Characterization of glutamate and [3H]D-aspartate outflow from various in vitro preparations of the rat hippocampus.
The characteristics of high-K+ and electrically evoked endogenous glutamate and [3H]D-aspartate release have been studied in multiple in vitro preparations of the rat hippocampus (transverse slices, granule cells cultures, synaptosomes and mossy fibre synaptosomes) under similar experimental conditions. High external K+ concentrations evoked [3H]D-aspartate and endogenous glutamate overflow in a concentration-dependent manner in all preparations (except it was not possible to measure endogenous glutamate outflow from granule cells). This effect was tetrodotoxin-insensitive but partially calcium-dependent. In slices, field electrical stimulation evoked an overflow of endogenous glutamate, but not of [3H]D-aspartate, in a frequency-dependent manner. This effect was concentration-dependently amplified by the glutamate uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylic acid (t-PDC). The electrically evoked glutamate overflow in the presence of t-PDC was tetrodotoxin-sensitive and calcium-dependent. In primary dentate gyrus cell cultures, electrical stimulation evoked an overflow of [3H]D-aspartate in a frequency-dependent manner, while endogenous glutamate outflow was not detectable. This effect could be inhibited by tetrodotoxin and by the N-type calcium channel blocker omega-conotoxin GVIA. Finally, the effect of adenosine has been studied in order to assess the pharmacological modulability of [3H]D-aspartate and endogenous glutamate stimulation-induced overflow. Adenosine was found to inhibit 35 mM K(+)- and 20 Hz electrical stimulation-induced [3H]D-aspartate and endogenous glutamate overflow. These effects were all prevented by the A1 receptor antagonist 8-cyclopentyl-1,3-dimethylxanthine (CPT). These data are in line with the hypothesis that reuptake plays a role in regulating glutamate release, and that [3H]D-aspartate represents a valid marker of endogenous glutamate under most (but not all) experimental conditions.
Muzzolini
A
A
Institute of Pharmacology, University of Ferrara, Italy.
Bregola
G
G
Bianchi
C
C
Beani
L
L
Simonato
M
M
D000241:Adenosine / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D004558:Electric Stimulation; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015203:Reproducibility of Results; D013779:Tetrodotoxin / Q000494:pharmacology; D014316:Tritium
D014316:Tritium; D001224:Aspartic Acid; D018698:Glutamic Acid; D013779:Tetrodotoxin; D000241:Adenosine; D011188:Potassium; D002118:Calcium