Early diabetes impairs visual function in mice through altering neuronal activity in the primary visual cortex

Diabetes damages both the retina, leading to retinopathy, and the central visual system, resulting in impaired directional selectivity and color vision in patients without retinopathy. Contrast sensitivity (CS) is a fundamental visual function that allows us to distinguish between objects and backgrounds. In this study, diabetic mice were used to observe the effects of early diabetes on the contrast sensitivity function of primary visual cortex (V1) neurons. Funduscopic examination revealed no retinopathy in mice at four weeks of diabetes. Multichannel electrophysiological recordings and interneuronal correlation analysis revealed that V1 neurons in diabetic mice exhibited significantly reduced CS compared to controls. Furthermore, these neuronal responses showed markedly decreased signal-to-noise ratios along with increased response variability. Notably, noise correlation in V1 of diabetic mice was significantly elevated, providing a basis for neuronal perceptual abnormalities in population neuronal coding. Partially, the dysfunction of neuronal populations and individual units in V1 of diabetic mice can be attributed to the disruption of the excitatory/inhibitory balance. In summary, our findings indicate that significant alterations in neuronal contrast sensitivity function occur in the primary visual cortex of diabetic mice prior to observable fundus lesions, reflecting diminished coding capacity in V1 neurons.