Opioid receptors

Opioid receptors are a group of G protein-coupled receptors with opioids as ligands. The endogenous opioids are dynorphins, enkephalins, endorphins, endomorphins and nociceptin. The opioid receptors are ~40% identical to somatostatin receptors (SSTRs). Opiates and opioids mimic the effect of these endorphins and interact predominantly with the mu-opioid receptor because they share structural similarities with the natural ligands.

Types of Opioid Receptors

There are four major subtypes of opioid receptors. Each of them is defined by the particular type of opioid that binds to it and by the specific physiological process that it controls. The four types are:

• Mu opioid receptor (MOR): These receptors are distributed throughout the central nervous system and are involved in pain regulation, reward, and addictive behaviors.

• Delta opioid receptor (DOR): These receptors are primarily found in the brain and are involved in mood regulation, convulsion control, and neuroprotection.

• Kappa opioid receptor (KOR): These receptors are found in the brain, spinal cord, and digestive tract. They are involved in pain regulation, stress response, and sedative effects.

• Nociceptin receptor (NOP): Also known as the ORL1 receptor, these receptors are involved in a variety of functions including pain regulation, anxiety, and depression.

Function

Opioid receptors are activated by a variety of natural and synthetic opioids. When activated, these receptors inhibit the release of neurotransmitters, thereby reducing the perception of pain. They also play a role in other physiological processes such as respiratory depression, euphoria, and physical dependence.

Clinical Significance

Opioid receptors are the primary targets of opioids, which are commonly used in medicine to relieve pain. However, the activation of opioid receptors can also lead to adverse effects such as addiction and tolerance. Understanding the function and regulation of opioid receptors is crucial for the development of safer and more effective opioid-based therapies.

See Also

• Opioid
• G protein-coupled receptor
• Neurotransmitter