Coordination of anti-epileptic inhibitory mechanisms in neocortex

Lead Research Organisation: Newcastle University
Department Name: Institute for Ageing and Health

Abstract

Epilepsy is among the most common serious neurological conditions, affecting over a half million people in the UK, and over 50 million worldwide. Given its prevalence, it is important to ask how epileptic and normal brains differ. One hypothesis is that normal brains are protected by a particular set of inhibitory neurons, which act like circuit breakers: they fire in response to surges of activity, when the risk of a seizure is high, and prevent activity spreading out from its site of origin. The importance of this idea is that it can explain many different facets of epilepsy, from how genetic mutations give rise to seizures, right up to the nature of EEG rhythms.

Recently we have developed new ways of studying epilepsy, using the latest microscopy and electrophysiology technology to film epileptiform activity with unprecedented resolution. This work has highlighted the unusual activity patterns of certain inhibitory neurons. These cells are connected by unusual electrical contacts called gap junctions. Other evidence also points to the importance of gap junctions in epilepsy, and thus they represent a potential new target for anti-epileptic drugs. We will therefore investigate how gap junctions affect the behaviour of this important group of neurons.

Our studies will initially involve a very detailed study of the electrical properties of these unusual networks of cells, coupled by gap-junctions. These are very important baseline studies because they will show how normal brain activity spreads. By charcterizing these normal activity patterns, we can then determine how activity changes in epilepsy. To do this, we will use one of the best mouse models of epilepsy, in which mice have the same genetic mutation which has been identified as the cause of a particularly severe type of epilepsy, called Dravets syndrome. These animals, which mimic exactly real human conditions, because they derive from the exact same genetic mutations, are about the best models there are of human epilepsy. We are entering a period when such models may be created with increasing ease, yet we do not have a good way of characterizing their epilepsy. Our studies will show how to do this, by characterizing different facets of epileptic activity with exquisite detail using latest electrophyiological and microscopy techniques.

Finally we will move from mouse to humans, making use of a truly unique set of recordings taken from real people who are undergoing neurosurgical treatment for their epilepsy. These recordings have been made at a top American hospital, and have already allowed us to uncover new ways of interpreting one of the most important neurological diagnostic tools, the EEG.

Technical Summary

This project is part of a long-running research agenda to determine what stops focussed bursts of activity spreading out to become full epileptic seizures. Once recruited to an epileptic event, pyramidal cells fire intensely on the crest of large rhythmic depolarizations. Prior to this however, is a period when they experience similarly large depolarizations but do not fire, suggestive of a powerful restraint. This inhibitory veto is a strong candidate for regulating activity at this critical juncture in the evolution of a seizure.
How is this inhibitory response to a network crisis coordinated? Undoubtedly synaptic mechanisms are involved, but an underexplored role is also likely played by gap-junctions (GJs). We hypothesize that the exact pattern of intense discharge of INs is determined by the electrotonic structure of the syncytia. We hypothesize also that the likelihood of activity spreading through the syncytial network is modulated by factors such as rising intracellular Ca2+, shifts in K+ balance and altered membrane K+ permeability. These factors will therefore determine the extent of the inhibitory surround effect. We will further explore the complementary role of discharges in syncytia of different interneuronal classes, and how these are coordinated.
To test these hypotheses, we will establish:
1. The electrotonic structure of gap-junction coupled, interneuronal syncytia
2. How ionic concentrations and neuromodulators influence syncytial behaviour
3. How syncytial behaviour is altered in transgenic mouse models of myoclonic epilepsy.
4. Whether "signature" electrophysiological features of syncytia activity can be seen in human recordings.

Planned Impact

Our research impacts directly on one of the most common serious neurological conditions: epilepsy. The WHO estimates that, worldwide, more than 50 million people are diagnosed with epilepsy; to put this in context, about half this number suffer from any form of dementia. Over the last 8 years, we have developed sophisticated new approaches to understanding various simple in vitro animal models of epileptic propagation, but importantly, our recent collaborations with Dr Catherine Schevon have shown clearly that these studies have direct relevance to epilepsy in humans. Furthermore, our detailed understanding of the spatial pattern of activity during in vitro epileptiform discharges indicated a potential pitfall for EEG localization of seizures. We have now confirmed this from human recordings, and this will lead to a revision of how epileptic activity is localized for neurosurgical procedures. Other parallel studies are seeking to translate our basic research findings to clinical practice by developing visual tests for assessing seizure risk. These studies provide a clear proof of principle showing how simple animal research impacts directly on clinical practice.

We also outline a comprehensive approach to characterizing epileptic phenotypes in transgenic mice. This can form a template for all future epilepsy studies on such mice, and further impact on related studies examining pharmacological approaches to managing epilepsy in these animals. AT is a core member of an application to form an MRC Mouse Network Research Consortium advising on the generation and research of transgenic mice. These initiatives will impact on pharmaceutical companies designing and testing novel anti-epileptics. It is notable that the main focus of our proposal, gap junctions, are not currently targeted by any anti-epileptic medication.

Publications

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Alfonsa H (2015) The contribution of raised intraneuronal chloride to epileptic network activity. in The Journal of neuroscience : the official journal of the Society for Neuroscience

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Codadu NK (2019) Divergent paths to seizure-like events. in Physiological reports

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Merricks EM (2015) Single unit action potentials in humans and the effect of seizure activity. in Brain : a journal of neurology

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Papasavvas CA (2015) Gain control through divisive inhibition prevents abrupt transition to chaos in a neural mass model. in Physical review. E, Statistical, nonlinear, and soft matter physics

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Parrish RR (2018) Simultaneous profiling of activity patterns in multiple neuronal subclasses. in Journal of neuroscience methods

 
Title Tsunami in the brain 
Description I transcribed an electrophysiological recording of a seizure into a piece of music, by equating different frequency bands of the signal to particular notes played by different musical instruments. I did the initial analysis using Matlab software, and then transcribed this into a written piece of music using the composing software, Sibelius, and also using this to create an audio file of the piece. This was the centrepiece of a presentation that we made at the British Science Festival in 2013, and is now posted online in efforts to raise money for epilepsy research at the following URL: http://www.epilepsyresearch.org.uk/tsunamis-in-the-brain/ 
Type Of Art Performance (Music, Dance, Drama, etc) 
Year Produced 2013 
Impact The video has been viewed several hundred times 
URL http://www.epilepsyresearch.org.uk/tsunamis-in-the-brain/
 
Description NC3Rs report on epilepsy research
Geographic Reach National 
Policy Influence Type Participation in a advisory committee
Impact Our study collated information pertaining to the use of animals in epilepsy research and provided guidance on such matters, as a published review.
URL https://www.ncbi.nlm.nih.gov/pubmed/26376175
 
Description Project Grant
Amount £147,334 (GBP)
Funding ID P1504 
Organisation Epilepsy Research UK 
Sector Charity/Non Profit
Country United Kingdom
Start 09/2015 
End 09/2017
 
Description Research grant, responsive mode
Amount £594,000 (GBP)
Funding ID BB/P019854/1 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC) 
Sector Public
Country United Kingdom
Start 10/2017 
End 09/2020
 
Description Schaefer Research Scholarship
Amount $250,000 (USD)
Organisation Columbia University 
Sector Academic/University
Country United States
Start 06/2016 
End 10/2017
 
Title Cl-out 
Description We developed a new optogenetic protein tool, which allows chloride to be actively removed from the cytosol of neurons, driven by light. since chloride levels are integral for functional synaptic inhibiiton, this tool serves to improve inhibition. 
Type Of Material Technology assay or reagent 
Year Produced 2016 
Provided To Others? Yes  
Impact Publication of proof of principle for this new optogenetic tool (Alfonsa et al, Nature Communications, 2016) 
URL https://www.ncbi.nlm.nih.gov/pubmed/27853135
 
Description Collaboration with Dr Cathy Schevon 
Organisation Columbia University
Department Department of Neurology
Country United States 
Sector Academic/University 
PI Contribution Consultant on RO1 award (April 2013) This award is now active. We are submitting a paper in November 2014, first author Merricks, and with myself as corresponding author.
Collaborator Contribution Analysis of data and co-authoring of papers and grant proposal
Impact Several publications already, but the RO1 will only activate in autumn, 2013
Start Year 2013
 
Description Schaefer Research Scholarship (Columbia University) 
Organisation Columbia University Medical Center
Country United States 
Sector Academic/University 
PI Contribution A personal award to myself, from Columbia University, to facilitate continued collaborative work on epilepsy.
Collaborator Contribution Award was for collaboration with Profs Cathy Schevon and Wayne Frankel (both at Columbia University Medical School).
Impact None yet
Start Year 2016
 
Title Novel optogenetic protein 
Description Development of new optogenetic protein, Cl-out, which is a light-sensitive, membrane bound protein, which drives chloride out of cells, when activated by light. 
IP Reference GB1601008.4 
Protection Patent application published
Year Protection Granted 2016
Licensed No
Impact Publication of description of the technique in Nature Communications, in 2016.
 
Description 1st IBRO-UCT African Advanced School of Epilepsy 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact I gave 3 seminars, ran tutorial groups and also ran practical classes to a group of about 40 students gathered from all across Africa.
Year(s) Of Engagement Activity 2015
URL http://ibro.info/events/ibro-uct-african-advanced-school-on-epilepsy/
 
Description 6th International Workshop on Seizure Prediction 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact I presented my research to an audience of experts in my field.
A PhD student of mine, Edward Merricks, also spoke at the meeting.
Arising from this, I co-authored a review article that has recently been accepted for publication in the journal, Clinical Neurophysiology. I am first and corresponding author.

Pending
Year(s) Of Engagement Activity 2013
URL http://www.iwsp6.org
 
Description Columbia University 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Neurology grand rounds at Columbia University Medical Center
Year(s) Of Engagement Activity 2017
 
Description Epilepsy workshop 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact A small workshop including mathematicians, physicists, computational modellers and biologists to discuss the nature of network activity in the brain, with particular reference to epilepsy
Year(s) Of Engagement Activity 2015
 
Description IBRO 2016 Workshop - Budapest 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Invited symposium speaker
Year(s) Of Engagement Activity 2016
URL http://www.ibro2016.hu/
 
Description IWSP6 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Type Of Presentation Keynote/Invited Speaker
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Collaborations pending
Year(s) Of Engagement Activity 2013
URL http://www.iwsp6.org/
 
Description NC3Rs Epilepsy Working Group 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact This has now been disbanded, following completion of our review, and the publication of our findings in the Journal of Neuroscience Methods (Lidster et al, doi: 10.1016/j.jneumeth.2015.09.007)

Pending
Year(s) Of Engagement Activity 2012,2013,2014,2015
 
Description Neuromouse 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Type Of Presentation Workshop Facilitator
Geographic Reach National
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Ongoing creation of new mouse models of neurological disease arising from genetic mutations.
Year(s) Of Engagement Activity 2012,2013
URL http://mrcmousenetwork.har.mrc.ac.uk/all-consortiums/neuromouse-integrated-and-translational-researc...
 
Description North East Epilepsy Research Meeting 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact 2014: About 100 delegates attended including senior research figures from Harvard (USA), Pisa (Italy) and Erasmus University (Rotterdam, Holland)
2015: similar size meeting. I chaired the session of talks by postdoctoral researchers

Pending - research collaborations
Year(s) Of Engagement Activity 2013,2014,2015
URL http://www.ncl.ac.uk/ion/news/neernm.htm
 
Description Tsunamis in the Brain:The science and sociology of Epilepsy 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact The event, held in Newcastle on 12th September, was attended by over 100 people, and there was an enthusiastic smaller group who relocated to a local cafe for further conversations.

The event was filmed and has now been posted on the Epilepsy Research UK website for fund raising purposes.(http://www.epilepsyresearch.org.uk/tsunamis-in-the-brain/)

It is also posted on youtube as a single 18min film, and also as a collection of 6 short separate sections
(https://www.youtube.com/watch?v=J1dunq_ABlM)
Year(s) Of Engagement Activity 2013
URL http://www.epilepsyresearch.org.uk/tsunamis-in-the-brain/
 
Description WONOEP 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Type Of Presentation Keynote/Invited Speaker
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Talk at a closed workshop meeting attended by 100 senior epilepsy researchers.

Collaborations pending
Year(s) Of Engagement Activity 2013
URL http://www.aesnet.org/events/2013-06-19/xii-workshop-on-neurobiology-of-epilepsy-wonoep-2013
 
Description Yale University 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact Seminar at Yale University Medical School
Year(s) Of Engagement Activity 2017