Differences in efferent projections from 5-hydroxytryptamine neurons in the dorsal raphe nucleus through virus tracing in mice
Objective To investigate the characteristics of efferent projections from 5-hydroxytryptamine(5-HT)-ergic neu-rons in the dorsal raphe nucleus(DRN)in mice,and to explore the differences in anatomical distribution of 5-HT-ergic neurons that project to different brain regions in the DRN.Methods A specific anterograde tracing virus rAAV2/9-Ef1α-DIO-mCherry was inject-ed into the DRN of Sert-Cre mice(n=3).After virus expression for four weeks,the mice underwent transcardiac perfusion,and the brains were removed and cut into 40 µm-thick coronal slices.The whole-slide immunofluorescence imaging scans were performed to observe the distribution of 5-HT-ergic neurons in the downstream projection brain regions of the DRN.The specific retrograde tracing viruses rAAV2/retro-EF1α-DIO-BFP,rAAV2/retro-EF1α-DIO-mCherry,and rAAV2/retro-EF1α-DIO-EGFP were injected into the nucleus ac-cumbens(NAc),central nucleus of the amygdala(CeA)and ventral tegmental area(VTA)of Sert-Cre mice(n=3),respectively.After virus expression for four weeks,the mice underwent transcardiac perfusion and the brains were collected.Then,slices containing the NAc,CeA,VTA and DRN were prepared for observing the anatomical distribution of virus-labeled 5-HT-ergic neurons in the DRN under a confocal fluorescence microscope.Results 5-HT-ergic neurons in the DRN extensively projected to the whole brain,including the piriform cortex,medial prefrontal cortex,NAc,basal forebrain,CeA,lateral sclerotic nucleus,lateral hypothalamus,and VTA.Notably,5-HT-ergic neurons projecting to the NAc were mainly distributed in the dorsal central and lateral regions of the DRN,5-HT-ergic neu-rons projecting to the CeA were mainly located in the dorsal lateral region of the DRN,and 5-HT-ergic neurons projecting to the VTA were mainly located in the ventral interfascicular region of the DRN.Conclusions The anatomical distribution of 5-HT-ergic neu-rons in the DRN that project to different brain regions are different,indicating the existence of relatively independent multiple parallel subsystems of 5-HT-ergic neurons within the DRN.
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