The effect of intra-locus coeruleus injection of 17beta-estradiol on inflammatory pain modulation in male rat.

Abstract

Estradiol is a neuroactive steroid found in several brain areas such as locus coeruleus (LC). It modulates nociception by binding to its receptors and also by allosteric interaction with other membrane-bound receptors like glutamate and GABA(A) receptors. LC is involved in noradrenergic descending pain modulation. In order to study the effect of 17beta-estradiol on both acute and persistent pain modulation and its mechanisms, formalin was injected into the male rat's hind paw. Formalin-induced responses including licking, flexing duration and paw jerking frequency were recorded for 60 min after injection of 50 microl of 2% formalin. The results of the current study showed that intra-locus coeruleus injection of 17beta-estradiol attenuated the second phase, but not the acute phase of formalin-induced pain (P<0.05). AMPA receptor antagonists CNQX had no effect on pain-modulatory effect of 17beta-estradiol. Estrogen and GABA(A) receptor antagonists (ICI 182,780 and bicuculline, respectively) could not reverse the antinociceptive effect of 17beta-estradiol. However, NMDA receptor antagonist APV significantly antagonized the analgesic effect of 17beta-estradiol on flexing behaviour (P<0.05). It may be concluded that the analgesic effect of 17beta-estradiol in formalin-induced inflammatory pain is mediated through interaction with membrane-bound receptors, probably the NMDA receptors.

• Authors: Roghaieh Khakpay, Saeed Semnanian, Mohammad Javan, Mahyar Janahmadi
• Journal: Behavioural brain research (Behav Brain Res) Vol. 214 Issue 2 Pg. 409-16 (Dec 25 2010) ISSN: 1872-7549 [Electronic] Netherlands
• PMID: 20600351 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: Copyright (c) 2010 Elsevier B.V. All rights reserved.

Chemical References

• Estrogen Antagonists
• Estrogens
• Formaldehyde
• Fulvestrant
• Estradiol
• 6-Cyano-7-nitroquinoxaline-2,3-dione
• 2-amino-5-phosphopentanoic acid
• Valine
• Bicuculline

Topics

• 6-Cyano-7-nitroquinoxaline-2,3-dione (pharmacology)
• Animals
• Bicuculline (pharmacology)
• Disease Models, Animal
• Estradiol (administration & dosage, analogs & derivatives, pharmacology)
• Estrogen Antagonists (pharmacology)
• Estrogens (pharmacology)
• Formaldehyde
• Fulvestrant
• Inflammation (drug therapy)
• Locus Coeruleus (drug effects)
• Male
• Microinjections
• Pain (chemically induced, complications, drug therapy)
• Rats
• Rats, Sprague-Dawley
• Valine (analogs & derivatives, pharmacology)