Regional mapping of low-affinity kainate receptors in mouse brain using [H-3](2S,4R)-4-methylglutamate autoradiography

Recent data indicate that (2S,4R)-4-methylglutamate is a selective agonist for low affinity (GluR5 and GluR6) kainate receptor subunits. In the presen t study, we have employed [H-3](2S,4R)-4-methylglutamate to examine low aff inity kainate receptor distribution in mouse brain. [H-3](2S,4R)-4-Methylgl utamate labelled a single site in murine cerebrocortical membranes (K-d = 9 .9 +/- 2.7 nM, B-max = 296.3 +/- 27.1 fmol mg protein(-1)). The binding of 8 nM [H-3](2S,4R)-4-methylglutamate was displaced by several non-NMDA recep tor ligands (K-i +/- S.E.M.): domoate (1.1 +/- 0.2 nM) > kainate (7.1 +/- 1 .1 nM) much greater than L-glutamate (187.6 +/- 31.9 nM) much greater than (S)-alpha -amino-3-hydroxy-5-methyl-4-isoazolepropionic acid (AMPA) (> 50 m uM). [H-3](2S,4R)-4-Methylglutamate autoradiography revealed a widespread r egional distribution of low affinity kainate receptors. Highest binding den sities occurred within deep layers of the cerebral cortex, olfactory bulb, basolateral amygdala and hippocampal CA3 subregion. Moderate labelling was also evident in the nucleus accumbens, dentate gyrus, caudate putamen, hypo thalamus and cerebellar granule cell layer. These data show that [H-3](2S,4 R)-4-methylglutamate is a useful radioligand for selectively labelling low affinity kainate receptors. (C) 2001 Elsevier Science B.V. All rights reser ved.