Behavioral effects of isatin on open field activity and immobility in the forced swim test in rats

Isatin is an endogenous selective inhibitor of monoamine oxidase (MAO) B, related to tribulin, whose activity and excretion in urine is increased during stress and anxiety. A previous study from our laboratory hypothesized that isatin may be a component of an alarm substance that rats secrete in the forced swim test. The present study tested that hypothesis by examining isatin's behavioral effects on open field activity and in the forced swim test. Male rats injected (i.p.) with isatin (0-160 mg/kg) ambulated less in the open field and were more immobile in the forced swim test than controls. These results did not support the hypothesis that alarm substance contains isatin and suggest, instead, that isatin has sedative or anxiolytic activity.