Anatomical and Biochemical Studies of the Opioid Peptides and Related Substances in the Brain

WATSON, S. J., H. AKIL AND J. M. WALKER. Anatomical and biochemical studies of the opioid peptides and related substances in the brain. PEPTIDES l: Suppl. 1, 11-20, 1980.--It is now clear that there are at least four opioid peptideneuronal 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.