| Objective That repair and regeneration of facial nerve injury is a complicated process. The regulation of nerve cell and the nutriment of regenerate environment is very important to the regeneration of impaired nerve and axon. In the present study we adapted a technique which allows a local administration of thyroid hormones in a closed system to investigate the effection of thyroid hormone in the regeneration of facial nerve; and to study the expression of NGF,BDNF in facial motorneuron (FMNs).Methods 25 New Zealand adult rabbit (age range, 6-8 months )were selected. These rabbits were divided into three groups(normal , operated and T3-treated groups). Five rabbits in normal control group were taken facial nerve and inferior-middle part of pons (containing facial nucleus) without any treatment. Select 20 New Zealand adult rabbits randomly, the effect of a single and local treatment with triiodothyronine(T3) on axonal growth across a gap between sectioned ends of facial nerve within silicone chambers was examined. After nerve transaction and surgical implantation, silicone chambers were filled with either a neutral PH solution of triiodothyronine dissolved in NaOH or with sterile solvent as control.4 and 6 weeks after surgery, the regenerated facial nerve was studied by morphological analysis. 4 weeks and 6 weeks after operation, the rabbits were killed by over dose of pentobarbital, rabbit brains were fixed by transcardial perfusion with saline, followed by perfusion and immersion in 4% paraformaldehyde. Inferior–middle parts of pons were cut and embeled with paraffin. The technique of immunohistochemistry SP were taken to test the expression change of NGF and BDNF in facial nucleus.Result Results of electron microscope demonstrates that the myelinated axons rate in normal control group is 68.61±1.22%, g-rate (axons diameter/fibre diameter) is 0.60±0.01.4 weeks after operation,the myelinated axons rate of thyroid hormone treatment group is 35.96±2.64%,and the myelinated axons rate of surgery control group is 16.87±1.11%;the g-rate in surgery control group(0.80±0.02) exceeds the g-rate in the T3-treated group(0.61±0.02).6 weeks after operation, the myelinated axons rate is 43.90±1.58% and g-rate is 0.59±0.01 in T3-treated group; in surgery control group, the myelinated axons rate is 23.42±1.31% and g-rate is 0.74±0.02.In a word, the result of electron microscope discovered significantly higher percentage of myelinated axons per total axon population in T3-treated group compared to surgery control group, and the myelinated axons had thicker myelin sheaths. t-test showed significant difference between the two groups(P < 0.01). The immunohistochemistry of facial motoneurons(FMNs) result discovered that the neurotrophic factor NGF and BDNF was expressed in the normal control group with the average number of NGF(20.25±2.52) and BDNF(25.65±2.06).4 weeks after operation, the expression of NGF and BDNF in surgery control group and T3-treated group is more than the expression in normal control group. The expression of NGF(39.75±2.73) and BDNF(50.03±3.98) in T3-treated group increased obviously than NGF(29.80±2.65) and BDNF(37.60±3.77) in surgery control group, t-test showed significant difference between the two groups(P<0.01).6 weeks after operation , the average number of NGF(45.35±1.86) and BDNF(59.53±2.59) in T3-treated group increased obviously than NGF(35.08±1.87) and BDNF(32.60±2.69) in surgery control group, t-test remained significant difference between the two groups(P<0.01). Conclusion Our research revealed that a single and localadministration of thyroid hormone at the level of the transected facial nerve is sufficient to rapidly set off several mechanisms which, in turn, produce a stimulating and lasting effect on peripheral nerve regeneration. It can increase the myelinated axons rate and myelin sheath thickness, moreover, thyroid hormone can increase the expression of NGF and BDNF in the facial motoneurons. |
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