Enhancement of preprotachykinin A gene expression by adjuvant-induced inflammation in the rat spinal cord: possible involvement of substance P-containing spinal neurons in nociception.

Effects of adjuvant-induced inflammation on the biosynthesis of substance P in the rat nervous system were examined by measuring the levels of mRNA encoding preprotachykinin A (PPT-A, the precursor protein of substance P). Following injection of adjuvant into the bilateral hind paws, the levels of PPT-A mRNA were significantly increased in the dorsal root ganglia at L4-L6 levels and the lumbar spinal cord, but not in the striatum, midbrain and medulla oblongata. After the unilateral injection of adjuvant which produced inflammation only in the injected hind paw, increase in the mRNA level was observed only on the treated side of the spinal cord. These results suggest that biosynthesis of substance P in the spinal and primary sensory neurons was increased by adjuvant-induced inflammation with hyperalgesia. Substance P-containing spinal neurons may be involved in processes related to pain.