Changes in Spinal Neural Circuit Plasticity in a Rat Sciatic Nerve Transection Model

ABSTRACT Background and Aim Changes in neural plasticity crucially modulate functional recovery after central nerve injury. To describe morphological peripheral nerve injury‐related changes, we comprehensively elucidated post‐sciatic nerve transection (post‐SNT) plasticity changes in the lumbar spinal corticospinal tract (CST), motor neurons, and cholinergic interneurons (CINs). Methods In a rat SNT model, we compared post‐SNT changes in lumbar spinal cord plasticity at 2, 4, and 6 weeks with those in the Sham group. Using neural tracers and immunohistochemistry, we labeled and analyzed the CST axonal number and volume, motor neuron cell‐body volume and synaptic inputs, and cholinergic interneuron (CIN) (medial and lateral, based on the distance from the central canal) number and synaptic inputs. Results Compared to the Sham group, the SNT groups showed no significant post‐SNT changes in CST axonal number and volume. Motor neuron cell‐body volume decreased by 29% at 6 weeks post‐SNT, and vesicular glutamate transporter 1 (vGlut1) and vesicular acetylcholine transporter (vAchT) synaptic inputs decreased by 82–93% and 27–42%, respectively, from 2 weeks post‐SNT onward. From 2 weeks post‐SNT onward, cell numbers were maintained, although vGlut1 synaptic inputs increased by 98%–68% in lateral CINs. At 6 weeks post‐SNT, a 44% reduction in cell numbers and a simultaneous 107% increase in vGlut1 synaptic inputs were noted in medial CINs. Conclusion Following SNT, although CST axonal numbers remained unchanged, plasticity changes were observed in motor neurons and in CINs. CINs exhibited distinct plasticity changes depending on their localization.