An Intro To Your Brain’s Opioid System

An Intro To Your Brain’s Opioid System – September 2014 – by Joe Cohen

The brain opioid systems are known to play an important role in motivation, emotion, attachment behaviour, the response to stress and pain, and the control of food intake (R).

There are four opioid receptors in our brain:

  1. mu-opioid (MOR),
  2. kappa-opioid (KOR),
  3. delta-opioid (DOR)
  4. nociceptin (NOP).  

Increasing these receptors or the molecules that bind to them will produce an opioid high.  

Mu-Opioid Receptors

Activation of the mu receptor by a substance such as morphine causes sedation, euphoria and decreased respiration (R).

Although morphine increases sedation, it decreases the total amount of deep sleep and rapid eye movement sleep in humans (R).

Individual differences in the function of the mu-receptor system predict personality traits that confer vulnerability to or resiliency against risky behaviors such as the predisposition to develop substance use disorders (R).

Delta-Opioid Receptors

Molecules that bind to delta opioid receptors show robust evidence of both antidepressant effects and also increase of BDNF production in the brain in animal models of depression. (R)

They also protect against heart damage from strokes by preconditioning our heart.(R)  DORs are neuroprotective as well and work in part by reducing TNF (R).

Activation of delta receptors produces some pain relief, although less than that of mu-opioid activators. (R)

Kappa-Opioid Receptors

Kappa activation actually produces a bad mood (dysphoria), some pain relief (analgesic), urination (diuretic) and in high dosages produce hallucinations (R).

Activation of the KOR opposes many of the effects of the MOR and can prevent addiction to morphine, alcohol, and cocaine.

It can cause an appetite increase and is activated by stress (R). 

KOR activation causes a release of prolactin, a hormone known for its important role in learning, neuronal plasticity and myelination (R). 

Ketamine, oxycodone, morphine and menthol all bind to KOR.


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