PAIN-MODULATION (DESCENDING PATHWAYS)

SUMMARY

INHIBITION
1. Relayed via the rostral ventromedial medulla (RVM) involving serotonergic neurons of the nucleus raphe magnus and noradrenergic neurons of the nucleus reticularis gigantocellularis.

2. Both receive input from the opioid receptor rich periaqueductal grey area of the midbrain (PAG).

3. The RVM is characterised by high levels of opioid & cannabinoid receptors that modulate resting facilitatory or inhibitory tone.

4. PAG and RVM receptors are the primary sites of action following systemic administration of opioids and cannabinoids.

5. At the dorsal horn, descending supraspinal inhibition results in the activation of opioid receptors and α2 adrenergic receptors that hyperpolarize presynaptic C-fibre and Aδ nociceptor terminals.

6. The response of dorsal horn neurons to descending serotonergic input from the nucleus raphe magnus is variable.

Reference(s)

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