Fluorescent polymer microspheres

Microparticle image velocimetry (μPIV) system (Lavision, Germany) was used to visualize the flow fields in the water droplet and the oil phase. The tracer particles used in the water droplet and the oil were fluorescent polymer microspheres with the excitation and emission wavelengths of 542 and 612 nm (Thermo Fisher Scientific, American), respectively, and hollow glass beads (Lavision, Germany). The mass percentage concentration of them were both 0.003%.

Mice were anaesthetized with isoflurane (induction 5%, maintenance 2%, RWD R510IP, China) and fixed in a stereotactic frame (RWD, China). Before the surgery, local analgesics (Lidocaine, H37022147, Shandong Hualu Pharmaceutical) were administered. A feedback-controlled heating pad (FHC) was used to maintain the body temperature at 35 °C. Glass pipettes (tip diameter 10–20 µm) connected to a Picospritzer III (Parker Hannifin Corporation) were filled with virus solutions and injected at following coordinates (posterior to Bregma, AP; lateral to the midline, LAT; below the brain surface, DV; in mm): mPFC: AP + 1.98, LAT ± 0.6, DV -1.62, angle 10°; Amygdala: AP -1.2, LAT ± 3.0, DV -4.35; NAc: AP + 1.0, LAT ± 1.0, DV -4.2; RE: AP -0.3, LAT ± 1.3, DV -4.5, angle 18°; dCA3: AP -1.5, LAT ± 2.1, DV -1.7; vCA1: AP -3.2, LAT ± 3.4, DV -1.5 or 3.5. To identify the injection site, the virus solution was typically mixed at 1:500 with blue beads (fluorescent polymer microspheres, Thermo Scientific).