Involvement of 5-hydroxytryptamine-containing neurons in antinociception produced by injection of morphine into nucleus raphe magnus or onto spinal cord

Michael R. Vasko, Iok-Hou Pang, Marthe Vogt

Research output: Contribution to journalArticle

51 Scopus citations

Abstract

We studied whether antinociception produced by injection of morphine into the nucleus raphe magnus (NRM) or superfusion onto the spinal cord involved serotonergic neurons that descend from brainstem to spinal cord. Involvement of 5-hydroxytryptamine (5-HT)-containing neurons was determined by correlating morphine-induced analgesia with an increase in turnover of 5-HT and by determining if depletion of cord 5-HT with the neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT) could attenuate the antinociceptive effects of morphine. When injected directly into the NRM, 10 μg of morphine produced profound analgesia as measured by the paw-pressure technique, and significantly increased the turnover of 5-HT in both posterior medulla and spinal cord. Depletion of cord 5-HT to less than 10% of control concentrations attenuated the antinociceptive effect of morphine injected into the NRM. When various concentrations of morphine (1, 10 or 50 μg) were injected directly into the spinal subarachnoid space, a dose-dependent analgesia was observed. No change in 5-HT turnover in spinal cord was observed with any dose of morphine superfused onto the cord. In addition, depletion of cord 5-HT with 5,7-DHT did not alter the analgesic response to either 1 or 10 μg of intrathecal morphine. These results suggest that although 5-HT-containing neurons descending from brainstem into spinal cord are involved with analgesia produced by morphine injection into the NRM, they are not involved in the analgesia induced by applying morphine directly to the cord.

Original languageEnglish
Pages (from-to)341-348
Number of pages8
JournalBrain Research
Volume306
Issue number1-2
DOIs
StatePublished - 23 Jul 1984

Keywords

  • 5,7-dihydroxytryptamine
  • 5-hydroxytryptamine
  • antinociception
  • morphine
  • nucleus raphe magnus
  • spinal cord

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