Foot shock-induced changes in blood and brain serotonin and related substances in rats

The effects of electric foot shock on peripheral and central serotonergic systems in rats have been studied. We have focused on the time course alterations with particular attention being paid to changes in 5-HT, 5-HIAA, tryptophan concentrations and 5-HIAA/5-HT ratios in blood and various parts of the brain, observed within 1 h following stress application. Blood and brain (7 regions) samples were taken immediately after electric foot shock, 30 min, 1 and 24 h later. In the blood stress induced a rise in tryptophan level as well as rises in 5-HT, 5-HIAA levels and 5-HIAA/5-HT ratio within 1 h following stressful treatment. Tryptophan concentration was found to be increased in every part of the brain within 1 h after electric foot shock application. In striatum it remained higher even after 24 h. 5-HT level showed a significant rise only in medulla, while hypothalamus was the sole region where a fall in 5-HT was found. In other parts of the brain 5-HT level remained unaffected by stress. 5-HIAA content increased in almost every brain area studied except cerebellum and striatum. 5-HIAA/5-HT ratios shared the same pattern of changes. Briefly, foot shock altered 5-HT turnover in various brain regions, in particular within the first hour following stress application, whereas delayed response to stress was rarely observed. Increased brain tryptophan level seems to be necessary to cope with the enhanced 5-HT metabolism caused by stress, reflecting as a rise in 5-HIAA concentration and 5-HIAA/5-HT ratio.