Inflammation of the temporomandibular joint (TMJ) produces an increase in preprodynorphin (PPD) mRNA expression in the spinal trigeminal nucleus (Vsp) and paratrigeminal nucleus (Pa5) of the rat. In this study, we further demonstrated that a portion of the TMJ inflammation-induced PPD mRNA positive neurons in the Vsp and Pa5 projected to the parabrachial nucleus (PB). In inflamed rats, the percentage of trigemino-and paratrigeminoparabrachial neurons with up-regulation of PPD mRNA was significantly increased in the ipsilateral Vsp(5.7 ± 1.8%) and Pa5 (22.8 ± 7.4%,n= 3) when compared with the contralateral side and with saline-treated controls (p< 0.05). These results suggest that the selective up-regulation of PPD mRNA in the Vsp and Pa5 following TMJ inflammation involves ascending trigeminal nociceptive pathways.