Int J Oral Biol.  2018 Sep;43(3):147-153. 10.11620/IJOB.2018.43.3.147.

Participation of Opioid Pathway in the Central Antinociceptive Effects of Eugenol

Affiliations
  • 1Department of Oral Physiology, School of Dentistry, Kyungpook National University, Daegu 41940, Republic of Korea. dkahn@knu.ac.kr

Abstract

The aim of the present study was to evaluate the central antinociceptive effects of eugenol after intraperitoneal administration. Experiments were carried out using male Sprague-Dawley rats. Subcutaneous injection of 5% formalin-induced nociceptive behavioral responses was used as the pain model. Subcutaneous injection of 5% formalin significantly produced nociceptive responses by increasing the licking time during nociceptive behavior. Subsequent intraperitoneal injection of 100 mg/kg of eugenol led to a significant decrease in the licking time. However, low dose of eugenol (50 mg/kg) did not affect the nociceptive behavioral responses produced by subcutaneous injection of formalin. Intrathecal injection of 30 µg of naloxone, an opioid receptor antagonist, significantly blocked antinociceptive effects produced by intraperitoneal injection of eugenol. Neither intrathecal injection of methysergide (30 µg), a serotonin receptor antagonist nor phentolamine (30 µg), an α-adrenergic receptor antagonist influenced antinociceptive effects of eugenol, as compared to the vehicle treatment. These results suggest that central opioid pathway participates in mediating the antinociceptive effects of eugenol.

Keyword

eugenol; antinociception; formalin; pain; opioid

MeSH Terms

Eugenol*
Formaldehyde
Humans
Injections, Intraperitoneal
Injections, Spinal
Injections, Subcutaneous
Male
Methysergide
Naloxone
Negotiating
Phentolamine
Rats, Sprague-Dawley
Receptors, Opioid
Serotonin
Eugenol
Formaldehyde
Methysergide
Naloxone
Phentolamine
Receptors, Opioid
Serotonin
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