Evidence for Synenkephalin-like Immunoreactivity in Pontobulbar Monoaminergic Neurons of the Cat

Using indirect immunofluorescence, evidence that enkephalin- and synenkephalin-like-immunoreactivities are colocalized within numerous monoaminergic neurons of the cat pontobulbar formation is presented. The colocalization concerns most catecholaminergic cell bodies in the locus coeruleus region and numerous serotoninergic cell bodies in the raphe nuclei. Synenkephalin is the 1-70 N-terminal region of the bovine adrenal medulla proenkephalin. Therefore, the proenkephalin (or a related) system seems to represent the biosynthetic pathway for the enkephalins immunodetected within these monoaminergic neurons.