Stimulation of VTA DA system increases DA but not 5-HT level in the striatum.

(A) Protocol of optogenetic stimulations and cocaine treatments. (B) Schematic of virus injection sites and optic fiber implantation sites for VTA stimulation in DAT-cre mices. (C) (Left) dLight expression and photometry fiber placement in the NAc co-labeled with tdTomato projection from VTA. (Middle) dLight expression and photometry fiber placement in the DS co-labeled with tdTomato projections from VTA. (Right) Optogenetic stimulation fiber placement and Chrimson-tdT expression in the VTA. Scale bars, 1 mm. (D) DA increases after optogenetic stimulation of VTA DA neurons (left) and i.p. cocaine injections (right) in NAc (red trace, n = 6) and DS (blue trace, n = 5). (E) Area under curve of DA signal in NAc and DS in 5 seconds during baseline and after optogenetic stimulation (Wilcoxon test; NAc: W = 21, z = 0.765, *P = 0.016, n = 6 mice; DS: W = 15, z = 0.198, *P = 0.031; n = 5 mice respectively). (F) Ratio of peak DA signal after optogenetic stimulation and peak DA signal after cocaine injection. (G) 5-HT increases after optogenetic stimulation of VTA DA neurons (left) and i.p. cocaine injections (right) in NAc (red trace, n = 4) and DS (blue trace, n = 6). (H) Area under curve of DA signal in DS in 5 seconds during baseline and after optogenetic stimulation (Wilcoxon test; NAc: W = 2, z = -0.01, P = 0.375, n = 3 mice; DS: W = 3, z = 0.00, P = 0.422, n = 6 mice respectively). (I) Ratio of peak 5-HT signal after optogenetic stimulation and peak 5-HT signal after cocaine injection.

Stimulation of DRN 5-HT system increases 5-HT but not DA level in the striatum.

(A) Schematic of virus injection sites and optic fiber implantation sites for DR stimulation in SERT-cre mice. (B) (Left) GRAB-5HT expression and photometry fiber placement in the NAc co-labeled with tdTomato projection from DR. (Middle) GRAB-5HT expression and photometry fiber placement in the DS co-labeled with tdTomato projections from DR. (Right) Optogenetic stimulation fiber placement and Chrimson-tdT expression in the DR. Scale bars, 1 mm. (C) DA increases after optogenetic stimulation of DR SERT neurons (left) and i.p. cocaine injections (right) in NAc (red trace, n = 4) and DS (blue trace, n = 4). (D) The area under the curve of DA signal in NAc and DS in 5 seconds during baseline and after optogenetic stimulation. (Wilcoxon test; NAc: W = 15, z = 0.05, *P = 0.031, n = 5 mice; DS: W = 8, z = 0.038, P = 0.125, n = 4 mice respectively). (E) Ratio of peak DA signal after optogenetic stimulation and peak DA signal after cocaine injection. (F) 5-HT increases after optogenetic stimulation of DR SERT neurons (left) and i.p. cocaine injections (right) in DS (blue trace, n = 2). (G) Area under curve of 5-HT signal in DS in 5 seconds during baseline and after optogenetic stimulation. (Wilcoxon test; DS: W = 15, z = 0.423, *P = 0.031, n = 4 mice respectively). (H) Ratio of peak 5-HT signal after optogenetic stimulation and peak 5- HT signal after cocaine injection.

DRN 5HT neurons make excitatory synapses onto OFC, pNAcSh, and VTA neurons.

(A) Top: Diagram of virus injection of AAV-Syn-FLEX-Chrimson-tdTomato in the DRN of SERT-Cre mice. Bottom: Representative image of tdTomato–expressing cell bodies of Sert neurons in the DRN. Scale bar, 200 uM. (B-F) Top: Localization of recordings in the DS (B), NAcSh anterior (C), OFC(D), NAcSh posterior (E) and VTA (F). Bottom: representative traces of p-pulse optical stimulation of Chrimsom+ fibers, before and after bath application of NBQX/AP5 (20 mM) in OFC (C), NAcSh posterior (D) and VTA (E) neurons. (G-I): Quantification of the amplitude of responses before and after NBQX/AP5 bath-application.