The injection pipette was not removed until 10 min after the end of the infusion to allow diffusion of the virus. Subjects for the behavioral experiment were injected with virus as described above, and dual fiberoptic cannulae (Doric Lenses) were implanted in order to have the tip of the fiberoptic cannulae (200 μm, 0.22 NA) above the left and the right LHb (A-P: −3.6 mm from bregma; M-L: ±0.75 mm;
D-V: −4.0 mm from dura) (see Figure S2) and were secured to the skull with screws and dental cement. Rats were injected subcutaneously with 5 mg/kg carprofen (NSAID) after surgery. Rats (n = 7 in ChR2-YFP group, n = 5 in mCherry control group) used for directed place preference (DPP) underwent surgery at 4–7 weeks old, and behavior experiments were conducted at least 3 weeks after LBH589 cell line surgery. DPP was carried out in a shuttle box (50 cm wide × 25 cm deep × 30 cm high; Coulbourne Instrument) equipped with a door separating the two halves and photocell detectors. Walls were modified in order to present different patterns to provide contextual differences. Photocell Selleck JNK inhibitor detectors allowed automatic monitoring of rat location in the cage for the duration
of testing. Optical activation of ChR2-YFP-expressing axons was performed by using an optical fiber coupled to a 473 nm solid-state laser diode (OEM Laser Systems) with 20 mW of output from the 200 μm fiber. Directed place preference was designed in order to monitor preference/aversion induced by optical stimulation of the LHb. Throughout the full duration of the test, rats were free to explore both sides of the cage. The first 10 min allowed us to measure preference for either context without manipulation. No preference was found during this first 10 min.
After this 10 min baseline period, optical stimulation (continuous 20 Hz, 5 ms pulse duration) was delivered while the animal was in one context (defined as “context A”). For the next 30 min, optical stimulation of the LHb occurred whenever the rat was located in context A. Optical stimulation was stopped when the animal was in the other side of the cage (context B). Avoidance scores were measured Doxorubicin mouse by taking time spent in context B minus time spent in context A divided by total time (120 s). Student’s t test compared avoidance score from period 10–40 min to baseline (0–10 min period). In a different set of DPP testing, pairing of the optical stimulation with context A (20 min) was switched to context B for another 20 min and then paired again with context A for the last 10 min of the 1 hr session (see schematic in Figure 3). One ChR2-YFP-expressing rat lost its cannula before the DPP reversal test, so only six ChR2-YFP-expressing rats were tested for reversal of DPP. Student’s t test compared avoidance score from periods 10–30, 30–50, and 50–60 min to baseline period (0–10 min). Two weeks after surgery, rats were anesthetized with isoflurane before decapitation and brain removal.