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Title

Dopaminergic agonists have both presynaptic and postsynaptic effects on the guinea-pig's medial vestibular nucleus neurons

Authors
Crambes, O.
Vidal, P. P.
Published in European Journal of Neuroscience. 1995, vol. 7, no. 4, p. 555-562
Abstract A number of studies have indicated a possible interaction between dopamine and the vestibular system. Using intracellular recordings in brainstem slices, we have tested the effects of dopamine and other dopaminergic compounds on guinea-pig medial vestibular nucleus (MVN) neurons. In normal medium, MVN neurons were depolarized by dopamine as well as by (-)quinpirole and piribedil, which are selective D2 dopaminergic agonists. The dependence of this effect on the presence of D2 receptors was confirmed by using (-)sulpiride, a D2 antagonist which blocked the depolarizing effect of dopamine. Dopaminergic D1 receptors were apparently not involved in this effect since a selective D1 agonist, SKF-38393, had no effect on MVN neurons and the D1 antagonist (+)SCH-23390 could not block the effect of dopamine. These depolarizing responses to dopamine must be due to a presynaptic action on terminals that normally release GABA spontaneously on MVN neurons, and tonically maintain them in a state of hyperpolarization. Indeed, such a spontaneous release was demonstrated to occur in the slice since application of bicuculline, a GABAA antagonist, depolarized MVN neurons in normal saline, but not in a high Mg2+/low Ca2+ solution known to block synaptic transmission. When dopamine was applied in conditions in which no GABAA-dependent transmission could occur (either in the presence of bicuculline or in a high Mg2+/low Ca2+ solution) only a hyperpolarizing, most probably postsynaptic, effect occurred. These results indicate that dopamine might exert in vivo a significant modulatory action on the vestibular system, either by a direct action on the vestibular neurons or by modulation of GABAergic transmission.
Keywords AnimalsBicuculline/pharmacologyCalcium/physiologyDopamine/pharmacologyDopamine Agonists/ pharmacologyElectrophysiologyGuinea PigsMicroelectrodesNeurons/ drug effectsPatch-Clamp TechniquesPiribedil/pharmacologyReceptors, Dopamine D1/agonistsReceptors, Dopamine D2/agonistsReceptors, Presynaptic/ drug effectsSynapses/ drug effectsTetrodotoxin/pharmacologyVestibular Nuclei/ cytology/ drug effects
Stable URL http://archive-ouverte.unige.ch/unige:10138
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PMID: 7620607
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