Which neurotransmitters are involved in the descending pain pathway?

• A. Dopamine and GABA
• B. Acetylcholine and glutamate
• C. Norepinephrine (NE) and serotonin (5-HT)
• D. Substance P and CGRP

Answer: (C)

The main concept here is that the brain can dampen pain signals as they travel to the spinal cord. The classic descending analgesic system uses two monoamines: norepinephrine and serotonin. Neurons from brainstem regions such as the locus coeruleus (noradrenergic) and the raphe nuclei (serotonergic) project down to the dorsal horn of the spinal cord. There they act on various receptors to inhibit the release of excitatory transmitters from primary afferents and to boost inhibitory influences, effectively reducing the transmission of nociceptive signals. This modulation helps suppress pain, and it’s why drugs that boost NE and 5-HT activity—like certain antidepressants or alpha-2 agonists—can have analgesic effects. The other options involve neurotransmitters more tied to direct nociceptor signaling or local dorsal-horn circuits (like substance P, CGRP, glutamate, or GABA) or systems not primarily responsible for the descending pain pathway, so they aren’t the main descending modulators.