Analgesic mechanisms of noradrenaline in the spinal dorsal horn

The superficial laminae of the spinal dorsal horn play important roles in nociceptive transmission and modulation. Noradrenergic fibers originated from brainstem pain-control system terminate and release noradrenaline (NA) in the superficial dorsal horn. The released NA might take part in the modulation of nociceptive transmission through the following pathways: (1) inhibits the glutamate and substance P release from primary afferent terminals; (2) increases the release of inhibitory neurotransmitters from lamina II (substantia gelatinosa) neurons. Morphological findings also raise the possibility that NA directly inhibits projection neurons in laminae I/III which convey the nociceptive information to the thalamus, thus inhibit nociceptive transmission at spinal level.