Routinely we use hydrogen peroxide(H2O2) incubation for the suppression of endogenous peroxidase activity in the tissues- for thick 20 - 50 micron brain tissue sections I advice incubation of the tissues sections for longer high strength H2O2 incubation followed by approx 30 min to 1hour incubation in Na2CO3/NaHCO3 buffer followed by 3 PBS rinses of 20 mins each. this help to remove residual H2O2. This will help in decreasing background staining after reaction with DAB with added H2O2. Please make sure your target marker is stable in alkaline environment.