mHTT Seeding Activity: A Marker of Disease Progression and Neurotoxicity in Models of Huntington's Disease.

Self-propagating, amyloidogenic mutant huntingtin (mHTT) aggregates may drive progression of Huntington's disease (HD). Here, we report the development of a FRET-based mHTT aggregate seeding (FRASE) assay that enables the quantification of mHTT seeding activity (HSA) in complex biosamples from HD patients and disease models. Application of the FRASE assay revealed HSA in brain homogenates of presymptomatic HD transgenic and knockin mice and its progressive increase with phenotypic changes, suggesting that HSA quantitatively tracks disease progression. Biochemical investigations of mouse brain homogenates demonstrated that small, rather than large, mHTT structures are responsible for the HSA measured in FRASE assays. Finally, we assessed the neurotoxicity of mHTT seeds in an inducible Drosophila model transgenic for HTTex1. We found a strong correlation between the HSA measured in adult neurons and the increased mortality of transgenic HD flies, indicating that FRASE assays detect disease-relevant, neurotoxic, mHTT structures with severe phenotypic consequences in vivo.

Characterization of microtubule-associated protein tau isoforms and Alzheimer's disease-like pathology in normal sheep (Ovis aries): relevance to their potential as a model of Alzheimer's disease.

Alzheimer's disease is a chronic neurodegenerative disease that accounts for up to 80% of all dementias. Characterised by deteriorations of memory and cognitive function, the key neuropathological features are accumulations of ß-amyloid and hyperphosphorylated tau, as 'plaques' and 'tangles', respectively. Despite extensive study, however, the exact mechanism underlying aggregate formation in Alzheimer's disease remains elusive, as does the contribution of these aggregates to disease progression. Importantly, a recent evaluation of current Alzheimer's disease animal models suggested that rodent models are not able to fully recapitulate the pathological intricacies of the disease as it occurs in humans. Therefore, increasing attention is being paid to species that might make good alternatives to rodents for studying the molecular pathology of Alzheimer's disease. The sheep (Ovis aries) is one such species, although to date, there have been few molecular studies relating to Alzheimer's disease in sheep. Here, we investigated the Alzheimer's disease relevant histopathological characteristics of 22 sheep, using anti-ß-amyloid (Abcam 12267 and mOC64) and phosphorylation specific anti-tau (AT8 and S396) antibodies. We identified numerous intraneuronal aggregates of both ß-amyloid and tau that are consistent with early Alzheimer's disease-like pathology. We confirmed the expression of two 3-repeat (1N3R, 2N3R) and two 4-repeat (1N4R, 2N4R) tau isoforms in the ovine brain, which result from the alternative splicing of two tau exons. Finally, we investigated the phosphorylation status of the serine396 residue in 30 sheep, and report that the phosphorylation of this residue begins in sheep aged as young as 2 years. Together, these data show that sheep exhibit naturally occurring ß-amyloid and tau pathologies, that reflect those that occur in the early stages of Alzheimer's disease. This is an important step towards the validation of the sheep as a feasible large animal species in which to model Alzheimer's disease.

Abnormal patterns of sleep and EEG power distribution during non-rapid eye movement sleep in the sheep model of Huntington's disease.

Sleep disruption is a common invisible symptom of neurological dysfunction in Huntington's disease (HD) that takes an insidious toll on well-being of patients. Here we used electroencephalography (EEG) to examine sleep in 6 year old OVT73 transgenic sheep (Ovis aries) that we used as a presymptomatic model of HD. We hypothesized that despite the lack of overt symptoms of HD at this age, early alterations of the sleep-wake pattern and EEG powers may already be present. We recorded EEG from female transgenic and normal sheep (5/group) during two undisturbed 'baseline' nights with different lighting conditions. We then recorded continuously through a night of sleep disruption and the following 24 h (recovery day and night). On baseline nights, regardless of whether the lights were on or off, transgenic sheep spent more time awake than normal sheep particularly at the beginning of the night. Furthermore, there were significant differences between transgenic and normal sheep in both EEG power and its pattern of distribution during non-rapid eye movement (NREM) sleep. In particular, there was a significant decrease in delta (0.5-4 Hz) power across the night in transgenic compared to normal sheep, and the distributions of delta, theta and alpha oscillations that typically dominate the EEG in the first half of the night of normal sheep were skewed so they were predominant in the second, rather than the first half of the night in transgenic sheep. Interestingly, the effect of sleep disruption on normal sheep was also to skew the pattern of distribution of EEG powers so they looked more like that of transgenic sheep under baseline conditions. Thus it is possible that transgenic sheep exist in a state that resemble a chronic state of physiological sleep deprivation. During the sleep recovery period, normal sheep showed a significant 'rebound' increase in delta power with frontal dominance. A similar rebound was not seen in transgenic sheep, suggesting that their homeostatic response to sleep deprivation is abnormal. Although sleep abnormalities in early stage HD patients are subtle, with patients often unaware of their existence, they may contribute to impairment of neurological function that herald the onset of disease. A better understanding of the mechanisms underlying EEG abnormalities in early stage HD would give insight into how, and when, they progress into the sleep disorder. The transgenic sheep model is ideally positioned for studies of the earliest phase of disease when sleep abnormalities first emerge.

Single-Cell RNA-Seq of Mouse Dopaminergic Neurons Informs Candidate Gene Selection for Sporadic Parkinson Disease.

Genetic variation modulating risk of sporadic Parkinson disease (PD) has been primarily explored through genome-wide association studies (GWASs). However, like many other common genetic diseases, the impacted genes remain largely unknown. Here, we used single-cell RNA-seq to characterize dopaminergic (DA) neuron populations in the mouse brain at embryonic and early postnatal time points. These data facilitated unbiased identification of DA neuron subpopulations through their unique transcriptional profiles, including a postnatal neuroblast population and substantia nigra (SN) DA neurons. We use these population-specific data to develop a scoring system to prioritize candidate genes in all 49 GWAS intervals implicated in PD risk, including genes with known PD associations and many with extensive supporting literature. As proof of principle, we confirm that the nigrostriatal pathway is compromised in Cplx1-null mice. Ultimately, this systematic approach establishes biologically pertinent candidates and testable hypotheses for sporadic PD, informing a new era of PD genetic research.

Increased plasma melatonin in presymptomatic Huntington disease sheep (Ovis aries): Compensatory neuroprotection in a neurodegenerative disease?

Melatonin is a pleiotrophic hormone, synthesised primarily by the pineal gland under the control of the suprachiasmatic nuclei (SCN). It not only provides a hormonal signal of darkness but also has neuroprotective properties. Huntington's disease (HD) is a progressive neurodegenerative disorder characterised by abnormal motor, cognitive and psychiatric symptoms. There is growing evidence, particularly from animal models, that circadian rhythms may also be disturbed in HD. We measured two circadian-regulated hormones, melatonin and cortisol, in plasma samples collected around-the-clock from normal and presymptomatic transgenic HD sheep (Ovis aries) at 5 and 7 years of age, to assess SCN-driven rhythms and the effect of genotype, sex and age. Melatonin-related precursors and metabolites (tryptophan, serotonin, kynurenine) were also measured by liquid chromatography (LC)-mass spectrometry (MS). At 5 years of age in both rams and ewes, plasma melatonin levels were significantly elevated in HD sheep. In ewes measured 2 years later, there was still a significant elevation of nocturnal melatonin. Furthermore, the daytime baseline levels of melatonin were significantly higher in HD sheep. Since increased melatonin could have global beneficial effects on brain function, we suggest that the increased melatonin measured in presymptomatic HD sheep is part of an autoprotective response to mutant huntingtin toxicity that may account, at least in part, for the late onset of disease that characterises HD.

Attenuated pupillary light responses and downregulation of opsin expression parallel decline in circadian disruption in two different mouse models of Huntington's disease.

Circadian deficits in Huntington's disease (HD) are recapitulated in both fragment (R6/2) and full-length (Q175) mouse models of HD. Circadian rhythms are regulated by the suprachiasmatic nuclei (SCN) in the hypothalamus, which are primarily entrained by light detected by the retina. The SCN receives input from intrinsically photosensitive retinal ganglion cells (ipRGCs) that express the photopigment melanopsin, but also receive input from rods and cones. In turn, ipRGCs mediate a range of non-image forming responses to light including circadian entrainment and the pupillary light response (PLR). Retinal degeneration/dysfunction has been described previously in R6/2 mice. We investigated, therefore, whether or not circadian disruption in HD mice is due to abnormalities in retinal photoreception. We measured the expression of melanopsin, rhodopsin and cone opsin, as well as other retinal markers (tyrosine hydroxylase, calbindin, PKCα and Brna3), in R6/2 and Q175 mice at different stages of disease. We also measured the PLR as a 'readout' for ipRGC function and a marker of light reception by the retina. We found that the PLR was attenuated in both lines of HD mice. This was accompanied by a progressive downregulation of cone opsin and melanopsin expression. We suggest that disease-related changes in photoreception by the retina contribute to the progressive dysregulation of circadian rhythmicity and entrainment seen in HD mice. Colour vision is abnormal in HD patients. Therefore, if retinal deficits similar to those seen in HD mice are confirmed in patients, specifically designed light therapy may be an effective strategy to improve circadian dysfunction.

Allelic series of Huntington's disease knock-in mice reveals expression discorrelates.

Identifying molecular drivers of pathology provides potential therapeutic targets. Differentiating between drivers and coincidental molecular alterations presents a major challenge. Variation unrelated to pathology further complicates transcriptomic, proteomic and metabolomic studies which measure large numbers of individual molecules. To overcome these challenges towards the goal of determining drivers of Huntington's disease (HD), we generated an allelic series of HD knock-in mice with graded levels of phenotypic severity for comparison with molecular alterations. RNA-sequencing analysis of this series reveals high numbers of transcripts with level alterations that do not correlate with phenotypic severity. These discorrelated molecular changes are unlikely to be drivers of pathology allowing an exclusion-based strategy to provide a short list of driver candidates. Further analysis of the data shows that a majority of transcript level changes in HD knock-in mice involve alteration of the rate of mRNA processing and/or degradation rather than solely being due to alteration of transcription rate. The overall strategy described can be applied to assess the influence of any molecular change on pathology for diseases where different mutations cause graded phenotypic severity.

Choosing an animal model for the study of Huntington's disease.

Since the identification of the causative gene in Huntington's disease (HD), a number of animal models of this disorder have been developed. A frequently asked question is: which of these models most closely recapitulates the human disease? In this Review, we provide an overview of the currently available animal models of HD in the context of the clinical features of the disease. In doing so, we highlight their strengths and limitations for modelling specific symptoms of the disease. This should highlight the animal model that is best suited to address a particular question of interest and, ultimately, to expedite the discovery of treatments that will prevent or slow the progression of HD.

Indices of comparative cognition: assessing animal models of human brain function.

Understanding the cognitive capacities of animals is important, because (a) several animal models of human neurodegenerative disease are considered poor representatives of the human equivalent and (b) cognitive capacities may provide insight into alternative animal models. We used a three-stage process of cognitive and neuroanatomical comparison (using sheep as an example) to assess the appropriateness of a species to model human brain function. First, a cognitive task was defined via a reinforcement-learning algorithm where values/constants in the algorithm were taken as indirect measures of neurophysiological attributes. Second, cognitive data (values/constants) were generated for the example species (sheep) and compared to other species. Third, cognitive data were compared with neuroanatomical metrics for each species (endocranial volume, gyrification index, encephalisation quotient, and number of cortical neurons). Four breeds of sheep (n = 15/sheep) were tested using the two-choice discrimination-reversal task. The 'reversal index' was used as a measure of constants within the learning algorithm. Reversal index data ranked sheep as third in a table of species that included primates, dogs, and pigs. Across all species, number of cortical neurons correlated strongest against the reversal index (r2 = 0.66, p = 0.0075) followed by encephalization quotient (r2 = 0.42, p = 0.03), endocranial volume (r2 = 0.30, p = 0.08), and gyrification index (r2 = 0.16, p = 0.23). Sheep have a high predicted level of cognitive capacity and are thus a valid alternative model for neurodegenerative research. Using learning algorithms within cognitive tasks increases the resolution of methods of comparative cognition and can help to identify the most relevant species to model human brain function and dysfunction.

An EEG Investigation of Sleep Homeostasis in Healthy and CLN5 Batten Disease Affected Sheep.

UNLABELLED: Sheep have large brains with human-like anatomy, making them a useful species for studying brain function. Sleep homeostasis has not been studied in sheep. Here, we establish correlates of sleep homeostasis in sheep through a sleep deprivation experiment. We then use these correlates to elucidate the nature of sleep deficits in a naturally occurring ovine model of neuronal ceroid lipofuscinosis (NCL, Batten disease) caused by a mutation in CLN5 In humans, mutations in this gene lead to cortical atrophy and blindness, as well as sleep abnormalities. We recorded electroencephalograms (EEGs) from unaffected and early stage CLN5(-/-) (homozygous, affected) sheep over 3 consecutive days, the second day being the sleep deprivation day. In unaffected sheep, sleep deprivation led to increased EEG delta (0.5-4 Hz) power during non-rapid eye movement (NREM) sleep, increased time spent in the NREM sleep state, and increased NREM sleep bout length. CLN5(-/-) sheep showed comparable increases in time spent in NREM sleep and NREM sleep bout duration, verifying the presence of increased sleep pressure in both groups. Importantly, CLN5(-/-) sheep did not show the increase in NREM sleep delta power seen in unaffected sheep. This divergent delta power response is consistent with the known cortical degeneration in CLN5(-/-) sheep. We conclude that, whereas sleep homeostasis is present in CLN5(-/-) sheep, underlying CLN5(-/-) disease processes prevent its full expression, even at early stages. Such deficits may contribute to early abnormalities seen in sheep and patients and warrant further study. SIGNIFICANCE STATEMENT: Sleep abnormalities pervade most neurological diseases, including the neuronal ceroid lipofuscinoses (NCLs). Here, we show that, in an ovine model of a variant late-infantile NCL, there is abnormal expression of sleep homeostasis. Whereas some sleep pressure correlates respond to sleep deprivation, the strongest electroencephalogram (EEG) correlate of sleep pressure, non-REM delta power, failed to increase. This highlights the relevance of sleep deficits in this disease, in which the drive for sleep exists but the underlying disease prevents its full expression. Sleep abnormalities could contribute to early disease symptoms such as behavioral disorder and cognitive decline. Our study also shows sleep homeostatic EEG correlates in sheep, opening up new opportunities for studying sleep in a large social mammal with complex human-like brain neuroanatomy.

A stop-signal task for sheep: introduction and validation of a direct measure for the stop-signal reaction time.

Huntington's disease (HD) patients show reduced flexibility in inhibiting an already-started response. This can be quantified by the stop-signal task. The aim of this study was to develop and validate a sheep version of the stop-signal task that would be suitable for monitoring the progression of cognitive decline in a transgenic sheep model of HD. Using a semi-automated operant system, sheep were trained to perform in a two-choice discrimination task. In 22% of the trials, a stop-signal was presented. Upon the stop-signal presentation, the sheep had to inhibit their already-started response. The stopping behaviour was captured using an accelerometer mounted on the back of the sheep. This set-up provided a direct read-out of the individual stop-signal reaction time (SSRT). We also estimated the SSRT using the conventional approach of subtracting the stop-signal delay (i.e., time after which the stop-signal is presented) from the ranked reaction time during a trial without a stop-signal. We found that all sheep could inhibit an already-started response in 91% of the stop-trials. The directly measured SSRT (0.974 ± 0.04 s) was not significantly different from the estimated SSRT (0.938 ± 0.04 s). The sheep version of the stop-signal task adds to the repertoire of tests suitable for investigating both cognitive dysfunction and efficacy of therapeutic agents in sheep models of neurodegenerative disease such as HD, as well as neurological conditions such as attention deficit hyperactivity disorder.

The Cambridge MRI database for animal models of Huntington disease.

We describe the Cambridge animal brain magnetic resonance imaging repository comprising 400 datasets to date from mouse models of Huntington disease. The data include raw images as well as segmented grey and white matter images with maps of cortical thickness. All images and phenotypic data for each subject are freely-available without restriction from (http://www.dspace.cam.ac.uk/handle/1810/243361/). Software and anatomical population templates optimised for animal brain analysis with MRI are also available from this site.

Expression levels of DNA replication and repair genes predict regional somatic repeat instability in the brain but are not altered by polyglutamine disease protein expression or age.

Expansion of CAG/CTG trinucleotide repeats causes numerous inherited neurological disorders, including Huntington's disease (HD), several spinocerebellar ataxias and myotonic dystrophy type 1. Expanded repeats are genetically unstable with a propensity to further expand when transmitted from parents to offspring. For many alleles with expanded repeats, extensive somatic mosaicism has been documented. For CAG repeat diseases, dramatic instability has been documented in the striatum, with larger expansions noted with advancing age. In contrast, only modest instability occurs in the cerebellum. Using microarray expression analysis, we sought to identify the genetic basis of these regional instability differences by comparing gene expression in the striatum and cerebellum of aged wild-type C57BL/6J mice. We identified eight candidate genes enriched in cerebellum, and validated four--Pcna, Rpa1, Msh6 and Fen1--along with a highly associated interactor, Lig1. We also explored whether expression levels of mismatch repair (MMR) proteins are altered in a line of HD transgenic mice, R6/2, that is known to show pronounced regional repeat instability. Compared with wild-type littermates, MMR expression levels were not significantly altered in R6/2 mice regardless of age. Interestingly, expression levels of these candidates were significantly increased in the cerebellum of control and HD human samples in comparison to striatum. Together, our data suggest that elevated expression levels of DNA replication and repair proteins in cerebellum may act as a safeguard against repeat instability, and may account for the dramatically reduced somatic instability present in this brain region, compared with the marked instability observed in the striatum.

Early and progressive circadian abnormalities in Huntington's disease sheep are unmasked by social environment.

Insidious changes in behaviour herald the onset of progressive neurodegenerative disorders such as Huntington's disease (HD), sometimes years before overt symptoms are seen. Sleep and circadian disturbances are particularly disruptive symptoms in patients with neurological disorders, but they are difficult to measure in humans. Here we studied circadian behaviour in transgenic HD sheep expressing the full-length human huntingtin protein with an expanded CAG repeat mutation in the juvenile range. Young HD sheep with no other symptoms exhibited circadian behavioural abnormalities that worsened with age. The most obvious change was a disturbed evening behaviour reminiscent of 'sundowning' that is seen in some patients with dementia. There were no structural abnormalities seen with magnetic resonance imaging, even in 5-year-old HD sheep. Interestingly, detection of the circadian abnormalities depended upon their social grouping. Abnormalities emerged in sheep kept in an 'HD-only' flock, whereas the behaviour of HD sheep kept mixed with normal sheep was relatively normal. Sleep-wake abnormalities in HD patients are also likely to be hidden, and may precede overt symptoms by many years. Sleep disruption has deleterious effects, even in normal people. The knock-on effects of sleep-wake disturbance may exacerbate, or even cause symptoms such as irritability and depression that are common in early stage HD patients. HD sheep will be useful models for probing the mechanisms underlying circadian behavioural disorder in HD.

Translational neurophysiology in sheep: measuring sleep and neurological dysfunction in CLN5 Batten disease affected sheep.

Creating valid mouse models of slowly progressing human neurological diseases is challenging, not least because the short lifespan of rodents confounds realistic modelling of disease time course. With their large brains and long lives, sheep offer significant advantages for translational studies of human disease. Here we used normal and CLN5 Batten disease affected sheep to demonstrate the use of the species for studying neurological function in a model of human disease. We show that electroencephalography can be used in sheep, and that longitudinal recordings spanning many months are possible. This is the first time such an electroencephalography study has been performed in sheep. We characterized sleep in sheep, quantifying characteristic vigilance states and neurophysiological hallmarks such as sleep spindles. Mild sleep abnormalities and abnormal epileptiform waveforms were found in the electroencephalographies of Batten disease affected sheep. These abnormalities resemble the epileptiform activity seen in children with Batten disease and demonstrate the translational relevance of both the technique and the model. Given that both spontaneous and engineered sheep models of human neurodegenerative diseases already exist, sheep constitute a powerful species in which longitudinal in vivo studies can be conducted. This will advance our understanding of normal brain function and improve our capacity for translational research into neurological disorders.

Age-, tissue- and length-dependent bidirectional somatic CAG•CTG repeat instability in an allelic series of R6/2 Huntington disease mice.

The expansion of simple sequence CAG•CTG repeats is associated with a number of inherited disorders including Huntington disease (HD), myotonic dystrophy type 1 and several of the spinocerebellar ataxias. Inherited disease-associated alleles usually exceed 40 repeats and may be in excess of 1,000 repeats in some disorders. Inherited allele length is inversely proportional to age at onset, and frequent germline expansions account for the striking anticipation observed in affected families. Expanded disease associated alleles are also somatically unstable via a pathway that is age dependent and tissue specific, and also appears to be expansion biased. Somatic expansions are thought to contribute toward both tissue specificity and disease progression. Here we have examined the somatic mutational dynamics in brain and peripheral tissues from an allelic series of R6/2 HD transgenic mice inheriting from 52 to >700 CAG repeats. We found age-dependent, tissue-specific somatic instability, with particularly large expansions observed in the striatum and cortex. We also found a positive increase in somatic instability with increasing allele length. Surprisingly, however, the degree of somatic variation did not increase in a linear fashion, but leveled off with increasing allele length. Most unexpectedly, the almost exclusive bias toward the accumulation of expansions observed in mice inheriting smaller alleles was lost, and a high frequency of large somatic contractions was observed in mice inheriting very large alleles (>500 repeats). These data highlight the bidirectional nature of CAG•CTG repeat instability and the subtle balance that exists between expansion and contraction in vivo. Defining the dynamics and tissue specificity of expansion and contraction is important for understanding the role of genetic instability in pathophysiology and in particular the development of novel therapies based on suppressing expansions and/or promoting contractions.

Restriction endonuclease TseI cleaves A:A and T:T mismatches in CAG and CTG repeats.

The type II restriction endonuclease TseI recognizes the DNA target sequence 5'-G^CWGC-3' (where W = A or T) and cleaves after the first G to produce fragments with three-base 5'-overhangs. We have determined that it is a dimeric protein capable of cleaving not only its target sequence but also one containing A:A or T:T mismatches at the central base pair in the target sequence. The cleavage of targets containing these mismatches is as efficient as cleavage of the correct target sequence containing a central A:T base pair. The cleavage mechanism does not apparently use a base flipping mechanism as found for some other type II restriction endonuclease recognizing similarly degenerate target sequences. The ability of TseI to cleave targets with mismatches means that it can cleave the unusual DNA hairpin structures containing A:A or T:T mismatches formed by the repetitive DNA sequences associated with Huntington's disease (CAG repeats) and myotonic dystrophy type 1 (CTG repeats).

Combining comparative proteomics and molecular genetics uncovers regulators of synaptic and axonal stability and degeneration in vivo.

Degeneration of synaptic and axonal compartments of neurons is an early event contributing to the pathogenesis of many neurodegenerative diseases, but the underlying molecular mechanisms remain unclear. Here, we demonstrate the effectiveness of a novel "top-down" approach for identifying proteins and functional pathways regulating neurodegeneration in distal compartments of neurons. A series of comparative quantitative proteomic screens on synapse-enriched fractions isolated from the mouse brain following injury identified dynamic perturbations occurring within the proteome during both initiation and onset phases of degeneration. In silico analyses highlighted significant clustering of proteins contributing to functional pathways regulating synaptic transmission and neurite development. Molecular markers of degeneration were conserved in injury and disease, with comparable responses observed in synapse-enriched fractions isolated from mouse models of Huntington's disease (HD) and spinocerebellar ataxia type 5. An initial screen targeting thirteen degeneration-associated proteins using mutant Drosophila lines revealed six potential regulators of synaptic and axonal degeneration in vivo. Mutations in CALB2, ROCK2, DNAJC5/CSP, and HIBCH partially delayed injury-induced neurodegeneration. Conversely, mutations in DNAJC6 and ALDHA1 led to spontaneous degeneration of distal axons and synapses. A more detailed genetic analysis of DNAJC5/CSP mutants confirmed that loss of DNAJC5/CSP was neuroprotective, robustly delaying degeneration in axonal and synaptic compartments. Our study has identified conserved molecular responses occurring within synapse-enriched fractions of the mouse brain during the early stages of neurodegeneration, focused on functional networks modulating synaptic transmission and incorporating molecular chaperones, cytoskeletal modifiers, and calcium-binding proteins. We propose that the proteins and functional pathways identified in the current study represent attractive targets for developing therapeutics aimed at modulating synaptic and axonal stability and neurodegeneration in vivo.

Behavioral therapy reverses circadian deficits in a transgenic mouse model of Huntington's disease.

Progressive disruption of circadian rhythmicity associated with disturbance of the sleep-wake cycle is one of the most insidious symptoms of Huntington's disease (HD) and represents a critical management issue for both patients and their care takers. The R6/2 mouse model of HD shows a progressive disruption of the circadian rhythmicity at both behavioral and molecular levels, although the intrinsic cellular machinery that drives circadian rhythmicity in individual cells appears to be fundamentally intact. Circadian rhythms are controlled by a master clock located in the suprachiasmatic nuclei (SCN) and can be synchronized by light and non-photic factors such as exercise. Here, we aimed to test whether or not stimulating the SCN directly could prevent the loss of circadian rhythmicity in R6/2 mice. We used combinations of bright light therapy and voluntary exercise as our treatment regimes. We found that all treatments had some beneficial effects, as measured by delayed disintegration of the rest-activity rhythm and improved behavioral synchronization to the light-dark cycle. The best effects were observed in mice treated with a combination of bright light therapy and restricted periods of voluntary exercise. Neither the cause nor the consequence of deteriorating sleep-wake activity in HD patients is known. Nevertheless, our findings can be translated immediately to human patients with little cost or risk, since both light therapy and restricted exercise regimes are non-pharmacological interventions that are relatively easy to schedule. Improved circadian rhythmicity is likely to have beneficial knock-on effects on mood and general health in HD patients. Until effective treatments are found for HD, strategies that reduce deleterious effects of disordered physiology should be part of HD patient treatment programs.

Progressive sleep and electroencephalogram changes in mice carrying the Huntington's disease mutation.

Sleep disturbances in Huntington's disease may be deleterious to the cognitive performance, affective behaviour, and general well-being of patients, but a comprehensive description of the progression of changes in sleep and electroencephalogram in Huntington's disease has never been conducted. Here we studied sleep and electroencephalogram disturbances in a transgenic mouse model of Huntington's disease (R6/2 mice). We implanted 10 R6/2 mice and five wild-type littermates with electromyography electrodes, frontofrontal and frontoparietal electroencephalogram electrodes and then recorded sleep/wake behaviour at presymptomatic, symptomatic and late stages of the disease. In addition to sleep-wake scoring, we performed a spectral analysis of the sleep electroencephalogram. We found that sleep and electroencephalogram were already significantly disrupted in R6/2 mice at 9 weeks of age (presymptomatic stage). By the time they were symptomatic, R6/2 mice were unable to maintain long periods of wakefulness and had an increased propensity for rapid eye movement sleep. In addition, the peak frequency of theta rhythm was shifted progressively from 7 Hz to 6 Hz during rapid eye movement sleep, whereas slow wave activity decreased gradually during non-rapid eye movement sleep. Finally, as the disease progressed, an abnormal electroencephalogram gamma activity (30-40 Hz) emerged in R6/2 mice irrespective of sleep states. This is reminiscent of the increased gamma power described in schizophrenic patients during sleep and events of psychosis. Gaining a better understanding of sleep and electroencephalogram changes in patients with Huntington's disease should be a priority, since it will enable clinicians to initiate appropriate investigations and to instigate treatments that could dramatically improve patients' quality of life.