Glutamate, the major excitatory neurotransmitter in the central nervous sys
tem, activates three different receptors that directly gate ion channels, n
amely receptors for AMPA (alpha-amino-3-hydroxy-5-methyl isoxozole propioni
c acid), NMDA (N-methyl-D-aspartate), and kainate, a structural analogue of
glutamate. The contribution of AMPA and NMDA receptors to synaptic transmi
ssion and plasticity is well established(1). Recent work on the physiologic
al function of kainate receptors has focused on the hippocampus(2), where r
epetitive activation of the mossy-fibre pathway generates a slow, kainate-r
eceptor-mediated excitatory postsynaptic current (EPSC)(3-5). Here we show
that high-intensity single-shock stimulation (of duration 200 microseconds)
of primary afferent sensory fibres produces a fast, kainate-receptor-media
ted EPSC in the superficial dorsal horn of the spinal cord. Activation of l
ow-threshold afferent fibres generates typical AMPA-receptor-mediated EPSCs
only, indicating that kainate receptors may be restricted to synapses form
ed by high-threshold nociceptive (pain-sensing) and thermoreceptive primary
afferent fibres. Consistent with this possibility, kainate-receptor-mediat
ed EPSCs are blocked by the analgesic mu-opiate-receptor agonist Damgo and
spinal blockade of both kainate and AMPA receptors produces antinociception
, Thus, spinal kainate receptors contribute to transmission of somatosensor
y inputs from the periphery to the brain.