Anxiogenic activity of isatin, a putative biological factor, in rodents.

Isatin (2,3-dioxoindole) has been proposed as a new biological factor, responsible for at least part of the activity of tribulin, an endogenous monoamine oxidase and benzodiazepine receptor binding inhibitory factor, which may serve as an endocoid marker of stress and anxiety. The putative anxiogenic activity of isatin was investigated in rats and mice. The doses chosen for the study, namely 15 mg/kg i.p. in mice and 20 mg/kg i.p. in rats, were based on preliminary behavioural studies. Yohimbine, a well established anxiogenic agent, was used for comparison and used at doses of 2 and 2.5 mg/kg i.p. in mice and rats, respectively. The experimental paradigms chosen have been shown to stand the tests of validity and reliability. Isatin induced significant anxiogenic activity in the open-field and elevated plus-maze tests in mice, and the social interaction test in rats, which were comparable to those induced by yohimbine. In addition, both isatin and yohimbine attenuated the effects of the anxiolytic agent diazepam in the open-field test. The investigations indicate that isatin has significant anxiogenic effect and support the contention that it and/or its biotransformation products may be responsible for at least part of the activity of tribulin demonstrated previously in animal models and in clinical situations of stress and anxiety.