Multiphasic effect of morphine on the release of substance P from rat trigeminal nucleus slices

Heberto Suarez-Roca, Lubna Abdullah, John R Zuniga, Sandra Madison, William Maixner

Research output: Contribution to journalArticlepeer-review

46 Scopus citations


It is generally accepted that morphine acts presynaptically to inhibit substance P (SP) release from afferent terminals in the trigeminal nucleus. Recent studies, however, provide evidence that opioids produce both inhibitory and excitatory effects on SP release which are concentration- and receptor subtype-dependent. In the present study, we have examined a wide range of morphine concentrations on K+ -evoked SP release from rat trigeminal nucleus caudalis slices. Immunoreactive SP was measured in perfusates. Morphine produces multiphasic effects on K+-evoked SP release without affecting basal release. A very low nannomolar concentration (1 nM) suppressed release, higher nanomolar concentrations (100-300 nM) facilitated release, a low micromolar concentration (3 μM) suppressed release, and a higher micromolar concentration (30 μM) facilitated release. These effects were abolished by opioid receptor blockade with naloxone (30 nM). Thus, morphine produces a complex bi-directional modulation of SP release from TNC which is concentration- and possibly receptor subtype-dependent.

Original languageEnglish (US)
Pages (from-to)187-194
Number of pages8
JournalBrain Research
Issue number2
StatePublished - May 8 1992


  • Morphine
  • Naloxone
  • Opioid receptor
  • Peptide release
  • Substance P
  • Trigeminal nucleus caudalis

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology


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