Fig. 3: Activation of the SC–SNc pathway triggers dopamine release in the dorsal striatum.

a Schematic diagram showing injections of AAV-hSyn-C1V1-mCherry in the SC and AAV-hSyn-GRAB-DA in the dorsal striatum (DS) of WT mice. b Schematic diagram showing implantation of optical fibers above the SNc and DS to apply photostimulation and fiber photometry recording, respectively. c An example coronal section with C1V1-mCherry expression in the SC. This experiment was repeated independently in five mice with similar results. d In acute SC slices, light pulses (2 ms, 561 nm, 10 Hz, 10 pulses) illuminating on C1V1-mCherry+ SC neurons reliably triggered action potential firing. e An example coronal section of ventral midbrain showing an optical-fiber track above the C1V1-mCherry+ axon terminals in the SNc (left), the boundary of which was determined according to the immunofluorescence of TH (right). This experiment was repeated independently in six mice with similar results. f An example coronal section with an optical-fiber track above the DS neurons expressing GRAB-DA sensor. This experiment was repeated independently in six mice with similar results. g, h Example traces (g) and input–output curve (h) of GRAB-DA signals evoked by photostimulation of the SC–SNc pathway with different laser power. EGFP was used as a control of GRAB-DA sensor. i, j Example traces (i) and quantitative analyses (j) of GRAB-DA signals evoked by photostimulation (561 nm, 5 pulses, 2 ms, 0.5 Hz, 10 mW) of the SC–SNc pathway in mice treated with saline or haloperidol (0.4 or 1.6 mg/kg). Number of mice was indicated in the graphs (h, j). Data in h, j are means ± SEM (error bars). Statistical analyses in h, j were performed by one-way ANOVA (***P < 0.001). Scale bars are indicated in the graphs.