Source:Clinical Neurophysiology, Volume 129, Issue 4
Author(s): P. Mareš
Cortical interhemispheric responses in rats may serve as an index of maturation. The first two waves monosynaptically elicited by callosal fibres can be reliably evoked since the postnatal day (PD) five. The latency and duration of these evoked potentials markedly shorten after PD7. Paired-pulse stimulations demonstrate fatiguability of immature cortex; potentiation of the second response takes place since the third week. Frequency potentiation appears in the fourth postnatal week.Epileptic afterdischarges (ADs) can be elicited by low-frequency rhythmic stimulation since PD9. Their duration is longest at PD12, then it shortens. If stimulation is repeated, adult animals exhibit postictal refractoriness, i.e. an inability to elicit the second AD. This refractoriness lasting up to 3 min appeared in the fourth postnatal week, animals at PD12 and 15 exhibit marked postictal potentiation – the second, testing AD is significantly longer than the first conditioning AD.The results demonstrate that electrical stimulation induces a purely cortical phenomenon (interhemispheric responses) earlier than the complex cortico-thalamo-cortical epileptic AD. Paired stimulations demonstrate that potentiation appeared earlier in epileptic ADs than in more simple cortical evoked potentials.This study was supported by US-Czech collaborative grants No. LH11015 and LH15032 and a project of Czech Academy of Sciences No. RVO 67985823.
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