Study On Changes Of Lateral Geniculate Nucleus In Experimental Optic Nerve Injury Models

Processes that damage the optic nerve often cause vision loss for which there is no current treatment. At the level of retina, there are extensive studies on related changes and mechanism after optic nerve injury, as well as optic nerve protection and regeneration. However, little is known regarding the changes of target neurons in central visual pathway after the injury. The present study was initiated to investigate the characteristic changes and mechanism in the lateral geniculate nucleus (LGN) at the different periods after the optic nerve injury, by establishing the optic nerve crush model of rats and the chronic hypertensive glaucoma model of monkeys. Such study may help us to get a deep insight into the changes in visual pathway after optic nerve injury, and provide related research evidence for future vision repair or restoration.Part One: Early changes in the lateral geniculate nucleus of rats with optic nerve crushUnilateral optic nerve crush injury was produced in Sprague-Dawley rats by using micro clips of 70 gram forces for 30 seconds in 35 rats. Sham operations were performed in a further 7 rats. 2h, 1d, 3d, 7d and 14 after the injury, C-Jun and c-Fos expressions in the retina and LGN were studied with a polyclonal antibody by immunohistochemistry and Western blot. Double immunolabelling of c-Fos and c-Jun respectively with calbindin D-28k or NeuN were studied in the LGN. Tri-immunolabelling of c-Jun, NeuN and TOTO-3 were studied in the retina.The results showed that after optic nerve crush on the right eye, the number of NeuN labelled neurons at the layer of retina ganglion cells was significantly decreased ipsilaterally at 7d and 14d postoperation. C-Junpositive cells were only observed in the nucleus of NeuN labelled neurons. The c-Jun immunoreactivity was visible after 2h, reached maximum at 3d post injury, then decreased at 7d, still visible at 14d.At the LGN, c-Fos was observed ipsilaterally in the medial subdivision of ventral LGN and intermediate geniculate nucleus. The c-Fos immunoreactivity was visible after 2h, reached maximum at Id post injury, then decreased at 3d and 7d, still a few was observed at 14d. Expression of calbindin D~28k was mainly observed in the medial subdivision of ventral LGN and IGN. 75%~-83% c-Fos positive cells were also calbindin D-28k immunopositive. OJun positive cells were observed both sides in all three subdivision of the LGN. The time course of c-Jun expression in the LGN was similar with that of c-Fos. The percent of colocalisation of c-Jun in NeuN labelled neurons was more 90% at all injury groups postoperation.Hence the conclusions are that optic nerve crush activates the expressions of immediate early genes in the LGN and retina among visual pathway. Calbindin D~28k is involved in the transmission of harmful stimulus in the central visual pathway, which implies that these neuronal changes in the LGN are at least not only the result of transneuronal degeneration from the retinal ganglion cells, but also reflect the activity-dependent plasticity of LGN itself.Part Two: Changes of lateral geniculate nucleus in a chronic hypertensive glaucoma model of monkeyLaser photocoagulation was applied to 15 adult rhesus monkeys by semiconductor frequency-doubled 532 laser and argon laser. The laser spot was aimed at the entire 360° functional trabecular meshwork using goniolens. A-scan, Heidelberg Retinal Tomograph and Retinal Flowmeter were applied to examine the topographic and blood flow parameters of the globe and optic disc in seven model eyes and control eyes. The results showed that at the fourth week after initial pressure elevation, the average intraocular pressure was 48. 4±10. 3-fflnjHg for frequency-doubled532 laser, and 44.2±7. OmmHg for argon laser. The successful rates of three times photocoagulation between two types of laser also have no significant difference. Compared with the control eyes, there are very significant differences of disc topographic parameters in the model eyes, except for the disc area. The model eyes presented characteristic glaucomatous morphological changes.After successfully induced the chronic hypertensive glaucoma model in rhesus monkeys with frequency-doubled 532 laser, we further investigate the neuronal and glial changes of LGN in the late stage of experimental monkey glaucoma. Four monkeys with 532 laser induced glaucoma in one eye and four control monkeys were studied. Parvalbumin (PV) and GFAP expressions in the LGN were studied with a monoclonal and a polyclonal antibody by immunofluorescene. Transmission electron microscopy (TEM) was also applied to observe the ultrastructural changes in the LGN.The results showed that compared with the control group, the axon of retinal ganglion cells were totally lost in the glaucoma groups. In the magnocellular layers and the parvocelluar layers connected to the affected model eyes, PV labelled neuron densities were decreased 53% and 66% respectively, cross sectional neuron areas were decreased 52% and 48% respectively, and GFAP positive glial cells were increased 198% and 234% respectively. There are significant differences of neuron densities and glial cells reaction between the magnocellular and parvocelluar layers. Moreover, in the magnocellular layers and the parvocelluar layers connected to the unaffected eyes, PV labelled neuron densities were decreased 14% respectively, and GFAP positive glial cells were increased 31% and 39% respectively. In addition, the results of TEM showed that there are partial swellings of mitochondria and endoplasmic reticulum, as well as a large amount of lipofuscin present in the LGN nerve cells. Different kinds of glial cells were also observed around the nerve cells.Hence the conclusions are that in the late stage of glaucoma monkeys, there are significant loss and atrophy of relay neurons and astrocytes reactive proliferation in the magnocellular layer and the parvocelluar...