Serotonergic and kynurenic pathways in rats exposed to foot shock

Electric foot shock was applied to rats and levels of tryptophan and its me tabolites were measured in the plasma, central nervous system and periphera l tissues. Metabolites of tryptophan are the results of the enhancement of serotonergic and kynurenine pathways. Plasma levels of tryptophan increased significantly immediately after the foot shock and returned to normal valu es within 24 h. Tryptophan levels also increased in all the brain areas imm ediately after stress application and returned to normal values within 24 h . Foot shock elevated the levels of kynurenine in the plasma, liver, kidney and every parts of the brain. 3-Hydroxykynurenine and kynurenic acid lever s were increased in the brain. The present observations suggest that stress activates not only serotonergic pathway but also kynurenine pathway in the central nervous system and periphery. Some metabolites of kynurenine pathw ay, such as 3-hydroxykynurenine, are neurotoxic while other metabolite, suc h as kynurenic acid, may be neuroprotective. Increase in serotonin level in the hypothalamus and midbrain stabilises emotion and prevents mood disorde rs. Therefore, some brain dysfunction resulting from stress may be prevente d by the metabolites of tryptophan. The balance of these functions may be i mportant in the maintenance of nerve integrity under stress conditions. (C) 2000 Elsevier Science Inc.