Gaze stabilization reflexes in the mouse: New tools to study vision and sensorimotor

__abstract__ Gaze stabilization reflexes are a popular model system in neuroscience for connecting neurophysiology and behavior as well as studying the neural correlates of behavioral plasticity. These compensatory eye movements are one of the simplest motor behaviors, consisting of a more or less spherical object that rotates with three degrees of freedom, without significantly changing the load during a movement trajectory. Additionally, it is a model system where the sensory input, consisting of visual and/or vestibular stimulation, can be fully controlled. The output, reflexive compensatory eye movements and electrophysiological activity, can be recorded and correlated with the sensory input. By manipulating those reflexive eye movements by using different combinations of sensory input, motor learning can be studied in a well‐controlled environment. In this thesis, we describe several innovative approaches that can be added to the neuroscientific arsenal. We are the first lab to describe how to record three dimensional eye movements in mice using video‐oculography. Additionally, we describe how compensatory eye movements can be used to quantify contrast sensitivity; the ability to detect small increments in shades of gray on a uniform background, which is one of the main limiting factors in a wide variety of visual tasks. This new and sensitive method is useful in characterizing mouse models where vision is affected as a result of mutations, aging, retinal degeneration or neurological impairment of the visual system

A dynamic deep sleep stage in Drosophila

Howmight one determine whether simple animals such as flies sleep in stages? Sleep inmammalsis a dynamic process involving different stages of sleep intensity, and these are typically associated with measurable changes in brain activity (Blake and Gerard, 1937; Rechtschaffen and Kales, 1968; Webb and Agnew, 1971). Evidence for different sleep stages in invertebrates remains elusive, even though it has been well established that many invertebrate species require sleep (Campbell and Tobler, 1984; Hendricks et al., 2000; Shaw et al., 2000; Sauer et al., 2003). Here we used electrophysiology and arousal-testing paradigms to show that the fruit fly, Drosophila melanogaster, transitions between deeper and lighter sleep within extended bouts of inactivity, with deeper sleep intensities after15 and30 min of inactivity. As in mammals, the timing and intensity of these dynamic sleep processes in flies is homeostatically regulated and modulated by behavioral experience. Two molecules linked to synaptic plasticity regulate the intensity of the first deep sleep stage. Optogenetic upregulation of cyclic adenosine monophosphate during the day increases sleep intensity at night, whereas loss of function of a molecule involved in synaptic pruning, the fragile-X mental retardation protein, increases sleep intensity during the day. Our results show that sleep is not homogenous in insects, and suggest that waking behavior and the associated synaptic plasticity mechanisms determine the timing and intensity of deep sleep stages in Drosophila

Paradigm of biased PAR1 (protease-activated receptor-1) activation and inhibition in endothelial cells dissected by phosphoproteomics

Thrombin is the key serine protease of the coagulation cascade and mediates cellular responses by activation of PARs (protease-activated receptors). The predominant thrombin receptor is PAR1, and in endothelial cells (ECs), thrombin dynamically regulates a plethora of phosphorylation events. However, it has remained unclear whether thrombin signaling is exclusively mediated through PAR1. Furthermore, mechanistic insight into activation and inhibition of PAR1-mediated EC signaling is lacking. In addition, signaling networks of biased PAR1 activation after differential cleavage of the PAR1 N terminus have remained an unresolved issue. Here, we used a quantitative phosphoproteomics approach to show that classical and peptide activation of PAR1 induce highly similar signaling, that low thrombin concentrations initiate only limited phosphoregulation, and that the PAR1 inhibitors vorapaxar and parmodulin-2 demonstrate distinct antagonistic properties. Subsequent analysis of the thrombin-regulated phosphosites in the presence of PAR1 inhibitors revealed that biased activation of PAR1 is not solely linked to a specific G-protein downstream of PAR1. In addition, we showed that only the canonical thrombin PAR1 tethered ligand induces extensive early phosphoregulation in ECs. Our study provides detailed insight in the signaling mechanisms downstream of PAR1. Our data demonstrate that thrombin-induced EC phosphoregulation is mediated exclusively through PAR1, that thrombin and thrombin-tethered ligand peptide induce similar phosphoregulation, and that only canonical PAR1 cleavage by thrombin generates a tethered ligand that potently induces early signaling. Furthermore, platelet PAR1 inhibitors directly affect EC signaling, indicating that it will be a challenge to design a PAR1 antagonist that will target only those pathways responsible for tissue pathology

Human Gaze Following Response Is Affected by Visual Acuity

The present study investigated how gaze following eye movements are affected by stimulus contrast and spatial frequency and by aberrations in central visual acuity due to refractive errors. We measured 30 healthy subjects with a range of visual acuities but without any refractive correction. Visual acuity was tested using a Landolt-C chart. Subjects were divided into three groups with low, intermediate, or good visual acuity. Gaze following responses (GFR) to moving Gabor patches were recorded by video-oculography. In each trial, the subjects were presented with a single Gabor patch with a specific spatial frequency and luminance contrast that moved sinusoidally in the horizontal plane. We observed that GFR gain decreased with increasing spatial frequency and decreasing contrast and was correlated with visual acuity. GFR gain was lower and decreased more for subjects with lower visual acuity; this was especially so for lower stimulus contrasts that are not tested in standard acuity tests. The largest differences between the groups were observed at spatial frequencies around 4 cpd and at contrasts up to 10%. Aberrations in central visual acuity due to refractive errors affect the GFR response depending on the contrast and spatial frequency of the moving stimulus. Measuring this effect may contribute to a better estimate of changes in visual function as a result of aging, disease, or treatments meant to improve vision

Monitoring storage induced changes in the platelet proteome employing label free quantitative mass spectrometry

Shelf life of platelet concentrates is limited to 5-7 days due to loss of platelet function during storage, commonly referred to as the platelet storage lesion (PSL). To get more insight into the development of the PSL, we used label free quantitative mass spectrometry to identify changes in the platelet proteome during storage. In total 2501 proteins were accurately quantified in 3 biological replicates on at least 1 of the 7 different time-points analyzed. Significant changes in levels of 21 proteins were observed over time. Gene ontology enrichment analysis of these proteins revealed that the majority of this set was involved in platelet degranulation, secretion and regulated exocytosis. Twelve of these proteins have been shown to reside in α-granules. Upon prolonged storage (13-16 days) elevated levels of α-2-macroglobulin, glycogenin and Ig μ chain C region were identified. Taken together this study identifies novel markers for monitoring of the PSL that may potentially also be used for the detection of "young" and "old" platelets in the circulation

Injection therapy and denervation procedures for chronic low-back pain: a systematic review

Injection therapy and denervation procedures are commonly used in the management of chronic low-back pain (LBP) despite uncertainty regarding their effectiveness and safety. To provide an evaluation of the current evidence associated with the use of these procedures, a systematic review was performed. Existing systematic reviews were screened, and the Cochrane Back Review Group trial register was searched for randomized controlled trials (RCTs) fulfilling the inclusion criteria. Studies were included if they recruited adults with chronic LBP, evaluated the use of injection therapy or denervation procedures and measured at least one clinically relevant outcome (such as pain or functional status). Two review authors independently assessed studies for eligibility and risk of bias (RoB). A meta-analysis was performed with clinically homogeneous studies, and the GRADE approach was used to determine the quality of evidence. In total, 27 RCTs were included, 14 on injection therapy and 13 on denervation procedures. 18 (66%) of the studies were determined to have a low RoB. Because of clinical heterogeneity, only two comparisons could be pooled. Overall, there is only low to very low quality evidence to support the use of injection therapy and denervation procedures over placebo or other treatments for patients with chronic LBP. However, it cannot be ruled out that in carefully selected patients, some injection therapy or denervation procedures may be of benefit

Archive of Darkness:William Kentridge's Black Box/Chambre Noire

Situating itself in histories of cinema and installation art, William Kentridge's Black Box/Chambre Noire (2005) raises questions about screens, exhibition space, site-specificity and spectatorship. Through his timely intervention in a debate on Germany’s colonial past, Kentridge’s postcolonial art has contributed to the recognition and remembrance of a forgotten, colonial genocide. This article argues that, by transposing his signature technique of drawings for projection onto a new set of media, Kentridge explores how and what we can know through cinematic projection in the white cube. In particular, his metaphor of the illuminated shadow enables him to animate archival fragments as shadows and silhouettes. By creating a multi-directional archive, Black Box enables an affective engagement with the spectres of colonialism and provides a forum for the calibration of moral questions around reparation, reconciliation and forgiveness

Drosophila strategies to study psychiatric disorders

For decades, Drosophila melanogaster has been used as a model organism to study human diseases, ranging from heart disease to cancer to neurological disorders [9]. For studying neurodegenerative diseases, Drosophila has been instrumental in understanding disease mechanisms and pathways as well as being an efficient tool in drug discovery studies. For some better-understood disorders, such as Fragile X (a mental retardation syndrome), clinical trials are being run, based in part on translational work in flies and rodents. However, Drosophila is currently less used to study psychiatric disorders such as autism, schizophrenia and attention deficit and hyperactivity disorder (ADHD), despite numerous discoveries of disease susceptibility genes that could be explored by reverse genetics or miss-expression studies. This deficit might be explained by (1) a lack of reliable tests to study more complex disease (endo)phenotypes in flies, (2) difficulties in translating disease symptoms into animal models and (3) the polygenetic nature of these diseases. In this review we discuss strategies to use D. melanogaster to study complex psychiatric disorders such as schizophrenia, autism and ADHD. Two common features of these diseases may be defective sleep and attention mechanisms, hence calling for better methods for quantifying and screening arousal thresholds in flies

Three-dimensional optokinetic eye movements in the C57BL/6J mouse

PURPOSE. To study three-dimensional optokinetic eye movements of wild-type C57BL/6J mice, the most commonly used mouse in oculomotor physiology. Optokinetic eye movements are reflexive eye movements that use visual feedback to minimize image motion across the retina. These gaze-stabilizing reflexes are a prominent model system for studying motor control and learning. They are three dimensional and consist of a horizontal, vertical, and torsional component. METHODS. Eye movements were evoked by sinusoidally rotating a virtual sphere of equally spaced dots at six frequencies (0.1-1 Hz), with a fixed amplitude of 5°. Markers were applied to the mouse eye and video oculography was used to record its movements in three dimensions. In addition, marker tracking was compared with conventional pupil tracking of horizontal optokinetic eye movements. RESULTS. Gains recorded with marker and pupil tracking are not significantly different. Optokinetic eye movements in mice are equally well developed in all directions and have a uniform input- output relation for all stimuli, including stimuli that evoke purely torsional eye movements, with gains close to unity and minimal phase differences. CONCLUSIONS. Optokinetic eye movements of C57Bl6 mice largely compensate for image motion over the retina, regardless of stimulus orientation. All responses are frequency-velocity dependent: gains decrease and phase lags increase with increasing stimulus frequency. Mice show strong torsional responses, with high gains at low stimulus frequency