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BACKGROUND: Radiation therapy is widely used to treat tumor of brain; however, irradiation of radiation into eye tissues may easily cause ischemia and hypoxia in retina and optic nerve tissue so as to induce radiation optic neurapathy. Noloxone is a specific antagonist of opiate receptor, and it can change injured effect of β -endorphin.OBJECTIVE: To observe the axoplasmic transport of optic nerve at various phases after radiation injury so as to investigate the mechanism and regularity of optic nerve injury; meanwhile, to verify the therapeutic effects of naloxone on radiation optic neurapathy.DESIGN: Randomized controlled animal study.SETTINGS: Medical College of Qingdao University, Changzhi Medical College.MATERIALS: A total of 40 healthy adult New Zealand rabbits, weighing 2 - 2.5 kg, of either gender, were checked by using slit lamp and ophthalmoscop before radiation in order to exclude eye diseases. FCC-7000 vertical kilocurie 60Co therapeutic machine was made in Yantai, China; in addition, naloxone was provided by Beijing Sihuan Pharmaceutical Factory.METHODS: The experiment was carried out in the Animal Experimental Laboratory, Medical College of Qingdao University from January 2005 to December 2006. The experimental rabbits were randomly divided into radiation group (n =16), treatment group (n =16), blank control group (n =4) and injured control group (n =4). Except blank control group, rabbits in other three groups were irradiated in as the center of optic chiasma including the area of optic nerve by using 60Co therapeutic machine. Radioactive source was 85 cm away from head, and the size of operative field was 5 cm× 5 cm. The radiation was performed once a day with the dosage of 3 Gy for 8 days in total. The total dosage was 24 Gy. When radioactive dosage reached 24 Gy, 2 mg/kg naloxone was dropped into ear vein of rabbits in the treatment group once a day for 10 days in total. Rabbits in the injured control group were only irradiated but not given any drugs.MAIN OUTCOME MEASURES: At 1, 10, 30 and 60 days after 24-Gy radiation, anterogradely labeled horseradish peroxidase (HRP) was used to measure optical density mean (OPTDM) in the radiation group and the treatment group; while, OPTDM was directly measured in the blank control group, and OPTDM was directly measured after radiation in the injured control group.RESULTS: All 40 experimental rabbits were involved in the final analysis. There were significant differences in OPTDM at various phases between radiation group and blank control group (P ＜ 0.05); in addition, there was significant difference in OPTDM in the treatment group at 1, 10, 30 and 60 days after 24-Gy radiation (P ＜ 0.05); otherwise, at 30 and 60 days after 24-Gy radiation, there was significant difference in OPTDM between radiation group and treatment group (P ＜ 0.05).CONCLUSION: Naloxone may improve optic nerve axoplasmic transport disorder induced by radiation so as to protect optic nerve.