A further evaluation of the effects of K+ depolarization on glutamate-evoked [3H]dopamine release from striatal slices.
Exogenous glutamate will evoke dopamine (DA) release from striatal slices in vitro. To further characterize glutamate-evoked DA release from striatal slices, experiments were designed to: 1) determine if sufficient endogenous glutamate can be released in vitro to presynaptically mediate [3H]DA release in the absence of Mg++ and 2) reevaluate how K+ depolarization affects glutamate-evoked [3H]DA release. Removal of Mg++ to potentiate N-methyl-D-aspartate (NMDA) receptor-mediated DA release increased 15 mM K(+)-evoked [3H]DA release to about 200% of control. The potentiation of this release was probably not mediated by NMDA receptors because it was not blocked by the glutamate receptor antagonists MK-801, 6,7-dinitroquinoxalinedione (DNQX) or kynurenate. Furthermore, the removal of Mg++ increased DA release substantially (200%) in the presence of 5 microM sulpiride and 10 microM nomifensine, indicating that DA reuptake and DA D2 autoreceptors are not primarily responsible for increased DA release. In the absence of Mg++, depolarization produced by 20 mM or greater [K+] inhibited DA released by exogenous glutamate, whereas a much higher [K+] was necessary to evoke endogenous glutamate release. In the presence of 1.5 mM Mg++, a reduction of the "Mg++ blockade" of NMDA receptors by 15 mM K+ depolarization during glutamate-evoked DA release was evaluated with and without the DA reuptake inhibitor nomifensine and the DA D2 antagonist sulpiride. DA released by K+ depolarization (Mg++ present) was markedly increased by 1 mM glutamate, but this effect was only partially reversed by kynurenate or high concentrations of either MK-801 (25 microM) or DNQX (100 microM).(ABSTRACT TRUNCATED AT 250 WORDS)
Bowyer
J F
JF
Division of Neurotoxicology, National Center for Toxicological Research, Jefferson, Arkansas.
Newport
G D
GD
Lipe
G W
GW
Frame
L T
LT
D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects* / Q000378:metabolism; D046508:Culture Techniques; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004298:Dopamine / Q000378:metabolism*; D018691:Excitatory Amino Acid Antagonists; D005260:Female; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D007736:Kynurenic Acid / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000187:drug effects
D018691:Excitatory Amino Acid Antagonists; D005971:Glutamates; D011810:Quinoxalines; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D018698:Glutamic Acid; C056723:FG 9041; D016291:Dizocilpine Maleate; D007736:Kynurenic Acid; D011188:Potassium; D004298:Dopamine