Microinjections of glutamate or morphine at coincident midbrain sites have different effects on nociceptive dorsal horn neurons in the rat

Earl Carstens, B. Stelzer, M. Zimmermann

Research output: Contribution to journalArticle

15 Scopus citations

Abstract

Responses of single lumbar spinal neurons to noxious skin heating (50°C, 10 s) were electrophysiologically recorded in barbiturate-anesthetized rats. Responses of all neurons were suppressed by electrical stimulation in the midbrain periaqueductal gray (PAG) or lateral reticular formation (LRF). Microinjection of glutamate (GLU, 0.1-0.3 μl, 0.5 M) into the PAG rapidly (within 15 s) suppressed (to 13-55% of control) the responses of 6 16 neurons with recovery within 8 min. The remainder were affected less at even higher doses (0.5-1 μl). Responses of 4 10 neurons were suppressed following GLU microinjected into the LRF. We also tested effects of microinjection of morphine (MOR, 5 μg/0.5 μl) into GLU-sensitive and insensitive PAG sites. Responses of 4 neurons were unaffected, 4 were enhanced (to 130-155%), and 2 suppressed (to 43 and 57%) following MOR in PAG, with enhancement or suppression beginning within 12-20 min and lasting 40 to over 70 min. The differing effects of GLU and MOR may reflect different mechanisms for the descending modulation of spinal nociceptive transmission.

Original languageEnglish (US)
Pages (from-to)185-191
Number of pages7
JournalNeuroscience Letters
Volume95
Issue number1-3
DOIs
StatePublished - Dec 19 1988
Externally publishedYes

Keywords

  • Descending inhibition
  • Dorsal horn neuron
  • Glutamate
  • Microinjection
  • Midbrain stimulation
  • Morphine
  • Noxious heat
  • Rat

ASJC Scopus subject areas

  • Neuroscience(all)

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