Sustained hyperalgesia can be induced in the rat by a single formalin injection and depends on the initial nociceptive inputs.
The present study was undertaken to find out if a hyperalgesia can be observed 1 week after a conditioning stimulation of the orofacial area of the rat. Sprague-Dawley rats received a left infraorbital infiltration with either bupivacaine or saline and then, 30 min thereafter, an injection of either saline or 10% formalin solution in the left upper lip. Four groups of animals were thus made up depending on their conditioning treatment. Seven days later, an algesimetric test initiated by a contralateral orofacial formalin injection was carried out. The duration of lip rubbing was significantly increased in formalin-conditioned groups. The hyperalgesia observed at 7 days was suppressed by an infraorbital nerve block carried out at the time of the conditioning stimulus. These results tend to indicate that a nociceptive message of short duration induces a trace in the central nervous system which can be retained for 1 week.
Cadet
R
R
Laboratoire de Physiologie Orofaciale, U.F.R. Odontologie, Clermont-Ferrand, France.
Aigouy
L
L
Woda
A
A
D000704:Analysis of Variance; D000818:Animals; D002045:Bupivacaine / Q000494:pharmacology*; D005557:Formaldehyde; D006930:Hyperalgesia / Q000139:chemically induced / Q000503:physiopathology*; D008046:Lip; D008297:Male; D009619:Nociceptors / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley
D005557:Formaldehyde; D002045:Bupivacaine