COMPARATIVE-STUDY IN THE RAT OF THE ACTIONS OF DIFFERENT TYPES OF STRESS ON THE RELEASE OF 5-HT IN RAPHE NUCLEI AND FOREBRAIN AREAS

The effects of several stress procedures on the release of 5-HT in the dorsal and median raphe nuclei (DRN and MRN, respectively) and in for ebrain structures of the rat brain innervated by both nuclei have been studied using intracerebral microdialysis. Handling for 30 sec, a sal ine injection and forced swimming for 5 min elevated significantly the 5-HT output in the MRN. The 5-HT output in the DRN was also enhanced by a saline injection. With regard to the forebrain structures examine d, handling and forced swimming increased dialysate 5-HT in the amygda la. The injection of saline induced a slight, but significant, elevati on of 5-HT in the medial prefrontal cortex. In contrast, the outflow o f 5-HT was significantly reduced in the ventral hippocampus and medial prefrontal cortex following forced swimming and this effect persisted well beyond the cessation of the swim session. These results indicate that the efflux of 5-HT in the MRN appears to respond to different fo rms of stress, whereas that in the DRN only increases after the inject ion of saline. The release of 5-HT in the forebrain structures is also dependent on the type of stress procedure and the region studied. (C) 1997 Elsevier Science Ltd.