We have studied the effects of two cannabinoid receptor agonists, WIN 55,212-2 and cannabinol, on nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression in the C6 glioma cell line. After 24 h of lipopolysaccharide (LPS) (1 microg/mL) and interferon-gamma (IFN-gamma) (300 U/mL) stimulation, a significant increase in NO production, evaluated as nitrite, was observed in the culture medium. WIN 55,212-2 (0.1-10000 nM) and cannabinol (0.3-30000 nM), dose-dependently inhibited nitrite production showing a different potency (WIN 55,212-2 EC(50): 4.2 nM; cannabinol EC(50): 700 nM). WIN 55,212-2 (100 nM), given concomitantly to the stimulus also inhibited iNOS expression but had no effect when added to the cells 2 h after LPS/IFN-gamma, indicating a possible interference at the protein synthesis level or at an earlier step, as gene transcription. The cannabinoid CB1 receptor antagonist, SR141716A (0.1-100 nM), but not the cannabinoid CB2 receptor antagonist, SR144528 (0.1-100 nM), reduced in a dose-related manner WIN 55,212-2-and cannabinol-induced inhibition of nitrite production. SR141161A also reversed the WIN 55,212-2-induced inhibition of iNOS expression. These data suggest that selective cannabinoid CB1 receptor activation, by inhibiting iNOS expression and NO overproduction in glial cells, might be helpful in NO-mediated inflammation leading to neurodegeneration.