Evaluating the impact of spreading depolarisations, post stroke, in the awake brain using graphene-enabled nanotechnology.

Stroke is a frequent cause of death and disability in adults worldwide. Ischaemic stroke is the result of a blockage in a cerebral blood vessel that supplies blood to a region of the brain, inducing a severe reduction in cerebral blood flow. Haemorrhagic stroke, or brain bleed, is the result of a cerebral vessel rupturing. This decrease in blood flow, which is needed to provide energy (oxygen and glucose) to the brain, results in the death of brain cells and loss of neurological function. The main damage to the brain happens very quickly, in the first few hours from when the stroke happened but can continue for days or even weeks. The region of the brain which has the lowest blood supply, and where brain cells die the quickest, is called the 'core' region. In contrast brain regions surrounding the core, that have reduced blood flow but with partially functioning brain cells, is called the 'penumbra'. The brain cells in the penumbra may, over time, die which expands the core region and contributes to greater damage to the brain. The penumbra region is the area of the brain that can be saved and is the main target for most stroke therapies. Waves of pathological brain signals called spreading depolarisations (SDs) are known to be major contributors to core expansion, and hence worsen stroke outcome. SDs spontaneously occur in the penumbra region, post stroke, and propagate throughout brain grey matter. As SDs propagate through the brain they depolarise brain cells and result in almost complete ion homeostasis failure. SDs also induce additional reduction of cerebral blood flow in the penumbra region, a region that is already experiencing a reduction in blood flow. Seizures can also occur post-stroke and their frequency is likely underreported due to the fact that many remain focal with little or no behavioural manifestation. A key problem when conducting research to design therapeutic strategies to suppress SDs is the lack of pre-clinical electrophysiological technology capable of detecting infraslow brain signals (below 0.1 Hz), where SDs are recorded, at high spatiotemporal resolution. The Wykes lab has successfully collaborated with the material scientists who designed and fabricate arrays of graphene-based neurophysiological probes capable of recording SDs across large areas of brain, demonstrating their usefulness for studying pathological brain signals in intact brain. We now aim to bring this cutting-edge technology to pre-clinical stroke research to gain a better understanding of the mechanisms of SD initiation and their involvement in worsening stroke severity, in the awake brain. Furthermore, we aim to design a therapeutic strategy that suppresses SDs and reduces stroke core expansion. This work will be a crucial first step in the maturity of this technology towards future clinical translation where we anticipate that it will greatly facilitate management of patients in the neuro-intensive care units.

Spontaneous waves of depolarisation have been observed in metabolically comprised but not yet irreversibly damaged stroke penumbra, termed spreading depolarisations (SDs). Importantly, expansion of the stroke core has been shown to directly correlate with the number of SDs, indicating that a therapeutic intervention to suppress SDs will have a positive impact on reducing infarct tissue expansion and stroke severity. A limitation when researching SDs, and the development of therapeutics to target SD initiation, has been a lack of appropriate tools to record them in vivo with high spatiotemporal fidelity. Improvements in technology capable of monitoring SDs in vivo, in the awake brain, with high spatiotemporal properties will have considerable impact to both preclinical and future clinical studies. Novel graphene solution-gated field-effect transistors (gFETs) arrays allow wide bandwidth electrophysiological recordings. These devices can record concurrently SDs AND higher frequency activity allowing us to also record neuronal suppression or epileptiform activity. This technology will enable the direct correlation between SDs and the expansion of the stroke core. Furthermore, gFETS will enable the evaluation of therapeutic interventions aimed at suppressing SDs. The aim of this proposal is to apply cutting edge gFET array technology to preclinical stroke research. This work will allow unprecedented insight into SD dynamics in the awake brain after ischemic and haemorrhagic stroke. Combined with pharmacological and neuromodulatory suppress SDs, gFETS arrays will allow us to directly determine the contribution SDs have to stroke core expansion and overall severity. Our programme of work will gain a better mechanistic understanding of SDs in the awake brain, evaluate SDs contribution to stroke severity, and identify potential therapies to suppress SDs initiation.