Characterization of the epileptiform activity induced by magnesium-free solution in rat amygdala slices: an intracellular study.

The effect of Mg2+-free medium on neuronal activity in the basolateral nucleus of the rat amygdala slice was studied using intracellular recording techniques. Removal of Mg2+ from perfusate resulted in the development of three types of spontaneous activity, EPSP-like, ictal-like, and interictal-like events. The ictal-like events consisted of a long-duration depolarizing potential with several recurrent interictal bursts riding on it. The tonic and clonic firing phases seen in ictal-like events closely resembled the tonic and clonic phases of seizures which may provide a new model for studying the mechanisms underlying the generation of ictal seizures. The duration of interictal-like events induced in Mg2+-free solution is 10- to 30-fold longer than that produced by a convulsant. Two factors, a small or absent epileptiform afterhyperpolarization and a high density of NMDA receptor binding sites within the basolateral amygdala nucleus, may account for this difference.