Abstract:
Retinitis Pigmentosa (RP) is a hereditary disease characterised by the progressive degeneration of rod and cone photoreceptors, ultimately leading to blindness. Despite extensive research, effective therapies remain scarce. Understanding how photoreceptor degeneration affects downstream retinal processing is crucial for developing targeted interventions. In this thesis, I investigate the functional consequences of RP on the retinal ganglion cells (RGCs), the final output neurons of the retina, using the Pde6brd10 (rd10, Chang et al. 2002) mouse model. This model closely mimics human RP, with rod degeneration beginning around postnatal day (P) 16, followed by secondary cone loss from P30 onwards. By P180, nearly all photoreceptors are lost, leading to significant
changes in retinal circuitry (e.g., Puthussery et al. 2009).
To study these effects, I performed two-photon Ca2+ imaging of RGCs in ex vivo retinal whole mounts from both rd10 and wild-type mice at four key time points: P30, P45, P90, and P180. Using a semi-automated cell classification approach, I assessed how photoreceptor degeneration influences RGC light responses, functional diversity, and signal reliability. I first confirmed that RGC density remained stable throughout degeneration, ruling out major cell loss as a confounding factor. However, the proportion of light-responsive RGCs declined significantly, with a 21% reduction between P30 and P45 and another 14% between P45 and P90. By P180, nearly all light responses were lost. To examine how the composition of functional RGC types changed over time,
I applied an established classification framework (Baden et al. 2016; Qiu et al.
2023; Gonschorek et al. 2024) to cluster RGC responses. Even at P90, most
wild-type RGC types were still present in rd10 retinae, suggesting that earlystage
degeneration does not immediately disrupt functional diversity. However, when investigating the fractions of broad response types (i.e. functional supergroups),
RGC subtypes with ‘Off’ response components (‘Off’ and ‘On-Off’ RGCs) exhibited greater vulnerability than ‘On’-RGCs, with ‘Fast-On’ cells showing the highest resilience. Additionally, direction-selective RGCs declined earlier than orientation-selective types, indicating differential sensitivity to retinal
rewiring.
These findings demonstrate that RP progression leads to differential disruptions
in RGC function, even in the absence of cell loss. This suggests that
degeneration-induced remodelling in the retinal network alters visual signal processing
at the level of the retinal output. This supports the idea that (yet
undiscovered) changes in the presynaptic retinal circuitry and/or other alterations
affect functional diversity among RGCs during degeneration, potentially
contributing to the observed differences in RGC response stability. One possible
explanation is an emerging imbalance between ‘On’- and ‘Off’-pathways, which
may differentially impact specific RGC types and their ability to maintain stable
responses. Understanding these circuit-level changes is essential for future
research on synaptic plasticity and retinal reorganisation in RP and may help
inform therapeutic strategies aimed at preserving functional vision in patients
with photoreceptor degenerations.
RGCs