RESUMO
Sodium nitroprusside (SNP) is a nitric oxide (NO) donor which actually is under assessment as a potential candidate for the treatment of schizophrenia. It is well documented that anxiety symptoms are a prominent future in various psychiatric diseases comprising schizophrenia. Prior research has shown that acute challenge with SNP (1-3 mg/kg) induced anti-anxiety effects in rats but these effects at high doses were confounded by sedation and were disappeared after repeated application of it. It is still unknown if administration of a lower SNP dose range, either acutely or sub-chronically, could induce anxiolytic-like behaviour. The present study was designed to investigate this issue in rats. For this aim, the light/dark and the open field tests were used. Acute challenge with SNP (0.1 and 0.3 mg/kg, 30 min before testing) did not affect rodents' performance in the above mentioned behavioural paradigms. Conversely, rats treated sub-chronically with SNP (0.1 and 0.3 mg/kg, once per day, for 5 consecutive days), displayed longer time spent in the light chamber of the light/dark box and in the central area of the open field with respect to their vehicle-treated counterparts. Interestingly, SNP did not influence the first latency to enter the dark chamber and the number of transitions between the light and dark compartments of the apparatus in the light/dark test and did not modify the number of squares crossed, grooming episodes and rearings in the open field test. Finally, acute administration of SNP (0.1, 0.3 and 1 mg/kg, 10 min before testing) also did not influence rats' performance in the light/dark test. The present results indicate that short-term repeated but not acute application of a range of low doses of the NO donor SNP in a dose-independent manner induced an anti-anxiety behaviour in the rat which was not accompanied by undesired effects.