Intracerebroventricular injection of kynurenic acid, but not kynurenine, induces ataxia and stereotyped behavior in rats.

In the present studies the behavioral-pharmacological effects of kynurenine and its metabolite kynurenic acid were investigated after intracerebroventricular (ICV) microinjection in rats. Kynurenine (0.1 and 0.2 mumol ICV) produced slight behavioral changes, but its metabolite kynurenic acid (0.2 mumol ICV) induced marked ataxia, stereotyped behavior and muscular hypotonia in a dose-dependent manner. The kynurenic acid-induced neurological symptoms were partially inhibited but not eliminated by ICV pretreatment with D-serine (0.5, 2.5, 5 mumol), which is a selective agonist at the strychnine-insensitive glycine binding site of the NMDA-receptor complex. Our results support the following conclusions: 1) kynurenine (0.1 or 0.2 mumol, ICV) results in slight stereotypy and ataxia, but the speed of its metabolism to kynurenic acid in this paradigm is not sufficient to produce concentrations of kynurenic acid, which are able to elicit marked ataxia and stereotypy; 2) the duration of kynurenic acid-induced behavioral abnormalities is correlated with the length of disappearance of micro-injected kynurenic acid from brain tissue; 3) D-serine which is an agonist at the glycine site linked to the NMDA complex, partially antagonizes but does not eliminate the neurological disturbances induced by ICV kynurenic acid injection.