Trigonelline

Male and female rats were administered trigonelline (Cayman Chemical, Ann Arbor, MI) in the drinking water to inhibit Nrf2 activation for the 6 week duration of wheel running [6 (link); 42 (link)]. No trigonelline was administered at any time post CCI surgery. trigonelline concentrations were based on the average water consumption for each rat from the prior week, to achieve average doses of 100 mg/kg (made fresh daily). We selected a pharmacological approach as it allows temporal control over inhibition of Nrf2, specifically during the period of voluntary wheel running. We did not include sham controls, as we have previously shown that trigonelline does not alter sensory thresholds in sham-operated animals [42 (link)]. Regular drinking water was used as vehicle control.

Dimethyl fumarate (Sigma-Aldrich, St. Louis, MO, USA) was suspended with methylcellulose (viscosity 15 cP, 2% w v⁻¹ in water; ACROS, Geel, Belgium) and administered by oral gavage. In our preliminary experiment, rats received escalating daily doses of Dimethyl fumarate (Days 1 and 2: 30 mg 5 ml⁻¹ kg⁻¹; Days 3 and 4: 100 mg 5 ml⁻¹ kg⁻¹; Days 5–7: 300 mg 5 ml⁻¹ kg⁻¹) beginning 14 days after SNI/sham surgery. In all subsequent experiments, rats and mice were administered Dimethyl fumarate for 5 days (300 mg 5 ml⁻¹ kg⁻¹, q.d.), beginning 14 days after SNI/sham surgery. Dosing took place from 8:00–10:00 am. Trigonelline (Cayman Chemical, Ann Arbor, MI, USA) was suspended with methylcellulose and administered to rats by oral gavage for 5 days (300 mg 5 ml⁻¹ kg⁻¹, b.i.d.), beginning 14 days after SNI/sham surgery. Dosing took place from 8:00–10:00 am and 4:00–6:00 pm. Equivolume methylcellulose (2% w v⁻¹) was used as vehicle control for both drugs. An independent investigator dosed the rats in order to maintain blinding to treatment groups for the other investigators who performed the behavioral testing and assays.