Effects of ovariectomy of rat on tongue neuropathy: Relevance to burning mouth syndrome.

Background/purpose: Burning mouth syndrome (BMS) is common in postmenopausal women, indicating that sex hormones are involved in disease pathogenesis. Recent studies have shown that the decreased nerve innervation of the papillae of the tongue may be related to neuropathic pain conditions in BMS. However, it remains unknown whether sex hormones contribute to changes in the nerve fiber density in the tongues of patients with BMS. Therefore, the aim of this study was to examine changes in pain intensity and nerve fiber density in the tongue of ovariectomized (OVX) rats subjected to surgical menopause to elucidate one aspect of the mechanism of pain onset in BMS. Materials and methods: Two groups of 9-week-old female Sprague-Dawley (SD) rats (ovariectomy; OVX and sham treatment; Sham) were established. Water containing capsaicin was provided at defined intervals to investigate oral capsaicin avoidance over a 2-week period. Serum circulating estrone (E1) and estradiol (E2) levels were measured in OVX and Sham rats. The protein gene product 9.5 immunoreactivity and transient receptor potential vanilloid 1 (TRPV1) in the tongues were also analyzed. Results: Two weeks after OVX treatment, intake of water containing capsaicin and serum levels of E1 and E2 significantly decreased. The nerve fiber density in fungiform papillae and connective tissue layer below the filiform papillae was also decreased. However, an abundant TRPV1-positive expression was observed in the tongue of OVX rats. Conclusion: These results indicate that decreased estrogen signaling causes neuropathy in tongue, resulting in tongue pain hypersensitivity in BMS.