(a) The tTARGIT system employs the combination of ‘Driver’ (AAV-hSYN-fDIO-tTA) and ‘Payload’ (AAV-TRE-DIO-Payload) AAVs. The Driver virus encodes a Flp-dependent tetracycline transactivator (tTA) under control of the human synapsin I (hSYN1) promoter and two tetracycline operators (TetO). The Payload virus encodes a Cre-dependent Payload transgene under control of the tetracycline response element (TRE). (b,c) Experimental scheme (b) and representative images (c) showing the detection of TdTomato (DSRed-IR, red) following the co-injection of AAV-hSYN-fDIO-tTA and AAV-TRE-DIO-ChR2-TdT into the VMH of (from left to right, as labeled) wild-type (WT), Slc17a6FlpO, LeprCre, or Slc17a6FlpO;LeprCre mice. (d,e) Experimental schematic (d) and representative images (e) showing the detection of TdTomato (DSRed-IR, red) following the injection of (from left to right, as labeled): (1) AAV-hSYN-fDIO-tTA, (2) AAV-TRE-DIO-ChR2-TdT, or the two viruses combined (1+2) into the VMH of Slc17a6FlpO;LeprCre mice. Scale bars = 100 μm.