Manganese-Enhanced MRI of Mouse Pain

MnCl₂ solution was injected into all mouse cohorts 23 h before the MEMRI scan (Figure 1). A solution of 100 mM MnCl₂ (MnCl₂⋅4H₂O; Sigma-Aldrich, St. Louis, MO, United States) was made with distilled water and diluted to 50 mM with saline (osmolarity, 275 mOsm/kg). The MnCl₂ solution was infused slowly through the tail vein using a syringe pump (KDS-100; KD Scientific, Holliston, MA, United States) for 60 min to a final dose of 75 mg/kg (final volume, 11.92 ml/kg) under continuous anesthesia (0.5–1.5% isoflurane; Mylan Inc., Tokyo, Japan) with monitoring of SpO₂ with a SomnoSuite (Towa Science, Tokyo, Japan); the mice were placed on a thermoregulated plate to maintain body temperature (Hattori et al., 2013 (link)). After MnCl₂ administration and confirmation of animal recovery from anesthesia, the mice were returned to their home cage and allowed to move freely with free access to food and water until the MRI acquisition. The mice were taken out of the home cage for <1 min for (1) intraplantar injection of formalin or saline (for all three cohorts) and (2) repeated (twice in total) intraperitoneal injections of CNO (for the third cohort). Details of these drug administrations are provided below.