1,721,099 research outputs found
Sleep, circadian and behavioural characterisation of two schizophrenia-relevant transgenic mouse models
Get PDFThe experiments described in this thesis involved the sleep, circadian and behavioural characterisation of two schizophrenia-relevant transgenic mouse models, both of which are models of altered glutamatergic function. Although schizophrenia cannot be recapitulated in rodents, the study of transgenic mouse models can yield insights into the roles of schizophrenia candidate genes in brain function and dysfunction. D-amino acid oxidase knockout (Dao-/-) mice do not express DAO, a glial peroxisomal enzyme that catalyses the degradation of D-amino acids including D-serine. In turn, D-serine is the primary endogenous co-agonist of the synaptic N-methyl-D-aspartate receptor, an ionotropic glutamate receptor that is strongly implicated in learning and memory, which may be hypoactive in schizophrenia. Given evidence of DAO overactivity in schizophrenia, DAO inhibiting drugs have been proposed as a potential treatment for the disorder. To assess the behavioural consequences of Dao inactivation, Dao-/- mice were subjected to a range of psychiatrically-relevant behavioural tests. Anxiety-like behaviour was increased in Dao-/- mice, while short-term memory performance was enhanced. By contrast, long-term spatial memory acquisition was unaltered in Dao-/- mice. However, the Morris watermaze performance of Dao-/- mice was critically dependent on the radial distance of the hidden platform from the side-wall. Analyses of spatial swimming behaviour revealed that Dao-/- mice demonstrated an increased preference for the periphery of the watermaze arena, which may be another manifestation of heightened anxiety. Prepulse inhibition testing revealed a complex interplay between genotype, sex and stress levels. Likewise, genotype-by-sex interactions were evident in the Morris watermaze and the novelty-suppressed feeding test. Dao-/- mice showed no evidence of sleep or circadian rhythm disruption (SCRD). Taken together, these results suggest that DAO inhibition might ameliorate the memory deficits of schizophrenia patients, although these effects may not extend to long-term associative memory. In addition, these benefits could come at the cost of heightened anxiety. Our data also imply that DAO inhibitors might have different effects in male and female patients. Metabotropic glutamate receptor 2 & 3 double-knockout (Grm2/3-/-) mice lack the inhibitory autoreceptors mGlu2 and mGlu3, which are encoded by the genes Grm2 and Grm3, respectively. Based on the results of genome-wide association studies, Grm3 is amongst the strongest schizophrenia candidate genes. The Grm2/3-/- mouse was used to assess the 'shared neuropathophysiology' hypothesis of SCRD in schizophrenia. This theory posits that the high co-morbidity of schizophrenia and SCRD stems from dysfunction in common brain mechanisms that underpin both pathologies. Consistent with this hypothesis, Grm2/3-/- mice displayed significant SCRD, characterised by reduced sleep duration and increased sleep fragmentation. They also demonstrated increased sensitivity to the circadian effects of light. These data are consistent with the 'shared neuropathophysiology' hypothesis, and tentatively suggest that mGlu3 dysfunction could contribute to SCRD in schizophrenia. Since memory performance is also impaired in Grm2/3-/- mice, this model could be an ideal tool with which to investigate the relationship between sleep disruption and cognitive performance. Finally, Grm2/3-/- mice displayed perturbed wheel-running rhythms under a standard light/dark cycle, despite the fact that their home-cage activity rhythms were unaltered in the absence of a running wheel. Although the basis of this phenotype is unclear, these data speak to the debate about the suitability of running-wheels as a circadian assay for psychiatrically-relevant mouse models
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Role of cryptochromes in retinal responses to light
Get PDFCryptochromes 1 and 2 (CRY1-2) are key components of the negative limb of the mammalian circadian clock. Like in many peripheral tissues, Cry1 and Cry2 are expressed in the retina where they are thought to play a role in regulating retinal circadian physiology. This thesis investigates the role of Cryptochromes in the mammalian retina. The localization and expression pattern of CRY1 and CRY2 in the mouse retina are described, showing that CRY1 is expressed throughout, whereas CRY2 expression is restricted to the outer retina. Furthermore, circadian rhythms in retinal physiology, including the photopic electroretinogram (ERG) b-wave amplitude, contrast sensitivity and the pupillary light response (PLR) are found to be all attenuated or abolished in CRY1-deficient mice. By contrast, these physiological rhythms are unaffected in mice lacking CRY2, and only photopic ERG rhythms are affected. As such, both CRY1 and CRY2 play roles in regulating normal retinal circadian rhythms, though CRY1 plays a dominant role. The role of melanopsin in retinal rhythms is also investigated. It is found that loss of melanopsin affects contrast sensitivity rhythms but not PLR rhythms. The work in this thesis suggests that the retinal circadian clock is composed of at least two independent networks of oscillators in the retina which regulate key aspects of retinal physiology. Lastly, this thesis investigates whether the retinal clock has any downstream effects on the SCN master pacemaker. The experimental results presented here suggest that the retinal clock is capable of rhythmically gating light input to the SCN clock, acting as a zeitnehmer
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Functional characterisation of key residues in the photopigment melanopsin
Get PDFMelanopsin (Opn4) is the opsin photopigment of intrinsically photosensitive retinal ganglion cells (ipRGCs). It has a conserved opsin structure and activation mechanism, yet demonstrates unusual functional properties that suggest it will possess unique structure-function relationships. The aim of this thesis was to characterise key OPN4 residues by examining the impact of non-synonymous mutations on melanopsin function. A genotype-driven screen of a chemically-mutagenized mouse archive led to the identification of a novel Opn4 mutant, S310A, located at a known opsin spectral tuning site. Action spectra from ipRGC and pupil light responses (PLR) of Opn4S310A mice revealed no change in wavelength of peak sensitivity. However, Opn4S310A PLR was significantly less sensitive at longer wavelengths, consistent with a short-wavelength shift in spectral sensitivity. This suggests S310A acts as a spectral tuning site in melanopsin. Next, the impact of naturally-occurring missense variants in human melanopsin (hOPN4) was examined in vitro. Fluorescent calcium imaging of 16 hOPN4 variants expressed in HEK293 cells revealed four hOPN4 variants abolished or attenuated responses to light (Y146C, R168C, G208S and S308F). These variants were located in conserved opsin motifs for chromophore binding or hydrogen-bond networks, functional roles apparently shared by melanopsin. Finally, two hOPN4 single nucleotide polymorphisms (SNPs) P10L and T394I, associated with abnormal non-image forming behaviour in humans, were explored in vivo. Using targeted viral-delivery of hOPN4 SNPs to mouse ipRGCs, a range of OPN4-driven behaviours, such as circadian photoentrainment and pupil light responses, were found to be comparable with hOPN4 WT control. Multi-electrode array recordings of ipRGCs transduced with hOPN4 T394I virus had significantly attenuated sensitivity and faster response offset, indicating this site may be functionally important for melanopsin activity but compensatory rod and cone input limits changes to non-image forming behaviour.</p
The regulation of circadian rhythms by the natural light environment
No full textAlmost all life on Earth has evolved under ~24hr cycles in environmental conditions such as light and temperature. Consequently, virtually all organisms have evolved internally generated near-24hr cycles in physiology and behaviour, known as circadian rhythms. However, these rhythms rarely have a period of exactly 24hrs. As such, daily adjustment by external time cues is required to align the phase of internal circadian rhythms with the external environment. This enables organisms to anticipate predictable daily changes in environmental conditions, and optimise physiology and behaviour to the varying demands of day and night. In mammals, the primary time cue is light, and therefore this process is referred to as photoentrainment. In nature, light is a complex and dynamic stimulus – changing in intensity and spectrum across the 24hr period. In addition, the timing of an organism’s activity can significantly influence the light available for photoentrainment. Despite these complexities, the vast majority of our knowledge of photoentrainment has been generated using rodent models under highly simplified laboratory conditions. The circadian system is very plastic, and as such, the disparity between laboratory and natural light environments is highly relevant for our understanding of photoentrainment. Therefore, in this thesis I take an ecologically guided approach to the study of photoentrainment, by incorporating two key elements of the natural light environment into laboratory studies. Firstly, the opportunity for behaviour to regulate light exposure, and secondly, the dynamic changes in both light intensity and spectrum that occur across the day/night cycle.
I initially characterise how mice are exposed to light under standard laboratory conditions, before developing a method to allow mice to self-modulate their light exposure. Under this paradigm mice sample their light environment most extensively at twilight, identifying an important role for behaviour in determining the timing of light exposure in naturalistic environments. We show that crepuscular light sampling is abolished in mice lacking a circadian clock, suggesting a feedback loop between light, the circadian clock and behaviour. The relative contribution of classical photoreceptors and melanopsin in driving this pattern of behaviour is then considered using knockout mouse models. Next, we extend our behavioural paradigm by simulating the experience of daylight and twilight on the mouse retina, and demonstrate that the spectral changes associated with twilight alters mouse behaviour. Finally, we consider reflectance as a further source of directional and seasonal variation in intensity and spectrum in the natural light environment, which has rarely been considered in previous studies. Collectively, our data highlight the important role of behaviour and naturally-occurring changes in intensity and spectrum in regulating photoentrainment. This thesis extends our understanding of circadian photoentrainment beyond simplified laboratory conditions, to naturalistic conditions comparable to those under which circadian rhythms evolved
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Investigating the genetic basis of sleep using forward genetics
Get PDFThe alternation between waking and sleep is regulated by the internal circadian clock and sleep-wake history, and is also influenced by the external environment. Although our understanding of the circadian aspect of sleep regulation has increased, the mechanisms underlying sleep homeostasis are still largely unknown. Independent of the circadian clock, only a limited number of genes have been associated with specific sleep-wake properties. Forward genetics provides an unbiased approach, which seeks to identify genes involved in specific biological processes. This project has focused on the Sleepy6 mouse line which was obtained via a forward genetics sleep screen. This model has a mutation in synaptobrevin 2, which results in a decreased sleep duration. We aimed to further characterise the sleep phenotype of this line, at a molecular and behavioural level, to gain novel insights into the regulation of sleep. Using molecular techniques to evaluate neurotransmitter levels and gene expression, we found no significant differences in the neurotransmitter pathways investigated. Behavioural assays highlighted hyperactivity, with a mild learning deficit. Electrophysiology recordings from the motor (M1) and visual (V1) cortical areas revealed that Sleepy6 homozygous mice have reduced amounts of rapid-eye movement sleep (REMS) and a strong decrease in the amplitude of electroencephalography (EEG) and local field potential (LFP) signals, especially during non-REMS when traces are reminiscent of the burst suppression patterns often observed during anaesthesia, rather than natural sleep. At a local level, neuronal firing in Sleepy6 homozygotes ceased for seconds at a time during non-REMS, coinciding with very low-amplitude EEG and LFP traces. Sleepy6 homozygous mice also displayed a longer latency to switch between vigilance states. Finally, the successful adaption of an elaborated version of the âtwo-processâ model of sleep regulation to recordings performed in mice suggests that sleep pressure decreases at a slower rate in Sleepy6 homozygotes. This result should be interpreted in light of the above findings, as the model relies on power in the slow-wave (0.5-4 Hz) range during non-REMS, which is affected by the very low-amplitude oscillations observed in this state in Sleepy6 homozygotes. This combination of in vivo and computational work using the Sleepy6 line provides new insights into the mechanisms that underlie sleep architecture and the alternation between vigilance states. It also has the potential to further our understanding of the mechanisms underpinning the generation of slow-waves and anaesthesia.</p
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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