INHIBITORY SPINAL PROJECTION NEURONS ARE CRITICAL FOR MOTOR COORDINATION AND LEARNING

Objective: The somatosensory system processes various stimuli and transmits sensory signals to the brain through projection neurons in the spinal cord. Inhibitory long-range projection neurons in the spinal cord have always been overlooked, as it has generally believed that the sensory system is predominantly composed of excitatory long-range projections neurons. Our present study aims to identify the long-range inhibitory projection neurons in the spinal cord and explore how the inhibitory ascending signals they generate shape motor outputs.
Methods: The identification of inhibitory spinal projection neurons (SPNs) was performed using a combination of viral tracing, immunostaining and RNAscope techniques. The properties of SPNs were characterized by electrophysiological recordings. The function of inhibitory SPNs was assessed through sensory- and motor-related behavioral evaluations.
Results: (1) A population of inhibitory neurons in the spinal cord formed a specialized ascending pathway that innervated a nucleus in the medulla. (2) The inhibitory SPNs were intermingled with their excitatory counterparts in the spinal cord. (3) Inhibitory SPNs exhibited distinct electrophysiological properties compared to excitatory SPNs. (4) The inhibitory SPNs were required for motor coordination and motor learning.
Conclusion: The inhibitory ascending signals are required for motor coordination and motor learning.