Mu opioid receptors in rat ventral medulla: Effects of endomorphin-1 on phrenic nerve activity

Tina Lonergan, Ann K. Goodchild, Macdonald J. Christie, Paul M. Pilowsky*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

43 Citations (Scopus)


Anatomical and in vitro studies suggest that mu opioid receptors (MOR) on pre-Bötzinger complex neurons are responsible for opioid induced respiratory depression (Grey et al., Science 286 (1999) 1566). However, mu opioid agonists injected in vivo, in other regions of the ventral respiratory group (VRG), produce respiratory depression, suggesting that opioids are widely distributed in the VRG. We therefore re-examined the distribution of the MOR in the ventral medulla and found MOR-immunoreactive neurons and terminals in all subdivisions of the VRG. Furthermore, we determined, in rats, the effects of a MOR agonist (endomorphin-1, 10 mM, 60 nl, unilateral), microinjected into different subdivisions of the VRG, on phrenic nerve activity. Endomorphin-1 produced changes in phrenic nerve frequency and amplitude, throughout the VRG. Unexpectedly, endomorphin-1 microinjected into the Bötzinger and pre-Bötzinger complexes consistently increased phrenic nerve frequency. These results support the widespread distribution of MOR in the VRG and also indicate that endomorphin-1, a postulated endogenous ligand, may differentially regulate respiration.

Original languageEnglish
Pages (from-to)165-178
Number of pages14
JournalRespiratory Physiology and Neurobiology
Issue number2-3
Publication statusPublished - 14 Nov 2003
Externally publishedYes


  • Brainstem
  • Control of breathing
  • Mammals
  • Mu opioid
  • Mu opioid receptors
  • Pre-Bötzinger region
  • Rat
  • Receptors
  • Respiratory depression


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