Primacy of Flexor Locomotor Pattern Revealed by Ancestral Reversion of Motor Neuron Identity

Overview

Journal Cell

Publisher Cell Press

Specialty Cell Biology

Date 2015 Jul 18

PMID 26186188

Citations 41

Authors

Timothy A Machado

Eftychios Pnevmatikakis

Liam Paninski

Thomas M Jessell

Andrew Miri

Affiliations

Soon will be listed here.

Abstract

Spinal circuits can generate locomotor output in the absence of sensory or descending input, but the principles of locomotor circuit organization remain unclear. We sought insight into these principles by considering the elaboration of locomotor circuits across evolution. The identity of limb-innervating motor neurons was reverted to a state resembling that of motor neurons that direct undulatory swimming in primitive aquatic vertebrates, permitting assessment of the role of motor neuron identity in determining locomotor pattern. Two-photon imaging was coupled with spike inference to measure locomotor firing in hundreds of motor neurons in isolated mouse spinal cords. In wild-type preparations, we observed sequential recruitment of motor neurons innervating flexor muscles controlling progressively more distal joints. Strikingly, after reversion of motor neuron identity, virtually all firing patterns became distinctly flexor like. Our findings show that motor neuron identity directs locomotor circuit wiring and indicate the evolutionary primacy of flexor pattern generation.

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