Opioids in Headache
Opioid analgesics are often divided into (1) the naturally occurring alkaloids derived from the opium poppy, (2) semisynthetic agents, and (3) synthetic compounds. The term opiate is supposed to be applied only to the first group, while opioids refer to any analgesic resembling or sharing key properties with this group. Opioids interact with opioid receptors of which there are several known types: mu, delta, and kappa. All 3 receptors when activated can promote analgesia. Opioid receptors are present on both sides of the first synapse in the nociceptive pathway (spinal cord dorsal horn for trunk and limb nociception; spinal trigeminal nucleus for facial and anterior head nociception), so both pain signal transmission and release of excitatory neurotransmitters are reduced by medications with opioid agonism.
Another way of classifying opioids, which is more helpful in assessing effects on pain, is to consider 3 groups divided as to their agonistic/antagonistic effects on opioid receptors: full agonists, partial agonists, and antagonists. Morphine and other opioid agonists probably work for head pain by modifying nociceptive input to the spinal trigeminal nucleus (nucleus caudalis), but it is fairly clear that they have no effect on the source of migraine pain – ie, neurovascular. For this reason, and others that will be covered later, their effectiveness in primary headache is limited.
Pharmacological Effects of Opioids
Opioid analgesics are often divided into (1) the naturally occurring alkaloids derived from the opium poppy, (2) semisynthetic agents, and (3) synthetic compounds. The term opiate is supposed to be applied only to the first group, while opioids refer to any analgesic resembling or sharing key properties with this group. Opioids interact with opioid receptors of which there are several known types: mu, delta, and kappa. All 3 receptors when activated can promote analgesia. Opioid receptors are present on both sides of the first synapse in the nociceptive pathway (spinal cord dorsal horn for trunk and limb nociception; spinal trigeminal nucleus for facial and anterior head nociception), so both pain signal transmission and release of excitatory neurotransmitters are reduced by medications with opioid agonism.
Another way of classifying opioids, which is more helpful in assessing effects on pain, is to consider 3 groups divided as to their agonistic/antagonistic effects on opioid receptors: full agonists, partial agonists, and antagonists. Morphine and other opioid agonists probably work for head pain by modifying nociceptive input to the spinal trigeminal nucleus (nucleus caudalis), but it is fairly clear that they have no effect on the source of migraine pain – ie, neurovascular. For this reason, and others that will be covered later, their effectiveness in primary headache is limited.
SHARE
