Measurement of amino acid levels in the vitreous humor of rats after chronic intraocular pressure elevation or optic nerve transection.
ABSTRACT To investigate whether the levels of free amino acids and protein in the vitreous of rat eyes are altered with chronic intraocular pressure (IOP) elevation or after optic nerve transection.
The concentrations of 20 amino acids in the vitreous humor were measured by high-performance liquid chromatography in both eyes of 41 rats with unilateral IOP elevation induced by translimbal photocoagulation. Eyes were studied 1 day and 1, 2, 4, and 9 weeks after initial IOP elevation. The same amino acids were measured in 41 rats 1 day and 2, 4, and 9 weeks after unilateral transection of the orbital optic nerve. The intravitreal protein level was assayed in additional 22 rats with IOP elevation and 12 rats after nerve transection. Two masked observers evaluated the amount of optic nerve damage with a semiquantitative, light-microscopic technique.
In rats with experimental glaucoma, amino acid concentrations were unchanged 1 day after treatment. At 1 week, 4 of 20 amino acids (aspartate, proline, alanine, and lysine) were higher than in control eyes ( < or = 0.01), but this difference was nonsignificant after Bonferroni correction for multiple simultaneous amino acid comparisons (none achieved < 0.0025). No amino acid was significantly different from control in the nerve transection groups (all > 0.05). Vitreous protein level was significantly higher in glaucomatous eyes than their paired controls at 1 day ( < 0.0001) and 1 week ( < 0.002). One day and 1 week after optic nerve transection, vitreal proteins were significantly elevated compared with control eyes from untreated animals ( < 0.0020 and < 0.0022, respectively), though not compared with their fellow eyes ( = 0.25 and 0.10).
Chronic experimental glaucoma and transection of the optic nerve increase the amount of protein in the rat vitreous above control levels. In the vitreous of rats with experimental glaucoma, a number of free amino acids were transiently elevated to a modest degree, but no significant difference in vitreous glutamate concentration was detected ( > 0.01).
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ABSTRACT: Damage resulting from a partial acute lesion of white matter in the central nervous system (CNS) gradually spreads also to neurons that escaped the primary injury, resulting in their degeneration. Such spreading has been referred to as secondary degeneration. In order to demonstrate that this degeneration is indeed secondary to that caused by the acute insult, as well as to investigate the mechanism underlying the spread of damage and ways in which to protect neurons from such damage, we have proposed the use of partial lesion of the rodent optic nerve as a model. In this model we examined whether an antagonist of a receptor-mediated channel, shown to be beneficial in gray matter lesions, can protect neurons from undergoing secondary degeneration following white matter lesion. A well-calibrated partial crush lesion inflicted on the optic nerve of adult rats was immediately followed by a single intraperitoneal injection of the N-methyl-D-aspartate receptor antagonist, MK-801 (1 mg/kg). Protection of neurons from secondary degeneration was assessed by retrograde labeling and by measurement of the visual evoked potential (VEP) response to light. Two weeks after the injury, the mean number of neurons that were still intact was about threefold higher in the MK-801-treated group than in the saline-treated control group, indicating a treatment-induced protection of neurons that had escaped primary injury. A positive VEP response to light was obtained in 90% of the MK-801 treated animals and in only 50% of injured controls. The questions regarding whether the secondary degeneration of initially spared neurons starts in their cell bodies or in their axons, and consequently the identity of the primary site of their protection by MK-801, are discussed in relation to the absence of N-methyl-D-aspartate receptors on nerve fibers. The present findings may have implications for both acute and chronic injuries of the CNS.Journal of Neurotrauma 10/1997; 14(9):665-75. · 4.30 Impact Factor
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ABSTRACT: This study was undertaken to examine whether unilateral injury to one optic nerve (ON) elicits a response in the microglia, neuroglia and ganglion cells of the retina and ON of the contralateral site as well. Bilateral activation of the transcription factor c-jun could be immunohistochemically detected in the ganglion cell layer 2 days after crush and later. Microglial cells were detected with the activation-specific antibodies MUC 102 and OX-42. They showed an immediate and clear pattern of activation within the contralateral ON and retina, although this response was less pronounced than in the directly lesioned site. Astrocytes and Müller cells showed a typical up-regulation of glial fibrillary acidic protein in the lesioned retina and only focal but virtually no generalized up-regulation in the contralateral eye. Ganglion cells whose axons had been crushed responded with vigorous axonal growth after 2 days in culture, in addition to exhibiting in situ reactions. However, ganglion cells of the contralateral retina responded with a moderate regeneration, too. Growth was less pronounced than in the crushed retina but significantly better than in retinas on untreated animals. The results suggest that unilateral lesion of the optic nerve elicits a defined response in the major cell types of the contralateral retinofugal system. The findings suggest that it is advisable to maintain caution in the use of the contralateral optic nerve and retina as a control in experiments dealing with cellular processes of de- and regeneration.Journal of Neurobiology 02/1999; 38(1):116-28. · 3.05 Impact Factor
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ABSTRACT: The death of retinal ganglion cells during glaucoma is thought to result from damage to their axons as they exit the eye through the lamina cribrosa. In this study, intraocular pressure in the rat was increased to twice the normal average by cauterizing two limbal-derived veins. To investigate whether retinal ganglion cells in the glaucomatous eye follow an apoptotic type of death, DNA breaks in nuclei were labeled in situ, using a method that specifically incorporates biotinylated deoxynucleotides by exogenous terminal deoxynucleotidyl transferase to the 3'-OH ends of DNA. The active nature of the death mechanism was demonstrated by the reduction in numbers of biotin-labeled nuclei after administration of the protein synthesis inhibitor, cycloheximide. Our results suggest that retinal ganglion cells of the adult rat die through apoptosis when the intraocular pressure is markedly increased. This raises new possibilities in the treatment of glaucomatous damage to the retina, by the potential interruptibility of a program for neuronal death.Experimental Eye Research 08/1995; 61(1):33-44. · 3.03 Impact Factor