DYSPLASTIC NEOCORTEX AND SUBCORTICAL HETEROTOPIAS IN METHYLAZOXYMETHANOL-TREATED RATS - AN INTRACELLULAR STUDY OF IDENTIFIED PYRAMIDAL NEURONS

Intracellular recordings were obtained using biocytin-filled electrode s from 78 neurones located in both dysplastic neocortex and subcortica l heterotopic aggregates in a model of neuronal migration disorder ind uced in rats by means of a double methylazoxymethanol injection given on embryonic day 15. Both regular spiking and intrinsically bursting p yramidal neurones were found in all of the examined structures and wer e synaptically activated by subcortical stimulation. In a neuronal sub population (22%) located in the neocortex as well as in the subcortica l heterotopic aggregates, the injection of depolarising current pulses elicited aberrant firing patterns, consisting of repetitive bursts of APs that gradually increased in duration and eventually merged in a l ong-lasting discharge. The gradual development of this 'excessive' bur sting behaviour suggests a progressive rundown of the slow components of the hyperpolarising afterpotential. (C) 1998 Elsevier Science Irela nd Ltd.