Mr compatible system

All animal studies were performed under protocols that comply with the
Guide for the Care and Use of Laboratory Animals (NIH
publication no. 85–23, Revised 1996) and were approved by the Animal
Care and Use Committee at our institution. An indwelling tail vein catheter was
established to deliver Gd-DTPA (Magnevist, 0.1 mM/kg body weight) and
Regadenoson, while ATL313 was delivered by an intraperitoneal (IP) bolus
injection. Mice were positioned supine in the magnet and body temperature was
maintained at 36 ± 0.5 °C using thermostated water. Anesthesia
was maintained using 1.25% isoflurane in O₂ inhaled through a
nose cone during imaging. The ECG, body temperature and respiration were
monitored during imaging using an MR-compatible system (SA Instruments, Stony
Brook, New York).

On the day of imaging, the animal was fed with 10g of Gadolinium (Gd)-labeled test meal after the 18-hour overnight fast. The Gd-labeled test meal was made of 10g Dietgel mixed with 22.4mg Gd-DTPA powder (#381667, Sigma Aldrich, St. Louis, USA) using a double-boiled liquefying approach. Immediately after it had ingested the meal, the animal was anesthetized with Isoflurane followed by implantation of a bipolar cuff electrode (Pt/Ir electrode; MicroProbes, Gaithersburg, MD, USA) onto the left cervical vagus nerve with a surgical procedure identical to that described in our previous work¹⁶ . The animal was then setup in prone position in the scanner. Respiration and body temperature were monitored with an MR-compatible system (SA Instruments Inc., Stony Brook, NY, USA) to ensure stable physiology. The leads of the electrode were connected to a pair of twisted wires that were connected to a current stimulator (A-M Systems Model 2200; A-M Systems, Sequim, WA, USA) placed outside of the MRI room. A bolus injection of 0.01 mg kg⁻¹ dexmedetomidine solution (0.05 mg mL⁻¹, Zoetis, NJ, USA) was administered subcutaneously (SC). Fifteen minutes after the bolus, dexmedetomidine was infused (SC) continuously throughout the experiment (0.03 mg kg⁻¹ h⁻¹). The dose of Isoflurane was lowered to 0.3–0.5% as soon as the animal’s respiratory rate began to decrease.