SUBSTANCE P AND GLUTAMATE MEDIATE CAPSAICIN-INDUCED REDUCTION OF GABA IMMUNOREACTIVITY IN CAT SPINAL SUPERFICIAL DORSAL HORN

In order to determine whether capsaicin-induced reduction of GABA immunoreactivity (GABA-IR) is related with transmitters released from primary afferent terminals, immunohistochemical technique for substance P and GABA was performed to observe the changes of SP-IR and GABA-IR profiles in the dorsal horn following unilatsral perineural treatment of capsaicin (98mM, for 30 min) alone and a combined treatment of NK-1 or NMDA receptor antagonist and capsaicin. The obvious reduction of SP-IR and GABA-IR in the ipsilateral laminae Ⅰ-Ⅱ of the dorsal horn was found 30 min after treatment of capsaicin. The capsaicin-induced reduction of GABA-IR positive fibers and neurons was significantly blocked by spinal pre-superfusion of NK-1 receptor antagonist spantide (50nM) and NMDA receptor antagonist APV (100μM). The mechanism that primary afferent transmitters-evoked activity of spinal intrinsic GABA-ergic neurons may be involved in modulation of spinal transmission of nociceptive information was discussed.