Modification of the responses of primate spinothalamic neurons to mechanical stimulation by excitatory amino acids and an N-methyl-d-aspartate antagonist

Excitatory amino acids (EAAs) are likely to play a key role in sensory transmission in the spinal cord. In the present study, the microiontophoresis technique was used to investigate the effects of l-glutamate (GLUT), N-methyl-d-aspartate (NMDA), and quisqualate (QUIS), as well as an NMDA receptor antagonist, AP-7, on the discharges evoked in nociceptive primate spinothalamic tract (STT) neurons by mechanical stimulation of the skin. Responses to innocuous brushing of the skin were facilitated by GLUT and NMDA (and in some neurons by QUIS) and sometimes reduced by AP-7. GLUT also facilitated the responses to noxious mechanical stimuli. The results are consistent with anatomical evidence for the presence of synapses that contain EAAs on primate STT cells and with the proposal that the co-release of EAAs and neuropeptides may contribute to hyperalgesia.