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Franklin D Echevarria, Rebecca M Sappington; IL-6 deficiency in the retina and its consequences on the murine visual system. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6335.
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The importance of IL-6 activity in the development and normal function of the CNS is becoming increasingly evident. To identify consequences of IL-6 deficiency on the murine visual system, we examined retinal layer structure, retinal ganglion cell (RGC) health and functional visual capacity in adult (7 mo) wild type (WT) and IL-6 knockout (KO) mice.
To determine impact on overall retinal structure, we used optical coherence topography (OCT) to measure the thickness of the retina as well as each retinal layer in WT and IL-6 KO mice. RGC health in these mice was ascertained using visual evoked potential (VEP), which measures N1 and P1 amplitude and latency of RGC based waveforms. To measure functional visual capacity, IL-6 WT and KO animals were subjected to Optokinetic Testing (OKT), which employs a rotating sine wave with variable spatial frequencies to measure visual spatial acuity threshold.
Based on OCT measurements, layer thickness in the IL-6 KO animals is compromised when compared to WT animals. Significantly thicker layers (p<0.05) in the IL-6 KO retina include the ganglion cell/neural fiber layer (RGC/NFL), inner plexiform layers (IPL), outer nuclear Layer (ONL) and outer plexiform layer (OPL). Interestingly, the inner nuclear layer (INL) in the IL-6 KO retina is the only layer that is significantly thinner compared to WT mice (p<0.05). Retinal ganglion cell activity measured by VEP was also found to be altered when compared to WT mice. The N1 amplitude of the IL-6 KO is 18.6% larger than in WT mice (p<0.05), while the N1 latency is 12.8% larger (p<0.001). No significant difference was found in the P1 amplitude or latency (p=0.43 & p=0.19 respectively). OKT testing determined the IL-6 KO mice have a 6% decrease in acuity threshold (p<0.05) when compared to IL-6 WT mice.
Our data suggest that loss of IL-6 is associated with changes in retinal structure and inner retina activity. Interestingly, these changes seem to translate into a visual deficit, specifically, a decrease in visual acuity threshold. Overall, these data continue to support the hypothesis that IL-6 is important for normal function in the CNS.
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