Reflex-related activation of putative pain facilitating neurons in rostral, ventromedial medulla requires excitatory amino acid transmission

M. M. Heinricher, S. M. Roychowdhury

Research output: Contribution to journalArticlepeer-review

42 Scopus citations


Although the importance of the rostral ventromedial medulla in pain modulation is generally accepted, the recognition that it can exert both pain facilitating and pain inhibiting influences, and that its constituent neuronal population is physiologically and pharmacologically heterogenous, is relatively recent. A class of neuron which may be a source of facilitating influences from the rostral ventromedial medulla has been identified in electrophysiological experiments. These neurons, termed 'on-cells,' are characterized by a sudden burst of activity beginning just before nocifensive reflexes. This burst of firing is thought to be a significant factor in brainstem control of nociceptive transmission under physiological conditions. The aim of the present study was to determine whether an excitatory amino acid is involved in generation of the reflex-related burst that defines on- cells, and more generally, to examine the role of excitatory amino acid neurotransmitters within the rostral ventromedial medulla of the rat. Iontophoretic application of the broad-spectrum excitatory amino acid receptor antagonist kynurenate significantly reduced the reflex-related on- cell burst, whereas ongoing firing was unaffected. Spontaneous activity of other medullary neurons was unchanged. These data demonstrate that release of an endogenous excitatory amino acid neurotransmitter is necessary for the activation of on-cells that is associated with nocifensive reflexes. In contrast, these receptors evidently play a much less significant role in maintaining the ongoing activity of any cell class in the rostral ventromedial medulla in lightly anaesthetized rats.

Original languageEnglish (US)
Pages (from-to)1159-1165
Number of pages7
Issue number4
StatePublished - Apr 14 1997


  • descending control
  • iontophoresis
  • kynurenate
  • nucleus raphe magnus
  • pain modulation
  • tail flick

ASJC Scopus subject areas

  • Neuroscience(all)


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