PT  - JOURNAL ARTICLE
AU  - Sandra R. Chaplan
AU  - Annika B. Malmberg
AU  - Tony L. Yaksh
TI  - Efficacy of Spinal NMDA Receptor Antagonism in Formalin Hyperalgesia and Nerve Injury Evoked Allodynia in the Rat
DP  - 1997 Feb 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 829--838
VI  - 280
IP  - 2
4099  - http://jpet.aspetjournals.org/content/280/2/829.short
4100  - http://jpet.aspetjournals.org/content/280/2/829.full
SO  - J Pharmacol Exp Ther1997 Feb 01; 280
AB  - Neuropathic pain remains a significant clinical problem. Current understanding implicates the spinal cord dorsal horn N-methyl-d-aspartate (NMDA) receptor apparatus in its pathogenesis. Previous reports have described NMDA antagonist reduction of nerve injury-induced thermal hyperalgesia and formalin injection-related electrical activity. We examined a panel of spinally administered NMDA antagonists in two models: allodynia evoked by tight ligation of the fifth and sixth lumbar spinal nerves (a model of chronic nerve injury pain), and the formalin paw test (a model wherein pretreatment with drug may preempt the development of a pain state). A wide range of efficacies was observed. In the nerve injury model, order of efficacy (expressed as percent of maximum possible effect ± S.E.), at the maximum dose not yielding motor impairment, was memantine (96 ± 5%) = AP5 (91 ± 7%) > dextrorphan (64 ± 11%) = dextromethorphan (65 ± 22%) > MK801 (34 ± 8%) > ketamine (18 ± 6%). For the formalin test, the order of efficacy was AP5 (86 ± 9%) > memantine (74 ± 5%) ≥ MK801 (67 ± 16%) > dextrorphan (47 ± 16%) > dextromethorphan (31 ± 12%) > ketamine (17 ± 15%). In the nerve injury model, no supraspinal action was seen after intracerebroventricular injections of dextromethorphan and ketamine. NMDA antagonists by the spinal route appear to be useful therapeutic agents for chemically induced facilitated pain as well as nerve injury induced tactile allodynia. It is not known what accounts for the wide range of efficacies. The American Society for Pharmacology and Experimental Therapeutics