EFFECT OF REPEATED COLD STRESS ON CAPSAICIN-EVOKED RELEASE OF GLUTAMATE FROM RAT SPINAL DORSAL HORN SLICES

We investigated the effect of repeated cold stress (RCS) on the capsai cin-evoked release of glutamate from the primary afferent fibers of th e rat, and compared this with the effect of inoculation of complete Fr eund's adjuvant (adjuvant inoculation). The release of glutamate was m easured using a fluorometric on-line continuous monitoring system in w hich the immobilized glutamate dehydrogenase column was connected to a n in vitro superfusion system. In the presence of 0.3 mu M tetrodotoxi n, the application of 1 mu M capsaicin to spinal dorsal horn slices ev oked glutamate release (18.6 +/- 1.2 pmol mg(-1) protein, n = 11). In rats subjected to RCS (RCS rats), the release of glutamate evoked by 1 mu M capsaicin was markedly increased to 272% (n = 6, P<0.05) of the value for the control group, although the basal release was not signif icantly altered (n = 6, P>0.05). Adjuvant inoculation produced a signi ficant increase in the basal and capsaicin (1 mu M) evoked release of glutamate to 141 and 344% (n = 6, P < 0.05) of the value for the contr ol group, respectively. The present results suggest that the facilitat ed release of glutamate from capsaicin-sensitive primary afferent term inals in the spinal dorsal horn is, al least in part, involved in the hyperalgesia of RCS rats as well as the complete Freund's adjuvant-ind uced hyperalgesia. (C) 1997 Elsevier Science Ireland Ltd.