Summation of excitatory and inhibitory synaptic inputs by motoneurons with highly active dendrites. J Neurophysiol 2008 Apr;99(4):1643-52
Date
02/01/2008Pubmed ID
18234978Pubmed Central ID
PMC3803147DOI
10.1152/jn.01253.2007Scopus ID
2-s2.0-40949096737 (requires institutional sign-in at Scopus site) 29 CitationsAbstract
We investigated summation of steady excitatory and inhibitory inputs in spinal motoneurons using an in vivo preparation, the decerebrate cat, in which neuromodulatory input from the brain stem facilitated a strong persistent inward current (PIC) in dendritic regions. This dendritic PIC amplified both excitatory and inhibitory synaptic currents two- to threefold, but within different voltage ranges. Amplification of excitatory synaptic current peaked at voltage-clamp holding potentials near spike threshold (about -55 to -50 mV), whereas amplification of inhibitory current peaked at significantly more depolarized levels (about -45 to -40 mV). Thus the linear sum of excitatory and inhibitory currents tended to vary from net excitatory to net inhibitory as holding potential was depolarized. The actual summed currents, however, diverged from the predicted linear currents. At the peak of excitation, summation averaged about 15% sublinear (actual sum was less positive than the linear sum). In contrast, at the peak of inhibition, summation averaged about 18% supralinear (actual more positive than linear). Moreover, these nonlinear effects were substantially larger in cells where the variation from peak excitation to peak inhibition for linear summation was larger. When descending neuromodulatory input was eliminated by acute spinalization, PIC amplification was not observed and summation tended to be either sublinear or approximately linear, depending on input source. Overall, in cells with strong PICs, nonlinear summation of excitation and inhibition does occur, but this nonlinearity results in a more consistent relationship between membrane potential and the summed excitatory and inhibitory current.
Author List
Hyngstrom AS, Johnson MD, Heckman CJAuthor
Allison Hyngstrom PhD Associate Professor in the Physical Therapy department at Marquette UniversityMESH terms used to index this publication - Major topics in bold
AnimalsBiogenic Monoamines
Cats
Decerebrate State
Dendrites
Electrophysiology
Interneurons
Membrane Potentials
Motor Neurons
Neural Conduction
Synapses
