Effects of MK-801 and morphine on spinal C-Fos expression during the development of neuropathic pain.
The purpose of this study was to investigate the expression of c-fos in the spinal cord during the development of allodynia, induced by peripheral nerve injury. Following tight ligation of the left L5 and L6 spinal nerves of Sprague- Dawley rat, the lumbar spinal cord was postfixed following perfusion. Frontal frozen sections of 40 microm were immunostained according to the peroxidase-antiperoxidase method. The allodynic threshold was checked with 8 calibrated von Frey filaments. MK-801 (0.3 mg/kg), morphine (3 mg/kg) and saline (as a placebo) were administered subcutaneously 30 min before, and 24 and 48 hrs after surgery. The tactile threshold decreased below 3 g since 2 days after surgery in the saline and morphine groups, but delayed a little in the MK-801 group. In the superficial layer the number of Fos-like immunoreactive neurones (Fos-LI) peaked at 2 hours and decreased thereafter, and reached normal levels 24 hrs following operation, for all groups. In the deep layer they were biphasic, - peaking at 2 and 24 hrs - in the saline group, but were suppressed in the morphine and MK-801 groups until 7 days following operation. The above discrepancy between the number of Fos-LI and the allodynic threshold showed that central sensitizations are not critically involved in the development of nerve injury induced tactile allodynia.
Lee
Youn-Woo
YW
Department of Anesthesiology, Yonsei University College of Medicine, C.P.O. Box 8044, Seoul 120-752, Korea. ywleepain@yumc.yonsei.ac.kr
Park
Kyung Ah
KA
Lee
Won Taek
WT
D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D016291:Dizocilpine Maleate / Q000494:pharmacology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006941:Hyperesthesia / Q000209:etiology / Q000378:metabolism*; D008026:Ligation; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000378:metabolism*; D013127:Spinal Nerves / Q000293:injuries; D014947:Wounds and Injuries / Q000150:complications
D000701:Analgesics, Opioid; D018691:Excitatory Amino Acid Antagonists; D016760:Proto-Oncogene Proteins c-fos; D016291:Dizocilpine Maleate; D009020:Morphine