Identified interneurons contributing to locomotion in mammals

The neural circuits which generate hindlimb locomotion are located in the spinal cord. These circuits are composed of several distinct interneuron populations organized to generate rhythm and recruit motor neurons in a precise pattern. Genetic techniques to target interneuron populations based on the expression of transcription factors during development together with computational modeling have significantly advanced our understanding of spinal locomotor circuits. Specific genetically identified interneuron populations contribute to rhythm generation, flexor–extensor alternation, and left–right coordination. Simulations of possible circuit architectures have suggested plausible mechanisms for these functions. Interneuron population-specific spinal cord injury (SCI)-induced plasticity and participation in recovery is beginning to be revealed and may benefit the targeting of spinal locomotor circuits for gait rehabilitation. Here, we review progress made with regards to genetically identified populations of spinal interneurons, function of specific interneurons during locomotion, contributions of interneuron populations to locomotor circuitry, and potential avenues for interneuron-specific targeting after SCI.