Katherine E. Davis
University of Manchester
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Featured researches published by Katherine E. Davis.
Current Biology | 2015
Jasmina Cehajic-Kapetanovic; Cyril Giles Eleftheriou; Annette E. Allen; Nina Milosavljevic; Abigail Pienaar; Robert Bedford; Katherine E. Davis; Paul N. Bishop; Robert J. Lucas
Summary Many retinal dystrophies result in photoreceptor loss, but the inner retinal neurons can survive, making them potentially amenable to emerging optogenetic therapies. Here, we show that ectopically expressed human rod opsin, driven by either a non-selective or ON-bipolar cell-specific promoter, can function outside native photoreceptors and restore visual function in a mouse model of advanced retinal degeneration. Electrophysiological recordings from retinal explants and the visual thalamus revealed changes in firing (increases and decreases) induced by simple light pulses, luminance increases, and naturalistic movies in treated mice. These responses could be elicited at light intensities within the physiological range and substantially below those required by other optogenetic strategies. Mice with rod opsin expression driven by the ON-bipolar specific promoter displayed behavioral responses to increases in luminance, flicker, coarse spatial patterns, and elements of a natural movie at levels of contrast and illuminance (≈50–100 lux) typical of natural indoor environments. These data reveal that virally mediated ectopic expression of human rod opsin can restore vision under natural viewing conditions and at moderate light intensities. Given the inherent advantages in employing a human protein, the simplicity of this intervention, and the quality of vision restored, we suggest that rod opsin merits consideration as an optogenetic actuator for treating patients with advanced retinal degeneration.
Journal of Alzheimer's Disease | 2013
Katherine E. Davis; Alexander Easton; Madeline J. Eacott; John Gigg
Episodic memory loss is a defining feature of early-stage Alzheimers disease (AD). A test of episodic-like memory for the rat, the What-Where-Which occasion task (WWWhich), requires the association of object, location, and contextual information to form an integrated memory for an event. The WWWhich task cannot be solved by use of non-episodic information such as object familiarity and is dependent on hippocampal integrity. Thus, it provides an ideal tool with which to test capacity for episodic-like memory in the 3xTg murine model for AD. As this model captures much of the human AD phenotype, we hypothesized that these mice would show a deficit in the WWWhich episodic-like memory task. To test the specificity of any episodic-like deficit, we also examined whether mice could perform components of the WWWhich task that do not require episodic-like memory. These included object (Novel Object Recognition), location (Object Location Task, What-Where task), and contextual (What-Which) memory, as well as another three-component task that can be solved without reliance on episodic recall (What-Where-When; WWWhen). The results demonstrate for the first time that control 129sv/c57bl6 mice could form WWWhich episodic-like memories, whereas, 3xTgAD mice at 6 months of age were impaired. Importantly, while 3xTgAD mice showed some deficit on spatial component tasks, they were unimpaired in the more complex WWWhen combination task (which includes a spatial component and is open to non-episodic solutions). These results strongly suggest that AD pathology centered on the hippocampal formation mediates a specific deficit for WWWhich episodic-like memory in the 3xTgAD model.
PLOS ONE | 2014
Katherine E. Davis; Sarah Fox; John Gigg
Mouse Alzheimers disease (AD) models develop age- and region-specific pathology throughout the hippocampal formation. One recently established pathological correlate is an increase in hippocampal excitability in vivo. Hippocampal pathology also produces episodic memory decline in human AD and we have shown a similar episodic deficit in 3xTg AD model mice aged 3–6 months. Here, we tested whether hippocampal synaptic dysfunction accompanies this cognitive deficit by probing dorsal CA1 and DG synaptic responses in anaesthetized, 4–6 month-old 3xTgAD mice. As our previous reports highlighted a decline in episodic performance in aged control mice, we included aged cohorts for comparison. CA1 and DG responses to low-frequency perforant path stimulation were comparable between 3xTgAD and controls at both age ranges. As expected, DG recordings in controls showed paired-pulse depression; however, paired-pulse facilitation was observed in DG and CA1 of young and old 3xTgAD mice. During stimulus trains both short-latency (presumably monosynaptic: ‘direct’) and long-latency (presumably polysynaptic: ‘re-entrant’) responses were observed. Facilitation of direct responses was modest in 3xTgAD animals. However, re-entrant responses in DG and CA1 of young 3xTgAD mice developed earlier in the stimulus train and with larger amplitude when compared to controls. Old mice showed less DG paired-pulse depression and no evidence for re-entrance. In summary, DG and CA1 responses to low-frequency stimulation in all groups were comparable, suggesting no loss of synaptic connectivity in 3xTgAD mice. However, higher-frequency activation revealed complex change in synaptic excitability in DG and CA1 of 3xTgAD mice. In particular, short-term plasticity in DG and CA1 was facilitated in 3xTgAD mice, most evidently in younger animals. In addition, re-entrance was facilitated in young 3xTgAD mice. Overall, these data suggest that the episodic-like memory deficit in 3xTgAD mice could be due to the development of an abnormal hyper-excitable state in the hippocampal formation.
PLOS ONE | 2015
Katherine E. Davis; Cyril Giles Eleftheriou; Annette E. Allen; Christopher A. Procyk; Robert J. Lucas
A direct projection from melanopsin-expressing intrinsically photosensitive retinal ganglion cells (ipRGCs) reaches the primary visual thalamus (dorsal lateral geniculate nucleus; dLGN). The significance of this melanopsin input to the visual system is only recently being investigated. One unresolved question is the degree to which neurons in the dLGN could use melanopsin to track dynamic changes in light intensity under light adapted conditions. Here we set out to address this question. We were able to present full field steps visible only to melanopsin by switching between rod-isoluminant ‘yellow’ and ‘blue’ lights in a mouse lacking cone function (Cnga3-/-). In the retina these stimuli elicited melanopsin-like responses from a subset of ganglion cells. When presented to anaesthetised mice, we found that ~25-30% of visually responsive neurones in the contralateral dLGN responded to these melanopsin-isolating steps with small increases in firing rate. Such responses could be elicited even with fairly modest increases in effective irradiance (32% Michelson contrast for melanopsin). These melanopsin-driven responses were apparent at bright backgrounds (corresponding to twilight-daylight conditions), but their threshold irradiance was strongly dependent upon prior light exposure when stimuli were superimposed on a spectrally neutral ramping background light. While both onset and offset latencies were long for melanopsin-derived responses compared to those evoked by rods, there was great variability in these parameters with some cells responding to melanopsin steps in <1 s. These data indicate that a subset of dLGN units can employ melanopsin signals to detect modest changes in irradiance under photopic conditions.
Nature Communications | 2017
Alexandra Tikidji-Hamburyan; Katja Reinhard; Riccardo Storchi; Johannes Dietter; Hartwig Seitter; Katherine E. Davis; Saad Idrees; Marion Mutter; Lauren Walmsley; Robert Bedford; Marius Ueffing; Petri Ala-Laurila; Timothy M. Brown; Robert J. Lucas; Thomas A. Münch
Rod and cone photoreceptors support vision across large light intensity ranges. Rods, active under dim illumination, are thought to saturate at higher (photopic) irradiances. The extent of rod saturation is not well defined; some studies report rod activity well into the photopic range. Using electrophysiological recordings from retina and dorsal lateral geniculate nucleus of cone-deficient and visually intact mice, we describe stimulus and physiological factors that influence photopic rod-driven responses. We find that rod contrast sensitivity is initially strongly reduced at high irradiances, but progressively recovers to allow responses to moderate contrast stimuli. Surprisingly, rods recover faster at higher light levels. A model of rod phototransduction suggests that phototransduction gain adjustments and bleaching adaptation underlie rod recovery. Consistently, exogenous chromophore reduces rod responses at bright background. Thus, bleaching adaptation renders mouse rods responsive to modest contrast at any irradiance. Paradoxically, raising irradiance across the photopic range increases the robustness of rod responses.Rod photoreceptors are thought to be saturated under bright light. Here, the authors describe the physiological parameters that mediate response saturation of rod photoreceptors in mouse retina, and show that rods can drive visual responses in photopic conditions.
PLOS ONE | 2012
Sophie J. Lyst; Katherine E. Davis; John Gigg; Reinmar Hager
Enhancing laboratory animal welfare, particularly in rodents, has been achieved through environmental enrichment in caging systems. Traditional enrichment such as adding objects has shown to impact development, reproductive and maternal performance as well as cognition. However, effects of increased spatial complexity as part of larger novel caging systems have not been investigated. While adoption of caging systems with increased spatial complexity seems uncontroversial from a welfare perspective, effects of such housing on the development and task performance of experimental animals remains unclear. In this study, we investigate differences in key behaviours and cognitive performance between Lister Hooded rats housed in traditional (single-shelf) cages (‘basic’) and those housed in larger cages with an additional shelf (‘enriched’). We found minor differences in maternal behaviour, such as nursing and offspring development. Further, we compared task performance in females, using a hippocampus-dependent task (T-maze) and a hippocampus-independent task (Novel Object Recognition, NOR). While in the T-maze no differences in either the rate of learning or probe trial performance were found, in the NOR task females housed in enriched cages performed better than those housed in basic cages. Our results show that increased spatial complexity does not significantly affect development and maternal performance but may enhance learning in females for a non-spatial task. Increased spatial complexity does not appear to have the same effects on behaviour and development as traditional enrichment. Thus, our results suggest no effect of housing conditions on the development of most behaviours in experimental animals housed in spatially enriched caging systems.
Behavioural Brain Research | 2017
Katherine E. Davis; Kathryn Burnett; John Gigg
HighlightsYoung 3xTgAD mice of both sexes exhibit contextual and Pavlovian fear memory.Cued fear responses are heightened in male 3xTgAD mice compared to controls.Female 3xTgAD mice display memory deficits during spontaneous alternation.Female 3xTgAD mice display spatial reference memory deficits in radial water maze.Less stressful alternatives to escape from water should be used for 3xTgAD mice. Abstract Rodent spatial memory is commonly tested using the water‐maze; however, there is a potential confound of stress on learning in this behavioural paradigm. This is particularly relevant when testing spatial memory in models of neurodegeneration, such as the 3xTg mouse model for Alzheimer’s disease. Here, we first confirmed that 3xTgAD mice express fear conditioning and then compared the performance of young and middle‐aged mice on short‐duration versions of the radial arm water‐maze (RAWM) and the minimally stressful T‐maze spontaneous alternation task. Our main questions were: (1) does the reliance on stressors in water‐maze training mask the true cognitive ability of 3xTgAD mice; and (2) are 3xTgAD mice similarly impaired in water‐maze and T‐maze protocols. Firstly, male and female 3xTgAD mice displayed intact freezing responses in both contextual and Pavlovian fear conditions. As male 3xTgAD mice displayed relatively enhanced fear responses the remaining tests were performed using only female 3xTgAD and control mice in order to equate for response to stressors. We found that alternation rates after both short and long delays were impaired at both ages in female 3xTgAD mice, indicative of robust spatial working memory deficits. For RAWM, again performance deficits were found in young 3xTgAD mice. As both tasks had similar efficacy at revealing early spatial memory deficits, we suggest that spontaneous behavioural protocols be prioritised over water maze testing in models such the 3xTgAD mouse as the former provide a far less stressful but equally effective alternative.
The Lancet | 2017
Jasmina Cehajic Kapetanovic; Cyril Giles Eleftheriou; Annette E. Allen; Nina Milosavljevic; Abigail Pienaar; Robert Bedford; Katherine E. Davis; Paul N. Bishop; Robert J. Lucas
Abstract Background Inherited retinal degenerations that lead to irreversible blindness due to progressive loss of rods and cones in the outer retina affect 1 in 2500 people worldwide. However, despite the substantial photoreceptor loss, the inner retinal neurons can survive, making them potentially amenable to emerging optogenetic therapies. The aim of this study was to determine whether it is possible to recreate vision in blind mice using ectopic expression of human rod opsin. Methods The rod opsin expressing adeno-associated virus serotype 2 vector, driven by either a non-selective or ON-bipolar cell-specific promoter, was injected intravitreally into adult rd1 mice, a mouse model of advanced retinal degeneration. Retinal function was assessed in vitro with multielectrode array recordings, and in vivo with electrophysiological recordings from the visual thalamus. Behavioural studies were developed to test the visual responses in treated mice under a range of light conditions. Findings Ectopically expressed human rod opsin, driven by either a non-selective or ON-bipolar cell-specific promoter, functioned outside native photoreceptors and restored visual function in rd1 mice. Electrophysiological recordings from retinal explants and the visual thalamus revealed changes in firing induced by simple light pulses, luminance increases, and naturalistic movies in treated mice. These responses could be elicited at light intensities within the physiological range and substantially below those required by other optogenetic strategies. Mice with rod opsin expression driven by the ON-bipolar specific promoter displayed behavioural responses to increases in luminance, flicker, coarse spatial patterns, and elements of a natural movie at natural levels of contrast and illuminance. Interpretation These data reveal that virally mediated ectopic expression of human rod opsin can restore vision under natural viewing conditions and at moderate light intensities. Given the inherent advantages of using a human protein, the simplicity of this intervention, and the quality of vision restored, we suggest that rod opsin merits consideration as an optogenetic actuator for treating patients with advanced retinal degeneration. Funding Medical Research Council (clinical research training fellowship to JCK), Medical Research Council Confidence in Concept Award, European Research Council.
European Journal of Neuroscience | 2016
Miguel Dasilva; Riccardo Storchi; Katherine E. Davis; Kenneth L. Grieve; Robert J. Lucas; Rae Silver
Melanopsin phototransduction allows intrinsically photosensitive retinal ganglion cells (ipRGCs) to maintain firing under sustained illumination and to encode irradiance. ipRGCs project to different parts of the visual system, including the superficial superior colliculus (sSC), but to date there is no description of melanopsin contributions to the activity of that nucleus. We sought to fill that gap using extracellular recordings to describe light response in the sSC. We failed to observe light responses in the sSC of mice lacking rod and cone function, in which melanopsin provides the only photoreception. Nor did the sSC of intact animals track very gradual ramps in irradiance, a stimulus encoded by melanopsin for other brain regions. However, in visually intact mice we did find maintained responses to extended light steps (30 s) and to an irradiance ramp upon which a high frequency (20 Hz) temporal white noise was superimposed. Both of these responses were deficient when the spectral composition of the stimulus was changed to selectively reduce its effective irradiance for melanopsin. Such maintained activity was also impaired in mice lacking melanopsin, and this effect was specific, as responses of this genotype to higher spatiotemporal frequency stimuli were normal. We conclude that ipRGCs contribute to irradiance‐dependent modulations in maintained activity in the sSC, but that this effect is less robust than for other brain regions receiving ipRGC input.
Behavioural Brain Research | 2013
Katherine E. Davis; Madeline J. Eacott; Alexander Easton; John Gigg