The Journal of Neuroscience, March 15, 1999, 19(6):2394-2400
Alteration of Descending Modulation of Nociception during the
Course of Monoarthritis in the Rat
Nicolas
Danziger,
Jeanne
Weil-Fugazza,
Daniel
Le Bars, and
Didier
Bouhassira
Institut National de la Santé et de la Recherche
Médicale U-161, 75014 Paris, France
Diffuse noxious inhibitory controls (DNIC), which involve
supraspinal structures and modulate the transmission of nociceptive signals, were investigated at different stages during the development of adjuvant-induced monoarthritis in the rat. After behavioral evaluation, recordings of trigeminal convergent neurons were performed in anesthetized animals with acute (24-48 hr) or chronic (3-4 weeks)
monoarthritis of the ankle. Inhibitions of C-fiber-evoked neuronal
responses during and after the application of noxious conditioning
stimuli to the ankle were measured to evaluate DNIC. The conditioning
stimuli consisted of mechanical (maximal flexion and graded pressures)
and graded thermal stimuli and were applied alternately to normal and
arthritic ankles. Behaviorally, the two groups of animals exhibited a
similar increased sensitivity to mechanical stimuli applied to the
arthritic joint (i.e., an increased ankle-bend score and a decreased
vocalization threshold to pressure stimuli). However, they showed
different electrophysiological profiles. In the animals with acute
monoarthritis, the DNIC-induced inhibitions produced by mechanical or
thermal stimulation of the arthritic joint were significantly increased
at all intensities compared with the normal joint. In contrast, in the
chronic stage of monoarthritis, the DNIC-induced inhibitions triggered
by thermal or pressure stimuli were similar for both ankles, except
with the most intense mechanical stimuli. This discrepancy between the
behavioral and electrophysiological findings suggests that inputs
activated during chronic monoarthritis may fail to recruit DNIC and may
thus be functionally different from those activated in the acute stage
of inflammation.
Key words:
nociception; pain modulation; chronic inflammation; animal model; diffuse noxious inhibitory controls; descending
controls
Copyright © 1999 Society for Neuroscience 0270-6474/99/1962394-07$05.00/0
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