Fig. 8: SC–SNc pathway promotes appetitive locomotion via SNc dopamine neurons.

a Schematic diagram showing injection of AAV-DIO-hM4Di-mCherry and AAV-ChR2-EYFP into the SNc and SC of DAT-IRES-Cre mice. b Schematic diagram showing implantation of an optical fiber above the SNc to apply light stimulation on ChR2-EYFP+ axon terminals from the SC. c An example coronal section of ventral midbrain showing the optical fiber track above the hM4Di-mCherry+ SNc dopamine neurons intermingled with ChR2-EYFP+ axons from the SC (left). The boundaries of SNc and VTA were delineated by the immunofluorescence of TH (right). This experiment was repeated independently in eight mice with similar results. d An example train of action potentials recorded from SNc dopamine neurons expressing hM4Di-mCherry (left) and quantitative analyses of spike number per minute before and 3 min after perfusion of CNO (10 μM) in ACSF (right). e The effect of light stimulation of the SC–SNc pathway on speed of approach during predatory hunting in mice without (Saline) and with (CNO) chemogenetic suppression of SNc dopamine neurons. f Chemogenetic suppression of SNc dopamine neurons with CNO significantly attenuated the net effect of SC–SNc pathway activation on the speed of approach. g The effect of light stimulation of the SC–SNc pathway on frequency of approach during predatory hunting in mice without (Saline) and with (CNO) chemogenetic suppression of SNc dopamine neurons. h Chemogenetic suppression of SNc dopamine neurons with CNO significantly attenuated the net effect of SC–SNc pathway activation on the frequency of approach. Number of cells (d) and mice (e-h) was indicated in the graphs. Data in d–h are means ± SEM (error bars). Statistical analyses in d–h were performed by one-sided Student’s t-tests (*P < 0.05; ***P < 0.001). Scale bars are indicated in the graphs.