Fig. 1: An independent subpopulation of DR 5-HT neurons project to the VTA.
From: A discrete serotonergic circuit regulates vulnerability to social stress
a AAV5-DIO-eArch-GFP was injected into DR of Sert-Cre mice. b Dense terminal expression in the VTA. Scale, 100 μm. c Two possible projection patterns: DR serotonergic neurons send collaterals to both A and B (top), or independent subpopulations send axons exclusively to either A or B (bottom). d Microinjections of AAVretro carrying different fluorescent proteins (eYFP or mCherry) were placed in the mPFC and VTA (left) or the NAc and VTA (right) to retrogradely label the cell bodies of projection neurons in the DR. e Each section includes a schematic (left) and the histology (right) of the AAVretro injection site in the mPFC (left), the NAc (center), and the VTA (right) of Sert-Cre mice. Scale, 1 mm. f, g Images of retrogradely labeled mPFC-projecting and VTA-projecting neurons (f), or NAc-projecting and VTA-projecting neurons (g) in DR. Violet, anti-Tph2 staining; green, retrogradely labeled DR-mPFC neurons (f) or retrogradely labeled DR-NAc neurons (g); and red, retrogradely labeled DR-VTA neurons. Scale, 100 μm. Insets: magnified images showing the neurons indicated with arrows in individual channels. Scale, 10 μm. h, i Pie charts depicting the percentage of mPFC-projecting only and mPFC/VTA-projecting only (h) (n = 7 sections from three mice), or NAc-projecting only and NAc/VTA-projecting only (i), VTA-projecting only, and AAV negative (unlabeled) in serotonergic neurons (Tph2+) in the DR (n = 6 sections from three mice). j, k Quantitation of dual-site retrograde tracing. The proportion of serotonergic neurons projecting to mPFC and VTA (j), or NAc and VTA (k) in 5-HTDR→VTA neurons for the co-injection experiments. l Schematic of the viral strategy. Injection of AAVretro-DIO-Flp into the VTA and AAV-fDIO-eYFP into the DR of Sert-Cre mice is shown. m Representative coronal sections stained with GFP staining showing fibers in target areas. Scale, 100 μm. mPFC: medial prefrontal cortex, PL: prelimbic cortex, IL: infralimbic cortex, DP: dorsal peduncular cortex, NAc: nucleus accumbens, BLA: basolateral amygdala, PVT: paraventricular thalamic nucleus, MD: mediodorsal nucleus of the thalamus, PVH: paraventricular hypothalamus, SN: substantia nigra, VTA: ventral tegmental area.
