The peroxidase enzymatic activity was then visualized with 3, 3′ diaminobenzidine tetrahydrochloride (DAB, 2%), 0.012% hydrogen peroxide in PBS (aromatase, ARO) or with DAB (2%), Nickel sulphate (25 mg/ml), 0.012% hydrogen peroxide in Sodium Acetate (0.175 M) (vasotocin, VT).