ABSTRACT
Isatin (2,3-dioxoindole), one of the components of tribulin, which has been postulated to function as an endogenous marker of stress and anxiety, was shown to induce a dose-related attenuation of learning acquisition in an active avoidance test and inhibition of learning retention, or memory, in a step-down passive avoidance paradigm and transfer latency in an elevated plus-maze, in rats. Earlier studies have indicated that isatin functions as a 5-hydroxytryptamine (5-HT)3 receptor agonist in its anxiogenic activity in rats and is an antagonist at mammalian atrial natriuretic peptide (ANP) receptors. Since 5-HT3 receptor antagonists and centrally administered ANP have been shown to facilitate learning and memory, the observed memory dysfunction induced by isatin can be attributed to its receptor activity at 5-HT3 and ANP receptors. The investigation also indicates that anxiogenic agents are likely to disrupt memory functions.