title: The influence of increased membrane conductance on response properties of spinal motoneurons.
abstract: During functional spinal neural network activity motoneurons receive massive synaptic excitation and inhibition, and their membrane conductance increases considerably - they are switched to a high-conductance state. High-conductance states can substantially alter response properties of motoneurons. In the present study we investigated how an increase in membrane conductance affects spike frequency adaptation, the gain (i.e., the slope of the frequency-current relationship) and the threshold for action potential generation. We used intracellular recordings from adult turtle motoneurons in spinal cord slices. Membrane conductance was increased pharmacologically by extracellular application of the GABAA receptor agonist muscimol. Our findings suggest that an increase in membrane conductance of about 40-50% increases the magnitude of spike frequency adaptation, but does not change the threshold for action potential generation. Increased conductance causes a subtractive rather than a divisive effect on the initial and the early frequency-current relationships and may have not only a subtractive but also a divisive effect on the steady-state frequency-current relationship.
authors.affiliation: Department of Neurobiology and Biophysics, Vilnius University, Sauletekio ave. 7, LT-10222 Vilnius, Lithuania. Electronic address: ramunas.grigonis@gmail.com.
authors.forename: Ramunas
authors.initials: R
authors.lastname: Grigonis
authors.affiliation: Department of Neuroscience and Pharmacology, University of Copenhagen, Blegdamsvej 3B, DK-2200 Copenhagen, Denmark.
authors.forename: Robertas
authors.initials: R
authors.lastname: Guzulaitis
authors.affiliation: Department of Neurobiology and Biophysics, Vilnius University, Sauletekio ave. 7, LT-10222 Vilnius, Lithuania.
authors.forename: Rokas
authors.initials: R
authors.lastname: Buisas
authors.affiliation: Department of Neurobiology and Biophysics, Vilnius University, Sauletekio ave. 7, LT-10222 Vilnius, Lithuania.
authors.forename: Aidas
authors.initials: A
authors.lastname: Alaburda
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D008564:Membrane Potentials / Q000502:physiology*; D009046:Motor Neurons / Q000187:drug effects* / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology; D014426:Turtles / Q000502:physiology
keywords: Action potential threshold; Frequency-current relationship; Gain; High-conductance state; Motoneuron; Spike frequency adaptation