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 unsu itable for a full range of developmental and aging studies. Therefore, we have explored the feasibility of using the rat retina at various a ges for in vitro excitotoxicity studies. In this model, retinal segmen ts were isolated in artificial cerebrospinal fluid (CSF) at 5 degrees C then incubated under various conditions at 30 degrees C and assessed histologically for signs of neurodegenerative changes. Retinal segmen ts from 7-, 30-, 120- and 660-day-old rats incubated in CSF for 3 h an d from 30-day-old rats incubated for 24 h retained a normal histologic al appearance. Thus, this preparation is suitable for in vitro studies pertaining to either acute or delayed excitotoxic phenomena in the ma mmalian CNS at any age from infancy to old age. Excitotoxin agonist ex periments in the 30-day-old rat retina revealed the surprising result that the non-NMDA agonists, kainate and AMPA, at a low concentration ( 100 mu M) damaged a much larger number of retinal neurons than NMDA di d at a very high concentration (10 mM).