Stress and/or tranylcypromine treatment affects serotonergic measures in blood and brain in rats

Since stress can alter serotonin (5-hydroxytryptamine, 5-HT) turnover in the brain and the periphery, the effects of different types of acute stress on serotonin and related substances in the whole blood and various brain areas in rats pretreated with tranylcypromine (TCP) were studied. TCP administered alone caused a rise in 5-HT, a fall in its metabolite (5-hydroxyindoleacetic acid, 5-HIAA) in the whole blood and in every part of the brain analyzed relative to controls. In rats given TCP and subjected to footshock or water-immersion restraint stress similar changes, but to a different extent, were observed. 5-HT level remained essentially constant except in the blood and the limbic system, whereas 5-HIAA level was found to be increased in the blood and the brain, mainly in the limbic system and the brainstem following footshock. Water-immersion restraint stress caused an increase in 5-HT only in the limbic system without any changes in 5-HT and 5-HIAA in the blood. Relative to controls, an increase in total tryptophan concentration in the whole blood and in every part of the brain was found only after footshock application with or without pretreatment with TCP. In conclusion, responses to stress in rats may depend upon the type of stimulus applied as well as of a concurrent administration of TCP. Some regional differences may account for an altered in vivo efficacy of this drug.