Somatostatin- and enkephalin-like immunoreactivities are frequently colocalized in neurons in the caudal brain stem of rat.

The medulla oblongata and pons of colchicine treated rats were analyzed with a double-staining technique using mouse monoclonal antibodies to somatostatin and rabbit polyclonal antibodies raised against methionine-enkephalin. Numerous cells reacted with both antisera but cells reacting with only one antiserum were also observed. Double-stained cells were most frequently encountered at all levels of the nucleus tractus solitarii, in a well defined group in the caudal medullary reticular formation, along the lateral ventral surface of the medulla oblongata, dorsolateral to the inferior olive and in the nucleus raphe magnus. These findings provide further examples of coexistence of two peptides and indicate the possibility that somatostatin- and enkephalin-like peptides are co-released.