STRESS-INDUCED CHANGES OF EXTRACELLULAR 5-HYDROXYINDOLEACETIC ACID CONCENTRATIONS FOLLOWED IN THE NUCLEUS-RAPHE-DORSALIS AND THE FRONTAL-CORTEX OF THE RAT

In the present paper, the effect of different stressors on extracellul ar 5-hydroxyindoleacetic acid (5-HIAA) concentrations in the frontal c ortex and the N. raphe dorsalis (NRD) of the rat were studied. The fol lowing stressful procedures were used: Immobilization, 10 min, cold, 2 0 min, and forced exercise in a rotating wheel, 2h. These procedures w ere compared with a handling procedure, 10 min. The extracellular 5-HI AA concentration was followed by in vivo voltammetry with carbon multi fibre electrodes in the awake animal. Handling had no significant effe ct on extracellular 5-HIAA concentrations neither in the frontal corte x nor the NRD, whereas immobilization and cold evoked significant incr eases in both brain areas. During and after forced exercise a signific ant increase was measurable only in the frontal cortex, while extracel lular 5-HIAA concentrations were unchanged in the NRD. Since it is ver y likely that the modulation of the activity of the central serotonine rgic system under stressful conditions is closely connected with chang es in behaviour and temperature regulation, we compared our findings o n extracellular 5-HIAA levels during stress with the effect of the 5-H T1A agonist (+)-8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT), a substance known to reduce body temperature. The i.p. injection of a l ow dose decreased significantly both, the extracellular 5-HIAA concent ration in the NRD and body temperature. Our results suggest that the s erotoninergic activation in the frontal cortex may prove to be a gener al response to stress which could function perhaps as a part of the ce ntral coping mechanism, whereas serotonin (5-HT) in the NRD may modula te specific regulatory responses such as body temperature.