Korean J Pain.  2006 Dec;19(2):137-141. 10.3344/kjp.2006.19.2.137.

Antinociceptive Effects of Intrathecal Melatonin on Formalin: and Thermal-induced Pain in Rats

• Chung ST
• Jin WJ
• Bae HB
• Kim SJ
• Choi JI
• Kang MW
• Jeong CY
• Yoon MH

• KMID: 2073918
• DOI: http://doi.org/10.3344/kjp.2006.19.2.137

Abstract

BACKGROUND
It has been known that melatonin is involved in the modulation of nociceptive transmission. However, the effect of melatonin administered spinally has not been examined. Therefore, we examined the effect of melatonin on the formalin-induced or thermal-induced nociception at the spinal level. METHODS: Intrathecal catheter was inserted into the subarachnoid space of male Sprague-Dawley rats. Pain was assessed by formalin test (induced by injection of 50microliter of a 5% formalin solution to the hindpaw) or Hot-Box test (induced by radiant heat application to the hindpaw). The effect of intrathecal melatonin was examined on flinching behavior in the formalin test or withdrawal response in Hot-Box test. RESULTS: Intrathecal melatonin produced a limited, but dose-dependent reduction of the flinching response during phase 1 and 2 in the formalin test. In addition, melatonin delivered at evening also decreased the flinching response in both phases of the formalin test. Melatonin restrictively increased the withdrawal latency in Hot-Box test. CONCLUSIONS: These results suggest that melatonin is active against the formalin- and thermal-induced nocicpetion at the spinal level, but the effect is limited.

Keyword

formalin test; melatonin; nociception; spinal cord; Sprague-Dawley rat; thermal test

MeSH Terms

Animals
Catheters
Formaldehyde*
Hot Temperature
Humans
Male
Melatonin*
Nociception
Pain Measurement
Rats*
Rats, Sprague-Dawley
Spinal Cord
Subarachnoid Space
Formaldehyde
Melatonin