A quantitative pharmacological analysis of some excitatory amino acid receptors in the mouse neocortex in vitro

Abstract

1The effects of 2-amino-5-phosphonovalerate and kynurenate, either alone or in combination, were tested on responses evoked by the excitatory amino acid agonists quinolinate, ibotenate, Nmethyl-D-aspartate and N-methyl-DL-aspartate by use of an in vitro preparation of mouse neocortex and artificial cerebrospinal fluid nominally free of magnesium. 2 Schild plots for 2-amino-5-phosphonovalerate, using each of the excitatory amino acids, were linear and had a slope not significantly different from one. The apparent pA2 values for 2-amino-5-phosphonovalerate using each of the excitatory amino acids were 4.98 (quinolinate), 5.00 (N-methyl-DL-aspartate), 4.92 (N-methyl-D-aspartate) and 5.05 (ibotenate). The apparent pA2 obtained using ibotenate was distinct from that of N-methyl-D-aspartate but there were no significant differences between pA2 estimates for quinolinate, N-methyl-D-aspartate or N-methyl-DL-aspartate. 3 Schild plots for kynurenate, using each of the excitatory amino acids, were linear and had a slope of 1.36 + 0.03, significantly greater than one. The estimated apparent pA2 values for kynurenate were 3.65 (quinolinate), 3.71 (N-methyl-DL-aspartate), 3.65 (N-methyl-D-aspartate) and 3.89 (ibotenate). The apparent pA2 obtained using ibotenate was distinct from that of the other agonists. 4 Experiments using combinations of 2-amino-5-phosphonovalerate and kynurenate indicated that both antagonists apparently acted competitively at receptors activated by ibotenate or by quinolinate. 5 These results indicate that ibotenate acts at a site distinct from that of quinolinate, N-methyl-Daspartate and N-methyl-DL-aspartate.

Non‐Competitive Antagonism of N‐Methyl‐D‐Aspartate by Displacement of an Endogenous Glycine‐Like Substance

“…Thus the lower concentrations of kynurenate appear to reduce NMDA not by an action at the glycine site but presumably at the NMDA recognition site itself. Evidence for such a mixed action of kynurenate has been reported previously Burton et al, 1988;Kemp et al, 1987;Mayer et al, 1988;Ascher et al, 1988;Birch et al, 1988a).…”

Amino acid pharmacology in neocortical slices: evidence for bimolecular actions from an extension of the Hill and Gaddum‐Schild equations

“…The neocortical slice preparation, originally described using rat tissue by Harrison & Simmonds (1985) and subsequently for mouse brain by Burton et al (1988) consists of slices of cerebral tissue containing cerebral cortex and corpus callosum, mounted in a two-chambered bath. The ventral margin of the cortex passes through a greased slot such that the corpus callosum is in one chamber and almost all of the cortical tissue in the other.…”

“…We then show how the classical Gaddum-Schild plot can be modified for situations in which the agonist:receptor stoichiometry is not 1:1 as traditionally assumed. Finally we illustrate the application of our model to data recently obtained by Burton et al (1988) on the actions of excitatory amino acids in the neocortical slice preparation.…”

Ammonium acetate inhibits ionotropic receptors and differentially affects metabotropic receptors for glutamate

“…The cortical wedge preparation described by Harrison and Simmonds (1985) and modified by Burton et al (1988) was used as previously described (Moroni et al, 1991;Carlfi and Moroni, 1992). Briefly, wedges were placed into a two-compartment bath and silicone grease was placed between the two portions of the bath.…”