2 Introduction

The effects of retinitis pigmentosa (RP) can simultaneously degrade an animal’s behaviors, organs, tissues, and cells. Originating from the disease’s loss of function mutations in the retina, electron microscopy images have shown that rod photoreceptor cells die and behavioral studies have shown that animals have difficulty navigating their environment. These observed changes are impactful in guiding treatment development for RP, yet the physiological changes that occur in between rod cell death and night blindness need clarification (Wright).

The major role of the retina is to encode the specifics of our visual environment through both the quantity and the precise timing of action potentials, and Retinitis Pigmentosa disrupts this process. Visual details about time and space are sent through axons in the optic nerve that get transformed into perceptions that will inform an animal’s actions. Beginning from the damage to the photoreceptors, RP in the retina operates by a process of scaling down this sensory information transmission mechanism. Therefore, understanding the changes to the information content and the changes to the spike firing precision have utility in this neurodegenerative context.

As a result of the drastic biological changes to the retina, a decline in the information transmitted to the brain and a loss of spike train precision are expected across the degeneration states. RP specifically originates from a loss of function in photoreceptor protein channels, but as these changes amplify the symptoms of RP on visual perception become drastic. The disease begins with the death of the rod photoreceptor cells that encode stimuli at darker light levels, making night time vision. As the disease progresses, the death of rods causes the death of the cone photoreceptor cells which are responsible for detecting the visual field at higher light levels and colors. Thus, symptoms should also manifest in the the beginning stages of all those visual sensations in human physiology, which is the retinal code.

Mice are bred with a mutation that creates dysfunctional CNG protein channels in the rod photoreceptor cells to inititate retinits pigmentosa. The CNGB gene is knocked out using the Cre-Lox recombinant, which can then be activated with the delivery of tamoxifin as a genetic treatment for RP. The death of photoreceptors also restructures the retina’s circuitry because downstream bipolar cells will have to adapt for the decline in photoreceptors. Thus, by looking at the alterations of the retinal code, this study explores the physiological restructuring that happens because of this disease. Delivery of treatment using tamoxifin initiates activation of the CNGB gene adding potential to explore how physiological changes manifest in the retinal code as functional CNG channels are produced.

19 retinas were extracted from mice and recorded on a microelectrode array to measure the firing by their ganglion cells. These cells were recorded across various stimuli: natural motion movies, checkerboard patterns at cone light level (daylight), and checkerboard patterns at rod-light levels (dark levels). Spikes from a single electrode may originate from multiple cells and multiple electrodes may contain a single cell, so a spike sorting software was used to attribute the spikes in all recordings to individual cells. The software uses PCA clustering of the spike features to identify the cluster of cells on the electrode array. A combination of manual and algorithmic spike sorting was done on some recordings to evaluate the effectiveness of the spike sorting algorithm in context of this experiment. The additional step of spiking sorting did not affect the the majority of recorded cells, which provided evidence for the effectiveness of the spike sorting in all the recordings.