ABSTRACT
The selectivity of opioid peptides for the parallel trilogy of opioid receptor subtypes was initially thought to follow a relatively discrete equation β-endorphin, as well as the enkephalins, act at mu and delta receptors, whereas dynorphin is relatively selective for kappa receptors. This chapter provides a brief overview of the anatomy and physiology of opioid peptides in the nucleus tractus solitarii (NTS). It focuses on the role of posttranslational processing in defining their receptor selectivities and cardioregulatory actions. Arterial blood pressure and heart rate are regulated by short- and long-loop pathways, both of which contain opioid peptide neurons, explaining, in part, the multiple actions of opioid peptides in cardiorespiratory homeostasis. The arcuate nucleus was initially thought to be the sole source of POMC peptides in the brainstem, but subsequent studies revealed a second POMC cell group localized in the caudal NTS, primarily in the commissural nucleus.
