Endogenous central opioid receptor system

The **endogenous central opioid system** consists primarily of three canonical G protein-coupled receptors—mu-, delta-, and kappa-opioid receptors—alongside their natural peptide ligands such as endorphins, enkephalins, dynorphins, and nociceptin. These receptors are widely distributed throughout the hypothalamus as well as other brain regions involved in reward processing, emotional regulation, pain modulation, feeding behavior control, neuroendocrine function (including prolactin secretion), stress response modulation, and addictive behaviors. In the hypothalamus specifically, activation of mu-opioid receptors can increase food intake depending on dietary preference; antagonism reduces deprivation-induced feeding. The interplay between opioidergic signaling in the hypothalamus also involves crosstalk with other neurotransmitters such as dopamine and serotonin for complex physiological outcomes like hormone release during pregnancy. Clinically relevant drugs targeting this system include both agonists used for analgesia or maintenance therapy in addiction treatment—and antagonists used for overdose reversal or relapse prevention—but all carry significant safety concerns related to abuse liability and adverse effects on respiratory function.

Other names

Endogenous opioid systemCentral opioid receptorsOpioidergic systemMu-opioid receptor (MOR)Delta-opioid receptor (DOR)Kappa-opioid receptor (KOR)Nociceptin/orphanin FQ peptide receptor (NOPR)

Agonists activate inhibitory G protein-coupled signaling via Gi/o proteins, reducing neuronal excitability and neurotransmitter release. Antagonists block these effects by preventing endogenous or exogenous opioids from binding.