Fig. 1

Repeated activation of DREADD-expressing neurons in the VTA reduces tumor size. a Schematic representation of the experimental design, which includes stereotactic injection of the virus to induce DREADD expression, injection of Lewis lung carcinoma tumor cells (LLC), repeated CNO injections for 14 days to activate the VTA dopaminergic neurons, and analysis of tumor size. For all in vivo experiments, the control mice were injected with the virus carrying the gene encoding mCherry but lacking the information encoding for DREADDs. These controls were treated, as the experimental group, with daily CNO injections. b Demonstration of localization and specificity of DREADD expression in the VTA. Upper panel: VTA localization based on the Allen Brain Atlas. Lower panel: Immunohistochemical demonstration of virus localization in the VTA indicated by mCherry staining (red) co-localized with TH expression (green) in the right VTA dopaminergic neurons (virus was injected unilaterally to the right hemisphere; scale bar, 500 μm). c c-Fos expression, indicating cell activation co-localized with DREADD expression in VTA neurons after 14 days of repeated CNO injections to tumor-bearing mice (scale bar, 50 μm). d Representative tumors dissected from control mice (injected with virus carrying the gene encoding mCherry but not the DREADD gene), and VTA-activated mice. Both groups were subjected to daily CNO injection for 14 days. e Size of LLC tumors following sacrifice in mice subjected to daily VTA activation for 14 days, and their controls (P < 0.014; Student’s t-test; mean ± s.e.m; n = 9, 11). Data represent two independent repeats. f Weight of LLC tumors following sacrifice in mice subjected to daily VTA activation for 14 days, and their controls (P < 0.003; Student’s t-test; mean ± s.e.m; n = 10, 11). Data represent two independent repeats. g Weight of B16 tumors following sacrifice in mice subjected to daily VTA activation for 21 days, and their controls (P < 0.03; Student’s t-test; mean ± s.e.m; n = 8, 9). Data represent two independent repeats. h Weight of LLC tumors following sacrifice in mice subjected to VTA activation every other day for 28 days, and their controls (P < 0.006; Student’s t-test; mean ± s.e.m; n = 9, 8). Data represent two independent repeats