Naloxone Inhibition Of Lipopolysaccharide-Induced Activation Of Retinal Microglia Is Partly Mediated Via The P38 Mitogen Activated Protein Kinase Signalling Pathway

OBJECTIVES: To investigate the effects and underlying mechanism of action of naloxone on lipopolysaccharide (LPS)-induced activation of retinal microglia in vitro. METHODS: Rat retinal microglia primary cultures were divided into four treatment groups: untreated; 1 mu g/ml LPS for 12 h; 0.5, 1.0 or 2.0 mu M naloxone for 30 min before LPS; 2.5 or 5.0 mu M SB203580 for 12 h before LPS and naloxone. Levels of tumour necrosis factor (TNF)-alpha and interleukin (IL)-1 beta were determined by enzyme-linked immunosorbent assay. Western blot analysis and double immunofluorescence examine activation activated protein were used to of the mitogen kinase (MAPK) signalling pathway. RESULTS: LPS induced an increase in TNF-alpha and IL-1 beta in culture supernatants, which was dose-dependently inhibited by naloxone. Naloxone also dose-dependently inhibited LPS-induced increases in phosphorylated p38 MAPK. Pretreatment of cells with SB203580 attenuated the inhibitory effect of naloxone on TNF-alpha and IL-1 beta production. CONCLUSIONS: Naloxone suppressed LPS-induced activation of cultured retinal microglia and this suppression appeared to occur partly through the p38 MAPK signalling pathway. Naloxone may have therapeutic potential in neurodegenerative diseases characterized by the activation of microglia.