Autoradiographic localisations of glutamatergic ligand binding sites in Xenopus brain

In the Xenopus central nervous system the binding sites for [3H]kainate and [3H]alpha-amino-3-hydroxy-5-methylisoxazolepropionate [( 3H]AMPA) are highly localised and the distributions of both ligands are largely coincident. The telencephalon was the most strongly labelled area with a relatively uniform distribution of binding sites. In addition, the infundibulum and the cerebellum were also heavily labelled. Areas containing a lower density of binding sites included the septum, the thalamus and the optic lobes. [3H]Kainate binding was potently inhibited by 1 microM AMPA in the presence of 0.1 M KSCN and [3H]AMPA binding was blocked by 1 microM kainate. These data are consistent with the hypothesis that kainate and AMPA bind to the same site on a single protein entity and that this unitary AMPA/KA binding protein may constitute the predominant type of excitatory amino acid receptor in the Xenopus brain.