naloxone and Retinal-Degeneration

Microglia-associated inflammation is closely related to the pathogenesis of retinal degenerative disorders. We have previously shown in vivo that naloxone protected photoreceptors from light-induced apoptosis possibly through inhibiting microglial activation. In this study, we attempted to explore the effect of lipopolysaccharide (LPS)-activated microglia on photoreceptor death and the influence of naloxone treatment using an in vitro retinal microglia and 661 W photoreceptor co-culture system. Immunofluorescent staining and ELISA measurements demonstrated that LPS activated microglia by changing the morphology and increasing the production of proinflammatory factors interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha. Flow cytometry analysis of annexin V/propidium iodide staining showed that LPS-activated microglia promoted the apoptosis of co-cultured 661 W photoreceptor cells. Naloxone inhibited microglial activation and decreased the release of IL-1beta and TNF-alpha but could not prevent photoreceptors from undergoing apoptosis. Considering the dual role of microglia-associated inflammation in both neurotoxicity and neuroprotection, modulating the function, rather than simply inhibiting their activation, might be a new therapeutic method for preventing photoreceptor degeneration.

Topics: Animals; Apoptosis; Cell Line; Coculture Techniques; Inflammation; Interleukin-1beta; Lipopolysaccharides; Microglia; Naloxone; Neuroprotective Agents; Photoreceptor Cells, Vertebrate; Rats; Rats, Sprague-Dawley; Retina; Retinal Degeneration; Tumor Necrosis Factor-alpha

In nonocular systems, activation of opioid receptors has been shown to ameliorate tissue damage induced by ischemic stress. The current study was an investigation of whether opioid receptors activated by endogenous or exogenous agonists can ameliorate ischemic retinal injury.. In an investigation of whether endogenous opioid receptor-activation reduces ischemic injury, the effects of the opioid antagonist naloxone (3 mg/kg; IP) on retinal neuroprotection induced by ischemic preconditioning (IPC) were evaluated. Whether exogenous opioid administration can reduce ischemic retinal injury was determined by pretreating rats with morphine (0.01-10 mg/kg) before injury. Morphometric and electroretinogram (ERG) analyses were used to assess the differences in retinal structure and function. The expression of opioid receptor subtypes was evaluated by Western blot and immunohistochemical analyses.. In control animals, 7 days after ischemic retinal injury, ERG a- and b-wave amplitudes were significantly reduced (23% and 41%, respectively). In addition, degeneration of the inner retina resulted in a 34% reduction in overall retina thickness. In animals receiving IPC before ischemic injury, ERG wave forms and retinal morphology were preserved. Pretreatment with naloxone reversed both the functional and structural retinal protection induced by IPC. In animals treated with morphine 24-hours before ischemic injury, ERG waveforms were preserved in a dose-dependent fashion (ED(50) = 0.18 mg/kg), and this protective response was reversed by naloxone pretreatment. Immunohistochemical and Western blot data demonstrated that the delta-, kappa-, and mu-opioid receptor subtypes are expressed in the retina.. These data provide evidence that activation of one (or more) opioid receptor(s) facilitates the development of IPC within the retina and can reduce ischemic retina injury.

Topics: Animals; Blotting, Western; Electroretinography; Female; Immunohistochemistry; Ischemic Preconditioning; Male; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Rats; Rats, Inbred BN; Receptors, Opioid; Reperfusion Injury; Retinal Degeneration; Retinal Vessels

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.

Topics: Animals; Apoptosis; Blotting, Western; Cell Movement; Electroretinography; Fluorescent Antibody Technique, Indirect; In Situ Nick-End Labeling; Injections, Intraperitoneal; Interleukin-1beta; Light; Male; Microglia; Naloxone; Neuroprotective Agents; Photoreceptor Cells, Vertebrate; Radiation Injuries, Experimental; Rats; Rats, Sprague-Dawley; Retinal Degeneration; Up-Regulation