Role of kainate receptors in nociception.

Nociceptive nerve fibers use L-glutamate as a fast excitatory neurotransmitter and it is therefore not surprising that both, ionotropic and metabotropic glutamate receptors play pivotal roles for transmission of nociceptive information in spinal cord. A subtype of ionotropic glutamate receptors, the kainate receptor, is present in spinal dorsal horn. However, its role has remained obscure as specific antagonists and agonists have become available only recently. Kainate receptors are present on small, including nociceptive, dorsal root ganglion cells and on intrinsic dorsal horn neurons, and those two locations can be targeted separately by appropriate agonists and antagonists. Postsynaptic kainate receptors on spinal dorsal horn neurons are activated by high intensity electrical stimulation of the dorsal root entry zone that activates nociceptive primary afferent fibers. In contrast, low intensity stimulation that activates only non-nociceptive fibers is ineffective. Selective blockade of kainate receptors may produce analgesia. Here, we review what is known about localization of kainate receptors in dorsal root ganglia and spinal dorsal horn and their physiological and pathophysiological importance with special reference to nociceptive pathways. A short overview on molecular biology and agonist and antagonist pharmacology is included.