Different effect of high doses of naloxone on spinal reflexes in normal subjects and chronic paraplegic patients

G. Sandrini, I. Milanov, J. C. Willer, E. Alfonsi, A. Moglia, G. Nappi

Research output: Contribution to journalArticlepeer-review

Abstract

There is still controversy over the effects of naloxone on spinal reflexes in view of the fact that both facilitatory and inhibitory activities have been observed. Dosage, supraspinal influences and interactions with different opiate receptors may account for the different findings. We investigated the effect of placebo (saline) and high doses of naloxone (1.66 mg/kg) on the monosynaptic (H reflex) and nociceptive polysynaptic reflex (RIII reflex) in five normal subjects and three chronic paraplegic subjects. Following the administration of naloxone, there were no changes in the Rill reflex threshold in either group. By contrast, there was a marked facilitation of the H reflex amplitude in the normal subjects, but not in the spinal cord-injured subjects after treatment with naloxone. Saline induced no changes in the Rill reflex threshold or the H reflex amplitude n either of the two groups. Our data suggest that under normal conditions the opiatergic modulation of the nociceptive reflex is not functionally active whereas the tonic inhibitory modulation of the monosynaptic reflex is mediated by descending pathways.

Original languageEnglish
Pages (from-to)5-8
Number of pages4
JournalNeuroscience Letters
Volume261
Issue number1-2
DOIs
Publication statusPublished - Feb 12 1999

Keywords

  • H-Reflex
  • Naloxone
  • Nociceptive reflex
  • Normal subjects
  • Paraplegia

ASJC Scopus subject areas

  • Neuroscience(all)

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