Functional and biochemical characteristics of a putative quisqualate-type receptor in rat striatum: effect of brain lesions

In vivo regulation of extracellular dopamine in the neostriatum: influence of impulse activity and local excitatory amino acids

It has been suggested that dopamine release can be evoked by excitatory amino acids acting on dopaminergic terminals, as well as by the classical process of impulse-evoked exocytosis. We used in vivo microdialysis to examine whether endogenous excitatory amino acids locally evoked dopamine efflux under basal conditions. Infusion of N-methyl-d-aspartate (NMDA) or kainate into the neostriatum increased extracellular dopamine, and this effect was blocked by co-infusion of 2-amino-5-phosphonovalerate (APV) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), respectively. However, neither these antagonists nor kynurenate decreased extracellular dopamine when administered alone. In contrast, infusion of tetrodotoxin into the medial forebrain bundle reduced extracellular dopamine to below the limit of detection of our assay. These and other findings reviewed in this report suggest to us that extracellular dopamine in the neostriatum is not stimulated locally by endogenous excitatory amino acids.

Release of gamma-[3H]aminobutyric acid from rat olfactory bulb and substantia nigra: differential modulation by glutamic acid

We have studied the glutamate modulation of gamma-[3H]aminobutyric acid ([3H]GABA) release from GABAergic dendrites of the external plexiform layer of the olfactory bulb and from GABAergic axons of the substantia nigra. In the olfactory bulb, [3H]GABA release was induced by high K+ and kainate, and not by aspartate and glutamate alone. However, when the tissue was conditioned by a previous K+ depolarization, glutamate and aspartate caused [3H]GABA release. The effect of glutamate was significantly enhanced when the GABA uptake mechanism was blocked by nipecotic acid. N-Methyl-D-aspartate and quisqualate did not cause [3H]GABA release under the same conditions. The acidic amino acid receptor antagonist 2-amino-4-phosphonobutyric acid and the N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovaleric acid significantly inhibited the K+-glutamate- and the kainate-induced [3H]GABA release. Mg2+ (5 mM), which blocks the N-methyl-D-aspartate receptors, significantly inhibited the K+-glutamate-induced but not the kainic acid-induced [3H]GABA release. The K+-glutamate-stimulated release, but not the K+-stimulated [3H]GABA release, was strongly inhibited by Na+-free solutions or by 300 nM tetrodotoxin. Apparently the glutamate-induced release of [3H]GABA occurs through an interneuron because it is dependent on the presence of nerve conduction. In the substantia nigra no [3H]GABA release was elicited by any of the glutamate agonists tested. The present results clearly differentiate between the effects of glutamate on the release of [3H]GABA from the substantia nigra and from the olfactory bulb.(ABSTRACT TRUNCATED AT 250 WORDS)