Exposure of rat spinal neurones to NMDA, AMPA and kainate produces only short-term enhancements of responses to noxious and non-noxious stimuli.
The ability of excitatory amino acids (EAAs) to modulate nociceptive and non-nociceptive responses was tested on spinal neurones of the anaesthetized rat. NMDA (N-methyl-D-aspartate), AMPA ((RS)-alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate) and kainate were applied by iontophoretic ejection to increase the background firing rate of each cell to approximately 25 spikes/s. Responses to noxious heat and pinch and innocuous tap stimuli were enhanced to similar degrees by all three EAAs and returned to control immediately following termination of EAA ejection. This result shows that, whilst NMDA does enhance synaptic responses of spinal neurones, this effect is little or no greater than for AMPA or kainate. Furthermore, the rapid recovery of nociceptive responses indicates that more than NMDA receptor activation alone is required to induce longer-term enhancement of nociceptive responses (hyperalgesia).
Cumberbatch
M J
MJ
Department of Physiology, School of Medical Sciences, University of Bristol, UK.
Herrero
J F
JF
Headley
P M
PM
D000818:Animals; D004594:Electrophysiology; D006358:Hot Temperature; D007608:Kainic Acid / Q000494:pharmacology*; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D009619:Nociceptors / Q000187:drug effects; D010146:Pain / Q000503:physiopathology*; D010812:Physical Stimulation; D051381:Rats; D017208:Rats, Wistar; D013116:Spinal Cord / Q000187:drug effects* / Q000473:pathology / Q000503:physiopathology; D013997:Time Factors; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology*
D016202:N-Methylaspartate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D007608:Kainic Acid