17-Beta-estradiol enhanced allodynia of inflammatory temporomandibular joint through upregulation of hippocampal TRPV1 in ovariectomized rats.

Abstract

Temporomandibular disorders (TMDs) predominantly affect reproductive female patients, with pain the most frequent complaint. Although estrogens are believed to play important roles in TMD pain, the mechanism underlying modulation of TMD pain by estrogens remains largely unknown. Accumulating evidence implies that the hippocampus is involved in sexual dimorphism of pain sensitivity. In this study, we investigated the hippocampal TRPV1 (transient receptor potential vanilloid 1) expression in ovariectomized rats that received 17-beta-estradiol substitution and found that 17-beta-estradiol enhanced the mechanical allodynia of inflamed temporomandibular joint (TMJ) induced by complete Freund's adjuvant. Real-time PCR and immunoblotting demonstrated that TMJ inflammation significantly induced hippocampal TRPV1 expression compared with the control group but failed to induce it in the ovariectomized rats that received no estradiol replacement. In addition, estradiol potentiated TMJ inflammation-induced hippocampal TRPV1 expression in a dose-dependent manner in the ovariectomized rats. In contrast, TRPV1 transcription in amygdala, prefrontal cortex, and thalamus was not affected by TMJ inflammation and estradiol. Immunostaining showed TRPV1 localized in the processes and cytoplasm of pyramidal neurons in CA1-CA3 regions of the hippocampus. Moreover, intrahippocampal injection of TRPV1 antagonists capsazepine and 5'-iodo-resiniferatoxin into the CA1 region of the hippocampus significantly attenuated allodynia of inflamed TMJ in both nonovariectomized and ovariectomized rats that received estradiol replacement. Our results suggested that hippocampal TRPV1 can modulate central pain processing and estradiol may contribute to the sexual dimorphism of TMD pain sensitivity through upregulation of TRPV1 expression in the hippocampus.

• Authors: Yu-Wei Wu, Ye-Ping Bi, Xiao-Xing Kou, Wen Xu, Li-Qun Ma, Ke-Wei Wang, Ye-Hua Gan, Xu-Chen Ma
• Journal: The Journal of neuroscience : the official journal of the Society for Neuroscience (J Neurosci) Vol. 30 Issue 26 Pg. 8710-9 (Jun 30 2010) ISSN: 1529-2401 [Electronic] United States
• PMID: 20592193 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• TRPV Cation Channels
• Trpv1 protein, rat
• Estradiol
• Freund's Adjuvant

Topics

• Animals
• Autistic Disorder
• Brain (drug effects, metabolism)
• Estradiol (metabolism)
• Female
• Freund's Adjuvant
• Hippocampus (drug effects, metabolism)
• Ovariectomy
• Pain (chemically induced, drug therapy, metabolism)
• Physical Stimulation
• Pyramidal Cells (drug effects, metabolism)
• Random Allocation
• Rats
• Rats, Sprague-Dawley
• TRPV Cation Channels (antagonists & inhibitors, metabolism)
• Temporomandibular Joint (metabolism)
• Temporomandibular Joint Disorders (chemically induced, drug therapy, metabolism)
• Up-Regulation