Orofacial deep and cutaneous tissue inflammation differentially upregulates preprodynorphin mRNA in the trigeminal and paratrigeminal nuclei of the rat

Preprodynorphin (PPD) and preproenkephalin (PPE) gene expression in a rat m odel of orofacial inflammation were examined in order to further characteri ze the neurochemical mechanisms underlying orofacial inflammation and hyper algesia. Deep and cutaneous orofacial inflammation was produced by a unilat eral injection of complete Freund's adjuvant (CFA) into the rat temporomand ibular joint (TMJ) or perioral skin (PO), respectively. RNA blot analysis o f the tissues including the spinal trigeminal complex revealed that the PPD mRNA level ipsilateral to TMJ inflammation was increased by 56.5 +/- 14.7% (n = 4) when compared to the Naive group, and was significantly greater th an the contralateral PPD mRNA Level (p < 0.05). The distribution of neurons that exhibited PPD mRNA after inflammation was localized by in situ hybrid ization (naive approximate to 0). In TMJ-inflamed rats (n = 6) PPD mRNA-pos itive neurons were found ipsilaterally in the medial portion of laminae I-I I of the upper cervical dorsal horn (4.5 +/- 0.3), the dorsal portion of th e subnucleus caudalis and caudal subnucleus interpolaris (5.2 +/- 0.3), and the paratrigeminal nucleus (6.4 +/- 1.2), A very localized induction of PP D mRNA was also identified in a group of neurons in the intermediate portio n of the subnucleus caudalis (2.4 +/- 0.4) in PO-inflamed rats (n = 6). The distribution of these PPD mRNA-positive neurons was somatotopically releva nt to the site of injury. There were no significant changes in PPE mRNA exp ression in both TMJ- and PO-inflamed rats. These results indicate that TMJ inflammation resulted in a more intense and widespread increase in PPD mRNA expression when compared to PO inflammation. These changes may contribute to persistent central hyperexcitability and pain associated with temporoman dibular disorders. (C) 1999 Elsevier Science B.V. All rights reserved.