Impaired cortico-striatal excitatory transmission triggers epilepsy

Abstract

STXBP1 and SCN2A gene mutations are observed in patients with epilepsies, although the circuit basis remains elusive. Here, we show that mice with haplodeficiency for these genes exhibit absence seizures with spike-and-wave discharges (SWDs) initiated by reduced cortical excitatory transmission into the striatum. Mice deficient for Stxbp1 or Scn2a in cortico-striatal but not cortico-thalamic neurons reproduce SWDs. In Stxbp1 haplodeficient mice, there is a reduction in excitatory transmission from the neocortex to striatal fast-spiking interneurons (FSIs). FSI activity transiently decreases at SWD onset, and pharmacological potentiation of AMPA receptors in the striatum but not in the thalamus suppresses SWDs. Furthermore, in wild-type mice, pharmacological inhibition of cortico-striatal FSI excitatory transmission triggers absence and convulsive seizures in a dose-dependent manner. These findings suggest that impaired cortico-striatal excitatory transmission is a plausible mechanism that triggers epilepsy in Stxbp1 and Scn2a haplodeficient mice.

Clinical and experimental insight into pathophysiology, comorbidity and therapy of absence seizures

“…These pharmacological and pharmaco-genetic results directly demonstrate a key role for the striatum in the control of absence seizures but are not supported by the lack of changes in the ictal firing of putative striatal fast-spiking and medium spiny neurons. Indeed, the latter result and other findings of Miyamoto et al (2019) are in contrast with previous observations in morphological identified striatal neurons of GAERS rats (see above) ( Fig. 6 ) ( Slaght et al , 2004 ).…”

“…A recent study on STXBP1 , a gene encoding the presynaptic protein Munc18-1, shows that injection of muscimol in the striatum of Stxbp1 −/− mice blocks their short (0.5–2 s) ethosuximide-sensitive absence seizures ( Miyamoto et al , 2019 ). Moreover, striatal application of NASPM, a selective blocker of calcium-permeable AMPA receptors, which are more abundant in the fast-spiking striatal interneurons than in the striatal medium spiny neurons ( Deng et al , 2007 ), elicits absence seizures in wild-type mice and (continuous) activation of Designer Receptor Exclusively Activated by Designer Drugs (DREADDS)-transfected fast-spiking striatal interneurons markedly reduces ASs in Stxbp +/− mice ( Miyamoto et al , 2019 ). These pharmacological and pharmaco-genetic results directly demonstrate a key role for the striatum in the control of absence seizures but are not supported by the lack of changes in the ictal firing of putative striatal fast-spiking and medium spiny neurons.…”

Thalamic activity patterns unfolding over multiple time scales predict seizure onset in absence epilepsy

“…Our results, in combination with these studies, suggest that the PO, and perhaps other thalamic or sub-cortical structures, may cascade the thalamocortical network into a pathological state. The long-lasting PiP that we identified may be the trigger itself, or may reflect a process that arises from other brain regions such as the striatum 87 . In any case, the distinct pre-seizure activity, if causative, must engage the larger thalamocortical network, and the mechanisms of this engagement will be the subject of future studies.…”

SCN2A channelopathies in the autism spectrum of neuropsychiatric disorders: a role for pluripotent stem cells?

“…Nevertheless, Scn2a haploinsufficient mouse models (Scn2a +/− ) show significant phenotypes linked to human disease and have been used to further elucidate the role of Na V 1.2 in both normal neurodevelopment and disease. Scn2a +/− mice display mild absence-like seizures, delayed spatial learning, increased contextual fear learning, impaired fear extinction, and hyperactivity [42,46,75,76], all of which may be related to ASD symptoms in humans. Cortical neurons from these mice display impaired excitability and impaired excitatory synapse function [61].…”