Question

What are the function(s) of Opioid receptors? Are there any specific features (e.g. enzyme, transmembrane protein)

Integrate the knowledge of the function with the structural properties of the cell.

Answer 1

There are three opioid receptors present in Opioids which exert their phamacological actions which are mu, delta and kappa whose genes have been cloned (Orpm, Orpd1 and Oprk1 respectively). Neurons in the brain release endogenous peptides like enkephalins, dynorphins and endorphin which activates the opioid receptors. Opioid receptors can also be activated exogenously by alkaloid opiates.

Mu-opioid receptors are a key molecular switch triggering brain reward systems and potentially initiating addictive behaviors. The lack of mu-receptors abolishes the analgesic effect of morphine, as well as place-preference activity and physical dependence. This receptor therefore mediates therapeutic and adverse activities of morphine, suggesting that further development of morphine-like compounds may necessarily lead to addictive analgesics.This receptors also maintain the drug use as well as craving and relapse.

Opioid receptors affect cell proliferation. It is observed that μ- and δ-receptor activation inhibits the growth of immature adrenals, stimulates adrenal regeneration, and does not affect proliferation of cultured adrenocortical cells.Many findings have mooted the concept that δ-opioid receptors play a crucial role in neurogenesis and neuroprotection. Some recent studies have shown that the OGF-OGFr (opioid growth factor-opioid growth factor receptor) system is a native biological regulator of cell proliferation in some cancers including ovarian cancer, hepatocellular cancer. More studies are, however, needed for the validation of this interesting observation and its underlying mechanisms.