Dissection of the cellular mechanisms of functional MRI using targeted optogenetics

Magnetic resonance imaging (MRI) is perhaps the biggest advancement in human imaging technology since
the discovery of X-rays by Roentgen. Initially it was used to provide structural information about the body
and the brain but it was the introduction of functional MRI (fMRI) that had the most profound impact on
neuroscience and basic cognitive research. Although fMRI is widely used in clinical and experimental
neurology, the fundamental cellular mechanism of fMRI remains poorly understood. This limits the value of
the information generated by this exciting technology. Brain is a highly complex organ and signals measured
by fMRI are indirect and although they do reflect activation and de-activation of nerve cells in various parts
of the brain. This research will look at the cellular basis of fMRI using a new technology called
"optogenetics" voted "Method of year 2010". Optogenetics allows us to make certain cells light sensitive,
such that we can switch them 'on' and 'off' using light. Quite simple we will be able to control the brain
via light and watch this happen in real time using the MRI scanner. Our results should not only shine a light
on how fMRI works, but also have wider implications for human brain research.

Functional MRI (fMRI) has made a dramatic impact on clinical neurology and basic research but the cellular basis of haemodynamic responses underlying BOLD signals remain elusive. Understanding the origins of BOLD signal is essential to make connections between basic and clinical neuroscience. BOLD signals reflect changes in blood flow, volume and the rate of O2 consumption. They are underpinned by the "functional hyperemia" which couples delivery of oxygenated blood to neuronal activity. The emerging consensus is that the reactive hyperemia is not a compensatory response to depletion of O2 but a feed-forward phenomenon. The link between neuronal activity and brain microcirculation is indirect. Recent evidence strongly implicates astrocytes in neurovascular coupling. However, much of the current knowledge comes from in vitro slice work and the role of astrocytes in neurovascular coupling and generation of BOLD signals remains poorly understood. We propose to use optogenetics to study the cellular mechanisms of fMRI and focus on astrocytes. Optogenetics permits targeted manipulation of the specified cell populations using light sensitive proteins. We were first to apply optogenetics to study astrocytes (Science, 2010, 329, 571-5) and are in an excellent position to study role of astroglia neurovascular coupling and fMRI. Astrocytes and neurones will be made to express various optogenetic tools to enable us to monitor the impact of their selective activation or deactivation on cortical microcirculation and this will be paralleled with fMRI at 9.4T. Signalling molecules essential for neurone-to astrocyte-to blood vessels signalling will be identified using genetic and pharmacological tools. Optogenetic activation of neuronal projections and natural stimuli will be applied in order to reveal how compromised astrocitic signalling changes vascular responses and BOLD signals. Our hypothesis is that astrocytes are fundamentally important for generation of BOLD signals.

fMRI has the most profound impact on neuroscience and basic cognitive research but its fundamental cellular mechanism remains poorly understood. This limits the value of the information generated by this exciting technology. This project aims to investigate the fundamental mechanisms of neurovascular coupling between neurones, astrocytes and blood vessels. It is expected to reveal fundamental mechanisms of brain function and therefore, the basic science value of these studies is very high. Basic neuroscientists or clinical researchers may certainly benefit from the proposed work. The results will be available to a wider scientific community via publication in the leading scientific journals.
We will also seek to improve the public perception of the value and role of the functional imaging and optogenetics. Both UoB and UCL provide public engagement mechanisms for ensure accurate representation to foster public support. We hope to generate some high profile papers which could be a good opportunity to generate press releases and give presentations to general public. Our recent publication in SCIENCE has attracted world-wide comments in media ranging from "Spiegel" and "Discover" magazines to various neuroscience blogs. ML is Director of the Cheltenham Science Festival, one of the largest science communication festivals in the world which provides great potential to engage with national communities about this work. In addition, this project includes numerous imaging experiments which sometimes generate very visually appealing images. Images from the SK laboratory have been used by the Physiological society, Royal Society, Wellcome trust, Experimental Physiology for generation of leaflets and brochures, this directly communicates the appeal of science to general public.
Capacity building. Wider physiological and pharmacological research communities, both in academia and pharmaceutical industry, would benefit from the wider introduction of optogenetics, which is at the heart of this proposal. Training personnel with skills in fMRI is clearly also a priority and will be essential to support wider implementation of this powerful technology. As indicated in the MRC feedback letter, building capability in optogenetics is of strategic importance to the UK science base.This project provides an excellent platform for training or personnel (PhD students and PostDocs) and dissemination of optogenetics in the UK.
Engagement and Communications. We actively engage the community in science and research we undertake by increasing public understanding of our discipline. UCL Media Relations provides excellent opportunities to engage with local and national communities. We will access existing UCL public engagement mechanisms to ensure accurate representation to foster public support.
Translational potential: In a longer term, our research may directly contribute to the improvement of human health. If we better understand how BOLD signals are generated this will have implications to the interpretation of the changes seen in patients, possibly help to improve diagnostics and interpret the results of treatments. It is also possible that the basic research into the mechanism of neurovascular coupling may offer new drug targets for treatment of brain disorders many of which are accompanied by changes in microcirculation. These drugs may prove to be effective in reducing morbidity and improving quality of life of patients with various neurologic diseases. We are in direct contact with the clinicians involved in human fMRI, who also sit on our advisory panel. This provides a direct conduit for clinical translation and will help to develop a strategy to analyze already available clinical fMRI datasets obtained in patients who were taking prescribed medications known to interfere with hypothesised signalling pathways.