Regulation of [3H]norepinephrine release by N-methyl-D-aspartate receptors in minislices from the dentate gyrus and the CA1-CA3 area of the rat hippocampus
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Abstract
It has been reported previously that N-methyl-D-aspartic acid induces a significant
release of [3H]norepinephrine preaccumulated in slices from the hippocampus. In the
present study, we investigated whether there are regional differences in the hippocampus
regarding this N-methyl-D-aspartate effect. In the absence of Mg2+, N-methyl-D-aspartate
(10-200 microM) induced the release of [3H]norepinephrine from superfused minislices
containing the dentate gyrus area or the CA1-CA3 region of the hippocampus. Such N-methyl-D-aspartate
effects on [3H]norepinephrine release were significantly higher in the dentate gyrus
than in the CA1-CA3 area. The N-methyl-D-aspartate effects in both hippocampal areas
were also reduced significantly by D-2-amino-5-phosphonovaleric acid (50 microM),
an antagonist of the N-methyl-D-aspartate receptor, and by tetrodotoxin, a blocker
of the voltage-dependent Na+ channels. The extent of this reduction was the same in
the dentate gyrus and the CA1-CA3 area. Further experiments, conducted in the presence
of Mg2+, demonstrated that N-methyl-D-aspartic acid increased K(+)-induced release
of [3H]norepinephrine from dentate gyrus minislices but not from the CA1-CA3 area.
The results are consistent with the existence of a higher density and/or different
subtypes of N-methyl-D-aspartate receptors modulating [3H]norepinephrine release in
the dentate gyrus as compared with the CA1-CA3 hippocampal area.