Figure 1. Groups of lumbar Pitx2⁺ interneurons are rhythmically active during fictive locomotion.

(a) Illustration of ventral root recordings and Ca²⁺ imaging from Pitx2⁺ interneurons (green) in hemisected spinal cords from Pitx2::Cre;GCAMP6 mice. (b) Pitx2⁺ interneurons visualized in the L1-3 upper lumbar regions in a neonatal hemisected spinal cord from a Pitx2::Cre;GCAMP6 mouse. (c) Ventral root output and examples of Ca²⁺ imaging traces from the four neurons marked in (b). (d) Phase plots depicting relationships between Ca²⁺ transients in interneurons and ventral root output for three neurons in L1-3 (top) and three neurons in L4-6 (bottom). Blue points represent the phasing of individual Ca²⁺ transients within a locomotor cycle, red points represent the mean direction and strength of the phasing for each neuron, and grey shading indicates the average duration of upper lumbar-related bursts. (e) Summary graph of mean direction and strength of phasing for all interneurons analyzed (L1-3, n=31; and L4-6, n=19).