Invest. Ophthalmol. Vis. Sci. 2020;61(7):2729.
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© ARVO (1962-2015); The Authors (2016-present)
Previous research has established that retinal signaling under dark-adapted conditions is perturbed during early diabetes. There is also evidence that levels of dopamine are diminished in early diabetes – because dopamine is integral to light adaptation it is likely that retinal responses under different lighting conditions may be abnormal. The purpose of this study was to discover whether light adaptation (LA) is impaired in the diabetic retina, and if so, what the underlying mechanism(s) might be.
Diabetes was induced in 5-week old C57BL/6J male mice via 3 consecutive IP injections of STZ (75mg/kg) dissolved in citrate buffer. After 6 weeks retinal slices and whole-mounts were prepared for electrophysiology and IHC, respectively. Whole-cell recordings of light-evoked (L) and spontaneous (s) inhibitory post synaptic currents (IPSCs) or excitatory post synaptic currents (EPSCs) were made from rod bipolar cells (RBCs) and ON sustained ganglion cells (GCs), respectively. Light responses were elicited at multiple intensities by a 30ms full-field LED stimulus (λ = 525 nm) before and after dopamine D1 receptor activation (SKF-38393, 20 µM) or LA (950 photons/µm2/s background). The peak amplitude and charge transfer (Q) were measured for all evoked responses and analyzed by 2-way ANOVA. Amplitude, frequency and τ were calculated for all sIPSCs/sEPSCs and analyzed via paired t-test. Retinal whole mounts were stained for either tyrosine hydroxylase/caspase-3 or GAD65/67/RBPMS, imaged and analyzed in imageJ.
In diabetic RBCs, neither dopamine D1R sensitivity or light adaptation of L-IPSC peak amplitude or Q, nor their effects upon sIPSC parameters, were impaired (p>0.05). However, the LA-induced decrease of ON ganglion cell L-EPSC Q was impaired in diabetes (p=0.014, control n = 10, diabetic n =11). No differences were found in LA’s effects upon sEPSC parameters (p>0.05), suggesting upstream changes. No change in cell density was found for dopaminergic (p=0.683), displaced (p=0.488), glycinergic (p=0.855) or GABAergic (p=0.389) amacrine cells, or GCs (p=0.743).
In early diabetes ON GCs receive excessive excitation under light-adapted conditions. However, this does not seem to be attributable to loss of inhibitory amacrine cells or their ability to respond to dopamine, nor due to the selective death of dopaminergic amacrine cells.
This is a 2020 ARVO Annual Meeting abstract.
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