Background and aims:
Burning mouth syndrome (BMS) is an intraoral burning sensation which often presents with a normal intraoral mucosa. The majority of BMS patients are post-menopausal women. An upregulation of nerve growth factor (NGF) has also been demonstrated in the subepithelial nerve fibers of tongue biopsies from BMS patients.
This study was designed to examine whether exogenously administered NGF into the tongue of sham and ovariectomized (OVX) rats would induce nocifensive responses.
Methods:
NGF (500 ng/10 μl, 1000 ng/10 μl) or phosphate buffered saline (10 μl) were administered into the tongue of sham or OVX adult female rats (N = 54 divided into 6 groups). After administration, spontaneous behaviors, volume of drink consumption and responses to stimulation by von Frey filaments were analyzed. Pre- and post-injection differences between groups were statistically analyzed with Kruskal Wallis test.
Results:
OVX rats showed a significant increase in facial grooming behaviors, especially chin rubbing (10 min after injection: p = 0.0135) and vacuous chewing (60 min after injection: p = 0.0194) following the NGF 1000 ng injection compared with sham rats. Consumption of sweetened milk did not show any significant difference between the groups (pre-injection: p = 0.181, post-injection: p = 0.864). The tongue withdrawal thresholds to mechanical stimulation in OVX decreased at 60 mins after NGF 500ng injection (p=0.015) and at 10 mins and 3 days after NGF 1000ng injection (p=0.023, 0.0143 respectively) compared with sham .
Conclusions:
NGF injection to the tongues in OVX rats induced nocifensive responses, which suggests that peripheral dysesthesia might result from elevated NGF in tongue tissue.

PAIN ASSESSMENT ON THE TONGUE OF RAT BY THE OBSERVATION OF SPONTANEOUS BEHAVIOR AND RESPONSES TO MECHANICAL STIMULATION