Korean J Anesthesiol.  1997 Mar;32(3):354-359. 10.4097/kjae.1997.32.3.354.

The Effect of Intrathecal Morphine, Clonidine and MK801 on the Formalin Test in the Rats

• Kwon JY
• Kim CH
• Kim HK
• Baik SW
• Kim IS
• Chung KS

• KMID: 2033319
• DOI: http://doi.org/10.4097/kjae.1997.32.3.354

Abstract

BACKGROUND
There has been much interest in the involvement of wind-up in the hyperalgesia and allodynia of chronic pain syndrome. To investigate the behavioral parallels of this wind-up phenomenon, we evaluated the effects of intrathecal morphine, clonidine and MK801 on the formalin test in the rats. METHOD: All experimental animals were divided randomly into six groups. In group 1(n=7), normal saline 50 l was administered through the intrathecal catheter(PE10, 8 cm in length). In group 2(n=7), morphine 10 g was administered through the catheter. In group 3(n=7), group 4(n=7), group 5(n=7) and group 6(n=7), clonidine 10 g, clonidine 20 g, MK801 1 g, MK801 10 g was administered in same manner, respectively. Thirty min after recoverying from anesthesia, 50 l 5% formalin was injected in the hind paw. To quantify the formalin response, we counted the number of spontaneous flinching for 60 min. RESULT: Intrathecal morphine(group 2) decreased the number of paw flinches in both phases 1 and 2 readily compared to control(p<0.05). In the clonidine(group 3 and 4), both groups decreased the number of flinching in both phases 1 and 2, but there was no significant difference between two groups. In group 5, intrathecal MK-801 decreased the number of paw flinches in phase 2. In group 6, intrathecal MK-801 decreased the number of paw flinches in both phases 1 and 2.
CONCLUSION
This study suggest that wind-up is readily blocked by pretreatment of morphine, clonidine and MK801.

Keyword

Analgesics; clonidine; MK801; morphine; Anesthetic technique; intrathecal; Animals; rats; Pain; formalin test; flinching; wind-up

MeSH Terms

Analgesics
Anesthesia
Animals
Catheters
Chronic Pain
Clonidine*
Dizocilpine Maleate*
Formaldehyde*
Hyperalgesia
Morphine*
Pain Measurement*
Rats*
Analgesics
Clonidine
Dizocilpine Maleate
Formaldehyde
Morphine