Intrathecal Administration of Bioactive Compounds

The following compounds were used in our experiments: fisetin (F; Cayman, Ann Arbor, MI, USA), peimine (P; Sigma‒Aldrich, St Louis, USA), artemisinin (Ar; Sigma‒Aldrich, St. Louis, MI, USA), astaxanthin (A; Sigma‒Aldrich, St Louis, USA), bardoxolone methyl (BM, Sigma‒Aldrich, St. Louis, MI, USA), 740 Y-P (7; Med Chem Express, Monmouth Junction, NJ, USA), morphine hydrochloride (M; Fagron, Krakow, Poland), buprenorphine (B; Polfa S.A., Warsaw, Poland) and oxycodone hydrochloride (O; Molteni Farmaceutici, Scandicci, Italy). All of these substances were administered via intrathecal injection (i.t.), a standard procedure in our laboratory [109 (link),111 (link)]. It is performed by using a Hamilton syringe with a thin needle in accordance with instructions described previously [112 (link)]. The injections were performed in the lumbar segment of the spinal cord (between the L5 and L6 vertebrae) with a volume of 5 µL, and the tail reflex was an indicator of correct administration.