Fig. 1.

Nitric oxide (NO) donors decreased the pain threshold without behavioral side effects. Administration of nitroglycerin (GTN) (10 mg/kg  i.p.) or sodium nitroprusside (SNP) (1 mg/kg  i.p.) induced cold allodynia evaluated in the cold plate test (A), and thermal hyperalgesia, evaluated in the hot plate test (B); 1, 2, and 4 h after injection. GTN and SNP did not alter spontaneous mobility, inspection activity (hole board test) (C), or motor coordination (rota rod test) (D) at any time point. Amphetamine (2 mg/kg  i.p.) was used as a positive control, and 10 mice per group were used. *P < 0.05, **P < 0.01, and ***P < 0.001 compared with the control group