A morphological study of denervation and reinnervation of neuromuscular junction and muscle spindle after sciatic nerve crush in mice / 中华显微外科杂志

ABSTRACT

Objective:To observe the denervation and reinnervation of the neuromuscular junction (NMJ) and muscle spindle after sciatic nerve crush in mice.Methods:From January, 2019 to October, 2019, 18 C57BL/6 mice were randomly and evenly divided into injured groups (sciatic nerve crush group, 12 mice) and control groups (sham group, 6 mice). Mice in the injured group were sacrificed at day-1, day-2, day-3 and 4 weeks after the sciatic nerve injury. Mice in the control group were sacrificed at day-3 and 4 weeks from the day of experiment. The tibialis anterior muscles with crushed nerve were collected for immunohistochemistry staining by neurofilament (NF), synaptophysin (Syn) and α-bungarotoxin (α-BTX). Data were analysed by unpaired t-test. P<0.05 was considered significant difference. Results:The completely denervation of NMJ reached (92.4±8.85)% at day-3 after the nerve crush, compared with (5.19±1.32)% in the control group ( P<0.05). However, the muscle spindle lost γ-motor neuron innervation at day-2 after the nerve crush and completely denervated at day-3 after the surgery. For the reinnervation, no difference of no reinnervation of NMJ [(3.02±0.78)% vs. (4.22±2.08)%], partial reinnervation of NMJ [(6.44±1.91)% vs. (7.94±2.12)%] and completely reinnervation of NMJ [(90.54±10.44)% vs. (87.84±13.89)%] were observed between the control group and the injured group 4 weeks after the injury. While, for the muscle spindle, only the acetylcholine receptors at each end were partly reinnervated. The innervation of the middle part of the muscle spindle was thin and discontinued without typical spiral winding structure. Conclusion:The denervation speed of NMJ and muscle spindle was comparable after the peripheral nerve injury. The γ-motor neuron lost innervation ahead of the sensory neuron in the muscle spindle. The reinnervation of NMJ is earlier than that of the muscle spindle, and the re-innervation of the γ-motor neuron is prior to the sensory neuron in the muscle spindle.