Tuning and playing a motor rhythm: how metabotropic glutamate receptors orchestrate generation of motor patterns in the mammalian central nervous system

Authors

  • Andrea Nistri,

    1. Neurobiology Sector, CNR-INFM DEMOCRITOS National Simulation Center, and S.P.I.N.A.L. Laboratory, International School for Advanced Studies (SISSA), Via Beirut 4, 34014 Trieste, Italy
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  • Konstantin Ostroumov,

    1. Neurobiology Sector, CNR-INFM DEMOCRITOS National Simulation Center, and S.P.I.N.A.L. Laboratory, International School for Advanced Studies (SISSA), Via Beirut 4, 34014 Trieste, Italy
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  • Elina Sharifullina,

    1. Neurobiology Sector, CNR-INFM DEMOCRITOS National Simulation Center, and S.P.I.N.A.L. Laboratory, International School for Advanced Studies (SISSA), Via Beirut 4, 34014 Trieste, Italy
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  • Giuliano Taccola

    1. Neurobiology Sector, CNR-INFM DEMOCRITOS National Simulation Center, and S.P.I.N.A.L. Laboratory, International School for Advanced Studies (SISSA), Via Beirut 4, 34014 Trieste, Italy
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  • Authors are in alphabetical order since they all contributed equally to this work.

Corresponding author A. Nistri: SISSA, via Beirut 4, 34014 Trieste, Italy. Email: nistri@sissa.it

Abstract

Repeated motor activities like locomotion, mastication and respiration need rhythmic discharges of functionally connected neurons termed central pattern generators (CPGs) that cyclically activate motoneurons even in the absence of descending commands from higher centres. For motor pattern generation, CPGs require integration of multiple processes including activation of ion channels and transmitter receptors at strategic locations within motor networks. One emerging mechanism is activation of glutamate metabotropic receptors (mGluRs) belonging to group I, while group II and III mGluRs appear to play an inhibitory function on sensory inputs. Group I mGluRs generate neuronal membrane depolarization with input resistance increase and rapid fluctuations in intracellular Ca2+, leading to enhanced excitability and rhythmicity. While synchronicity is probably due to modulation of inhibitory synaptic transmission, these oscillations occurring in coincidence with strong afferent stimuli or application of excitatory agents can trigger locomotor-like patterns. Hence, mGluR-sensitive spinal oscillators play a role in accessory networks for locomotor CPG activation. In brainstem networks supplying tongue muscle motoneurons, group I receptors facilitate excitatory synaptic inputs and evoke synchronous oscillations which stabilize motoneuron firing at regular, low frequency necessary for rhythmic tongue contractions. In this case, synchronicity depends on the strong electrical coupling amongst motoneurons rather than inhibitory transmission, while cyclic activation of KATP conductances sets its periodicity. Activation of mGluRs is therefore a powerful strategy to trigger and recruit patterned discharges of motoneurons.

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