GLUR1 AND GLUR2 3 SUBUNITS OF THE AMPA-TYPE GLUTAMATE-RECEPTOR ARE ASSOCIATED WITH PARTICULAR TYPES OF NEURON IN LAMINAE I-III OF THE SPINAL DORSAL HORN OF THE RAT/

GluR1 and GluR2 subunits of the pha-amino-3-hydroxy-5-methyl-4-isoxazo lepropionate (AMPA) receptor are expressed at high levels by neurones in laminae I-III of rat spinal dorsal horn, an area which contains num erous, densely packed small neurones. In order to determine whether th ese subunits are expressed by inhibitory or excitatory neurones, we co mbined pre-embedding immunocytochemistry with antibodies that recogniz e either GluR1, or an epitope common to GluR2 and 3, with postembeddin g detection of gamma-aminobutyric acid (GABA) and glycine. Most (78%) of the neurones with GluR1-immunoreactivity were GABA-immunoreactive, and some of these were also glycine-immunoreactive, whereas nearly all (97%) of the GluR2/3-immunoreactive neurones were not GABA- or glycin e-immunoreactive. We carried out double-immunofluorescence and confoca l microscopy to provide further information on the neurochemistry of c ells that express these subunits. As expected, all neurotensin-and vir tually all somatostatin-immunoreactive cells (which are thought to be excitatory interneurones) were GluR2/3- but not GluR1-immunoreactive, whereas parvalbumin-containing cells (most of which are GABAergic) pos sessed GluR1-, but usually not GluR2/3-immunoreactivity. Neurones that contained nitric oxide synthase (most of which are GABAergic) were mo re variable, with 57% GluR1-immunoreactive and 41% GluR2/3-immunoreact ive. Cholinergic neurones in lamina III (which are also GABAergic) inv ariably showed each type of GluR-immunoreactivity. These results sugge st that neuronal populations in laminae I-III have characteristic patt erns of GluR expression: GluR1 is particularly associated with inhibit ory neurones, and GluR2 with excitatory neurones. This makes it likely that some of the AMPA receptors present on the inhibitory interneuron es lack the GluR2 subunit, and may therefore have significant Ca2+-per meability.