A chronic model of epilepsy in organotypic brain slice cultures of the rat entorhinal cortex

Epilepsy is a serious neurological disorder affecting around 50 million people world wide. Research into basic mechanisms of the disorder relies heavily on the use of animals. A favoured approach in this area is to establish chronic epileptic conditions in vivo and then use brain tissue from these animals in in vitro experiments to determine changes in neuronal networks that accompany overt chronic seizures. The in vivo chronic models involve instigating a severe acute seizure in the experimental animal, which is followed after a latent period of weeks to months by establishment of chronic spontaneous recurrent seizures. However, determination of changes underlying the development of the chronic condition is difficult, as the approach dictates that longitudinal changes in synaptic networks over the development phase cannot be conducted in a single animal. Individual animals must be sacrificed at arbitrary time points without knowledge of where that animal is in the chronic development process. This makes for a high degree of variability in the data, and is extremely expensive in terms of the total number of animals required. The current application seeks to development an in vitro model of the whole process in tissue from individual animals. Brain slices will be prepared from normal rats, and maintained in long-term organotypic cultures. After a period of stabilisation they will be subjected to a similar acute insult to that induced in the in vivo models, and thereafter monitored (electrophysiologically and histologically) at regular intervals to establish changes occurring during the period leading to appearance of chronic electrographic seizures activity. Since multiple slices can be prepared from a single animal, these can be used to monitor longitudinal changes in network activity in that animal, with untreated slices from the same animal used as parallel controls. Such an approach has the major advantages of eliminating the need for the severe and stressful acute induction phase in the animals, and dramatically reducing the number of animals needed to establish time-dependent changes in networks leading to chronic seizures. We will develop this model in organotypic slices taken from young adult animals and once the model is established we will use it to investigate changes in glutamate and GABA transmission that underlie the development of chronic seizures.