[Neuropeptide-mediated transmission of nociceptive information and its regulation. Novel mechanisms of analgesics].

Substance P and somatostatin may be transmitters of nociceptive information, which are involved in the transmission of pressure and heat nociceptive information, respectively, in the spinal dorsal horn. Calcitonin gene-related peptide, which is present in the primary sensory neurons having substance P or somatostatin, may function as a pain-promoting substance and be involved in the production of inflammation-induced hyperalgesia. The descending noradrenergic system plays a role in inhibiting nociceptive transmission in the spinal dorsal horn, and inhibits the release of substance P evoked by noxious mechanical stimulation. Persistent noxious stimuli increase the release of Met-enkephalin from the nucleus reticularis gigantocellularis, which promotes the activity of the descending noradrenergic system. Morphine activates the descending noradrenergic system, acting on the nucleus reticularis gigantocellularis. Morphine also activates the descending serotonergic system, which inhibits the release of somatostatin evoked by thermal noxious stimulation.