Abstract
Abstract: :
Purpose: Light insults activated retinal microglia suggesting its possible role in the photoreceptor degeneration process (Zhang, C. et al, ARVO 2003). By inhibiting microglial cells, minocycline showed neuroprotective effects in brain ischemia and in neurodegenerative disorders such as Parkinsons diseases. We evaluated the protective effects of minocycline on rod and cone photoreceptors in light–induced retinal degeneration in mouse. Methods: Nineteen five–week old Balb/cJ mice were divided into three groups: normal baseline (6), light–damaged (9), and minocycline treated group (5). Light–damaged and treated group mice were exposed to 3.5 Klux light for three hours. Treated mice received intraperitoneal injection of minocycline at the dose of 50 mg/kg for one week after light exposure and the normal and light–damaged mice received same volume of vehicle. At day 7 after light exposure, we recorded dark– and light–adapted ERG and dark–adapted 10 Hz flicker ERGs. The ratio of rod–driven/cone–driven flicker b–wave response (Lei, B. and Chang, B. ARVO 2003) and rod– and cone–driven oscillatory potentials (OPs) were studied. Results: In light–damaged mice, dark–adapted a– and b–wave and light–adapted b–wave amplitudes were decreased to about 15% of normal. Minocycline preserved the amplitudes to 60%, 55%, and 45% respectively. Dark–adapted flicker ERG rod–/cone–driven b–wave ratios were 3.62 in normal, 20.00 in light–damaged, and 5.56 in treated mice, suggesting cone function was more affected in light damage and minocycline preserved more rod function. In OPs analysis, cone–driven OPs were not recordable in light damaged mice. In treated group about 20% of rod– and cone–driven OPs were preserved. Conclusions: Our results support the hypothesis that rods and cones have different fates in light–induced retinal degeneration. Middle–wavelength light caused more severe damage to the cone system function than the rod system. Minocycline significantly preserved both rod and cone function, and the rod system function was better preserved.
Keywords: neuroprotection • photoreceptors • electroretinography: non–clinical