Figure 1.

Experimental design and timeline, behavioral pain measurement and S1R western blotting. (A) Our studies involved three type of rats; spared nerve injury (SNI), sham, and control. The SNI rats underwent axotomy and ligation of the tibial and common peroneal nerves, with cautious sparing of the sural nerve; the sham rats underwent a surgery similar to SNI rats but without nerve injury; and the controls were left as naive rats (i.e., no surgery was performed). Both SNI and sham operations were performed at t = 0 day followed by pain assessment (von Frey tests) four weeks post-surgery. In the groups for the S1R western blotting experiment, the sciatic nerves were excised from rats, and neuroma was separated from the injured nerve, S1R was extracted from those sample for western blotting analysis. In the other groups, each rat underwent magnetic resonance imaging (MRI) of the thigh region (containing sciatic nerve), followed by injection of the radiotracer ([¹⁸F]FTC-146), and subsequent positron emission tomography (PET) imaging. Immediately after PET scanning, both sciatic nerves (left and right) from each rat in each group were harvested and used for either whole nerve autoradiography or sectioned nerve autoradiography and histology. (B) Mechanical allodynia, as evidenced by a reduction in the pressure leading to the withdrawal of paw, was assessed in SNI and sham groups via standard von Frey testing. Average paw withdrawal thresholds are depicted for left and right paws of rats in each group. (C) S1R western blotting results showed S1R expression was significantly elevated at neuroma site in the injured nerve. (D) Representative S1R western blotting image (Br = brain; N = Neuroma; LN = Left Nerve; RN = Right Nerve). Error bars represent standard error of the mean value. ***p<0.005, *p<0.05