Aims: To clarify the mechanisms of hypersensitivity and spontaneous pain in intraoral structures in rats with diabetes mellitus (DM) accompanied by reduced saliva.
Methods: Adult male Sprague-Dawley rats received a single injection of streptozocin (50 mg/kg) to induce DM. Saliva volume, intraoral hypersensitivity to menthol and capsaicin solutions, and head-withdrawal thresholds (HWTs) to noxious heat and mechanical stimulation of the tongue and whisker pad were measured.
Results: On day 7 after streptozocin injection, rats with DM had a significantly reduced spontaneous saliva volume, polydipsia, capsaicin aversion of the intraoral mucosa, and a reduced HWT to noxious mechanical stimulation of the whisker pad skin. The HWT to noxious mechanical stimulation of the tongue reduced further on day 14 after streptozocin injection. These symptoms are similar to the orofacial and intraoral complaints of patients with DM. Meanwhile, reduction of HWT to noxious heat stimulation of the tongue and whisker pad were not observed. These results indicate that spontaneous intraoral mucosal pain and mechanical facial hypersensitivity are antecedent symptoms before mechanical hypersensitivity of the tongue.
Conclusion: The mechanisms of saliva reduction, spontaneous intraoral mucosa pain, and mechanical hypersensitivity of intraoral and facial structures induced by DM involve both peripheral and autonomic neuropathies. Tongue hypersensitivity to noxious mechanical stimulation might be aggravated by xerostomia.