Inhibition of Excitatory Amino Acid‐Stimulated Phosphoinositide Hydrolysis in the Neonatal Rat Hippocampus by 2‐Amino‐3‐Phosphonopropionate

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Abstract
The effects of excitatory amino acid agonists and .alpha.-amino-.omega.-phosphonocarboxylic acid antagonists on phosphoinositide hydrolysis in hippocampal slices of the 7-day neonatal rat were examined. Significant stimuation of [3H]inositol monophosphate formation was observed with ibotenate, quisqualate, L-glutamate, L-aspartate, .alpha.-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, L-homocysteate and kainate. N-Methyl-D-aspartate had no effect. Of these agonists, ibotenate and quisqualate were the most potent and efficacious. Stimulations by ibotenate and quisqualate were partially inhibited by L-2-amino-4-phosphonobutyrate (10-3 M), but this antagonist had no effect on L-glutamate, .alpha.-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, or kainate. At 10-3 M, D,L-2-amino-3-phosphonopropionate completely inhibited ibotenate and quisqualate stimulations, partially inhibited L-glutamate stimulation, and had no effect on .alpha.-amino-3-hydroxy-5-methyl-4-isozazolepropionic acid-, kainate-, or carbachol-induced [3H]inositol monophosphate formation. Concentration-effect experiments showed D,L-2-amino-3-phosphonopriopionate to be five times more potent as an antagonist of ibotenate-stimulated phosphoinositide hydrolysis than L-2-amino-4-phosphonobutyrate. Thus in the neonatal rat hippocampus, like in the adult rat brain, D,L-2-amino-3-phosphonopropionate is a selective and relatively potent inhibitor of excitatory amino acid-stimulated phosphoinositide hydrolysis. Because this glutamate receptor is uniquently sensitive to D,L-2-amino-3-phosphonopropionate, these studies provide further pharmacological evidence for the existence of a novel excitatory amino acid receptor subtype that is coupled to phosphoinositide hydrolysis in brain.

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