EFFECT OF LOCAL INJECTION OF 8-OH-DPAT INTO THE DORSAL OR MEDIAN RAPHE NUCLEI ON EXTRACELLULAR LEVELS OF SEROTONIN IN SEROTONERGIC PROJECTION AREAS IN THE RAT-BRAIN

Using in vivo microdialysis, we have examined the effects of local adm inistration of 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) into either the dorsal (DRN) or the median (MRN) raphe nucleus on extracel lular levels of serotonin (5-HT) in the corresponding projection field s, namely striatum and ventral hippocampus in the anaesthetized rat. L ocal injection of 8-OH-DPAT (0.5-mu-g/0.1-mu-l) in the DRN reduced ext racellular 5-HT levels in the striatum (-55%) and to a lesser extent i n the hippocampus (-22%). When injected at the same dose in the MRN, 8 -OH-DPAT caused a marked decrease in 5-HT output in the hippocampus (- 41%) and had no effect in the striatum. Autoradiographic studies perfo rmed on brains from animals that received a local injection of [8H]8-O H-DPAT into either the DRN or MRN under similar experimental condition s indicated that the radioactivity remained localized within each midb rain raphe nucleus. These results confirm anatomical data demonstratin g that the striatum and the ventral hippocampus receive their serotone rgic innervation preferentially from the DRN and the MRN, respectively .