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Dynamic interactions of excitatory and inhibitory inputs in hypoglossal motoneurones: respiratory phasing and modulation by PKA
Author(s) -
Saywell Shane A.,
Feldman Jack L.
Publication year - 2004
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.054528
Subject(s) - bicuculline , inhibitory postsynaptic potential , excitatory postsynaptic potential , strychnine , neuroscience , chemistry , motor neuron , biology , spinal cord , gabaa receptor , receptor , biochemistry
The balance of excitation and inhibition converging upon a neurone is a principal determinant of neuronal output. We investigated the role of inhibition in shaping and gating inspiratory drive to hypoglossal (XII) motoneuronal activity. In neonatal rat medullary slices that generate a spontaneous respiratory rhythm, patch‐clamp recordings were made from XII motoneurones, which were divided into three populations according to their inhibitory inputs: non‐inhibited, inspiratory‐inhibited and late‐inspiratory‐inhibited. In late‐inspiratory‐inhibited motoneurones, blockade of GABA A receptors with bicuculline abolished inspiratory‐phased inhibition and increased the duration of inspiratory drive currents. In inspiratory‐inhibited motoneurones, bicuculline abolished phasic inhibition, which frequently revealed excitatory inspiratory drive currents. In non‐inhibited motoneurones, neither bicuculline nor strychnine markedly changed inspiratory drive currents. Inhibitory currents in XII motoneurones were potentiated by protein kinase A (PKA) activity. Intracellular dialysis of the catalytic subunit of PKA or bath application of the PKA activator Sp‐cAMP significantly increased the amplitude of expiratory‐phased IPSCs without any change in IPSP frequency. Inspiratory‐phased inhibition in inspiratory‐inhibited motoneurones was potentiated by Sp‐cAMP. We conclude that inspiratory‐phased inhibition is prevalent in neonatal XII motoneurones and plays an important role in shaping motoneuronal output. These inhibitory inputs are modulated by PKA, which also modulates excitatory inputs.