α-Adrenergic receptor agonists, but not antagonists, alter the tail-flick latency when microinjected into the rostral ventromedial medulla of the lightly anesthetized rat

C. M. Haws, Mary Heinricher, H. L. Fields

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Abstract

The present experiments, part of an ongoing study designed to characterise the role norepinephrine (NE) in regulating the activity of putative nociceptive modulatory neurons in the rostral ventromedial medulla (RVM), assessed the effects of α-adrenergic receptor-selective agents on the nociceptive threshold (as measured by the tail-flick withdrawal response on noxious heat). These microinjection studies were carried out in the barbiturate-anesthetized rat, a preparation which is favourable for acute neurophysiological studies. The data obtained demonstrate that, as observed by others in the awake animal, activation of α2-adrenergic receptors in the RVM produces hypoalgesia. However, unlike in the awake animal, when antagonists selective for either the α1- or α2-adrenergic receptor are microinjected alone into the RVM there is no change in the nociceptive threshold. These data suggest that the α2-adrenergic receptor has a postsynaptic location and that barbiturate anaesthesia suppresses a tonically active or noxious stimulus-activated noradrenergic input to the RVM that is present in the awake animal.

Original languageEnglish (US)
Pages (from-to)192-195
Number of pages4
JournalBrain Research
Volume533
Issue number2
DOIs
Publication statusPublished - Nov 19 1990
Externally publishedYes

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Keywords

  • Antinociception
  • Brainstem
  • Microinjection
  • Noradrenaline
  • Rat

ASJC Scopus subject areas

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

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