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

Lead Research Organisation: University of St Andrews
Department Name: Psychology

Abstract

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.

Technical Summary

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.

Planned Impact

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.

Publications

10 25 50
 
Description Our research has led to a number of novel findings regarding the roles of glial cells within neuronal networks, which should be of interest to a broad scientific audience.
• We have generated strong evidence that spinal cord glial cells communicate with neurons, regulating neuronal activity and the output of locomotor control networks, by releasing purine transmitters.
• We have provided novel information about how spinal neurons communicate directly with glial cells. This primarily involves activation of a specific receptor (mGluR5) expressed on glial cells. However, we have also shown that there are many other neurotransmitters that could be involved in neuron-glia communication. Thus, we have evidence of bi-directional communication between neurons and glia in the spinal cord.
• We have revealed that modulation of neuronal output by glial-derived purines is dependent on co-activation of dopamine receptors. Alongside this work, we have discovered that Na/K pumps serve as a target for dopamine-mediated modulation, which also affects motor network output.
• Our extensive, high resolution imaging has shown that spinal cord synapses that are associated with glial cells (tripartite synapses) exhibit greater structural and molecular diversity. Furthermore, we have found that the expression of postsynaptic proteins is altered following pharmacological activation of glial cells, supporting a causative link between the presence of glial cells and the complexity of synaptic structure.
Exploitation Route We expect that our novel findings will guide the work of other researchers aiming to decipher the interactions between neurons and glia throughout the nervous system and the roles that such interactions play in the neural control of behaviour. Our findings are also likely to guide translational research focussed on a range of diseases in which glial cells are implicated. By providing new insight into the bi-directional communication between neurons and glia, we hope that our work has revealed new targets for the development of novel treatments for a range of neurodegenerative diseases in which glial cells are thought to contribute.
Sectors Education,Healthcare,Pharmaceuticals and Medical Biotechnology

 
Description Explorathon Public Outreach Evening 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact We ran an interactive exhibit which involved a mock (but as realistic as possible) experimental setup of the kind we utilise during our BBSRC-funded project to record the activity of spinal motor control circuits and study the influence of glial cells on these circuits. Visitors could directly interact with the setup - moving electrodes under a microscope to attach them to real mouse spinal cord tissue. Alongside the demonstration, we discussed our area of research and current research aims. Our display was one of several on the night. Based on data collected on the night, the event was very well-received. We have been told that our display was singled out and praised by several visitors who gave feedback via video interviews.
Year(s) Of Engagement Activity 2016,2017
URL http://www.explorathon.co.uk/standrews
 
Description Interview for Royal Society of Edinburgh YouTube Quiz-a-Whiz series 
Form Of Engagement Activity A broadcast e.g. TV/radio/film/podcast (other than news/press)
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact Quiz-a-Whiz' is an initiative setup by the Royal Society of Edinburgh (RSE). School pupils and teachers are encouraged to submit a question and the RSE asks a leading expert to record the answer and posts a video of this YouTube.
Year(s) Of Engagement Activity 2017
URL https://www.youtube.com/watch?v=MJGQZ-ZukHg
 
Description School visit (Crail, Fife) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact The postdoc hired on this grant and I ran a day of workshops for students (and teachers) at a local primary School. We began with a brief presentation then used specimens, and models to convey basic information about the nervous system and our research. We used an interactive model of a synapse to explain the combined roles of neurons and glial cells, which is the subject of our current study. Following the event, the head teacher of the School reported considerable interest amongst the students. The students worked on the topic further in class using some of what they learnt during our workshop.
Year(s) Of Engagement Activity 2016
 
Description University of St Andrews Science Discovery Day 
Form Of Engagement Activity Participation in an open day or visit at my research institution
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact We ran an interactive display teaching visitors about the basics of the nervous system including what it is "made up of" and some of our research concerning spinal motor system and Motor Neurone Disease. This involved the use of brain models, real specimens that visitors could hold, spinal cord sections visualised using microscopes and a hands-on model of a synapse that included neurons and glial cells. One of our key goals was to teach visitors that the brain is made up of more than just neurons by introducing them to glial cells and explaining some of their roles in synaptic transmission. We assessed the impact of our interactive display by asking visitors to complete a short survey. In response to a multi-choice question asking what they thought the brain was made up of, 68% of our 41 respondents chose the option "neurons and glial cells". All respondents either 'strongly agreed' or 'agreed' that they "learnt new things about the brain". 87% of respondents 'strongly agreed' or 'agreed' that they were " now more interested in learning about the brain". Our display also sparked many discussions with visitors about various aspects of neuroscience including the research we are currently undertaking. Overall, it seems that we were successful in educating visitors about the presence of glial cells in the nervous system and we increased peoples interest in learning more about the nervous system and its constitutive parts.
Year(s) Of Engagement Activity 2016,2018,2019