Anatomical and biochemical studies of the opioid peptides and related substances in the brain

Abstract

It is now clear that there are at least four opioid peptide-neuronal systems in mammalian brain: the enkephalins, beta-endorphin and dynorphin. The focus of this presentation will be twofold--to focus on the multiple transmitter problem as typified by the beta-END/alpha-MSH arcuate neuronal system, and to describe the newly-discovered dynorphin neuronal system. The beta-END/alpha-MSH neurons have been studied using antisera directed against different portions of the 31K precursor (ACTH/beta-LPH/beta-END). Although ACTH can be detected in brain, the final products of the brain 31K system seem to be beta-END and alpha-MSH (similar to the intermediate lobe of pituitary). It is emphasized that "normally" these neurons would appear to release two neuronally active substances. Recently, a second set of alpha-MSH immunoreactive neurons was discovered in rat brain. These neurons are not immunoreactive for any other part of the 31K precursor and are distributed quite differently than the arcuate beta-END/alpha-MSH cell group. Dynorphin is another major class of opioid peptide. It has been studied and found in magnocellular neurons and posterior pituitary. The relations between dynorphin and leu-enkephalin cells continues to be unclear.