Synaptic Changes in AMPA Receptor Subunit Expression in Cortical Parvalbumin Interneurons in the Stargazer Model of Absence Epilepsy.

Nadia K Adotevi,Beulah Leitch

doi:10.3389/fnmol.2017.00434

Nadia K Adotevi, Beulah Leitch

Open Access

https://doi.org/10.3389/fnmol.2017.00434

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Abstract

Feedforward inhibition is essential to prevent run away excitation within the brain. Recent evidence suggests that a loss of feed-forward inhibition in the corticothalamocortical circuitry may underlie some absence seizures. However, it is unclear if this aberration is specifically linked to loss of synaptic excitation onto local fast-spiking parvalbumin-containing (PV+) inhibitory interneurons, which are responsible for mediating feedforward inhibition within cortical networks. We recently reported a global tissue loss of AMPA receptors (AMPARs), and a specific mistrafficking of these AMPARs in PV+ interneurons in the stargazer somatosensory cortex. The current study was aimed at investigating if cellular changes in AMPAR expression were translated into deficits in receptors at specific synapses in the feedforward inhibitory microcircuit. Using western blot immunolabeling on biochemically isolated synaptic fractions, we demonstrate a loss of AMPAR GluA1–4 subunits in the somatosensory cortex of stargazers compared to non-epileptic control mice. Furthermore, using double post-embedding immunogold-cytochemistry, we show a loss of GluA1–4-AMPARs at excitatory synapses onto cortical PV+ interneurons. Altogether, these data indicate a loss of synaptic AMPAR-mediated excitation of cortical PV+ inhibitory neurons. As the cortex is considered the site of initiation of spike wave discharges (SWDs) within the corticothalamocortical circuitry, loss of AMPARs at cortical PV+ interneurons likely impairs feed-forward inhibitory output, and contributes to the generation of SWDs and absence seizures in stargazers.

Highlights

Absence epilepsy is the most common early-onset epilepsy, accounting for about 10–17% of all pediatric epilepsies (Matricardi et al, 2014)
To analyze relative expression of AMPA receptors (AMPARs) at synapses in epileptic stargazers compared to NE littermates, somatosensory cortex tissue was separated into subcellular components by biochemical fractionation (Figure 1A)
PSD95 and CaMKII, were enriched in synaptic fractions (TxP), with very low levels in the total lysate (S1). β-actin was present in all fractions except the extrasynaptic membrane (TxS), whereas pan-cadherin was detected in all fractions (Figure 1B)

Summary

Introduction

Absence epilepsy is the most common early-onset epilepsy, accounting for about 10–17% of all pediatric epilepsies (Matricardi et al, 2014). It is a non-convulsive, generalized genetic epilepsy characterized by sudden, brief loss of consciousness, which can occur 100s of times a day (Berg et al, 2010). Despite years of extensive research into seizure mechanisms, this has not translated into the development of novel anti-epileptic drugs (AEDs) with increased efficacy for treatment (Loscher, 2017). In order to develop safe and targeted patient-specific AEDs, there is a need to identify the different cellular and molecular mechanisms underlying absence seizures, taking into account possible variations in geneticallydifferent patients

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