Disruption of the substance P receptor (neurokinin-1) gene does not prevent upregulation of preprotachykinin-A mRNA in the spinal cord of mice following peripheral inflammation

The neuropeptide substance P is thought to play an important role in nocice ption, although the function of the peptide remains controversial. Followin g peripheral inflammation there is a pronounced upregulation of substance P expression both in sensory neurons and in postsynaptic neurons within the spinal cord. We have examined the levels of expression of mRNA encoding sub stance P and dynorphin following the development of inflammatory hyperalges ia in mice in which the substance P receptor gene, also known as the neurok inin-1 receptor gene, has been disrupted by homologous recombination. We sh ow that inflammatory hyperalgesia following injection of complete Freund's adjuvant develops normally in animal that lack the neurokinin-1 receptor an d that expression of mRNAs encoding substance P and the neuropeptide dynorp hin are upregulated regardless of the genotype of the mouse. This suggests that substance P activity is not required for the development and maintenan ce of inflammatory hyperalgesia and that the upregulation of substance P ex pression is mediated by neurotransmitters other than substance P.