Electrophysiological evidence for a tonic activity of the spinal cord intrinsic opioid systems in a chronic pain model.
The aim of this electrophysiological investigation was to evaluate the activity of the spinal endogenous opioid systems in a chronic pain model, the arthritic rat. The activity of nociceptive non-specific dorsal horn neurons (n = 23) were recorded in 23 spinal unanesthetized decerebrated rats. Naloxone (1 mg/kg i.v.) induced a highly significant increase in the spontaneous firing rate of these neurons. This observation is in favor of a tonic activity of spinal opioid endogenous systems in such a disease. In addition, the same dose of naloxone facilitates the transmission of noxious messages at the spinal level as revealed by the large enhancement of the responses of these neurons to C-fiber stimulation. These results are in good agreement with behavioral data showing that such a relatively high dose of naloxone induced well-reproducible hyperalgesia and with some biochemical observations showing an increase of levels and biosynthesis of endogenous opioids in the spinal cord of the arthritic rat.
Lombard
M C
MC
I.N.S.E.R.M., Unité de Recherche de Neurophysiologie Pharmacologique (U161), Paris, France.
Besson
J M
JM
D000818:Animals; D001168:Arthritis / Q000503:physiopathology*; D001169:Arthritis, Experimental / Q000503:physiopathology*; D003655:Decerebrate State; D004558:Electric Stimulation; D004723:Endorphins / Q000502:physiology; D005071:Evoked Potentials / Q000187:drug effects; D008297:Male; D009270:Naloxone / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000187:drug effects / Q000502:physiology / Q000503:physiopathology*
D004723:Endorphins; D009270:Naloxone