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Peripheral NMDA receptors are involved in long‐term hyperalgesia and spinal microglia activation induced by formalin injection
Author(s) -
Zhao Xin,
Cheng Juan,
Yang XiaoRong,
Qin LiRong,
Liu NaiHong,
Zhang Yu,
Kang YuMing,
Qiao JianTian,
Zhang* Ce
Publication year - 2006
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.20.4.a776-c
Subject(s) - microglia , hyperalgesia , peripheral , nmda receptor , receptor , neuroscience , medicine , chemistry , immunology , inflammation , biology , nociception
Recent studies show that subcutaneous injection of formalin produce a long‐term hyperalgesia (LTH), and a strong activation of spinal microglia lasting the similar period. This study is to investigate if peripheral NMDA receptors are involved in the formalin‐induced LTH and the activation of spinal microglia by observing both behavioral responses examined by thermal paw withdrawal latency (PWL) and microglia activation examined by OX‐42 immunocytochemistry. In PWL observations, rats received formalin injections of two hind paws, while MK‐801 (30 nmol, n=5) was injected into one hind paw 15 min before formalin and the drug injections repeated in 4 consecutive days, respectively, and PWL observations were carried out for rats lasted 10 days. In OX‐42 examinations, animals using the same trial of drug injections while three doses of MK‐801 (10 nmol, 30 nmol, 50 nmol, n=5) was given rats and the animals killed 7 days post drug injections for OX‐42 examinations. Results showed that: 1) peripheral formalin induced LTH examined by PWL which peaked at 7 days after formalin injection and lasted up to 2 weeks; 2) peripheral injection of formalin also induced long‐term activation of microglia examined by OX‐42 7 days post drug injections; 3) peripheral administration of MK‐801 produced a significant suppression of the LTH; and 4) peripheral administration of MK‐801 produced a significant and dose‐dependent inhibition of microglia activation showing the 21.5%, 33.6%, 44.5% suppression of OX‐42, respectively.