Anesthesia Induction and Physiological Monitoring for Rodent fMRI

In preparation for fMRI procedures, rats were endotracheally intubated and mechanically ventilated using a small animal MR-compatible ventilator (CWE Inc., MRI-1, Ardmore, PA). Anesthesia was initially maintained under constant isoflurane (1.5–2%) mixed with medical air. Next, tail vein catheterization was performed for intravenous drug and contrast agent injections (see below). Immediately following intubation and tail vein catheterization, animals were placed within a head-holder, and harnessed to a small animal cradle (both plastic and custom-made). The cradle was lined with a circulating water blanket connected to a temperature-adjustable water bath located outside the scanner room (Thermo Scientific, Waltham, MA). A rectal probe was employed and core body temperature was maintained at 37 ± 0.5 °C. Mechanical ventilation volume and rate were adjusted to maintain EtCO₂ of 2.8–3.2% and SpO₂ above 96%, using capnometry (Surgivet, Smith Medical, Waukesha, WI) and pulse oximetry (MouseOx Plus, STARR Life Science Corp., Oakmont, PA). EtCO₂ values from the capnometry system were previously calibrated against invasive sampling of arterial blood gas, reflecting a pCO₂ level of 30–40 mm Hg22 (link)23 (link).