Inhibitory interneurons within the deep dorsal horn integrate convergent sensory input to regulate motor performance

SUMMARY

To achieve smooth motor performance in a rich and changing sensory environment, motor output must be constantly updated in response to sensory feedback. Although proprioception and cutaneous information are known to modulate motor output, it is unclear whether they work together in the spinal cord to shape complex motor actions such as locomotion. Here we identify the medial deep dorsal horn (mDDH) as a “hot zone” of convergent proprioception and cutaneous input for locomotion. Due to increased responsiveness to sensory input, inhibitory interneurons in the mDDH area are preferentially recruited in locomotion. To study inhibitory interneurons in this area, we utilize an intersectional genetic strategy to isolate and ablate a population of parvalbumin-expressing glycinergic interneurons in the mDDH (dPVs). Using histological and electrophysiological methods we find that dPVs integrate proprioceptive and cutaneous inputs while targeting ventral horn motor networks, suggesting a role in multimodal sensory processing for locomotion. Consistent with this, dPVs ablation alters step cycle parameters and kinematics in a speed and phase dependent manner. Finally, we use EMG muscle recordings to directly show that dPVs are part of a cutaneous-motor pathway. Our results indicate that dPVs form a critical node in the spinal sensorimotor circuitry.