Morphine Tolerance Effects on Neurotransmitters and Related Receptors: Definition, Overview and Update

Morphine is the essential opioid drug that use in the clinic to attenuate chronic and severe pain. However long-term administration of morphine leads to the development of anti-nociceptive morphine tolerance. Mechanisms that involved in morphine tolerance are complicated and affect a different part of CNS and change neural circuits. One of the most critical candidates for the development of morphine tolerance are neurotransmitters Which makes the communication between neurons and establish neural circuits. The most prominent neurotransmitters that involved in the development of morphine tolerance are NMDA one of the most popular excitatory neurotransmitter, GABA most important inhibitory neurotransmitter in CNS, and monoaminergic neurotransmitters: dopamine, noradrenaline, adrenaline and serotonin have a lot of crucial roles in CNS. Also, Changes that occur in the level of opioid receptors, neurotransmitters and its receptors make alternation cross-talk between neurons. Understanding these changes help us to have an overall concept about the development of morphine tolerance.