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Changes in extracellular dopamine levels in the nucleus accumbens induced by low frequency stimulation of the ventral subiculum/CA1 region of the hippocampus Taepavarapruk, Pornnarin


The present study utilized microdialysis in freely-moving rats to investigate 1) changes in extracellular dopamine (DA) level in the nucleus accumben (NAc) induced by electrical stimulation of the ventral subiculum/CAl (Vsub/CAl) area of hippocampus, and 2) the role of metabotropic glutamate receptors (mGluRs) in mediating DA release in the NAc induced by low frequency stimulation of Vsub/CAl. It has been shown that electrical stimulation of Vsub/CAl at 2 Hz for 100 secinduces a significant decrease (p < 0.05) in basal DA levels in the NAc which is long lasting throughout the 2 hr monitoring period. Reverse dialysis of the specific antagonist at mGluRl/2, (+)-α-methyl-4-carboxyphenylglycine (MCPG), at doses 10 μM and 100 μM, did not prevent the suppressive effects on DA levels induced by low frequency stimulation of Vsub/CAl. However, reverse dialysis with the group 2 and 3 mGluR antagonist, (+)-α-methyl-4-phosphonophenylglycine (MPPG), at dose of 100 μM and 1mM, significantly blocked the prolonged suppressive effects of 2 Hz Vsub/CAl stimulation on DA efflux. These results suggest that presynaptic group 2 and 3 mGluRs are likely to be involved in a mechanism underlying the late phase of synaptic transmission at glutamatergic-dopaminergic synapses in the NAc. However, the question which specific mGluR subtypes are responsible for these initial and long lasting suppressive mechanisms will require further research.

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