The nitric oxide donor molsidomine induces anxiolytic-like behaviour in two different rat models of anxiety

• The effects of the nitric oxide donor molsidomine on anxiety were studied.
• Molsidomine induced anxiolysis in rats.
• The effects of molsidomine cannot be attributed to changes in locomotor activity.

Experimental evidence indicates the implication of the nitric oxide (NO) in anxiety. Contradictory results were reported however, concerning the effects of NO donors in animal models of anxiety disorders. The present study investigated the effects of the NO donor molsidomine on anxiety-like behaviour and compared them with the anxiolytic diazepam in rats. For this purpose, the light/dark and the open field tests were used. The effects of molsidomine on motility were also assessed. Intraperitoneal (i.p.) administration of molsidomine (1 and 4 mg/kg) did not influence rats' performance either in the light/dark or in the open field test. Administration of 2 mg/kg molsidomine significantly prolonged the time spent in the light chamber in the rats compared with the vehicle-treated animals, did not affect the first latency to enter the dark chamber and did not influence the number of transitions between the light and dark compartments of the apparatus. In the open field test, rats that received 2 mg/kg molsidomine spent more time in the central zone of the apparatus and exhibited an increment of rearing episodes compared with control and to molsidomine 1 and 4 mg/kg-treated rats. Nevertheless, molsidomine, at any dose tested, did not alter locomotor activity compared with vehicle-treated rats in a motility test. The present results indicate that the 2 mg/kg molsidomine induced anxiolytic-like effects in the light/dark and open field tests in the rat cannot be attributed to changes in locomotor activity. The magnitude of the molsidomine (2 mg/kg)-induced anxiolytic-like effects was not different to that produced by the benzodiazepine anxiolytic diazepam (1 mg/kg).