Tachykinin peptides are distributed widely in the nervous system and have been shown to play a prominent role in nociceptive pathways in the spinal cord and dorsal root ganglia. This study investigated the inflammation-induced response of dorsal horn projection neurons and local circuit neurons expressing preprotachykinin (PPT) mRNA using RNA blot analysis and in situ hybridization histochemistry. To identify projection neurons, fluorogold was injected into the parabrachial area of the brainstem. In laminae I, II and V/VI ipsilateral to inflammation, there was a differential increase in the number of neurons exhibiting PPT mRNA. In lamina I, the number of spinal projection neurons containing PPT mRNA showed a greater than 200% increase. The identification of spinal projection neurons with inflammation-induced increases in PPT mRNA suggests that tachykinin peptides may act as neurotransmitters in nociceptive CNS projection pathways.