Presence of kynurenic acid and kynurenine aminotransferases in the inner retina

Kynurenine aminotransferases (KATs I and II) are pivotal to the synthesis of kynurenic acid (KYNA), the only known endogenous glutamate receptor antagonist and neuroprotectant. This study is the first to identify KYNA in the rat retina and to examine immunohistochemically the distribution of KAT isoforms. As determined by HPLC, KYNA concentration in the retina was 99.9 +/- 24.6 pmol/g wet wt. Immunohistochemical experiments showed that both KATs were present in the retina. KAT I was preferentially localised on Muller cell endfeet while KAT II was expressed in cells within the ganglion cell layer. In conclusion, KYNA is present and synthesised in the inner retina. This may suggest a modulatory role in glutamate-mediated retinal neurotransmission. NeuroReport 12:3675-3678 (C) 2001 Lippincott Williams & Wilkins.