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MK 801 suppresses dynorphin A(1-17)--induced facilitation of nociceptive responses to formalin in rats

Q1 Wenxiu , LU Chongr Rang

Department of Physiology, Fen Yang College, Fenyang 032200；Department Anesthesiology, The Center Hospital of Taiyuan Taiyuan 030001

Abstract

To explore the facilitation of nociceptive response by dynorphin(Dyn)A in a model of for malin test in rats，the effects of single intrathecal injection(i. t.)of normal saline(NS)，MK 801(antagonist of NMDA receptor)，naloxone(antagonist of opioid receptor)，or Dyn A(1一17) were observed，and the effects of i. t. MK 801 or naloxone followed by i. t. Dyn A(1一17) were observed as well .The nociceptive licking and biting induced by injection of formalin exhibited two phases·The first phase lasted for a relatively short period of 3一9 min，and the second phase lasted for a relatively longer period after a 3 to 6- min quietness .The results showed that there were no differences in the first phase in all groups;however，there were differences in the second phase as follows:(1)the duration of nociceptive
response was significantly increased in Dyn A(1一17) group(489. 5士22. 5 s) as compared to that of NS group(344. 7士12. 9 s)，MK-801 group(331.4士20. 7 s) or naloxone group(352. 5士18.4 s)(P<0. 01 in three cases);(2) the duration of nociceptive response was significantly shortened in MK 801 plus Dyn A(1一17) group(285. 7士19. 4 s) as compared to that of Dyn A(1一17) group(P<0.01)，but
there were no significant differences as compared to that of MK 801 group;and(3) there was no significant difference in the second phase between naloxone plus Dyn A(1一17) group(473.8士17. 8 s) and Dyn A(1一17) group，but the duration of nociceptive response was longer than that of NS group or nalox-
one group(P<0. 0l in both)·The results obtained suggest:(1)at the spinal cord，Dyn A(1一17) facilitates nociceptive responses;(2) NMDA receptors，but not opioid receptors，are possibly involved in the nociception by Dyn A(1一17).

Key words: dynorphin A(1一17);NMDA receptor;MK 801;;;;

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Citing This Article：

Q1 Wenxiu , LU Chongr Rang. MK 801 suppresses dynorphin A(1-17)--induced facilitation of nociceptive responses to formalin in rats. Acta Physiol Sin 2003; 55 (1): (in Chinese with English abstract).