Orofacial pain increases peptide precursor mRNA levels in the trigeminal nucleus caudalis of the rat.

Abstract

Changes in the levels of c-fos mRNA and neuropeptide precursor mRNA in the trigeminal nucleus caudalis (TNC) in response to orofacial pain induced by the injection of 5% formalin into the facial skin of anesthetized rats were investigated by in situ hybridization histochemistry. After injection of the formalin into the upper lip, the number of neurons expressing c-fos mRNA increased, followed by increases in the number of neurons expressing preprodynorphin, preprogalanin and preprotachykinin mRNA in the superficial layers of the ipsilateral TNC. Levels of preprosomatostatin mRNA and preprocholecystokinin mRNA did not change.