Changes Of Extraocular Muscle After Single Direct Injection Of Nerve Growth Factor In Rabbits

Objective To evaluate the changes of adult rabbit extraocular muscle after direct injection of nerve growth factor (NGF)Methods In the self-control study, the left eyes of10adult rabbits were selected as the experimental group, and the right eyes as the contro1group.5μg(0.05mL) NGF was injected into the superior rectus muse le of each experimental eye, and the identical volume of sterilized saline into each control eyes. One week after injection, muscle force and mus cle fiber cross-sectional areas were examined. The morphology of the mu scles both in the experimental group and the control group was studied by hematoxylin-eosin staining and Van Gieson staining under the light mi croscope, and the proliferating cell nuclear antigen (PCNA) positive c ells in superior rectus muscle were determined by immunohistochemistry.Results (1) Muscle force measurement: There were statistical signi ficance on muscle strength of single twitch and tetanus at all stimulation frequencies(10,40,100and200Hz)between the experimental group and the control group.(2)The myofibers mean cross-sectional area of the superior rectos muscle was (9.67±1.82) mm2in the experimental group, and (6.97±1.90) mm2in the control group, with a significant difference between t hem(t=2.79,P=0.02). The perimeter of the superior rectus muscle was(167.20±35.55) μm in the experimental group and(127.44±33.64) μm in the c ontrol group, with a significant difference between them(t=3.06,P<0.01).T he frequencies of large and middle fibers in the muscles were higher in t he experimental group than in the control group (χ2=64.16, P<0.01).(3) The proportion of PCNA positive cells was higher in the experimental g roup (21.93±5.08)%than that in the control group((12.97±2.68)%(P<0.01).The total proportion of PCNA positive cells was higher in the expe rimental group than that in the control group(χ2=54.61, P<0.01). Conclu sion Single direct injection of NGF into extraocular muscles is an safe an d effective procedure. NGF can increase muscle force and myofibers cross-sectional area of extraocular muscle and promotes the proliferation of ext raocular muscle fibers.