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 extracellular 5-hydroxyindoleacetic acid (5-HIAA) concentrations in the frontal cortex and the N. raphe dorsalis (NRD) of the rat were studied. The following stressful procedures were used: Immobilization, 10 min, cold, 20 min, and forced exercise in a rotating wheel, 2h. These procedures were compared with a handling procedure, 10 min. The extracellular 5-HIAA concentration was followed by in vivo voltammetry with carbon multifibre electrodes in the awake animal. Handling had no significant effect on extracellular 5-HIAA concentrations neither in the frontal cortex nor the NRD, whereas immobilization and cold evoked significant increases in both brain areas. During and after forced exercise a significant increase was measurable only in the frontal cortex, while extracellular 5-HIAA concentrations were unchanged in the NRD. Since it is very likely that the modulation of the activity of the central serotoninergic system under stressful conditions is closely connected with changes in behaviour and temperature regulation, we compared our findings on extracellular 5-HIAA levels during stress with the effect of the 5-HT1A agonist (+)-8-hydroxy-2-(di-n-propylamino)tetraline (8-OH-DPAT), a substance known to reduce body temperature. The i.p. injection of a low dose decrease significantly both, the extracellular 5-HIAA concentration in the NRD and body temperature. Our results suggest that the serotoninergic activation in the frontal cortex may prove to be a general response to stress which could function perhaps as a part of the central coping mechanism, whereas serotonin (5-HT) in the NRD may modulate specific regulatory responses such as body temperature.