Depression of mGluR-mediated IPSCs by 5-HT in dopamine neurons of the rat substantia nigra pars compacta

Authors

  • E. Paolucci,

    1. Fondazione Santa Lucia IRCCS, Experimental Neurology, Via Ardeatina 306, 00179 Rome, Italy
    2. Department of Neuroscience, University of Tor Vergata, Rome, Italy
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    • *

      E.P. and N.B. contributed equally to this work.

  • N. Berretta,

    1. Fondazione Santa Lucia IRCCS, Experimental Neurology, Via Ardeatina 306, 00179 Rome, Italy
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    • *

      E.P. and N.B. contributed equally to this work.

  • A. Tozzi,

    1. Fondazione Santa Lucia IRCCS, Experimental Neurology, Via Ardeatina 306, 00179 Rome, Italy
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  • G. Bernardi,

    1. Fondazione Santa Lucia IRCCS, Experimental Neurology, Via Ardeatina 306, 00179 Rome, Italy
    2. Department of Neuroscience, University of Tor Vergata, Rome, Italy
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  • N. B. Mercuri

    1. Fondazione Santa Lucia IRCCS, Experimental Neurology, Via Ardeatina 306, 00179 Rome, Italy
    2. Department of Neuroscience, University of Tor Vergata, Rome, Italy
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: Dr Nicola Berretta, as above.
E-mail: n.berretta@hsantalucia.it.

Abstract

Dopamine neurons of the substantia nigra pars compacta receive a prominent serotonin (5-HT) projection from the dorsal raphe nucleus and important functional interactions between the serotonergic and the dopaminergic system have been postulated. In the present report we examined the role of 5-HT in the modulation of the metabotropic glutamate receptor-mediated inhibitory postsynaptic current (mGluR-IPSC) in midbrain dopamine neurons, and we found a reversible depression of this synaptic response at concentrations of 5-HT ranging from 100 nm to 30 µm (EC50 1.06 µm). This resulted in a shift towards excitation of the overall dopamine neuron response to glutamatergic synaptic input. This effect was not because of a direct modulation of the Ca2+-sensitive K+ conductances underlying the mGluR-IPSC, but was associated with a decrease in the intracellular calcium signal triggered by mGluR stimulation. Similar results were obtained with α-methyl-5-hydroxytryptamine and 5-methoxytryptamine, but not with 5-carboxamidotryptamine or 1-(3-chlorophenyl) piperazine. No significant depression of the mGluR-IPSC by 5-HT was observed in the presence of the 5-HT2 antagonist cinanserin or the 5-HT4 receptor antagonist RS 23597–190, whereas the 5-HT2C antagonist RS 102221 was ineffective. Our results demonstrate a powerful inhibition of the mGluR-IPSC by 5-HT in midbrain dopamine neurons, most probably through stimulation of 5-HT2A and 5-HT4 receptors.

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