Elucidating the role of surviving neurons in morphological and functional recovery after brain injury in zebrafish

When somebody injures their brain, for instance during a fall or an accident, they often have life-long problems from this brain injury. This is because the human brain is unable to repair itself when it has been damaged. In contrast to humans, a small tropical fish called the zebrafish can repair many organs after an injury, including the brain. Once we understand how zebrafish manage to repair their brains, we may be able to use this knowledge to help patients with brain injury.
In our lab we use larval zebrafish to study the processes that enable these animals to repair their brains. Larval zebrafish are a great model system to address this question because they are very small and almost entirely transparent. This means we can easily put them under a microscope and observe the processes that happen in the brain after an injury, which is a huge advantage when asking questions about how the brain manages to repair itself.
One thing that zebrafish can do that humans cannot do very well is to make new nerve cells after an injury, to replace the ones that have been lost. Much research has focussed on how these new nerve cells are made, and we are beginning to understand this process in some detail. However, another aspect of the brain repair process has received less attention, and that is the role that surviving nerve cells play in repairing the brain. In our lab we have already obtained results that show that surviving nerve cells move into the injury site in the days after the injury. This suggests that they actively 'patch up' the damage that has been caused by the injury. We now need to understand whether the presence of surviving nerve cells in the lesion site helps to restore the function of the damaged brain tissue.
For this we will test whether stopping nerve cells from moving into the injury site allows another type of cell, called a glial cell, to accumulate there. This is important because when many glial cells accumulate at the site of an injury they can form a so-called 'glial scar'. This glial scar sits in the lesion site and prevents the rebuilding of normal brain tissue, so when a glial scar is present the brain tissue cannot function normally again. Therefore it will be interesting to find out whether the accumulation of glial cells at the injury site can be reduced when there are nerve cells there.
We will also test whether individual nerve cells can contribute to restoring the function of damaged brain tissue, by studying whether damaged nerve cells manage to repair the part of the cell that is needed for receiving information from other nerve cells. This part of the cell is called a dendrite, and it is necessary for a nerve cell to function properly. Therefore it will be important for us to determine whether nerve cells manage to repair their dendrites because this could be another way for them to contribute to restoring the function of injured brain tissue.
In summary, the work in this project will help us to understand an important aspect of brain repair, namely how surviving nerve cells contribute to the recovery of the structure and function of the injured brain. Ultimately, these results may help us to develop new treatments for patients with brain injury.

In contrast to mammals, zebrafish can repair their brains after injury. They are hence a useful model system in which to study the mechanisms that enable successful brain repair. Important progress has been made in understanding reactive proliferation and regenerative neurogenesis in zebrafish, but little is known about the injury responses of neurons that survive an insult. Our preliminary data using mechanical injury to the larval zebrafish optic tectum suggest that surviving neurons from the vicinity of the injury site move into the lesion path in the days after an insult. This raises the possibility that they play a key role in restoring tissue architecture and function. Here we propose to document the injury responses of surviving neurons at the tissue and cellular level; to investigate the molecular mechanisms regulating these responses; and to define the contribution that surviving neurons make towards the restoration of brain tissue architecture and function. At the tissue level, we will use in vivo confocal imaging to determine the timecourse of the movement of surviving neurons into the injury site, to investigate whether this movement is regulated by Rho GTPase signalling, and to determine whether the presence of surviving neurons within the lesion path can prevent the excessive accumulation of astroglia-like cells. At the cellular level, we will document injury-induced structural plasticity in the dendrites of tectal neurons through live imaging, and determine whether this is regulated by Rho GTPases. Furthermore, we will use functional in vivo calcium imaging to map the receptive fields of tectal neurons before and after injury, and to determine whether changes in receptive field properties are driven by injury-induced changes in dendrite morphology. This work will yield fundamental insights into the contribution of surviving neurons towards morphological and functional recovery after brain injury in a regeneration-competent organism.

In the proposed work we will elucidate the role that surviving neurons play in morphological and functional recovery after brain injury in larval zebrafish. We expect that the project will have a wide range of benefits, both within the academic community and in a wider societal context.

Scientific findings
The proposed project will span multiple scientific fields, and we therefore expect that our results will be of interest to researchers in a range of different disciplines. Scientists interested in our work will include basic and clinical neuroscientists as well as researchers working in tissue repair biology and regenerative medicine. To maximise scientific benefit, we will disseminate our results widely by publication in international peer-reviewed journals, by presentations at national and international meetings, and in invited lectures at universities and research institutes. The results from this project will also lay the foundation for further research in my own research group, and will thereby ensure its continued funding.

Resources
Newly generated genetically modified fish will be available directly from us, and from the European Zebrafish Resource Center.

Training
The postdoc and any MSc students working on the project will acquire a wide range of technical skills along with broad theoretical knowledge relevant to the project. As members of my research group, CDBS, and the wider Edinburgh Neuroscience community, they will be exposed to new ideas and cutting-edge research on a daily basis, which will greatly benefit their scientific careers.

Commercial exploitation
The mechanistic insights gained through the proposed work may contribute towards the development of novel therapeutic approaches for the treatment of brain injury in humans. Therefore, we expect that our results will generate substantial interest in the commercial biomedical research community. To ensure early identification of commercial potential, we will be in regular contact with Edinburgh Research and Innovation (ERI), the commercial arm of the University. Staff at ERI will provide guidance on commercialisation of our results, and in particular support for any patent applications.

Communications and engagement
We expect that the proposed project will meet with broad interest in the general public since neuroscience, tissue repair biology, and zebrafish research are all topics that usually attract considerable attention from lay audiences. Over the course of the project, we will communicate with the general public through various different channels including press releases, news updates on different University websites, seminar series, and public engagement events. In particular, we will be in regular contact with Dr Jane Haley, the Edinburgh Neuroscience coordinator, who runs an extensive public engagement programme. Planned activities include schools visits within the getBRAINY workshops series, hosting high school pupils in the lab within the Science Insights programme, and running stalls with drop-in activities at the Edinburgh International Science Festival and the Midlothian Science Festival.

Capability
People employed in the project will receive extensive training in both research and transferable skills. In particular, they will learn to work as members of a team, improve their organisational skills, optimise their time management, and hone their presentation and communication skills, all of which are invaluable assets in the job market.