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Invest Ophthalmol Vis Sci. 2008 Jun;49(6):2589-98. doi: 10.1167/iovs.07-1173.

Neuroprotective effects of naloxone against light-induced photoreceptor degeneration through inhibiting retinal microglial activation.

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Department of Ophthalmology, Eye and ENT Hospital of Fudan University, Shanghai, People's Republic of China.



To determine the role of microglial activation in light-induced photoreceptor degeneration and the neuroprotective effects of naloxone as a novel microglial inhibitor.


Sprague-Dawley rats were exposed to intense blue light for 24 hours. Daily intraperitoneal injection of naloxone or PBS as a control was given 2 days before exposure to light and was continued for 2 weeks. Apoptotic cells were detected by the TUNEL assay, and anti-OX42 antibody was used to label retinal microglia. Western blot was applied to evaluate the retinal interleukin (IL)-1beta protein levels. Retinal histologic examination and electroretinography (ERG) were also performed to evaluate the effects of naloxone on light-induced photoreceptor degeneration.


TUNEL-positive cells were noted in the outer nuclear layer (ONL) of the retina as early as 2 hours and peaked at 24 hours after exposure to light. OX42-positive microglia occurred in the ONL and subretinal space at 6 hours, peaked at 3 days, and changed morphologically from the resting ramified to the activated amoeboid. Expression of IL-1beta protein was also significantly increased at 3 days. Compared with the control, the number of microglia in the outer retina was significantly decreased in the naloxone-treated group at 3 days, and the thickness of ONL and the amplitudes of dark-adapted a- and b-waves were also well preserved at 14 days.


The activation and migration of microglia and the expression of neurotoxic factor (IL-1beta) coincide with photoreceptor apoptosis, suggesting that activated microglia play a major role in light-induced photoreceptor degeneration. Inhibiting microglial activation by naloxone significantly reduces this degeneration.

[Indexed for MEDLINE]

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