μ-opioid receptors often colocalize with the substance P receptor (NK1) in the trigeminal dorsal horn

Sue A. Aicher, Ann Punnoose, Alla Goldberg

Research output: Contribution to journalArticle

65 Scopus citations

Abstract

Substance P (SP) is a peptide that is present in unmyelinated primary afferents to the dorsal horn and is released in response to painful or noxious stimuli. Opiates active at the μ-opiate receptor (MOR) produce antinociception, in part, through modulation of responses to SR MaR ligands may either inhibit the release of SP or reduce the excitatory responses of second-order neurons to SR. We examined potential functional sites for interactions between SP and MOR with dual electron microscopic immmunocytochemical localization of the SP receptor (NK1) and MOR in rat trigeminal dorsal horn. We also examined the relationship between SP- containing profiles and NK1-bearing profiles. We found that 56% of SP- immunoreactive terminals contact NK1 dendrites, whereas 34% of NK1- immunoreactive dendrites receive SP afferents. This result indicates that there is not a significant mismatch between sites of SP release and available NK1 receptors, although receptive neurons may contain receptors at sites distant from the peptide release site. With regard to opioid receptors, we found that many MOR-immunoreactive dendrites also contain NK1 (32%), whereas a smaller proportion of NK1-immunoreactive dendrites contain MOR (17%). Few NK1 dendrites (2%) were contacted by MOR-immunoreactive afferents. These results provide the first direct evidence that MORs are on the same neurons as NK1 receptors, suggesting that MOR ligands directly modulate SP-induced nociceptive responses primarily at postsynaptic sites, rather than through inhibition of SP release from primary afferents. This colocalization of NK1 and MORs has significant implications for the development of pain therapies targeted at these nociceptive neurons.

Original languageEnglish (US)
Pages (from-to)4345-4354
Number of pages10
JournalJournal of Neuroscience
Volume20
Issue number11
StatePublished - Jun 1 2000

    Fingerprint

Keywords

  • Analgesia
  • Dental pain
  • Electron microscopy
  • Neuropeptide
  • Opioid receptors
  • Pain
  • Substance P
  • Substantia gelatinosa
  • Tachykinin receptor
  • Trigeminal nucleus caudalis

ASJC Scopus subject areas

  • Neuroscience(all)

Cite this