Abstracts

Rationale: Postictal refractoriness is absent in 12-day-old rats and develops during the third postnatal week. EEG and motor performance was studied to find out if these phenomena correlate with postictal refractoriness. Methods: Male Wistar rats 12 and 25 days old were implanted with cortical electrodes. Epileptic afterdischarges (ADs) of the spike-and-wave type were elicited by rhythmic electrical stimulation of the sensorimotor cortex and EEG was recorded before and for at least five minutes after the AD. EEG was digitalized at 1 kHz frequency and power density spectra were calculated. In the second experiment another group of rats was exposed to open field and age-appropriate motor tests (righting reflex, negative geotaxis, ascending ladder and bar holding) immediately and 5 min after AD. Control animals had implanted electrodes but they were not stimulated. Each age group in either experiment consisted from 10 animals. Results: Changes in EEG activity tightly correlated with postictal refractoriness. Twelve-day-old rat pups exhibited immediately after the AD the same EEG activity as before stimulation whereas in 25-day-old animals even three minutes were not sufficient for EEG recovery - frequency was slower and amplitude lower. Spontaneous locomotion in open field was suppressed after AD in 12-day-old rats (they walked for a shorter distance and with lower velocity than controls) meanwhile locomotion of 25-day-old ones in the experimental group did not differ from results in the control group. Motor performance was compromised in both age groups with the exception of bar holding in 12-day-old rat pups. Conclusions: Only some individual phenomena (EEG) exhibit after cortical seizures the same time profile as postictal refractoriness, spontaneous locomotion was more affected in 12- than in 25-day-old rats. This study was supported by a US-Czech collaborative grant No.LH11015 and by a project of the Czech Academy of Sciences No.67985828.