Role of macrophages in trigeminal ganglia in ectopic orofacial pain associated with pulpitis

This study aimed to elucidate the role of macrophages in the trigeminal ganglia (TG) in developing pulpitis-associated ectopic orofacial pain. Rats underwent maxillary pulp exposure, and Fluoro-Gold (FG) was administered in the ipsilateral whisker pad (WP). Head withdrawal threshold (HWT) upon mechanical stimulation of the WP was recorded, and liposomal clodronate clophosome-A (LCCA; macrophage depletion agent) was administered to the TG at three and four days after pulp exposure. Immunohistochemically, TG sections were stained with anti-Iba1 (a macrophage marker) and anti-Nav1.7 antibodies. Pulp exposure decreased HWT and increased the number of Iba1-IR cells near FG-labelled TG neurons. LCCA inhibited the decrease in HWT and stopped the increase of FG-labelled Nav1.7-IR TG neurons in the pulpitis group. Activation of macrophages by pulpitis induces the overexpression of Nav1.7 in TG neurons receiving inputs from WP, resulting in pulpitis-induced ectopic facial mechanical allodynia.