A local anesthetic (lidocaine with epinephrine) or saline (control) was injected into the tissue surrounding the left mandibular first molar of Wistar rats. The tooth was then pulp-exposed, and the cavity was sealed with flowable composite. After 0 (normal pulp with local anesthetic or saline pretreatment), 24, and 72 hours, the contralateral side of thalamus was retrieved and subjected to immunohistochemistry for phospho-p38 MAPK and glial fibrillary acidic protein and real-time polymerase chain reaction analysis of p38-MAPK family (MAPK 13 and MAPK 14) mRNAs.
The area immunopositive to phospho-p38 MAPK increased until 72 hours after pulp exposure in both local anesthetic–pretreated and saline-pretreated animals, but the rate of increase was lower in the local anesthetic–pretreated animals. The density of glial fibrillary acidic protein–expressing astrocytes showed a significant increase only in the saline-pretreated animals. Expression levels of MAPK 13 and MAPK 14 mRNAs increased at 24 hours and still higher at 72 hours in the saline-pretreated animals. Notably, MAPK 13 and MAPK 14 mRNA levels at 24 and 72 hours in the local anesthetic–pretreated animals showed significantly lower levels than those in the saline-pretreated animals.
It was concluded that pulp injury–induced up-regulation of MAPK 13, MAPK 14, and phospho-p38 MAPK in the thalamus 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.