Colocalization of immunoreactive proenkephalin and prodynorphin products in medullary neurons of the rat.

This study addressed the possible coexistence of products of the proenkephalin and prodynorphin opioid peptide precursors in single neurons of the central nervous system of the rat. Antisera directed against met-enkephalin-arg-gly-leu and against Dyn B were used in immunohistochemical preparations of sections through the rat medulla. Examination of serial three micron frozen sections stained alternately with the two different antisera revealed that the majority of labelled neurons stain with only one of the two antisera. In specific area, however, immunoreactive m-enk and Dyn B could be detected in the same neuron. This was particularly true of the caudal ventrolateral nucleus of the solitary tract, where the two peptides were colocalized in most neurons. Other areas where the two peptides coexist include the midline raphe and the nucleus reticularis paragigantocellularis. These data provide the first evidence for colocalization of different opioid peptide families in single CNS neurons.