Exploring NR2 Subunit Antagonists for Trigeminal Neuropathic Pain

The effects of NR2 subunit antagonists on mechanical allodynia and hyperalgesia were evaluated on postoperative day 14. Animals that displayed mechanical allodynia and hyperalgesia following compression of the trigeminal nerve root were used for assessments. For intracisternal injection, individual rats were anesthetized with mixture of ketamine (0.2 g/kg) and xylazine (0.02 g/kg). Anesthetized rats were individually mounted on a stereotaxic frame and a polyethylene tube (PE10, CalyAdams, Parsippany, NJ) was implanted for intracisternal injection on postoperative day 11, as described previously [42 (link)-45 (link)]. The polyethylene tube was inserted through a tiny hole made in the atlantooccipital membrane and dura, using a 27 gauge syringe needle. The tip of the cannula was placed at the obex level. The polyethylene tube was subcutaneously led to the top of the skull and secured in place by a stainless steel screw and dental acrylic resin. In the 72 hour recovery period after surgery, NR2 subunit antagonists were intracisternally administered. For confirmation of the placement of the intracisternal cannula and the extent of the spread of the drugs, pontamine sky blue dye was injected at the end of the tests. The animals that showed motor dysfunction or mal-position of the catheter after intracisternal catheterization were excluded from the analysis. Mechanical allodynia and hyperalgesia was determined 15, 30, 60, 120, 180, 360 and 1440 min after intracisternal administration of NR2 subunit antagonists.