Freezing of enkephalinergic functions by multiple noxious foci: a source of pain sensitization?
BACKGROUND
The functional significance of proenkephalin systems in processing pain remains an open question and indeed is puzzling. For example, a noxious mechanical stimulus does not alter the release of Met-enkephalin-like material (MELM) from segments of the spinal cord related to the stimulated area of the body, but does increase its release from other segments.


RESULTS
Here we show that, in the rat, a noxious mechanical stimulus applied to either the right or the left hind paw elicits a marked increase of MELM release during perifusion of either the whole spinal cord or the cervico-trigeminal area. However, these stimulatory effects were not additive and indeed, disappeared completely when the right and left paws were stimulated simultaneously.


CONCLUSIONS
We have concluded that in addition to the concept of a diffuse control of the transmission of nociceptive signals through the dorsal horn, there is a diffuse control of the modulation of this transmission. The "freezing" of Met-enkephalinergic functions represents a potential source of central sensitization in the spinal cord, notably in clinical situations involving multiple painful foci, e.g. cancer with metastases, poly-traumatism or rheumatoid arthritis.
Cesselin
François
F
Team Pain, INSERM UMRS 975, CNRS UMR 7225, Paris, France. francois.cesselin@upmc.fr
Bourgoin
Sylvie
S
Mauborgne
Annie
A
Hamon
Michel
M
Le Bars
Daniel
D
D000818:Animals; D004744:Enkephalin, Methionine / Q000378:metabolism*; D004745:Enkephalins / Q000378:metabolism; D005121:Extremities; D008297:Male; D009433:Neural Inhibition; D010146:Pain / Q000503:physiopathology*; D011498:Protein Precursors / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000503:physiopathology; D014275:Trigeminal Caudal Nucleus / Q000378:metabolism*; D014279:Trigeminal Nucleus, Spinal / Q000378:metabolism
D004745:Enkephalins; D011498:Protein Precursors; C029992:proenkephalin; D004744:Enkephalin, Methionine