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Y. Shenk, R.A. Rejdak, F. Schuettauf, E. Okuno, Z. Zagorski, E. Zrenner, K. Kohler; Expression of Kynurenine Aminotransferases (KAT I and KAT II) in the Rat Retina during Ontogeny . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1597.
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Purpose: Kynurenine aminotransferases (KAT I and II) are pivotal to the synthesis of kynurenic acid (KYNA), the only known endogenous glutamate receptor antagonist. After showing the presence of KYNA and KATs in the adult rat retina (Rejdak et al., Neuroreport 2001, 12) the present study examines the cellular expression of KAT I and KAT II in the rat retina during ontogeny. Method: Immunohistochemistry was performed on rat retinal sections at different developmental ages between the day of birth and the adult stage (P0, P7, P14, P90) using specific antibodies against KAT I, KAT II and glutamine synthetase as a marker for Müller cells. Retinal ganglion cells (RGC) were retrogradly labeled by Fluorogold injected into the superior colliculi 4 days before immunohistochemistry. Results: Both KAT I and KAT II immunoreactivity was present from P0 on , at all developmental ages analysed, but showed different spatial distribution and temporal expression patterns. At the P0 and P7, KAT I expression was observed from the border of the neuroblast layer to the vitreal border, i.e. in the forming inner plexiform layer, the GCL and FL. However somata in the GCL were free of labelling. At P14 a strong KAT I immunoreactivity was observed in Müller cell endfeet and their processes not extending beyond the GCL. No staining was observed in the outer retina. KAT II was expressed in the IPL, cell bodies in the GCL and FL at P0 and P7. From P14 on KAT II expression in the IPL decreased, at P90 somata were only faintly stained whereas Müller cell endfeet appeared still prominently stained. Double labelling studies showed that KAT I was expressed in Müller cell endfeet while KAT II was observed both on RGC and Müller cell endfeet in the adult rat retina. Conclusion: Since glutamate receptors, which are preferential targets of KYNA, play an important role in retinal development, the heterogenity of KAT I and II ontogenic profile may play a neuromodulatory role in processes of synapse formation in the retina during development.
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