Suppression of a hind limb flexion withdrawal reflex by microinjection of glutamate or morphine into the periaqueductal gray in the rat

Earl Carstens, M. Hartung, B. Stelzer, M. Zimmermann

Research output: Contribution to journalArticle

22 Scopus citations

Abstract

Microinjection into the midbrain periaqueductal gray (PAG) or lateral reticular formation (LRF) of the neuronal excitant glutamate produces analgesia, and suppresses the responses of a fraction of spinal dorsal horn neurons to noxious heat applied to ventral hind paw skin. Microinjection of morphine into the PAG also produces analgesia, but has been reported to frequently facilitate, as well as to suppress or have no effect, on nociceptive spinal neurons. In anesthetized rats, we tested whether (a) glutamate microinjections into PAG or LRF, and (b) morphine microinjections into PAG, affected the isometric force of hind limb withdrawal elicited by the same noxious heat stimuli on the hind paw as used in single-unit studies of dorsal horn neurons. Glutamate (0.5 M; 0.1-0.5 μl) microinjected at 9 12 PAG and 8 10 LRF sites suppressed the reflex, and had no effect or facilitated th from the remaining sites. Morphine (5 μg in 0.5 μl) microinjected at each of 10 PAG sites suppressed the reflex in a naloxone-reversible manner. Suppression usually began shortly after morphine, peaked at 20-40 min, and lasted > 60 min. The integrated flexion reflex thus appears to be more susceptible to chemical midbrain stimulation under these experimental conditions, compared to previous studies of single dorsal horn neurons.

Original languageEnglish (US)
Pages (from-to)105-112
Number of pages8
JournalPain
Volume43
Issue number1
DOIs
StatePublished - 1990
Externally publishedYes

Keywords

  • (Rat)
  • Flexion withdrawal reflex
  • Glutamate
  • Morphine
  • Noxious heat
  • Periaqueductal gray

ASJC Scopus subject areas

  • Clinical Neurology
  • Psychiatry and Mental health
  • Neuroscience(all)
  • Neurology
  • Pharmacology
  • Clinical Psychology

Fingerprint Dive into the research topics of 'Suppression of a hind limb flexion withdrawal reflex by microinjection of glutamate or morphine into the periaqueductal gray in the rat'. Together they form a unique fingerprint.

  • Cite this