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Progress in brain research (1)
Akay, Turgay (1)
Brownstone, Robert M (1)
Brownstone, Robert M. (1)
Bui, Tuan V. (1)
Jessell, Thomas M (1)
Martin, James F (1)
Miles, Gareth B (1)
Zagoraiou, Laskaro (1)
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Spinal interneurons providing input to the final common path during locomotion
Bui, Tuan V.
Progress in brain research
As the nexus between the nervous system and the skeletomuscular system, motoneurons effect all behaviour. As such, motoneuron activity must be well-regulated so as to generate appropriately timed and graded muscular contractions. Accordingly, motoneurons receive a large number of both excitatory and inhibitory synaptic inputs from various peripheral and central sources. Many of these synaptic contacts arise from spinal interneurons, some of which belong to spinal networks responsible for the generation of locomotor activity. Although the complete definition of these networks remains elusive, it is known that the neural machinery necessary to generate the basic rhythm and pattern of locomotion is contained within the spinal cord. One approach to gaining insights into spinal locomotor networks is to describe those spinal interneurons that directly control the activity of motoneurons, so called “last-order” interneurons. In this review, we briefly survey the different populations of last-order interneurons that have been identified using anatomical, physiological, and genetic methodologies. We discuss the possible roles of these identified last-order interneurons in generating locomotor activity, and in the process, identify particular criteria that may be useful in identifying putative last-order interneurons belonging to spinal locomotor networks.
A cluster of cholinergic pre-motor interneurons modulates mouse locomotor activity
Martin, James F
Jessell, Thomas M
Miles, Gareth B
Mammalian motor programs are controlled by networks of spinal interneurons that set the rhythm and intensity of motor neuron firing. Motor neurons have long been known to receive prominent ‘C-bouton’ cholinergic inputs from spinal interneurons, but the source and function of these synaptic inputs have remained obscure. We show here that the transcription factor Pitx2 marks a small cluster of spinal cholinergic interneurons, V0C neurons, that represents the sole source of C-bouton inputs to motor neurons. The activity of these cholinergic interneurons is tightly phase-locked with motor neuron bursting during fictive locomotor activity, suggesting a role in the modulation of motor neuron firing frequency. Genetic inactivation of the output of these neurons impairs a locomotor task-dependent increase in motor neuron firing and muscle activation. Thus V0C interneurons represent a defined class of spinal cholinergic interneurons with an intrinsic neuromodulatory role in the control of locomotor behavior.
cholinergic interneurons; synapses; locomotor activity; neuromodulation
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