Opioids Natural opiates Semi-synthetic opiates Synthetic opiates Endogenous opiates Opiate antagonists
History of opioids • Opium, the sap of the seed pod of Papaver somniferum, referred to as early as 3000 B.C. and found in Spanish burial sites dated 4200 B.C. • Greeks and Romans used opium to produce constipation, sleep, and ultimately as a panacea: Hippocrates, Pliny, and Galen • May be the gall of Scripture (Matt. 27:34)
More history... • Opium use spread from its origins in Turkey with the expansion of Islam. • Arab traders took it to India and China. • In Persia, Avicenna (ibn-Sina, 980-1037) recommended opium for eye disease and diarrhea. • In 1644, the Chinese emperor banned tobacco smoking; Chinese switched to smoking opium.
And some more history... • Arabs trading with Vienna brought opium back to Europe • Paracelsus (1493-1541) and Thomas Sydenham, (1624-1689), father of clinical medicine • "Among the remedies which it has pleased Almighty God to give to man to relieve his sufferings, none is so universal and so efficacious as opium."
Opium and politics • British control of opium production in India • Usage in Britain climbed during the 1800s • Peaked at >10 pounds per 1000 people, 1870 • Laudanum • The Opium Wars (1841, 1856-58, 1860)
Legal controls on opium • The Chinese effort: Opium dens • Britain’s Pharmacy Act, 1868 • The disease model and the British system • The American experience: 13 pounds per 1000 people: patent medicines, soldiers’ disease (or army disease) in Civil War • Laudanum and paregoric • Harrison Narcotics Act, 1914 • Heroin banned in 1924
Analgesia • Nociceptors: Activated by physical or chemical injury or threat of injury • When stimulated, nociceptive neurons ultimately trigger the release of substance P. • Opioids, both endogenous and as drugs, inhibit the release of substance P: analgesia. • Pain information is relayed to the RAS, the thalamus, the somatosensory cortex (for early pain), and the anterior cingulate cortex and the limbic system (for late pain).
Brain blocking of pain • Thalamus, brainstem, and limbic system have many opioid receptors • Descending neurons travel from sites in the brainstem, such as the PAG, in the raphe (which releases 5-HT)and near the locus ceruleus (which releases NE), in turn activating descending neurons. • Descending neuron activity inhibits the release of glutamate and substance P in the spinal cord. • Spinal interneurons release endorphins to inhibit spinal projection neurons.
Opiate analgesia • In the spinal cord: • On spinal interneurons, morphine mimics endorphins • On descending neurons: • Directly inhibiting the spinal projection neuron • Directly inhibiting the spinal interneuron • Directly exciting the inhibitory opioid interneuron
Opiate analgesia in the brain • Morphine acts on opioid receptors in PAG and raphe • Activation inhibits cells in the spinal cord • Locus ceruleus cells normally excite (with NE) spinal pain transmission • PAG and opioid action on locus ceruleus hyperpolarize and thus inhibit m-receptors
Opiates: Natural and semi-synthetic • Morphine (10% of opium) and codeine, .5% • Isolated by Frederick Serturner, 1803 • Injected with invention of hypodermic needle, 1853 • Heroin: Morphine with two acetyl groups • Diacetylmorphine made by Bayer in 1898, sold as non-addictive • Dreser, inventor of aspirin, used the same trick of adding an acetyl group to get heroin
Synthetic opiates • Meperidine (Demerol): Shorter-acting • Methadone (Dolophine): Orally effective • Pentazocine (Talwin, 1967) • Propoxyphene (Darvon) • Buprenorphine (Buprenex): Partial agonist • Oxycodone (OxyContin®, Percodan®, Percocet®) • Hydrocodone (Vicodin®, Lorcet®, 200 generics
Opiate antagonists • Pure antagonists: Naloxone and naltrexone • Mixed agonist-antagonists: Nalorphine Endogenous opiates • Enkephalins and endorphins
Opioid receptors • Three genetically-controlled sets of receptors: m (mu), k (kappa), and d (delta) • Mu receptors are in all pain-control areas of the brain and spinal cord, in the respiratory control centers, and nucleus accumbens. Mu receptors respond to morphine and fentanyl (China White).
Opioid receptors... • Kappa receptors are in pain areas and nucleus accumbens, but also in deeper layers of cerebral cortex. Kappa receptors respond to mixed agonist-antagonists, like pentazocine (Talwin) • Delta receptors are found in pain areas, nucleus accumbens, and limbic system. They respond to endogenous opiates.
Opioid addiction • Most opioids increase DA activity from VTA to nucleus accumbens • However, k-agonists like dynorphin decrease DA activity associated with aversive effects of opioids
Dealing with opioid addiction • Mixed tolerance and receptor-specific cross-tolerance develop rapidly • Sensitization may occur for the craving effect • Dependence and cross-dependence are dramatic • May require lifelong opioid therapy • Lifestyle factors are associated with opioid addiction: lack of productivity • Naltrexone maintenance therapy • Methadone or LAAM maintenance therapy • Buprenorphine (a partial mu agonist) maintenance: less euphoria permits larger prescriptions
Why do people abuse opioids? • Predisposition: • Psychopathological basis for euphoria • Deficient endorphin systems • Painful emotional states • Maintenance: • Avoid withdrawal (Negative reinforcement) • Experience euphoria (Positive reinforcement) • Alleviate painful emotional states • Damaged endorphin system need opioids • Cuing by environment and/or mood state