Persistent Inward Currents in Spinal Motoneurons and Their Influence on Human Motoneuron Firing Patterns

Persistent inward currents (PICs) are present in many types of neurons and likely have diverse functions. In spinal motoneurons, PICs are especially strong, primarily located in dendritic regions, and subject to particularly strong neuromodulation by the monoamines serotonin and norepinephrine. Beca...

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Published in:The Neuroscientist (Baltimore, Md.) Md.), 2008-06, Vol.14 (3), p.264-275
Main Authors: Heckman, C.J., Johnson, Michael, Mottram, Carol, Schuster, Jenna
Format: Article
Language:English
Subjects:
Action Potentials - physiology
Animals
Biogenic Monoamines - physiology
Dendrites - physiology
Dendrites - ultrastructure
Electric properties
Electrophysiology
Humans
Influence
Ion Channels - physiology
Monoamines
Motor neurons
Motor Neurons - physiology
Muscle, Skeletal - innervation
Muscle, Skeletal - physiology
Neural Inhibition - physiology
Noradrenaline
Physiological aspects
Properties
Serotonin
Spinal Cord - cytology
Spinal Cord - physiology
Spine
Synaptic Transmission - physiology
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Summary:Persistent inward currents (PICs) are present in many types of neurons and likely have diverse functions. In spinal motoneurons, PICs are especially strong, primarily located in dendritic regions, and subject to particularly strong neuromodulation by the monoamines serotonin and norepinephrine. Because motoneurons drive muscle fibers, it has been possible to study the functional role of their PICs in motor output and to identify PIC-mediated effects on motoneuron firing patterns in human subjects. The PIC markedly amplifies synaptic input, up to fivefold or more, depending on the level of monoaminergic input. PICs also tend to greatly prolong input time course, allowing brief inputs to initiate long-lasting self-sustained firing (i.e., bistable behavior). PIC deactivation usually requires inhibitory input and PIC amplitude can increase to repeated activation. All of these behaviors markedly increase motoneuron excitability. Thus, in the absence of monoaminergic input, motoneuron excitability is very low. Yet PICs have another effect: once active, they tend to sharply limit efficacy of additional synaptic input. All of these PIC effects have been detected in motoneuron firing patterns in human subjects and, hence, PICs are likely a fundamental component of normal motor output. NEUROSCIENTIST 14(3):264–275, 2008. DOI: 10.1177/1073858408314986
ISSN:1073-8584
1089-4098
DOI:10.1177/1073858408314986