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)
Jaffé
E H
EH
Laboratorio de Neuroquímica, Instituto Venezolano de Investigaciones Científicas, Caracas.
Vaello
M L
ML
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D018756:GABA Antagonists; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D007608:Kainic Acid / Q000494:pharmacology; D008297:Male; D009830:Olfactory Bulb / Q000378:metabolism*; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000037:antagonists & inhibitors; D013378:Substantia Nigra / Q000378:metabolism*; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000596:Amino Acids; D002121:Calcium Channel Blockers; D018756:GABA Antagonists; D005971:Glutamates; D014316:Tritium; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D011188:Potassium; D007608:Kainic Acid