Expression and Function of Heat Shock Protein 90 in the Central Nervous System of the Desert Locust, Schistocerca gregaria

In this thesis, I investigated the expression and function of the molecular chaperone heat shock protein 90 (HSP90) in the central nervous system (CNS) of the desert locust, Schistocerca gregaria. In Chapter 1, I reviewed the structure, function and CNS expression of HSP90, and argued that its role as a 'meta-regulator' of complex biological pathways and its ability to stabilise behavioural and morphological phenotypes suggests it could adaptively stabilise activity in the CNS.

In Chapter 2, I exploited unique properties of the locust hind leg motor control system to gain experimental access to a monosynaptic glutamatergic synapse. The stability of synaptic transmission – measured indirectly with extracellular muscle recordings – was unaffected by pharmacological inhibition of HSP90. In seeking to verify drug penetration into the locust CNS, subsequent intracellular electrophysiological experiments using drugs with reported effects at the synapse failed to replicate previously published findings. In Chapter 3, an extensive and computationally-intensive simulation-based Bayesian power analysis concluded that further intracellular experiments would not be sufficiently powered to robustly detect likely experimental outcomes with the resources available following the COVID-19 pandemic. In Chapter 4, I demonstrated for the first time in any invertebrate that constitutive expression of HSP90 (at the protein level) was greater in the CNS than in non-neural tissue. I attempted to investigate where HSP90 was expressed in the CNS, but none of the five selected anti-HSP90 antibodies passed all validation criteria required for their use in immunofluorescence microscopy.

In Chapter 5, I contextualised the major findings of my thesis and suggest promising avenues for future experiments to explore. The rigorous experiments and power analysis presented in this thesis make distinct and original contributions in the form of (a) independent replication of published work and (b) broad methodological issues that have far-reaching implications for the meaningful design and interpretation of experiments.