The Role of Neural Activity in Enhancing Axon and Presynaptic Regeneration in the Adult Injured Neocortex In Vivo

The human brain is a highly complex system comprised of billions of neurons interconnected to each other to form functional neural circuits. Normal brain function is dependent on effective communication between neurons, a process that requires the establishment of synapses within the circuit. Several diseases that affect the brain result from impairments in the communication between neurons, which is why it is essential to understand how neural circuits are established and the mechanisms underlying circuit plasticity. We are particularly interested in understanding how the regeneration of neural circuits can be enhanced to restore connectivity and function after a brain lesion. Specifically, we aim to test the hypothesis that the activity of surviving neurons can elicit the regeneration of axons and synapses within the circuits, in order to overcome the functional deficits that result from an injury. We have previously demonstrated that certain populations of cortical neurons exhibit enhanced spontaneous regenerative capacity in comparison to others, and we are now interested in understanding the cellular and molecular mechanisms responsible for this differential response to injury between diverse neuronal populations. This knowledge will help us identify targets for future therapeutic interventions. With the prospect of developing strategies to enhance functional regeneration after injury, we will also manipulate neural activity by directly stimulating neurons within a circuit. Different stimulation protocols will be employed, in order to identify the parameters that are most effective in restoring structural and functional recovery. We will take advantage of powerful genetic, imaging and stimulation tools that allow manipulating neural activity and visualizing neurons in the living brain of laboratory animals. The ultimate aim of this research proposal is therefore to gain new and fundamental insights into the cellular and molecular mechanisms that regulate the regeneration of cortical neural circuits, in the hope that this knowledge will, in the future, translate into new ways to promote neural plasticity and functional recovery after brain injury.

Careful regulation of synaptic connectivity in the adult brain is essential for normal brain function. It is now clear that even mild alterations in synapse morphology and function give rise to cognitive impairment, and pharmacological agents able to counteract these alterations may improve the symptoms of some of such conditions. The neocortex, a brain area unique to mammals, is affected in numerous developmental and degenerative diseases as well as acute injuries, with long-range excitatory projections being particularly vulnerable. While in the periphery damaged nerves are known to mount a regenerative response, this does not successfully happen in the central nervous system and cortical damage usually leads to devastating and irreparable consequences. Devising new strategies to promote the repair of cortical circuits is therefore a major goal. However, due to the challenge of tracking axons and large numbers of bona fide presynaptic terminals over extended periods of time in vivo, profound gaps remain in our understanding of cortical axon and presynaptic regeneration. The objective of this proposal is to determine how neural activity, a critical regulator of neuronal structure and dynamics during development, can enhance axon and presynaptic connectivity in damaged cortical circuits in vivo. To address this issue, I propose to combine high-resolution in vivo 2-photon axonal and presynaptic imaging assays established by my team, strengthened by the ability to manipulate neural activity and gene expression in single neurons in vivo. The project will thus deliver critical insights into how synaptic connectivity and repair are controlled in the living brain. This knowledge is needed to design drugs and stimulation-based treatments that can fine-tune the rate of axonal and synaptic reorganization for neurological intervention.

This is a basic research project and the immediate beneficiaries are likely to be other academics, but the links I have established with neurologists and clinician scientists studying brain repair, locally, nationally and internationally, will support the translation of any results.
Damage of long-range cortical projections underlies several diseases. Our research is expected to focus future studies on determining whether and how electrical activity can improve the symptoms of the many neurodevelopmental and degenerative diseases, which affect the cortex.
We would therefore hope that our research will directly influence additional research at many levels, eventually leading to new treatments.
The regulation of synaptic connectivity in the brain is a central topic in neuroscience and medicine. Other research groups working in this field will benefit from our insights into the mechanisms controlling presynaptic connectivity in the injured brain. The broader scientific community will benefit from our advancements, which will include new ways to promote functional brain repair. These data could potentially lead to the development of new leads and targets to promote neural circuit repair in a variety of neurological conditions where cortical circuitry is affected.

This project will generate Big Data sets, both from imaging large populations of presynaptic terminals in vivo and advanced electron microscopy experiments. Elucidating the mechanisms of presynaptic connectivity in the injured cortex will have profound impacts for models of synaptic connectivity and plasticity in the brain. In collaboration with Claudia Clopath, a computational neuroscientist at Imperial, we have set out to do modelling work based on our in vivo imaging data. This is a key component for linking synaptic plasticity to memory and for understanding the consequences of synaptic connectivity disruptions.

A main goal of this proposal is to develop and promote international partnerships, to encourage the movement of researchers between the UK and overseas. Using correlative 2-photon-focused ion beam scanning electron microscopy (FIBSEM) in collaboration with the group of Dr. Graham Knott in Lausanne, we will generate a unique data set comprising ultrastructural reconstructions corresponding to lesioned axons previously imaged in vivo. We will be able to compare the ultrastructural features of regenerating and non-regenerating axons. This data set will be very attractive for computational and cell neuroscientists interested in modelling the disruption of synaptic connectivity upon injury. Sharing our data with such researchers will maximize the impact of our research on the field of synaptic reorganization.

The findings of this study will be presented at national and international scientific conferences and published in open-access journals, thus aiding the free exchange of information and materials among scientists and the general public. Together with Imperial College media centre I will promote public engagement and popularize the proposed science. I have experience in giving public talks on science participating in the University of the 3rd Age, British Science Festival, Strictly Science, mentoring pupils interested in science under the social mobility www.socialmobility.org.uk scheme and commenting on scientific discoveries in the media to engage in activities that bring the excitement of science to the public.

Using this network we will reach out to industry to exploit our discoveries and maximize their impact with pharmaceutical companies. Our longitudinal imaging paradigm will also contribute to the efforts of 3Rs as it can reduce the number of animals to be used for research. Compared with current approaches it allows us to monitor axon and synaptic remodelling before and after any manipulation within the same animals (i.e. without the need for a separate control group).