Fig. 1

Experimental design in this study. (a) The experimental design of BOLD-fMRI study. Rats were anesthetized by continuous intravenous infusion of dexmedetomidine (0.05 mg/kg/h) and rocuronium bromide (9 mg/kg/h). Before the formal fMRI study of the brain response to SNI, forepaw and hind paw stimulation-evoked BOLD responses were confirmed twice to ensure that the rats’ physiological conditions were suitable for fMRI and to confirm that the sciatic nerve was functionally intact. After confirmation, a 10-min fMRI session was conducted (yielding 300 images) with nerve transection at the 151st scan. (b) The experimental design of MEMRI study. The rats were divided into two groups. The purpose of the first group was to understand the cumulative brain activity during the first 24 h after neuropathic pain initiation, whereas that of the second group was to understand the cumulative brain activity on Day 8 after neuropathic pain initiation. The rats in the first group were anesthetized by isoflurane for SNI surgery. After SNI, a saline solution of 120 mM MnCl₂ (75 mg/kg; 2.25 mL/h) was injected into the tail vein. MEMRI scanning was performed 24 h after MnCl₂ infusion under 2% isoflurane anesthesia. The rats in the second group initially received SNI surgery under anesthesia by ketamine hydrochloride (75 mg/kg, i.p.) and xylazine (15 mg/kg i.p.). The rats received MnCl₂ infusion under isoflurane anesthesia 1 week later, and MEMRI scanning was performed 24 h after MnCl₂ infusion under 2% isoflurane anesthesia. (c) The experimental design of electrophysiology study. One week after electrode implantation, the EFP of the thalamocortical pathway was recorded twice before SNI for a baseline system stability check under 1.5–2% isoflurane anesthesia. Subsequently, each rat received SNI under the same anesthesia protocol as that of the BOLD-fMRI experiment, dexmedetomidine (0.05 mg/kg/h) and rocuronium bromide (9 mg/kg/h). During SNI, multiunit activities were recorded from 5 min before SNI to 25 min after SNI