[3H]Norepinephrine Release from Hippocampal Slices Is an In Vitro Biochemical Tool for Investigating the Pharmacological Properties of Excitatory Amino Acid Receptors

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Abstract
[3H]Norepinephrine ([3H]NE) efflux from preloaded rat hippocampal slices was increased in a dose-dependent manner by excitatory amino acids, with the following order of potencies: N-methyl-D-aspartate (NMDA) > kainic acid (KA) > L-glutamate .gtoreq. D,L-homocysteate > L-aspartate > quinolinic acid > quisqualic acid. The effect of the excitatory amino acids was blocked by physiological concentrations of Mg2+, with the exception of KA. D,L-2-Amino-7-phosphonoheptanoic acid dose-dependently inhibited the NMDA effect (ID50 = 69 .mu.M), whereas at 1 mM it was ineffective versus KA. The release of [3H]-NE induced by quinolinic acid was blocked by 0.1 mM D,L-2-amino-7-phosphonoheptanoic acid. .gamma.-D-Glutamylglycine dose-dependently inhibited the KA effect with an ID50 of 1.15 mM. Tetrodotoxin (2 .mu.M) reduced by 40 and 20% the NMDA and KA effects, respectively. The data indicate that [3H]NE release from hippocampal slices can be used as a biochemical marker for pharmacological investigations of excitatory amino acid receptors and their putative agonists and antagonists.