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To determine the importance of the NMDA receptor (NMDAR) in pain hypersensitivity after injury, the NMDAR1 (NR1) subunit was selectively deleted in the lumbar spinal cord of adult mice by the localized injection of an adeno-associated virus expressing Cre recombinase into floxed NR1 mice. NR1 subunit mRNA and dendritic protein are reduced by 80% in the area of the virus injection, and NMDA currents, but not AMPA currents, are reduced 86-88% in lamina II neurons. The spatial NR1 knock-out does not alter heat or cold paw-withdrawal latencies, mechanical threshold, or motor function. However, injury-induced pain produced by intraplantar formalin is reduced by 70%. Our results demonstrate conclusively that the postsynaptic NR1 receptor subunit in the lumbar dorsal horn of the spinal cord is required for central sensitization, the central facilitation of pain transmission produced by peripheral injury. [ABSTRACT FROM AUTHOR]

Presents a study which examined the effect of genetic ablation of kainate (KA) receptors on synaptic transmission at mossy-fiber pyramidal cell synapse. Heteromeric combinations which form KA receptors; Generation and molecular characterization of KA2[sup-I-] mutant mice; Mossy-fiber long-term plasticity in KA2[sup-I-] mice.

Multimeric assemblies of kainate (KA) receptor subunits form glutamate-gated ion channels that mediate EPSCs and function as presynaptic modulators of neurotransmitter release at some central synapses. The KA2 subunit is a likely constituent of many neuronal kainate receptors, because it is widely expressed in most neurons in the CNS. We have studied the effect of genetic ablation of this receptor subunit on synaptic transmission at the mossy-fiber-CA3 pyramidal cell synapse in hippocampal slices, where kainate receptors are localized to both presynaptic and postsynaptic sites. We found that both postsynaptic and presynaptic mossy-fiber kainate receptor function is altered in neurons from KA2-/- mice. The presynaptic facilitatory autoreceptor, which modulates glutamate release from mossy-fiber terminals, had a reduced affinity for exogenous agonists and synaptic glutamate. Although presynaptic facilitation attributable to homosynaptic glutamate release was normal at mossy-fiber synapses in KA2-/- neurons, heterosynaptic kainate receptor-mediated facilitation resulting from the spillover of glutamate from CA3 collateral synapses was absent. Consistent with a decrease in glutamate affinity of the receptor, the half-decay of the postsynaptic kainate-mediated EPSC was shorter in the knock-out mice. These results identify the KA2 subunit as a determinant of kainate receptor function at presynaptic and postsynaptic mossy-fiber kainate receptors.