Nitric oxide released from brain homogenates following MO treatment was assessed using Griess reagent as described previously. Briefly, 100 mL of Griess reagent (Sigma, St. Louis, USA) was added to 100 mL of brain homogenate and incubated in dark for 15 min. The intensity of the color developed was estimated at 540 nm with the help of a Benchmark plus 96-well ELISA plate reader (Biorad, CA, USA). The amount of nitrite accumulated was calculated (in mM) from a standard curve constructed with different concentrations of sodium nitrite [21] .