Presynaptic low- and high-affinity kainate receptors in nociceptive spinal afferents.

Presynaptic ionotropic glutamate receptors are increasingly attributed a role in the modulation of sensory input at the first synapse of dorsal root ganglion (DRG) neurons in the spinal dorsal horn. Central terminals of DRG neurons express AMPA and NMDA receptors whose activation modulates the release of glutamate, the main transmitter at these synapses. Previous work, with an antibody that recognizes all low-affinity kainate receptor subunits (GluR5, 6, 7), provided microscopic evidence of presynaptic kainate receptors in unidentified primary afferent terminals in superficial laminae of the spinal dorsal horn (Hwang SJ, Pagliardini S, Rustioni A, Valtschanoff JG.

Ionotropic glutamate receptors are expressed in GABAergic terminals in the rat superficial dorsal horn.

Ionotropic glutamate receptors (IGR), including NMDA, AMPA, and kainate receptors, are expressed in terminals with varied morphology in the superficial laminae (I-III) of the dorsal horn of the spinal cord. Some of these terminals can be identified as endings of primary afferents, whereas others establish symmetric synapses, suggesting that they may be gamma-aminobutyric acid (GABA)-ergic. In the present study, we used confocal and electron microscopy of double immunostaining for GAD65, a marker for GABAergic terminals, and for subunits of IGRs to test directly whether IGRs are expressed in GABAergic terminals in laminae I-III of the dorsal horn.