Rats (N = 6 per experimental group) were perfused transcardially with 250 ml cold saline, 4 h after GTN or vehicle administration. Brains were immediately removed and chopped into parts; brain areas of interest were dissected out and used for the preparation of total extracts. The samples were homogenized on ice with a homogenizer in at least 5 volumes of modified RIPA buffer (Tris 50 mM, pH 7.4, NaCl 150 mM, EDTA 1 mM, SDS 0,2 %) supplemented with cocktail inhibitors protease. Then, they were incubated on ice for 20 min. The tissue lysate was centrifuged at 10,000 × g for 45 min at 4 °C and supernatants stored at −80 °C. Protein assay was performed by bicinchoninic acid (BCA) method. A 20 μg of protein were submitted to SDS-poliacrylamide gels 10 % and transferred onto a PVDF membrane (Amersham Biosciences). After blocking with 5 % dry milk, the blots were probed overnight at 4 C° with rabbit polyclonal anti-nNOS serum (1:1000; Cayman Chemical) or anti-eNOS serum (1:1000; Santa Cruz Bioctenology) and then probed for 1 h with an anti-rabbit horseradish peroxidase coupled secondary antibody (1:10000; Amersham Biosciences). An enhanced chemiluminescence system (ECL Advance; Amersham Biosciences) was used for visualization. Membranes were also probed with a rabbit polyclonal anti-β actin antibody (1:1000; Santa Cruz Biotechnology) as a housekeeping protein.