| Abstract No.: | A-B1024 |
| Country: | Canada |
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| Title: | GLUTAMATERGIC PROJECTIONS FROM DORSAL AND MEDIAN RAPHE TO THE MEDIAL SEPTUM AND HIPPOCAMPUS |
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| Authors/Affiliations: | 1 Jesse Jackson; 2 Brian Bland; 2 Michael Antle;
1 Douglas Hospital Research Center, Department of Psychiatry, McGill University, Montreal, QC, Canada; 2 University of Caglary, AB, Canada
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| Content: | The brainstem raphe nuclei are typically assigned a role in serotonergic brain function. However, many non-serotonergic neurons also reside within the dorsal and median raphe and project to both hippocampus and medial septum although the neurochemical phenotype of these neurons remains unknown. We injected the retrograde tracer cholera toxin subunit B into the dorsal hippocampus and medial septum of rats and used triple labelling immunofluorescence for cholera toxin, tryptophan hydroxlase, and vesicular glutamate transporter 3 (VGLUT3) to identify serotonergic and glutamatergic cell populations in the median and dorsal raphe. We found a large population of cholera toxin labelled neurons in the median raphe expressing VGLUT3 in addition to neurons expressing tryptophan hydroxlase. Sixteen percent of labelled neurons had both VGLUT3 and tryptophan hydroxlase. The dorsal raphe to hippocampus projection was less numerous, predominately serotonergic, and possessed 30% of retrogradely labelled neurons with both tryptophan hydroxlase and VGLUT3. Median raphe neurons projecting to the medial septum were largely VGLUT3 positive and 10% of the neurons expressed both tryptophan hydroxlase and VGLUT3. Contrary to the median raphe, dorsal raphe projections to the medial septum were predominately serotonergic and 22% of cholera toxin positive cells expressed trypophan hydroxlase and VGLUT3. Therefore, the enigmatic non-serotonergic projection from the median raphe to the forebrain appears to be glutamatergic. In addition, these results demonstrate a dissociation between glutamatergic and serotonergic median raphe afferent inputs to the medial septum and hippocampus suggesting divergent and/or complimentary roles of these pathways in modulating cellular activity within the septohippocampal network. |
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