Participation of GABAB receptors in cortical postictal excitability in immature rats
Arrest of seizures is due to an active inhibition and is followed in mature brain by period of refractoriness markedly present one min after the end of seizures. To study changes in cortical excitability after epileptic seizures we used electrical stimulation of sensorimotor cortical area in immature rats – 25-day-old ones with mature postictal refractoriness and 12-day-old where postictal potentiation of afterdischarges (ADs) is present instead of refractoriness at one minute after the end of the conditioning AD. GABAB receptor antagonist CGP35348 was found to partly suppress postictal refractoriness. In present study not only an antagonist CGP46381 (3 and 10 mg/kg i.p.) but also positive allosteric modulator of GABAB receptors CGP7930 (20 and 40 mg/kg i.p.) were used to study the role of GABAB receptors in both age groups. They were injected immediately after testing AD and 10 min later the two stimulations were repeated. CGP46381 partly antagonized postictal refractoriness in 25-day-old rats but did not significantly affect ADs in 12-day-old animals. CGP7930 did not significantly change ADs duration in either age group.
GABAB receptors participate in mechanism of postictal refractoriness but did not play an important role in 12-day-old rats where potentiation instead of refractoriness is present.