Anatomy and physiology of a nociceptive modulatory system.

H. L. Fields, Mary Heinricher

Research output: Contribution to journalArticle

212 Citations (Scopus)

Abstract

Although efferent control of sensory transmission is a well-established concept, a specific network for nociceptive modulation has only recently been discovered. This network includes interconnected components at midbrain, medullary and spinal levels. At the midbrain level, electrical stimulation of the periaqueductal grey (p.a.g.) inhibits spinal neurons that respond to noxious stimuli as well as nociceptor-induced reflexes and escape behaviour in a variety of species. Midbrain stimulation also produces analgesia in patients with clinically significant pain. The rostral ventral medulla (r.v.m.) has similar behavioural and physiological effects and mediates midbrain antinociceptive actions at the level of the spinal cord. Endorphins are present at all levels of this nociceptive modulating network. Opiate microinjections at p.a.g., r.v.m. or spinal levels produce analgesia, presumably by mimicking the actions of the endorphins. The nociceptive modulatory system is diffusely organized, highly interconnected and appears to act as a unit whether activated by opiates or electrical stimulation. There are two classes of r.v.m. neurons the activity of which is correlated with the occurrence of reflexes induced by noxious stimulation. One class (the on-cell) accelerates, the other class (the off-cell) pauses just before tail flick. Both classes project to the spinal cord and are excited by electrical stimulation of the midbrain. However, when morphine is injected either systemically or into the p.a.g., the off-cell is excited and the on-cell stops firing. The off-cell is probably the r.v.m. output cell that inhibits nociceptive transmission at the level of the spinal cord. The function of the on-cell is not clear. The nociceptive modulatory system can be activated by a variety of stressful environmental factors, which are often, but not necessarily, noxious. The idea that the system acts as a simple negative feedback circuit is not consistent with its known properties.

Original languageEnglish (US)
Pages (from-to)361-374
Number of pages14
JournalPhilosophical transactions of the Royal Society of London. Series B: Biological sciences
Volume308
Issue number1136
StatePublished - Feb 19 1985
Externally publishedYes

Fingerprint

escape behavior
Opiate Alkaloids
Physiology
anatomy
Endorphins
physiology
Anatomy
environmental factor
Mesencephalon
Neurons
Periaqueductal Gray
brain
spinal cord
Electric Stimulation
endorphins
Spinal Cord
cells
Morphine
analgesia
reflexes

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Agricultural and Biological Sciences (miscellaneous)

Cite this

Anatomy and physiology of a nociceptive modulatory system. / Fields, H. L.; Heinricher, Mary.

In: Philosophical transactions of the Royal Society of London. Series B: Biological sciences, Vol. 308, No. 1136, 19.02.1985, p. 361-374.

Research output: Contribution to journalArticle

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