Distribution of cells containing mRNAs encoding substance P and neurokinin B in the rat central nervous system

The family of tachykinins includes the neuropeptides substance P, neurokinin A, and neurokinin B. The distribution of substance P in the central nervous system has been studied immunohistochemically but the lack of specific antibodies has prevented similar studies of neurokinin B. Recent molecular genetics techniques have revealed the sequences for the complementary DNAs that code for the substance P and neurokinin B precursors. These results have permitted the design of specific probes to differentiate between substance P and neurokinin B transcripts by using in situ hybridization histochemistry. Our probes, 48-base synthetic oligodeoxynucleotides labeled with 35S revealed extensive and distinct patterns of cell labeling for both substance P and neurokinin B throughout the rat central nervous system. The distribution of substance-P-mRNA-containing cells that we observed confirmed and extended previous immunocytochemical descriptions. Cells containing transcripts for either tachykinin were present in the neocortex, hippocampus, olfactory bulb and associated areas, caudate-putamen, hypothalamus, medial habenula, superior colliculus, central gray, and dorsal horn of the spinal cord. However, their distributions within these areas were usually quite different. Other areas contained only one tachykinin cell type: e.g., the nucleus of the lateral olfactory tract contained only neurokinin B cells whereas the raphe nuclei had only substance P cells. This study demonstrates the sensitivity and specificity of in situ hybridization histochemistry for mapping peptidergic neurons and lays the foundation for further investigations of the roles of these two tachykinins in the central nervous system.