[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.