The cerebral hemisphere of the turtle in vitro. An experimental model with spontaneous interictal-like spikes for the study of epilepsy

Abstract 

Slice in vitro preparations have been useful to study the cellular basis of some epilepsy related phenomena. However, the cellular mechanisms that generate ictal activity remain poorly understood. Therefore, an experimental in vitro model capable of generating seizure-like activity might contribute to the study of the cellular basis of seizures. The outstanding resistance to hypoxia of turtles enabled us to develop an in vitro preparation that keeps all the cortical neural circuitry intact. A whole cerebral hemisphere of the turtle Chrysemys d'orbigny was isolated (n=45) and simultaneous electrographic and intracellular recordings were performed in the medial cortex. The electrographic activity was composed by a non-rhythmic, low-voltage (10–20 μV) activity interrupted by spontaneous large (50–700 μV) sharp waves (LSWs). The cellular counterpart of the LSWs was often a burst of action potentials that resembled the paroxysmal depolarisation shift (PDS). Bicuculline (20–40 μM, n=20) increased the interictal-like activity and in some preparations (3 out of 20) provoked seizure-like events. Complex bursting activity and a slow afterhyperpolarisation were cellular events observed during seizures. We propose that this model might be a valuable tool for the study the cellular mechanisms involved in the transition from the interictal to the ictal activities.

Keywords:  Epilepsy, In vitro hemispheric brain, Turtle medial cortex, Interictal spike, Paroxysmal depolarization shift, Seizure-like activity