Influence of occlusal interferences on the activation of trigeminal-spinal nucleus astroglia and microglia in rats

Objective To investigate the morphological changes in microglia and astroglia before and after the removal of occlusal interferences in rats and to further understand whether astroglia and microglia activation is involved in experimental occlusal interference-induced masticatory muscle pain.Methods Male Sprague-Dawley rats (200-220 g) were used. Crowns of two heights (0.2 mm and 0.4 mm) were bonded to the right maxillary first molars to establish experimental rat models of occlusal interference. The rats were randomly assigned to one of five groups of twelve rats each: sham-occlusal interference control group, 0.4 mm occlusal interference group, 6-day removal of 0.4 mm occlusal interference group, 0.2 mm occlusal interference group, and 6-day removal of 0.2 mm occlusal interference group. The rats were sacrificed by transcardiac perfusion after deep anesthetization on days 3, 5, 7, and 14. Brain stem sections were obtained and processed for immunofluorescence staining of GFAP and OX-42. Expression levels were semiquantitatively analyzed.Results ① Based on the markers OX-42 and GFAP, trigeminal-spinal nucleus (Vsp) microglia and astroglia showed no activation in the sham-occlusal interference control group. ② In the 0.4 mm and 0.2 mm occlusal interference groups, Vsp microglia and astroglia showed mild to moderate activation after 3-7 days of occlusal interference. Vsp astroglia remained activated on day 14, but Vsp microglia did not. At the same time point, the 0.4 mm occlusal interference group had greater activation than the 0.2 mm occlusal interference group. ③ In the 6-day removal of 0.4 mm and 0.2 mm occlusal interference groups, microglia and astroglia activation decreased after removal of the occlusal interference. Vsp astroglia remained activated on day 14, but microglia showed no activation.Conclusion Microglia and astrocyte activation is induced in the Vsp after experimental occlusal interference. The astrocytes remained activated for longer than the microglia. The glia activation level is closely related to the intensity of occlusal interference