Coexistence of substance P and calcitonin gene-related peptide in the frog spinal cord.

The localization of substance P (SP) and calcitonin gene-related peptide (CGRP) was studied in the untreated spinal cord of the frog using single or double immunohistochemical stainings. SP and CGRP appear to coexist in the primary afferent fibers and in the marginal and submarginal dorsal horn zones, as well as in the dorsolateral zone. In other parts of the spinal cord CGRP immunoreactivity was scanty while diffuse SP systems were seen, suggesting that the coexistence of the two peptides is restricted to primary afferent fibers.