Functional mapping of dorsal and median raphe 5-hydroxytryptamine pathways in forebrain of the rat using microdialysis.
Recent neurochemical studies of the properties of 5-hydroxytryptamine (5-HT) pathways arising from the dorsal raphe nucleus (DRN) and median raphe nucleus (MRN) have measured extracellular 5-HT in brain regions with reported preferential DRN or MRN 5-HT inputs. Here, we have tested whether electrical stimulation of the DRN and MRN releases 5-HT in rat forebrain regions in a pattern that fits the reported distribution of DRN/MRN pathways. The effect on extracellular 5-HT of electrical stimulation (5 Hz, 300 microA, 20 min) of the DRN, and then MRN, was determined in six regions of the anaesthetised rat. Stimulation of the DRN evoked a short-lasting but clear-cut release of 5-HT (+70-100%) in regions (frontal cortex, dorsal striatum, globus pallidus, and ventral hippocampus) reported to receive a 5-HT projection from the DRN. Regions receiving an MRN innervation (dorsal hippocampus, medial septum, and ventral hippocampus) released 5-HT (+70-100%) in response to MRN stimulation. Regions reported to receive a preferential DRN innervation (frontal cortex, dorsal striatum, and globus pallidus) did not respond to MRN stimulation. Of two regions (dorsal hippocampus and medial septum) reported to receive a preferential MRN innervation, one did not respond to DRN stimulation (dorsal hippocampus) although the other (medial septum) did. In summary, electrical stimulation of the DRN and MRN released 5-HT in a regionally specific pattern. With the exception of one region (medial septum), this pattern of release bears a strong relationship to the distribution of 5-HT projections from the DRN and MRN reported by anatomical studies. The combination of raphe stimulation with microdialysis may be a useful way to study the in vivo neurochemistry of DRN/MRN 5-HT pathways.
McQuade
R
R
Department of Clinical Pharmacology, Radcliffe Infirmary, University of Oxford, England, U.K.
Sharp
T
T
D000818:Animals; D001931:Brain Mapping / Q000379:methods*; D003342:Corpus Striatum / Q000378:metabolism; D004558:Electric Stimulation; D005110:Extracellular Space / Q000378:metabolism; D005625:Frontal Lobe / Q000378:metabolism; D005917:Globus Pallidus / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007700:Kinetics; D008297:Male; D017551:Microdialysis; D016548:Prosencephalon / Q000378:metabolism*; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012688:Septum Pellucidum / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*
D012701:Serotonin; D006897:Hydroxyindoleacetic Acid