Methods: Thirty-two adult ferrets were prepared under anaesthesia (ketamine 25 mg/kg, xylazine 2 mg/kg, i.m.) to allow tooth pulp stimulation, recording from the digastric muscle and i.v. injections at a subsequent experiment. In 16 of these animals pulpal inflammation was induced by introducing human caries into a deep buccal cavity. Five days later animals were re-anaesthetised (alfaxalone, induction: 10 mg/kg, maintenance: 4-14 mg/kg/h, i.v.) and the jaw opening reflex (JOR) threshold was measured (if applicable). In half the animals tooth pulp stimulation commenced at 10 times the threshold of the JOR for 10 minutes (non-inflamed n = 4, inflamed n =4) or 60 minutes (non-inflamed n = 4, inflamed n = 4). The remaining animals were kept under anaesthesia for 10 minutes (non-inflamed n = 4, inflamed n = 4) or 60 minutes (non-inflamed n = 4, inflamed n = 4). All animals were immediately perfused with fixative and brainstems processed for phosphorylated p38 (p-p38) immunohistochemistry.
Results: Bilateral labelling for p-p38 was present in subnucleus caudalis in all groups. Significantly more p-p38 labelling was seen in animals with inflamed pulps than in those with non-inflamed pulps at both time points in both non-stimulated and stimulated groups (P < 0.05 in all cases, unpaired t-test). Conclusion: These results demonstrate that activation of p38 is increased in the trigeminal nucleus following tooth pulp inflammation. Therefore p38 may play an important role in sensitisation of trigeminal neurones and represents a potential therapeutic target for trigeminal pain. (Supported by BBSRC/GSK).