An ex vivo rat retinal preparation for excitotoxicity studies

Although the isolated chicken embryo retina has been a very useful in vitro preparation for studying mechanisms of excitotoxicity, it is an avian rather than mammalian tissue and its embryonic age makes it unsuitable for a full range of developmental and aging studies. Therefore, we have explored the feasibility of using the rat retina at various ages for in vitro excitotoxicity studies. In this model, retinal segments were isolated in artificial cerebrospinal fluid (CSF) at 5°C then incubated under various conditions at 30°C and assessed histologically for signs of neurodegenerative changes. Retinal segments from 7-, 30-, 120- and 660-day-old rats incubated in CSF for 3 h and from 30-day-old rats incubated for 24 h retained a normal histological appearance. Thus, this preparation is suitable for in vitro studies pertaining to either acute or delayed excitotoxic phenomena in the mammalian CNS at any age from infancy to old age. Excitotoxin agonist experiments in the 30-day-old rat retina revealed the surprising result that the non-NMDA agonists, kainate and AMPA, at a low concentration (100 μM) damaged a much larger number of retinal neurons than NMDA did at a very high concentration (10 mM).