Colocalization of dynorphin-A(1-17) and dynorphin-A(1-8) within some perikarya of rat duodenum: immunohistochemical evidence for the presence of two separate dynorphinergic systems.

Adjacent serial sections through the rat duodenum were alternately stained for immunofluorescence microscopic studies with specific anti-sera directed to the opioid peptides dynorphin-A(1-17) and dynorphin-A(1-8), respectively. This resulted in the evidence that two separate dynorphinergic neuron populations are present there: intramural neurons, revealing a colocalization of dynorphin-A(1-17) and dynorphin-A(1-8), were round, contained a large and round nucleus and were lying sporadically in the longitudinal muscle layer as well as bulb-shaped neurons expressing only a dynorphin-A(1-8) immunoreactivity. The latter were recognized abundantly in the myenteric plexus. Myenteric plexus nerve fibres and terminals were immunoreactive for dynorphin-A(1-8), but not for dynorphin-A(1-17). Dynorphin-A(1-8) immunostained nerve terminals formed close contacts with large non-dynorphinergic myenteric plexus perikarya. These findings might indicate that dynorphin-A(1-8) is processed directly from its prodynorphin ('preproenkephalin B') precursor within myenteric plexus perikarya and indirectly via dynorphin-A(1-17) within intramural perikarya, indicating the presence of two separate dynorphinergic systems in the rat duodenum.