ABSTRACT
Dravet syndrome (Dravet) is a rare and severe form of developmental epileptic encephalopathy. Antiseizure medications (ASMs) for Dravet patients include valproic acid (VA) or clobazam (CLB), with or without stiripentol (STP), while sodium channel blockers like carbamazepine (CBZ) or lamotrigine (LTG) are contraindicated. In addition to their effect on epileptic phenotypes, ASMs were shown to modify the properties of background neuronal activity. Nevertheless, little is known about these background properties alterations in Dravet. Here, utilizing Dravet mice (DS, Scn1a A1783V/WT), we tested the acute effect of several ASMs on background electrocorticography (ECoG) activity and frequency of interictal spikes. Compared to wild-type mice, background ECoG activity in DS mice had lower power and reduced phase coherence, which was not corrected by any of the tested ASMs. However, acute administration of Dravet-recommended drugs, VA, CLB, or a combination of CLB + STP, caused, in most mice, a reduction in the frequency of interictal spikes, alongside an increase in the relative contribution of the beta frequency band. Conversely, CBZ and LTG increased the frequency of interictal spikes, with no effect on background spectral properties. Moreover, we uncovered a correlation between the reduction in interictal spike frequency, the drug-induced effect on the power of background activity, and a spectral shift toward higher frequency bands. Together, these data provide a comprehensive analysis of the effect of selected ASMs on the properties of background neuronal oscillations, and highlight a possible correlation between their effect on epilepsy and background activity.
ABSTRACT
OBJECTIVE: Dravet syndrome (Dravet) is a severe childhood epileptic encephalopathy. The disease begins with a febrile stage, characterized by febrile seizures with otherwise normal development. Progression to the worsening stage features recurrent intractable seizures and the presentation of additional nonepileptic comorbidities, including global developmental delay, hyperactivity, and motor deficits. Later in life, at the stabilization stage, seizure burden decreases, whereas Dravet-associated comorbidities persist. To date, it remains debated whether the nonepileptic comorbidities result from severe epilepsy or represent an independent phenotypic feature. METHODS: Dravet mice (DS) faithfully recapitulate many clinical aspects of Dravet. Using wild-type (WT) and DS at different ages, we monitored multiple behavioral features as well as background electroencephalogram (EEG) activity during the different stages of Dravet epilepsy. RESULTS: Behavioral tests of WT and DS demonstrated that some deficits manifest already at the pre-epileptic stage, prior to the onset of convulsive seizures. These include motor impairment and hyperactivity in the open field. Deficits in cognitive functions were detected at the onset of severe spontaneous seizures. Power spectral analysis of background EEG activity, measured through development, showed that DS exhibit normal background oscillations at the pre-epileptic stage, a marked reduction in total power during the onset of severe epilepsy, and a subsequent smaller reduction later in life. Importantly, low EEG power at the stage of severe frequent convulsive seizures correlated with increased risk for premature death. SIGNIFICANCE: Our data provide a comprehensive developmental trajectory of Dravet epilepsy and Dravet-associated comorbidities in mice, under controlled settings, demonstrating that the convulsive seizures and some nonepileptic comorbidities may be uncoupled. Moreover, we report the existence of an inverse correlation, on average, between the power of background EEG and the severity of epileptic phenotypes, suggesting that such measurements may potentially serve as a biomarker for Dravet severity.
