Abnormal brain state distribution and network connectivity in aSYNGAP1rat model

Abstract

Mutations in the SYNGAP1 gene are one of the common predictors of neurodevelopmental disorders, commonly resulting in individuals developing autism, intellectual disability, epilepsy, and sleep deficits. EEG recordings in neurodevelopmental disorders show potential to identify clinically translatable biomarkers to both diagnose and track the progress of novel therapeutic strategies, as well as providing insight into underlying pathological mechanisms. In a rat model of SYNGAP1 haploinsufficiency in which the exons encoding the calcium/lipid binding and GTPase activating protein domains have been deleted (Syngap+/Δ-GAP) we analysed the duration and occurrence of wake, non rapid eye movement and rapid eye movement brain states during 6 hour multi-electrode EEG recordings. We find that although Syngap+/Δ-GAP animals spend an equivalent percent time in wake and sleep states, they have an abnormal brain state distribution as the number of wake and non rapid eye movement bouts are reduced and there is an increase in the average duration of both wake and non rapid eye movement epochs. We perform connectivity analysis by calculating the average imaginary coherence between electrode pairs at varying distance thresholds during these states. In group averages from pairs of electrodes at short distances from each other, a clear reduction in connectivity during non rapid eye movement is present between 11.5 Hz and 29.5 Hz, a frequency range that overlaps with sleep spindles, oscillatory phenomena thought to be important for normal brain function and memory consolidation. Sleep abnormalities were mostly uncorrelated to the electrophysiological correlate of absence seizures, spike and wave discharges, as was the imaginary coherence deficit. Sleep spindles occurrence, amplitude, power and spread across multiple electrodes were not reduced in Syngap+/Δ-GAP rats, with only a small decrease in duration detected. Nonetheless, by analysing the dynamic imaginary coherence during sleep spindles, we found a reduction in high connectivity instances between short-distance electrode pairs. Finally comparing the dynamic imaginary coherence during sleep spindles between individual electrode pairs, we identified a group of channels over the right somatosensory, association and visual cortices that have a significant reduction in connectivity during sleep spindles in mutant animals. This matched significant reduction in connectivity during spindles when averaged regional comparisons were made. These data suggest that Syngap+/Δ-GAP rats have altered brain state dynamics and EEG connectivity, which may have clinical relevance for SYNGAP1 haploinsufficiency in humans.

Absence seizures and sleep abnormalities in a rat model ofGRIN2Bneurodevelopmental disorder

“…61 Mitogen-activated protein kinases phosphorylate core clock gene regulators [62][63][64][65][66][67] , and these pathways are affected in SYNGAP1, NLGN3, FMR1 and SCN2A deficient mice and rats [68][69][70][71] , which also present with sleep impairments. 22,70,72,73 Thus, inadequate GluN2B cellular signalling could in part contribute to the sleep alterations observed in Grin2b +/mutants. Future work will need to investigate whether dysregulation in diurnal behavioural patterns is present, and whether and to what extent mitogen-activated protein kinase activity and clock gene modulation is affected by GluN2B haploinsufficiency.…”

“…We utilized a previously published automatic SWD detector algorithm to quantify SWDs. 22,23 Spectral analysis allowed for the identification of harmonic peaks in the SWD frequency range. The code used for analysis is available at https://github.com/Gonzalez-Sulser-Team/SWD-Automatic-Identification.…”

Hyperexcitability and translational phenotypes in a preclinical mouse model of SYNGAP1-Related Intellectual Disability

“…Power spectral analysis, herein, identified harmonic peaks. Using the earlier described methodology, that defined sleep stages (NREM sleep, REM sleep or wake), using 5 s recording epochs, it was reported that Syngap +/Δ−GAP rats spent an equivalent percentage of time in all states when compared with WT littermate controls 54 , but exhibited less NREM and wake bouts, similar to our report that found reduced amount of time in slow wave sleep and wake, albeit differing from the report herein that identified substantially elevated delta power (<p<0.0001) and significantly elevated theta spectral power (<0.05). Direct comparison of our data presented herein is complicated given the vastly different methodologies, species, EEG acquisition time, channels utilized to acquire data, and analysis of the signal.…”

“…In summary, over 20 years since its discovery, we have built on earlier work to identify a combinatorial and corroborative report on electro-and neurophysiological biomarkers for SRID precision therapeutic development 54,75,[77][78][79] . Our key novelty, from prior reports, lies in the reporting and analytic combination of: i) in vitro HD-MEA recording and analysis using dissociated and plated cortical neurons from WT and Syngap1 +/cortices, in parallel, with ii) in vivo wireless, cortical EEG, capturing cortical circuitry and bridging 2D in vitro electrophysiological properties with 3D, live, awake, behaving, in vivo neurophysiological outcomes.…”

“…Our key novelty, from prior reports, lies in the reporting and analytic combination of: i) in vitro HD-MEA recording and analysis using dissociated and plated cortical neurons from WT and Syngap1 +/cortices, in parallel, with ii) in vivo wireless, cortical EEG, capturing cortical circuitry and bridging 2D in vitro electrophysiological properties with 3D, live, awake, behaving, in vivo neurophysiological outcomes. To date, 2D SRID cellular modeling work had been limited to traditional patch clamp electrophysiology in the various mouse and rat models 54,79 . This is the first report using HD-MEAs in neurons lacking Syngap1 exhibited increased network activity by a greater number of bursts with less time between bursts, compared to neurons from WT cortices.…”