Opioid effects on pain pathways include which of the following mechanisms?

Opioid effects on pain pathways include which of the following mechanisms?

• A. Only inhibit ascending pathways
• B. Inhibit ascending pain pathways, activate descending inhibitory pathways, and reduce release of excitatory neurotransmitters
• C. Only activate descending inhibitory pathways
• D. Increase release of substance P

Answer: (B)

Opioids produce analgesia by modulating pain signaling at multiple levels: they blunt the transmission of nociceptive signals in ascending pathways from the spinal cord to the brain, they engage the brain’s descending inhibitory systems (originating in regions like the periaqueductal gray and projecting to the spinal cord) to further suppress pain transmission, and they decrease the release of excitatory neurotransmitters such as substance P and glutamate at the dorsal horn synapses. At the cellular level, mu-opioid receptor activation reduces calcium influx presynaptically (lowering neurotransmitter release) and increases potassium conductance postsynaptically (hyperpolarizing neurons), which together lessen the activity of pain pathways. That combination is why this option is best: opioids don’t act only on one direction of modulation, they both inhibit ascending signals and activate descending inhibition while also dampening excitatory transmitter release. They certainly do not increase substance P release.

Opioids produce analgesia by modulating pain signaling at multiple levels: they blunt the transmission of nociceptive signals in ascending pathways from the spinal cord to the brain, they engage the brain’s descending inhibitory systems (originating in regions like the periaqueductal gray and projecting to the spinal cord) to further suppress pain transmission, and they decrease the release of excitatory neurotransmitters such as substance P and glutamate at the dorsal horn synapses. At the cellular level, mu-opioid receptor activation reduces calcium influx presynaptically (lowering neurotransmitter release) and increases potassium conductance postsynaptically (hyperpolarizing neurons), which together lessen the activity of pain pathways.

That combination is why this option is best: opioids don’t act only on one direction of modulation, they both inhibit ascending signals and activate descending inhibition while also dampening excitatory transmitter release. They certainly do not increase substance P release.