Effect of intrathecally administered noradrenergic antagonists on nociception in the rat

Jacqueline Sagen, Herbert K. Proudfit

Research output: Contribution to journalArticlepeer-review

114 Scopus citations


Recent evidence suggests that some groups of noradrenergic neurons found in the brainstem have axonal connections in the spinal cord dorsal horn and may be involved in the control of pain sensitivity. Such evidence includes the demonstration that intrathecal injection of noradrenergic agonists increases nociceptive threshold (hypoalgesia). The present studies examined whether the descending noradrenergic system is tonically active and, if so, what noradrenergic receptor subtypes mediate the actions of endogenously-released norepinephrine. These studies involved the measurement of nociceptive threshold before and after the intrathecal injection of noradrenergic antagonists having different relative affinities for α-noradrenergic receptor subtypes. The intrathecal administration of α-noradrenergic antagonists produced a dose-dependent decrease in nociceptive threshold (hyperalgesia). This finding is consistent with the proposal that tonically-active bulbospinal noradrenergic neurons modulate the processing of nociceptive information in the spinal cord. The potency and duration of the hyperalgesia was correlated with the relative potency of the antagonists for the α-2 noradrenergic receptor. The relative potencies were as follows: yohimbine > phentolamine > WB 4101 > prazosin. Thus, endogenous norepinephrine which is tonically released from bulbospinal axon terminals may interact preferentially with noradrenergic receptors of the α-2 type.

Original languageEnglish (US)
Pages (from-to)295-301
Number of pages7
JournalBrain Research
Issue number2
StatePublished - Sep 24 1984
Externally publishedYes


  • analgesia
  • hyperalgesia
  • intrathecal injection
  • noradrenergic antagonists
  • pain
  • spinal cord
  • α-receptors

ASJC Scopus subject areas

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


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