Basic science of pain

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J Bone Joint Surg Am. 2006 Apr;88 Suppl 2:58-62.

Basic science of pain.

DeLeo JA.

Dartmouth-Hitchcock Medical Center, Dartmouth Medical School,

Neuroscience Center at Dartmouth, Department of Anesthesiology,

Lebanon, NH 03756, USA.

The origin of the theory that the transmission of pain is through a

single channel from the skin to the brain can be traced to the

philosopher and scientist Rene Descartes. This simplified scheme of

the reflex was the beginning of the development of the modern

doctrine of reflexes.

Unfortunately, Descartes' reflex theory directed both the study and

treatment of pain for more than 330 years. It is still described in

physiology and neuroscience textbooks as fact rather than theory. The

gate control theory proposed by Melzack and Wall in 1965 rejuvenated

the field of pain study and led to further investigation into the

phenomena of spinal sensitization and central nervous system

plasticity, which are the potential pathophysiologic correlates of

chronic pain.

The processing of pain takes place in an integrated matrix throughout

the neuroaxis and occurs on at least three levels-at peripheral,

spinal, and supraspinal sites. Basic strategies of pain control

monopolize on this concept of integration by attenuation or blockade

of pain through intervention at the periphery, by activation of

inhibitory processes that gate pain at the spinal cord and brain, and

by interference with the perception of pain.

This article discusses each level of pain modulation and reviews the

mechanisms of action of opioids and potential new analgesics. A brief

description of animal models frames a discussion about recent

advances regarding the role of glial cells and central nervous system

neuroimmune activation and innate immunity in the etiology of chronic

pain states.

Future investigation into the discovery and development of novel,

nonopioid drug therapy may provide needed options for the millions of

patients who suffer from chronic pain syndromes, including syndromes

in which the pain originates from peripheral nerve, nerve root,

spinal cord, bone, muscle, and disc.