Plastic changes of synapses and excitatory neurotransmitter receptors in facial nucleus following facial-facial anastomosis

Abstract

The remodeling process of synapses and neurotransmitter receptors of facial nucleus were observed. Models were set up by facial-facial anastomosis in rat. At post-surgery day (PSD) 0, 7, 21 and 60, synaptophysin (p38), NMDA receptor subunit 2A and AMPA receptor subunit 2 (GluR2) were observed by immunohistochemical method and semi-quantitative RT-PCR, respectively. Meanwhile, the synaptic structure of the facial motorneurons was observed under a transmission electron microscope (TEM). The intensity of p38 immunoreactivity was decreased, reaching the lowest value at PSD day 7, and then increased slightly at PSD 21. Ultrastructurally, the number of synapses in nucleus of the operational side decreased, which was consistent with the change in P38 immunoreactivity. NMDAR2A mRNA was down-regulated significantly in facial nucleus after the operation (P<0.05), whereas AMPAR2 mRNA levels remained unchanged (P>0.05). The synapses innervation and the expression of NMDAR2A and AMPAR2 mRNA in facial nucleus might be modified to suit for the new motor tasks following facial-facial anastomosis, and influenced facial nerve regeneration and recovery.

Gene expression of NMDA and AMPA receptors in different facial motor neurons

“…An explanation for the poor functional recovery of the facial nerve is the abnormal activity pattern of the axotomized motor neurons, which necessarily involves the constitution and activity of ionotropic glutamate receptors . Our study indicated that the expression levels of GluR2, GluR3, and NR1 mRNA were higher, and that the expression of GluR1, GluR4, NR2a, NR2b, NR2c, and NR2d mRNA were lower in dormant FMNs than in reinnervating FMNs.…”

“…Nevertheless, detecting and sampling processes, including the manual collection of specimens, in situ hybridization, or regular RT-PCR, would unavoidably affect the reproducibility of results and thereby decreased the power of a study. 4,5 Our previous study showed that the GluR2 mRNA level in the whole facial nucleus region at the operated side did not exhibit evident changes as compared with the normal side. 4 Yet, this study, by employing LCM, found that GluR2 mRNA level varied with different FMNs in the facial nucleus at the operated side.…”

“…Prior studies examined the mRNA expression of ionotropic glutamate receptor subunits in the whole facial nucleus region. Nevertheless, detecting and sampling processes, including the manual collection of specimens, in situ hybridization, or regular RT‐PCR, would unavoidably affect the reproducibility of results and thereby decreased the power of a study . Our previous study showed that the GluR2 mRNA level in the whole facial nucleus region at the operated side did not exhibit evident changes as compared with the normal side .…”

“…Sprague-Dawley rats, each weighing 220 to 250 g, were subjected to facial-facial anastomosis as previously described. 4,16,17 All of the animal experiments were conducted in strict accordance with the guidelines for the handling and treatment of animals and were approved by the Institutional Animal Care and Use Committee of Tongji Medical College, Wuhan, China. All of the animals were raised in a room at 208C to 258C, with 12-hour alternating light/dark cycles, and with free access to standard food and water.…”

“…3 The facial nucleus and other brain regions express the genes of multiple glutamate receptors, and changes in the expressions may affect the motor excitability of the facial nucleus after peripheral injury, but the mechanism underlying the axotomy-induced motoneuron reaction remains elusive. [4][5][6] Moreover, the microenvironment of the nucleus is characterized by an intricate interaction among neurons, astrocytes, microglial, and immune cells. [7][8][9][10] The tissue heterogeneity has been a major obstacle to separately target FMNs in molecular study.…”