Mechanisms of Resilience in Neural Networks for Locomotion

Outlined below is my project proposal as a potential PhD candidate in neuroscience in the Pulver
laboratory. The project is provisionally entitled 'Mechanisms of Resilience in Neural Networks for
Locomotion'.
Resilience is an indispensable aspect of life. Behavioural resilience can be defined generally as the
ability to retain stability in behavioural output in the face of perturbations. Individuals exhibit
different capacities for resilient behaviour [16, 18, 19]. Despite resilience's universality, relatively
little is known about the neural and biochemical mechanisms underpinning behavioural resilience
and robustness. This project aims to elucidate the mechanisms of neural resilience in an animal
model by studying the interaction amongst three conserved, but relatively understudied
components of neural networks: biogenic pumps, ion transporters, and astrocytes.
Astrocytes - support cells for neurons - are highly conserved and have roles in a diversity of
processes from neurodevelopment to synaptic homeostasis [1-4]. Many synapses are comprised of
neurons and astrocytes with loss of astrocytes leading to neural network dysfunction [20-22].
However, explaining how astrocytes enable robustness is at its infancy. The interaction between
neuromodulators that promote flexibility in neural networks and astrocytes remains largely
unexplored [5,6]. Interestingly, Drosophila astrocytes may act as signal mediators between
flexibility-promoting neuromodulators encoding chemotaxis [11]. In zebrafish, astrocytes monitor
visual information and actively suppress futile motor outputs (figure 1A) [12]. Thus, a growing
body of work suggests that astrocytes can encode behavioural states and intervene to enable
adaptive behaviour.
Na
+/
K
+
pumps and other ion transporters are also highly conserved elements of neuronal and glial
cell membranes, being positioned to adaptively modulate activity. Previous work suggests Na
+/
K
+

pumps encode motor memory in multiple species [8]. The Na
+/
K
+
ATPase pump may enable prolethal
levels
of
activity
during
fight-or-flight
responses
whilst
simultaneously
reining
in
activity
to

minimse
lasting
damage
[7].
Within
mice,
Xenopus
tadpoles
and
Drosophila
larva
[8],
Na
+/
K
+
pumps
regulate locomotory activity via inducing ultraslow hyperpolarisations (usAHP), modulated by
neurohormones associated with stress. Mutations within these pumps is inculcated in a variety of
stress-induced conditions [10, 14-16]. Evidence suggests a functional interaction between Na
+/
K
+

pumps and cation transporters (Na
+
/Ca
2+
exchanger and PMCA) (figure 1B) [17]. Nevertheless, the
functional organization of this nexus and the role(s) that each component plays in enabling neural
network robustness remains largely unexplored in any model organism.

Here, I will integrate calcium imaging, electrophysiology, and computational modelling to evaluate
whether Na
+
/K
+
pumps and other ion exchangers in neurons and astrocytes are critical
determinants of robustness in neural networks. The genetically-tractability of Drosophila larvae
alongside their clearly defined rhythmic outputs make them ideal for assessing robustness. Firstly,
I will use dual-colour calcium imaging to explore the correlation between astrocytes and neurons
activity with and without dominant-negative Na
+/
K
+
pump mutations (DTS1) within 3
rd
instar
Drosophila larva. Secondly, I will explore, using patch-clamp electrophysiology, the effect of DTS1
mutations on astrocytes and motor neurons output. Specifically, I will measure pump mutations'
effects on i) usAHP and ii) inter-segmental phase (a metric of resilience [13]) (figure 1C). Time
permitting, I may recapitulate experiments in existing computational models of the larval locomotor
network. Broadly, by perturbing networks using a variety of stress conditions (e.g., temperature,
acute pharmacology, op