Animal husbandry and all experimental procedures were in accordance with the guidelines from the National Institutes of Health and were approved in advance by the Gallo Center Institutional Animal Care and Use Committee. Standard stereotaxic procedures were used to infuse virus (Cre-inducible
ChR2 viral construct serotyped with AAV5 or AAV10 coat proteins; see Supplemental Experimental Procedures for details) in the VTA and implant optical fibers dorsal to the VTA. All coordinates are relative to bregma in mm. Although Ivacaftor placements varied slightly from subject to subject, behavioral data from all subjects were included; see Figure S3 for a summary of placements and associated behavioral variability. Two small burr holes were drilled unilaterally over the VTA at the following coordinates: AP −5.4 and −6.2; ML ± 0.7. A custom-made 31 gauge infuser was used to deliver 1.0 μl of virus at two depths in each hole (DV −8.2 and −7.0, all coordinates from skull surface) for a MEK inhibitor total of 4.0 μl virus delivered unilaterally to the VTA. Each 1.0 μl of virus was infused at a speed of 0.1 μl per minute using a syringe pump (Harvard Apparatus). The virus infuser was left in place for an additional 10 min following each injection before it was slowly removed. A third burr hole was drilled (AP −5.8; ML ± 0.7) for the
insertion of an implantable optical fiber targeted just dorsal to the VTA (DV −7.3). The implanted fiber was made in-house with optical fiber (BFL37-300, Thorlabs) and a metal ferrule (F10061F360, Fiber Instrument Sales) and was secured to the skull surface
with five metal screws and dental cement. The following coordinates were used to infuse virus to other target structures: locus coeruleus (AP −9.6, −10.5; ML 1.5, DV −7.75), medial septum (AP 0.5, ML 0.5, DV −6.5, −7.5), nucleus basalis (AP −1.5, ML 2.5, DV −7.0, −6.0), and nucleus accumbens (AP 1.6; ML 2; DV 6 and 8). Experimental sessions were conducted in operant conditioning chambers (32 cm W × 32 cm L × 35 cm H; Med Associates Inc.) contained within sound-attenuating cubicles. The left panel was fitted with two nosepoke ports (5 cm from floor, separated by 18 cm), each with three LED lights at Dipeptidyl peptidase the rear. Prior to training sessions, rats were gently attached to patch cables made in-house with optical fiber (BFL37-200, Thorlabs) encased in a durable metal spring covering (PS95, Instech). These cables terminated with a metal ferrule connector (F10061F250, Fiber Instrument Sales) that was secured to the rats’ cranial implant with a fitted ceramic sleeve (F18300SSC25, Fiber Instrument Sales) and were attached at the other end to an optical commutator (Doric Lenses). This commutator was connected via a second optical patch cable to a 100 mW DPSS 473 nm laser (OEM Laser Systems). The commutator was affixed to a counter-balanced lever arm (Med Associates) to minimize cable weight and provide lift when rats were rearing.