Effects of Pre-Emptive Morphine, Ibuprofen or Local Anesthetic on Fos Expression in the Spinal Trigeminal Nucleus Following Tooth Pulp Exposure in the Rat

In the present study, we used Fos expression as an index of nociceptive input to the spinal trigeminal nucleus after exposure of the coronal pulp tissue of maxillary right first molars and examined the effects of pretreatment with an opioid, a nonsteroidal anti-inflammatory drug or a local anesthetic before pulp exposure. Exposure of the tooth pulp produced a significant increase in Fos-like immunoreactivity in the superficial laminae of subnucleus caudalis; pretreatment with a control infiltration injection of saline directly above the maxillary molar 30 min before pulp exposure had no effect on Fos expression. Pretreatment with morphine 30 min before pulp exposure dose-dependently (2.5, 5, and 10 mg/kg subcutaneously) reduced Fos expression in subnucleus caudalis whereas pretreatment with ibuprofen (10-100 mg/kg subcutaneously) did not significantly affect Fos expression. Local anesthetic pretreatment was effective in reducing Fos expression only for the long acting bupivacaine; lidocaine without and with epinephrine (1:100,000) failed to significantly affect Fos expression. These results suggest that pre-emptive opioid treatment can decrease postoperative central nervous system changes associated with tooth pulp injury, and therefore, may decrease postoperative pain. Given the effects of local anesthetic on Fos expression, a combination of long acting local anesthetic with pre-emptive opioid would likely be most efficacious in decreasing postoperative dental pain.