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Neuron. 2011 Sep 22;71(6):1071-84. doi: 10.1016/j.neuron.2011.07.011. Epub 2011 Sep 21.

Identification of minimal neuronal networks involved in flexor-extensor alternation in the mammalian spinal cord.

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Mammalian Locomotor Laboratory, Department of Neuroscience, Karolinska Institutet, Stockholm S-17177, Sweden.


Neural networks in the spinal cord control two basic features of locomotor movements: rhythm generation and pattern generation. Rhythm generation is generally considered to be dependent on glutamatergic excitatory neurons. Pattern generation involves neural circuits controlling left-right alternation, which has been described in great detail, and flexor-extensor alternation, which remains poorly understood. Here, we use a mouse model in which glutamatergic neurotransmission has been ablated in the locomotor region of the spinal cord. The isolated in vitro spinal cord from these mice produces locomotor-like activity-when stimulated with neuroactive substances-with prominent flexor-extensor alternation. Under these conditions, unlike in control mice, networks of inhibitory interneurons generate the rhythmic activity. In the absence of glutamatergic synaptic transmission, the flexor-extensor alternation appears to be generated by Ia inhibitory interneurons, which mediate reciprocal inhibition from muscle proprioceptors to antagonist motor neurons. Our study defines a minimal inhibitory network that is needed to produce flexor-extensor alternation during locomotion.

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