New model of cortical epileptic foci in freely moving developing rats

Electrocorticographic and motor phenomena produced by epileptogenic foci were studied in freely moving rats with implanted electrodes in five age groups (7, 12, 18, 25 days and adults). Foci were induced by local application of a 1 or 2 mM solution of bicuculline methiodide to the sensorimotor cortical area by means of an implanted cannula in 106 rats. Interictal focal discharges formed by mono- to triphasic spikes (in rats aged 18 days and more) or sharp waves (in 7-day-old rats) were recorded in all animals. Spontaneous transition into an ictal phase was common in all age groups, there was no clear dependence on the age. Ictal EEG was formed by spike-and-wave rhythm in rats 18 days old and older, by huge delta waves in the youngest rats. Electroclinical correlation was poor in the youngest rats and ameliorated with age. The most frequent motor counterpart of focal discharges was represented by a jerk of the contralateral limbs or of the whole body. EEG seizures were mostly accompanied by clonus of facial and forelimb muscles, but EEG ictal phases without any motor correlate were also common.