This electrophysiological study uses the mixed
peptidase inhibitor kelatorphan and the selective kappa-antagonist
nor-binaltorphimine (
nor-BNI) to investigate whether there is altered modulation of spinal nociceptive transmission by endogenous
opioids 3 h after injection of
carrageenan into the ipsilateral paw. Intrathecal
kelatorphan (5-250 micrograms) inhibited the C-fibre evoked response of dorsal horn neurones in both normal and
carrageenan animals, with no difference in this inhibitory effect found between the 2 groups of animals. In both groups of animals, this inhibition reached a plateau at 50%. Thus there was no change in the effects exerted by the spinal
enkephalins at this point in the inflammatory state.
Nor-BNI (10 and 100 micrograms) produced a bidirectional change in the C-fibre evoked response of dorsal horn neurones in both normal and
carrageenan animals, facilitating the evoked response of some neurones whilst inhibiting others. The magnitude of the change in the neuronal response induced by
nor-BNI in
carrageenan animals was significantly greater than that seen in normal animals, suggesting a greater release of spinal
dynorphin in the inflammatory state. Dorsal horn neurones showed a bidirectional change in response as
carrageenan-induced
inflammation developed, although the direction of this change did not correlate with the subsequent direction of effect of
nor-BNI. There was, however, a significant correlation between the magnitude of the change in the C-fibre evoked response after the injection of
carrageenan and the magnitude of change produced in the same cells by
nor-BNI.(ABSTRACT TRUNCATED AT 250 WORDS)