Abstract
The possible modulation exerted by glutamate on substance P (SP) release from the rat spinal cord has been investigated. The N-methyl-D-aspartate (NMDA) receptor agonist, NMDA (1 μM), increased SP basal outflow by 46.5±10.9% (n=3, P<0.01) without changing the evoked release of the peptide. Conversely, NMDA antagonists but not 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) inhibited both electrically-evoked and capsaicin-induced release of SP. In particular, D-2-amino-5-phosphonopentanoate (D-AP5; 50 μM) inhibited electrically-evoked and capsaicin-induced release of SP by 93±2.4% and 93.2±3.8% (n=12, P<0.01), respectively. Functional pharmacological evidence is provided for glutamate exerting a positive feedback on SP release evoked by C fibre stimulation via NMDA receptor activation.
Keywords: SP, glutamate, NMDA receptor, heteroreceptors, release, spinal cord, capsaicin, electrical stimulation
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