POSSIBLE ROLE OF THE NUCLEUS RAPHE DORSALIS IN ANALGESIA BY PERIPHERAL STIMULATION - THEORETICAL CONSIDERATIONS

Direct stimulation of the Nucleus Raphe Dorsalis (NRD) appears to be v ery effective for obtaining analgesia. However, the possible role of t he NRD in analgesia by peripheral stimulation, e.g. electro-acupunctur e or Transcutaneous Electrical Nerve Stimulation (TENS), has received less attention. Most studies indicate that in particular the nucleus r eticularis gigantocellularis, the nucleus raphe magnus, the nucleus re ticularis magnocellularis, the locus coeruleus, and the periaqueductal grey may participate in the supraspinal mechanism for the antinocicep tive effect of peripheral stimulation. This paper is meant to present some theoretical considerations about the role the NRD might play in a nalgesia by peripheral stimulation. Little direct evidence suggests th at the NRD/serotonergic system might contribute to this type of analge sia. The analgesic role of specifically the serotonergic neurons of th e NRD in peripheral stimulation could be supported by indirect evidenc e. From studies concerning direct stimulation of the NRD, two other me chanisms by which peripheral stimulation might exert antinociceptive e ffects through the NRD have been hypothesized. Stimulation-parameters affecting the effectiveness of peripheral NRD stimulation will be disc ussed.