Glial cell involvement in spinal motor control: cheering from the side-lines or part of the team?

Research investigating the function of the brain and spinal cord (central nervous system) typically focuses on the role of nerve cells. However, recent work suggests that other cells, called glial cells, also control brain activity and therefore behaviour. Furthermore, the dysfunction of glial cells is known to be involved in many disorders of the central nervous system. Given the potential importance of glial cells in both health and disease, and the lack of widespread acceptance that glial cells are more than just 'support cells', we aim to provide clear evidence of involvement of glial cells in the control of neural networks and ultimately behaviour. We will achieve this by studying the role of glial cells in neural networks of the spinal cord which control movement. We have chosen networks of the spinal cord because, unlike most networks in the brain, they are relatively well-defined and we know and can measure the behaviour they control.

Our research will involve the use of state-of-the-art genetic, physiological and imaging techniques that allow us to measure the activity of neurons and glial cells and study their interactions. Using isolated pieces of mouse spinal cord we will first define the mechanisms of bi-directional signalling between glial cells and neurons. We will then examine the effect that glia to neuron signalling has on the network of neurons in the spinal cord which controls walking. This network can be studied using isolated mouse spinal cord tissue which can generate the electrical signals that control walking even when 'in a dish'. Next, we will study glia to neuron signalling in human cells. We will use new technology which allows stem cells to be derived from human skin samples. These stem cells can then be turned into glial cells and spinal neurons which can be grown together and studied in the lab.

By defining the ways in which glial cells and neurons of the spinal cord communicate and the effect this signalling has on neural networks that control movement, we will provide important new information about the role of glial cells in the generation of central nervous system activity and ultimately the control of behaviour. In addition, given that many diseases of the brain and spinal cord involve glial cells, the basic knowledge we generate about the function of glial cells (in mice and importantly also humans) will be critical for future studies targeting glial cells to design new treatments for a range of diseases.

Our overall aim is to establish whether astrocytes represent active components of neural networks controlling defined behaviours. We will focus on tractable motor networks of the spinal cord which are relatively well-defined and control measurable behaviours. We will delineate bi-directional astrocyte-neuron signalling and its role in motor control networks using a combination of state-of-the-art electrophysiological, imaging and molecular genetic techniques. Astrocyte to neuron signalling (gliotransmission) will first be investigated using patch-clamp recordings to measure the effects of astrocyte activation (via agonists of the astrocyte-specific Protease-activated receptor-1, optogenetic activation, or depolarisation) on genetically-defined populations of interneurons and motoneurons in mouse spinal cord tissue. Given our previous findings, we expect adenosine to be the primary gliotransmitter within the spinal cord. Next, neuron to astrocyte signalling will be investigated using patch-clamp recordings and Ca2+ imaging of astrocytes during neuronal stimulation (via depolarisation or optogenetic activation). The consequences of gliotransmission for network activity will then be investigated in mouse spinal cord preparations which generate locomotor-related activity in vitro. We will investigate the activity of astrocytes (fluctuations in intracellular Ca2+ and membrane potential) during locomotor network activity and assess the effects of astrocyte stimulation or inhibition (using glial toxins, or genetic inhibition of gliotransmitter release) on the output of the locomotor network. Finally, we will investigate the nature of bi-directional astrocyte-neuron signalling in cultures of neurons and astrocytes derived from human induced pluripotent stem cells. Together our findings will significantly advance understanding of the role of astrocytes within neuronal networks and may aid in the development of treatments for many neurological disorders involving glial cells.

Our proposed research will benefit a wide range of academics studying neural networks in both health and disease. We will provide basic information highlighting mechanisms of glia-neuron interactions that need to be considered when trying to decipher the normal function of neural networks as well as the mechanisms of disease underlying a myriad of disorders affecting the CNS. Our findings will also impact the teaching and training of future research leaders. We hope to influence the curricula of both undergraduate and postgraduate courses such that new findings on gliotransmission are integrated into classrooms and workshops. We will also train the PDRA hired on the project in a range of cutting edge techniques and help develop their skills in critical thinking and project management. The PDRA will then be able to apply these skills to other research posts or other employment sectors.

Beyond academia, our work will impact researchers in the private sector, such as those working for pharmaceutical companies aiming to develop new treatments for the many diseases of the CNS that involve glial cells. Our research will highlight new therapeutic targets relating to glia-neuron interactions and help develop a human cell-based model that may provide a more relevant and effective tool for drug discovery and development than existing animal models. In the longer term this will impact human health by leading to new treatments for a range of devastating neurological conditions. We face a global demographic shift towards an ageing population, and it is well established that age is the greatest risk factor for the development of many neurodegenerative conditions. Therefore new strategies that prevent, halt the progression of, or treat these disorders will have profound economic and social impact.

Our findings will also have a general impact on the public's understanding of the brain by highlighting glial cells, alongside nerve cells, as important contributors to the brains computational power and potential mediators of disease.