Fiber optic cannula

The fabricated electrode array was separated from the Si wafer substrate by PMMA dissolution in acetone, and the retrieved Si wafer was used for top PI layer etching by RIE. The electrode array was stamped with a PDMS stamp and the bottom PI layer was etched by RIE. The PDMS slab with the electrode array was stamped with the PLGA waveguide film whose surface is lightly swollen by an acetonitrile solvent to remove the PDMS slab after drying. We completed the integration by separating the PLGA waveguide film with the electrode array and PMDS master mold. Then, ACF cables (Elform) were bonded to the via regions of the electrode array interconnects for connection to an external data acquisition system. Additionally, fiber optic cannula (Ø1.25 × 6.4 mm ceramic ferrule, Ø105 μm core, 0.22 NA, l = 2 mm, Thorlabs) were precisely aligned to the entrance of the PLGA waveguides on the customized head-stage made by 3D printing and bonded using Norland Optical Adhesive 76 (NOA 76, Norland Products).

Mice were anesthetized with Dormitor (1 mg/ml in PBS) and Ketamine (100 mg/ml in PBS) cocktail at 10 µl/g mouse weight. The virus was injected intracranially into each hemisphere (0.5 µl/hemisphere, 0.1 µl/min) aiming at the lateral amygdala (LA) at the following coordinates: anterior-posterior −1.4, medial-lateral ±3.3, dorsal-ventral 4.65 (relative to Bregma). In optogenetic experiments, after virus injection, intracranial optic fiber (Thorlabs, Fiber Optic Cannula, Ø1.25 mm Stainless Ferrule, Ø200 µm Core, 0.39 NA) was implanted on the same line and 0.5 mm above the virus injection coordinates. Animals were allowed to recuperate for 4 weeks before behavioral experiments.

The genetically encoded optical dopamine sensor dLight 1.3 was expressed in dorsal striatum using a viral vector approach. In the same surgery, a fiber optic cannula (200 μm core, Thorlabs) was inserted (~100 μm in-depth dorsal to the AAV injection site) and fixed using dental cement. For signal acquisition, custom-written LabVIEW software was modified to control the recording hardware. LEDs of 470 nm (for dLight) and 405 nm (for isosbestic signal) were alternately turned on and off at 40 Hz, and bulk fluorescence was acquired using a photomultiplier (H10721; Hamamatsu, photonics). The signal was sampled at 1 kHz with a data acquisition device (NI USB 6211) and downsampled to 40 Hz for further analysis. The acquired photometry data were processed with custom-written code in MATLAB. First, a fitting curve was estimated and subtracted from the original signal to remove exponential and linear signal decay during the recording session. A linear fit was applied to align the 405 nm signal to the 470 nm signal, and then the fitted 405 nm signal was subtracted from the 470 nm channel and divided by the fitted 405 nm signal to calculate ΔF/F values. The ΔF/F time-series trace was normalized using z-scores to account for data variability across animals and sessions^{61 ,62} . Representative 470 nm and 405 nm signals are shown separately in Fig. 2b.

Rats were anesthetized with ketamine hydrochloride (70 mg/kg) and xylazine (5 mg/kg) injected intraperitoneally. To reduce pain and inflammation, rats were injected with carprofen (Zoetis) subcutaneously prior to all surgical procedures. Rats were placed in a stereotaxic frame, and an incision was made to expose bregma and lambda. Six anchor screws (Stoelting) were inserted into the skull anterior to the targeted injection site. A small craniotomy was made to target the LC (AP, −12 mm; ML, −1.25 mm from bregma), and a 32-gauge infusion needle attached to a 10 μl Hamilton syringe (Hamilton) was stereotaxically lowered to the target depth (5.5 mm below the pial surface) at an angle of 20° posterior to vertical (Quinlan et al., 2019 (link)). A total volume of 1 μl of virus was infused at a rate of 0.1 μl/min. The needle was held in place for 5 min after the completion of the infusion to allow the virus to diffuse, then slowly raised and removed from the brain. A Ø400 µm core, 0.39 NA, fiber-optic cannula (Thorlabs) was then stereotaxically placed just above the injection site (5.4–5.45 mm below the pial surface) and cemented in place with acrylic. The incision was closed with sutures, and a topical antibiotic cream was applied to the incision site. Rats received 3–7 d of recovery before training was resumed.