Establishing a cat model of acute optic nerve injury

Abstract

Background In order to investigate the progress in optic nerve injury and the following regeneration and repair, many kinds of animal models of optic nerve injury have been established, such as models of acute and chronic ocular hypertension, compression, amputating wound, ischemia reperfusion or hypoxia, intravitreal injection of excitatory amino acids, etc. However, most of these models are established by squeezing intraorbital optic nerve, and suitable for ophthalmology, and there are fewer models suitable for the acute cranial contusion in neurosurgery. Objective To observe the changes of optic nerve after acute injury, and the characteristics of methods for establishing model of acute optic nerve injury in cats. Design A complete randomized grouping and controlled animal trial. Setting Department of Neurosurgery, General Hospital of Ji'nan Military Area Command of Chinese PLA. Materials Twenty-eight healthy adult cats, common degree, either sex, weighing 2.0–3.5 kg, were provided by the animal experimental center of Fudan University. The cats were randomly divided into control group ( n =3) and model group ( n =25), and 5 cats in the model group were observed at 6 hours and 1, 3, 7 and 14 days after injury respectively. JX-2000 biological signal processing system (Department of Physiology, Second Military Medical University of Chinese PLA, Shanghai); Inverted phase contrast microscope (Olympus); Axioplan 2 imaging microgram analytical system (Labsystems). Methods The experiments were carried out in the Department of Neurosurgery, General Hospital of Jinan Military Area Command of Chinese PLA from June 2004 to June 2005. The cats in the model groups were made into models of acute optic nerve injury: The cats were anesthetized, then the limbs were fixed in a lateral recumbent position. Pterion approach in human was imitated, the operative incision was made along the line between lateral canthus and tragus, and it could be seen deep along the skull base that white optic nerve (about 3 mm) went through optic foramen and entered into brain tissue. It was squeezed with noninvasive vascular clip for 20 seconds, then the clip was removed, and then the skull was closed after it was examined to be no bleeding. The size of bilateral pupils, direct and indirect light reflexes were observed postoperatively. Successfully established models were judged by larger operated pupil than controlateral one, disappearance of direct light reflex and the existence of indirect light reflex. No model establishment was performed in the control group. Each cat was tested with flash visual evoked potential (F-VEP) to observe the electrophysiological changes before and after experiment. All the cats in the control group and model groups were killed under anesthesia before model establishment and at 6 hours, 1, 3, 7 and 14 days after model establishment respectively, and the pathological changes of the optic nerve after injury were observed under electron microscope and light microscope. Main outcome measures VEP and the ultrastructural changes of optic nerve after acute optic nerve injury in both groups. Results All the 28 cats were involved in the analysis of results. ▪ VEP results: The VEP latencies were obviously different between the control group and model group at each time point ( P < 0.05), whereas there were no obvious differences among different time points in the model group ( P > 0.05). The VEP amplitudes were obviously different between the control group and model group at each time point ( P < 0.05), whereas there were no obvious differences among different time points in the model group ( P > 0.05). ▪ Ultrastructural changes of the optic nerve: Under electron microscope, normal optic nerve myelin sheath had complete structure, tramal plates were clear and arranged tightly, axolemma was complete, whereas the structures of endoneurium, myelin sheath, tramal plates, axolemma and axon were in disorders after optic nerve injury. Conclusion Models of acute optic nerve injury established by squeezing intracranial optic nerve with noninvasive vascular clip can be applied in studying intracranial acute optic nerve injury.