PLASTIC REMODELING OF SPINAL NEURONS AND PERICELLULAR SYNAPSES FOLLOWING PERIPHERAL NERVE TRANSECTION

Peripheral nerve injury induces plastic remodeling in the spinal cord, yet the temporal characteristics of synaptic reorganization remain incompletely understood. This study investigated time-dependent changes in neurons and pericellular synapses in the lumbar spinal cord following sciatic nerve transection in rats. Lumbar spinal cords were analyzed at 2, 4, and 6 weeks after unilateral transection and compared with sham-operated controls. Corticospinal axons were labeled with biotinylated dextran amine, motoneuron soma volume was assessed using Fluoro-Gold retrograde labeling, cholinergic interneurons were identified by vesicular acetylcholine transporter immunoreactivity, and pericellular synapses were evaluated using vGlut1 and vesicular acetylcholine transporter markers. No significant differences were observed in corticospinal axonal volume between transection and sham groups at any time point. Motoneuron soma volume was significantly reduced at 6 weeks after transection. In contrast, the number of cholinergic interneurons was preserved throughout the 6-week observation period. Pericellular synapses surrounding motoneurons were reduced following nerve transection. Conversely, pericellular synapses associated with cholinergic interneurons exhibited a distinct temporal pattern, with a significant increase in vGlut1-positive synapses at 2 and 6 weeks after injury, while vesicular acetylcholine transporter–positive synapses were significantly increased at 2 and 4 weeks. These findings indicate that peripheral nerve transection induces selective and time-dependent synaptic reorganization in the spinal cord without loss of cholinergic interneurons. The differential temporal enhancement of excitatory and cholinergic inputs onto cholinergic interneurons may represent dynamic compensatory circuit-level adaptations following peripheral nerve injury.