Background: Kynurenic acid (KYNA) is the only known endogenous glutamate receptor antagonist and neuroprotectant. After showing the presence of KYNA and its synthesising enzymes in the adult rat retina, we examined developmental changes of KYNA content in both vascularised rat and avascular chicken retinas.
Methods: Retinas from Brown Norway rats and White Leghorn chickens at different developmental stages between the embryonic and the adult stages were used. KYNA levels were investigated with HPLC.
Results: KYNA was present in both rat and chicken retinas during ontogeny. The mean (+/- SE) concentration of KYNA found in the embryonic rat retina (E20) was 95+/-10 pmol/g wet wt. The KYNA content sharply increased within the following 3 days reaching a peak at birth (P0) of 702+/-77 pmol/g wet wt. At the end of the second postnatal week KYNA content decreased to 211+/-29 pmol/g wet wt. A further decrease was observed subsequently, with KYNA levels of 100+/-24.6 pmol/g wet wt at 3 month and 58+/-4 pmol/g wet wt at 12 month. Significant differences in KYNA concentrations between the embryonic and post-hatching stages were also observed in the chicken retina. In 12-day-old embryonic (E12) retinas the KYNA level was 364+/-48 pmol/g wet wt, and in E16 embryos it was 440+/-80 pmol/g wet wt. It significantly decreased to 200+/-38 pmol/g wet wt at P0 and stayed more or less at this level until P21 (217.5+/-23.5 pmol/g wet wt).
Conclusion: KYNA is present in the rat and chicken retinas in high concentrations during early developmental stages. This suggests that KYNA may play a neuromodulatory role in the retina during development.