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Open Access Research

Decreased pain threshold and enhanced synaptic transmission in the anterior cingulate cortex of experimental hypothyroidism mice

Jun Yi1, Jian-yong Zheng2, Wei Zhang3, Shan Wang3, Zhi-fu Yang3* and Ke-feng Dou1*

Author Affiliations

1 Department of General Surgery, Xijing Hospital; The Fourth Military Medical University, Xi’an 710032, China

2 State Key Laboratory of Cancer Biology and Institute of Digestive Diseases, Xijing Hospital; The Fourth Military Medical University, Xi’an 710032, China

3 Department of Pharmacy, Xijing Hospital; The Fourth Military Medical University, Xi’an 710032, China

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Molecular Pain 2014, 10:38  doi:10.1186/1744-8069-10-38

Published: 18 June 2014

Abstract

Background

Thyroid hormones are essential for the maturation and functions of the central nervous system. Pain sensitivity is related to the thyroid status. However, information on how thyroid hormones affect pain processing and synaptic transmission in the anterior cingulate cortex (ACC) is limited. Nociceptive threshold and synaptic transmission in the ACC were detected in the experimental hypothyroidism (HT) mice.

Results

HT was induced by methimazole and potassium perchlorate in distilled drinking water for 4 weeks. The threshold of pain perception to hot insults, but not mechanical ones, decreased in hypothyroid mice. After treatment with tri-iodothyronine (T3) or thyroxine (T4) for 2 weeks, thermal pain threshold recovered. Electrophysiological recordings revealed enhanced glutamatergic synaptic transmission and reduced GABAergic synaptic transmission in the ACC. Supplementation with T3 or T4 significantly rescued this synaptic transmission imbalance. In the same model, HT caused the up-regulation of the GluR1 subunit of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor and NR2B-containing N-methyl-D-aspartate receptors, but it down-regulated γ-aminobutyric acid A receptors in the ACC. Supplementation with T3 or T4 notably recovered the levels of above proteins.

Conclusions

These results suggest that HT promotes hypersensitivity to noxious thermal, and that supplementation with T3 or T4 rescues the imbalance between excitatory and inhibitory transmission in the ACC.

Keywords:
Thyroid hormone; Pain; Anterior cingulate cortex