Opioid-neurotransmitter interactions: significance in analgesia, tolerance and dependence.
Opioid analgesics influence the function of a number of neurotransmitter systems including classical neurotransmitters, neuropeptides and endogenous opioids. The role of these interactions in analgesia, tolerance and dependence is reviewed. Opioids inhibit the release of substance P from high threshold primary afferents, depress the activity of dorsal horn neurons and increase activity in serotonergic and noradrenergic neurons projecting from brainstem to spinal regions. Chronic administration of opioids modifies the dynamics of classical transmitters and those of endogenous opioid peptides in the brain, spinal cord and the pituitary gland. However, the effects observed are very variable. Several neuropeptides (vasopressin, MIF, alpha-MSH, CCK and dynorphin) have been reported to modify acute and chronic effects of opioids. Tolerance and dependence seen after opiate administration may involve changes in the function of these peptides.
D000701:Analgesics, Opioid / Q000494:pharmacology; D004347:Drug Interactions; D004361:Drug Tolerance; D004723:Endorphins / Q000502:physiology; D006801:Humans; D009294:Narcotics / Q000494:pharmacology*; D009419:Nerve Tissue Proteins / Q000494:pharmacology; D009420:Nervous System / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects; D009293:Opioid-Related Disorders; D013116:Spinal Cord / Q000187:drug effects; D009435:Synaptic Transmission / Q000187:drug effects
D000701:Analgesics, Opioid; D004723:Endorphins; D009294:Narcotics; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents