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Previous studies from our laboratory have demonstrated that social isolation is
anxiogenic and may change the effects of many psychotropic drugs (1 -4). These
effects are generally attributed to "isolation stress". However, there is no report
concerning the role of nitric oxide in isolation stress rats. Therefore, the present
experiments were designed to investigate the effects of a nitric oxide synthase
inhibitor, nitro-L-arginine-methyl ester (L-NAME) on the elevated plus-maze
behavior in social isolation stress rats. Male Wistar rats were obtained from weaning
(21 days of age) and reared in groups of five or six rats/cage (social rearing) or singly
(isolation rearing). After five weeks, each rat was placed individually onto the
elevated plus-maze following intraperitonean injection with either saline or L-NAME
30 min before a 5 min test. The results showed that pretreatment with L-NAME (5, 10
and 50 mg/kg i.p.) in isolation reared rats produced a dose-related anxiolytic profile
(increase in the percentage of open arm entries and time spent) on the elevated plus-maze.
However, the anxiolytic-like property of L-NAME was not observed in socially
reared rats. The present results indicate that nitric oxide synthase inhibitor possesses
anxiolytic property in social isolation stress rats, and may represent a novel class of
therapeutics for anxiety disorders.
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