SENSITIZATION OF THE NERVOUS-SYSTEM, INDUCED BY 2 SUCCESSIVE HINDPAW INFLAMMATIONS, IS SUPPRESSED BY A LOCAL-ANESTHETIC

Two hindpaw injections of carrageenin were performed 7 days apart and the time-course of the vocalization thresholds to pressure (VTPP) of a ll the 4 paws of the rat were measured after both injections. The firs t injection of carrageenin induced an increase in the circumference of the injected paw and a significant reduction of the VTPPs of all the 4 paws. The pain-related behavior of both hindpaws was enhanced, when carrageenin was injected for the second time not only into the previou sly inflamed, but also into the contralateral hindpaw. However, the ab normal responses of the forepaws were not increased by this second hin dpaw inflammation. Both after the first and the second injection of ca rrageenin, the decrease of the VTPPs of all 4 paws was antagonized by lidocaine with epinephrine (LE) injected into the inflamed paw. This a nesthetic effect was of a shorter duration after the second than after the first injection of carrageenin. Presumably, the imprint that is l eft in the nervous system after the first hindpaw inflammation, takes place at a relatively limited segmental level. In addition, it is poss ible to influence the established sensitization of the nervous system by treating the peripheral process itself, even when the first injury has primed the nervous system to the second injury. However, there sti ll seems to exist some excitatory influences that cannot be suppressed by the local anesthetic. (C) 1998 Elsevier Science B.V. All rights re served.