Immunohistochemical localization of substance-P, somatostatin, and methionine-enkephalin in the spinal cord and dorsal root ganglia of the North American opossum, Didelphis virginiana.

The occurrence and distribution of substance-P (SP), somatostatin (SOM), and enkephalin (ENK) were studied in the North American opossum, a generalized marsupial. Substance-P immunoreactivity was present in the tract of Lissauer as well as within lamina I, the outer part of lamina II, the lateral portion of laminae III through VII, and lamina X at all spinal levels. Although present, it was very spare in the ventral horn. Substance-P was also localized within autonomic areas of the thoracolumbar cord. ENK immunoreactivity was present in laminae I-III and laminae VII-X, as well as within autonomic areas. There was more ENK immunoreactivity in the ventral horn than SP. The densest aggregates of ENK, however, were found within the outer part of lamina II. In contrast, SOM could not be localized within the spinal cord of the opossum. (See NOTE ADDED IN PROOF).