Methods: A local anesthetic (lidocaine with epinephrine, AstraZeneca) or saline was injected into the tissue surrounding the mandibular left first molar of Wistar rats (n = 24). The tooth was then pulp-exposed, and the cavity was sealed with flowable composite (UniFill FlowAGC). After 0 (normal pulp with local anesthetic or saline pretreatment), 24 and 72 h (n = 4 in each experimental group), the contralateral thalamus was retrieved and subjected to immunohistochemistry for phospho-p38 MAPK and GFAP, and real-time PCR analysis of p38-MAPK family (MAPK 13 and MAPK 14) mRNAs.
Results: The density of phospho-p38 MAPK-positively stained area increased until 72 hours after pulp exposure with both local anesthetic- and saline-pretreated animals, but the rate of increase was slower in the local anesthetic-pretreated animals. The density of GFAP+ astrocytes showed a significant increase only in the saline-pretreated animals. Expression levels of MAPK 13 and MAPK 14 mRNAs in the saline-pretreated animals were significantly higher than those in the saline-pretreated animals at 24 and 72 h.
Conclusions: Upregulation of MAPK 13, 14 and phospho-p38 MAPK in the thalamus after pulp injury was suppressed by the local anesthetic pretreatment, suggesting the involvement of p38 MAPK signaling pathways in the glial cell-neuronal interaction induced by pulpal nociception.