Behavioral and Transcriptomic Changes Following Brain-Specific Loss of Noradrenergic Transmission.

Noradrenaline (NE) plays an integral role in shaping behavioral outcomes including anxiety/depression, fear, learning and memory, attention and shifting behavior, sleep-wake state, pain, and addiction. However, it is unclear whether dysregulation of NE release is a cause or a consequence of maladaptive orientations of these behaviors, many of which associated with psychiatric disorders. To address this question, we used a unique genetic model in which the brain-specific vesicular monoamine transporter-2 (VMAT2) gene expression was removed in NE-positive neurons disabling NE release in the entire brain. We engineered VMAT2 gene splicing and NE depletion by crossing floxed VMAT2 mice with mice expressing the Cre-recombinase under the dopamine β-hydroxylase (DBH) gene promotor. In this study, we performed a comprehensive behavioral and transcriptomic characterization of the VMAT2DBHcre KO mice to evaluate the role of central NE in behavioral modulations. We demonstrated that NE depletion induces anxiolytic and antidepressant-like effects, improves contextual fear memory, alters shifting behavior, decreases the locomotor response to amphetamine, and induces deeper sleep during the non-rapid eye movement (NREM) phase. In contrast, NE depletion did not affect spatial learning and memory, working memory, response to cocaine, and the architecture of the sleep-wake cycle. Finally, we used this model to identify genes that could be up- or down-regulated in the absence of NE release. We found an up-regulation of the synaptic vesicle glycoprotein 2c (SV2c) gene expression in several brain regions, including the locus coeruleus (LC), and were able to validate this up-regulation as a marker of vulnerability to chronic social defeat. The NE system is a complex and challenging system involved in many behavioral orientations given it brain wide distribution. In our study, we unraveled specific role of NE neurotransmission in multiple behavior and link it to molecular underpinning, opening future direction to understand NE role in health and disease

Characterization of the sleep-wake cycle in the TgCRND8 mouse model of Alzheimer's disease: from early to advanced pathological stages

Individuals affected by Alzheimer's disease (AD) experience a progressive decline in cognitive function eventually leading to a debilitating loss of memory, reasoning and communication. Although AD is readily associated with such cognitive symptoms, patients can also experience behavioural and psychological symptoms, including perturbations of the sleep-wake cycle. Features of sleep-wake cycle disturbances in AD patients include increased nocturnal awakenings and a decrease in slow-wave non-rapid eye movement sleep (NREMS) and rapid eye movement sleep (REMS). Furthermore, changes in sleep quality can also be detected, as measured by the electroencephalogram (EEG) power spectrum. To determine if the TgCRND8 mouse model of AD mimics sleep alterations observed in AD patients, TgCRND8 mice were studied at 3, 7 and 11 months of age, representing differing pathological stages as defined by amyloid plaque load and distribution, as well as by the appearance of neuritic pathology, present from 5 months of age. Polysomnographic recordings were performed and the vigilance state durations over the light and dark cycles of 3, 7, and 11-month-old TgCRND8 were measured. During the active (dark cycle) and resting (light cycle) phases, at all ages studied, TgCRND8 mice spent a significantly greater amount of time awake and a significantly lower amount of time in NREMS when compared to non-transgenic (NTG) mice. Time spent in REMS was decreased during the active phase at 3 and 7 months of age in TgCRND8, while total time spent in REMS during the resting phase was not significantly affected in TgCRND8 at 3, 7 or 11 months. Following total sleep deprivation, 3-month-old TgCRND8 showed an effective recovery response, suggesting that alterations of the homeostatic regulation of the sleep-wake cycle may not contribute to sleep deficits observed at this age. The observed profile of sleep-wake cycle alterations supports the use of TgCRND8 mice as a model to study certain features of sleep-wake cycle disturbances associated with AD, such as increased wakefulness and decreased NREMS during the resting phase. Spectral power analysis of dark phase vigilance states revealed an increase in slow gamma power (20-50 Hz) during wakefulness at all ages studied and a decrease in slow-wave power <1 Hz during NREMS at 3 and 11 months of age. Brain rhythms during REMS were not altered at 3 months of age, however 7 and 11-month-old TgCRND8 displayed a decrease in alpha power (9-14 Hz) and an increase in slow gamma power (20-50 Hz) was also detected at 7 months. The observed tendency towards an increase in the spectral power of fast rhythms (slow gamma) is consistent with the pronounced increase in wakefulness observed in TgCRND8 and may reflect early changes in neuronal activity at the network level associated with amyloid pathology in the absence of severe neurodegeneration. Given the role of noradrenergic transmission within the ascending arousal system (AAS) in the regulation of vigilance states and promotion of arousal and the evidence for compensatory increases in noradrenergic signaling in AD, prazosin, an alpha-1-adrenoreceptor antagonist was administered to 3.5-month-old NTG and TgCRND8 mice to determine if this could restore normal NREMS levels in TgCRND8 mice. At a lower dose (2 mg/kg) prazosin increased NREMS in NTG mice but not in TgCRND8. However at a higher dose (5 mg/kg) an increase in NREMS was observed in both genotypes. Given that a different response to alpha-1-adrenoreceptor blockade was observed at a lower dose between the two genotypes, it may be possible that alterations in the noradrenergic regulation of the sleep-wake cycle are present in 3.5-month-old TgCRND8 and may explain why a higher dose (5mg/kg) of prazosin is required to achieve an increase in NREMS in TgCRND8.Les individus atteints par la maladie d'Alzheimer (MA) démontrent une diminution des fonctions cognitives conduisant à une perte de la mémoire, le raisonnement, et la communication. Bien que la MA est associés à ses symptômes cognitifs, les patients peuvent aussi démontrer des symptômes non-cognitifs, tels que les troubles du sommeil. Les troubles du sommeil chez les patients atteintes de la MA incluent des éveils nocturne plus nombreux, et plus longues en duré que chez les sujets âgés sains, ainsi qu'une diminution du sommeil lent profonde, et dans les stades avancés, une diminution du sommeil paradoxal. Des changements dans la qualité du sommeil sont aussi présent, et peuvent être détecté par l'analyse des puissances spectrale des rythmes associés aux différents stades de sommeil. Pour déterminer si le modèle de la MA, la souris TgCRND8, reproduit les troubles de sommeil que l'on voit chez les patients, nous avons étudié la souris TgCRND8 a 3, 7 et 11 mois, des âges qui représentent des différentes stades pathologiques, définit par la quantité et la distribution de plaques amyloïdes ainsi que la pathologie neuritique, présent à partir de 5 mois. Durant la phase nocturne et la phase diurne, à tous les âges étudié, les souris TgCRND8 démontre une augmentation du temps passé éveillé et une diminution du sommeil lent en comparaison avec les souris non-transgénique (NTG). Une diminution du sommeil paradoxal a été observé à 3 et a 7 mois durant la phase nocturne, par contre, cet effet n'était pas présent durant la phase diurne à 3, 7 ou 11 mois. Après une dépravation total du sommeil, les souris TgCRND8 âges de 3 mois ont démontré une récupération homéostatique effective, suggèrent qu'une altération des mécanismes homéostatiques qui gèrent le sommeil ne contribue pas aux troubles de sommeil observé chez ses souris, à cette âge. L'analyse quantitative de l'électroencéphalogramme (EEG) a révèle une augmentation de la puissance spectrale dans la bande de fréquence gamma lent (20-50 Hz) durant l'éveil a 3, 7 et 11 mois et une diminution de la puissance spectrale des fréquences <1 Hz durant le sommeil lent a 3 et 11 mois. Durant le sommeil paradoxal, une diminution de la puissance spectrale dans la bande de fréquence alpha (9-14 Hz) a été observé à 7 et 11 mois et une augmentation dans la bande de fréquence gamma lent (20-50 Hz) à 7 mois. La tendance d'une augmentation de la puissance spectrale dans les bandes de fréquences rapide (gamma) est en accords avec l'augmentation prononcé du temps passe éveillé que l'on observe chez les TgCRND8 et pourraient être relié à des changements d'activité neuronale associé à l'accumulation de pathologie amyloïdes en absences de neurodégénérescence chez les souris TgCRND8. Étant donné le rôle de la transmission noradrénergiques dans la promotion de l'éveil, ainsi que les études démontrant la possibilités d'augmentation compensatoire d'activité noradrénergiques chez les patients atteints de la MA, les effets de prazosin, un antagonistes de récepteurs alpha-1-adrenergiques, ont été testé chez des souris NTG et TgCRND8 âges de 3.5 mois pour déterminé ci cela pourrait rétablir le sommeil lent chez les souris TgCRND8. A une dose de 2mg/kg, prazosin a augmenté la quantité total de sommeil lent chez les souris NTG mais pas les souris TgCRND8. A une dose plus élevé de 5 mg/kg, une augmentation de la quantité total du sommeil lent a été observé chez the souris NTG et aussi chez les souris TgCRND8. Etant donné que les souris TgCRND8 démontre une réaction différente à la dose faible de prazosin (2 mg/kg) en comparaison aux souris NTG, il est possible qu'il existe une altération dans le contrôle noradrénergique du sommeil chez les souris TgCRND8, est pourrait expliqué exigence d'une dose plus élevé (5 mg/kg) pour atteindre une augmentation du sommeil lent

Sleep-Wake Cycle Dysfunction in the TgCRND8 Mouse Model of Alzheimer's Disease: From Early to Advanced Pathological Stages.

In addition to cognitive decline, individuals affected by Alzheimer's disease (AD) can experience important neuropsychiatric symptoms including sleep disturbances. We characterized the sleep-wake cycle in the TgCRND8 mouse model of AD, which overexpresses a mutant human form of amyloid precursor protein resulting in high levels of β-amyloid and plaque formation by 3 months of age. Polysomnographic recordings in freely-moving mice were conducted to study sleep-wake cycle architecture at 3, 7 and 11 months of age and corresponding levels of β-amyloid in brain regions regulating sleep-wake states were measured. At all ages, TgCRND8 mice showed increased wakefulness and reduced non-rapid eye movement (NREM) sleep during the resting and active phases. Increased wakefulness in TgCRND8 mice was accompanied by a shift in the waking power spectrum towards fast frequency oscillations in the beta (14-20 Hz) and low gamma range (20-50 Hz). Given the phenotype of hyperarousal observed in TgCRND8 mice, the role of noradrenergic transmission in the promotion of arousal, and previous work reporting an early disruption of the noradrenergic system in TgCRND8, we tested the effects of the alpha-1-adrenoreceptor antagonist, prazosin, on sleep-wake patterns in TgCRND8 and non-transgenic (NTg) mice. We found that a lower dose (2 mg/kg) of prazosin increased NREM sleep in NTg but not in TgCRND8 mice, whereas a higher dose (5 mg/kg) increased NREM sleep in both genotypes, suggesting altered sensitivity to noradrenergic blockade in TgCRND8 mice. Collectively our results demonstrate that amyloidosis in TgCRND8 mice is associated with sleep-wake cycle dysfunction, characterized by hyperarousal, validating this model as a tool towards understanding the relationship between β-amyloid overproduction and disrupted sleep-wake patterns in AD

TgCRND8 mice show alterations in brain oscillatory activity during wakefulness, NREM and REM sleep.

<p>Normalized power spectrums from 0.125–50 Hz during wakefulness <b>(A)</b>, NREM <b>(C)</b>, and REM sleep <b>(E)</b>, and normalized spectral power quantifications of key frequency bands during wakefulness <b>(B)</b>, NREM (<b>D</b>) and REM sleep <b>(F)</b> at 3 (NTg n = 7, Tg n = 8), 7 (NTg n = 5, Tg n = 7) and 11 months (NTg n = 6, Tg n = 4). (<b>A</b> and <b>B</b>) During wakefulness, 3-month-old TgCRND8 show a reduction in delta power (0.5–4.5 Hz), and at all ages, higher beta (14–20 Hz) and low gamma power (20–50 Hz) in comparison to NTg. (<b>C</b> and <b>D</b>) at all ages studied, NREM sleep delta power (0.5–4.5 Hz) was preserved in TgCRND8 in comparison to NTg. Seven-month-old TgCRND8 mice showed higher NREM low gamma power (20–50 Hz) in comparison to NTg. (<b>E</b> and <b>F</b>) The REM sleep power spectrum was unaltered in 3-month-old TgCRND8 mice, while 7 and 11-month-old TgCRND8 showed reduced REM sleep theta power (7–10 Hz) in comparison to NTg. Seven-month-old TgCRND8 also show higher REM sleep low gamma power (20–50 Hz) in comparison to NTg. The data represented above include vigilance state spectral power analysis of the dark phase (i.e. active phase) for wakefulness and of the light phase (i.e. resting phase) for NREM and REM sleep. Error bars represent SEM. Two-way ANOVA, followed by Tukey’s post-hoc test. * <i>P</i><0.05, ** <i>P</i><0.01, *** <i>P</i><0.001.</p

TgCRND8 mice show sleep-wake cycle disruption at early and advanced pathological stages.

<p>Hourly time courses (<b>A</b>) and cumulative percent duration (<b>B</b> and <b>C</b>) of wake, NREM and REM sleep across the light and dark phases at 3 (NTg n = 7, Tg n = 8), 7 (NTg n = 5, Tg n = 7) and 11(NTg n = 6, Tg n = 4) months of age. (<b>B)</b> During the dark phase, 3, 7 and 11-month-old TgCRND8 spend more time awake and less time in NREM sleep in comparison to NTg. Three and 7-month-old TgCRND8 mice also show a significant decrease in the percent time spent in REM sleep during the dark phase in comparison to NTg. (<b>C)</b> During the light phase, 3, 7 and 11-month-old TgCRND8 spend more time awake and less time in NREM sleep in comparison to NTg. Total time spent in REM sleep did not differ significantly between TgCRND8 and NTg during the light phase, at all ages studied. Error bars represent SEM. Panel <b>A</b> was analyzed by two-way ANOVA, followed by Bonferroni test for multiple comparisons. Panels <b>B</b> and <b>C</b> were analyzed by two-way ANOVA, followed by Tukey’s post-hoc test, * <i>P</i><0.05, ** <i>P</i><0.01, ***<i>P</i><0.001.</p

Quantification of Aβ₄₂ levels from key regions regulating the sleep-wake cycle.

<p>Quantification of total Aβ_<b>42</b> levels from the prefrontal cortex, hypothalamus, thalamus and brainstem of 3 (n = 7), 7 (n = 9) and 11-month-old (n = 7) TgCRND8 mice. Picograms (pg) of total Aβ_<b>42</b> are normalized to milligrams (mg) of protein per sample. (<b>A, B and C)</b> At 3, 7 and 11 months of age the prefrontal cortex contains the highest level of total Aβ_<b>42</b>, differing significantly from the hypothalamus, thalamus and brainstem. (<b>C)</b> At 11 months of age, the thalamus contains significantly higher total Aβ_<b>42</b> than the brainstem. (<b>D)</b> Progression of total Aβ_<b>42</b> overexpression in the prefrontal cortex, hypothalamus, thalamus and brainstem at 3, 7 and 11 months of age. Error bars represent SEM. Fig <b>4A</b>, <b>4B</b> and <b>4C</b> were analyzed by one-way ANOVA for the effect of brain region at a given age, followed by Tukey’s post-hoc. * Denotes a significant difference between the prefrontal cortex and each other region. # Denotes a significant difference between the thalamus and the brainstem. */^#<i>P</i><0.05, ** <i>P</i><0.01, *** <i>P</i><0.001.</p

Three-month-old TgCRND8 mice differ from NTg in their homeostatic response to total sleep deprivation.

<p>Normalized NREM sleep power spectrums from 0.125–40 Hz and quantification of NREM delta power (0.5–4.5 Hz) <b>(A)</b>, time spent awake <b>(B)</b>, time spent in NREM sleep <b>(C),</b> and time spent in REM sleep <b>(D)</b> under baseline and rebound conditions in 3-month-old NTg (n = 7) and TgCRND8 mice (n = 9). Total sleep deprivation (TSD) was performed for 6 hours, beginning at the onset of the light phase. The rebound period corresponds to the 2-hour period immediately following TSD. (<b>A)</b> Both TgCRND8 and NTg mice show a significant shift towards higher NREM delta power during the rebound period in comparison to baseline. Interestingly, the NREM delta power rebound response was blunted in TgCRND8 mice, with an 18% and 27% increase between baseline and rebound in TgCRND8 and NTg, respectively. (<b>B)</b> TgCRND8 show a significant decrease in time spent awake during the rebound period in comparison to baseline. No significant change in time spent awake during the rebound period in comparison to the baseline period was observed in NTg, and this response did not differ significantly from TgCRND8. (<b>C)</b> TgCRND8 show a significant increase in time spent in NREM sleep during the rebound period in comparison to baseline. No significant change in time spent in NREM sleep during the rebound period in comparison to the baseline was observed in NTg, and this response did not differ significantly from that observed in TgCRND8. (<b>D)</b> TgCRND8 show a significant increase in time spent in REM sleep during the rebound period in comparison to baseline. No significant change in time spent in REM sleep during the rebound period in comparison to the baseline period in NTg, and this response differed significantly from that observed in TgCRND8. Time spent in REM sleep during the rebound period was significantly greater in TgCRND8 in comparison to NTg. Error bars represent SEM. Mixed design two-way ANOVAs followed by simple effects analysis or Tukey’s post hoc where appropriate, * <i>P</i><0.05, ** <i>P</i><0.01, *** <i>P</i><0.001.</p

Prazosin differentially affects NREM sleep in 3.5-month-old TgCRND8 and NTg mice.

<p>Time spent in NREM sleep during the 2-hour period following administration of the α_<b>1</b>-adrenergic antagonist, prazosin, at 1 (<b>A</b>), 2 (<b>B</b>) and 5 (<b>C</b>) mg/kg versus vehicle in 3.5-month-old NTg and TgCRND8 mice. Prazosin or vehicle was administered at 10:00 AM via an intraperitoneal injection. (<b>A)</b> Treatment with Prazosin at 1 mg/kg does not significantly affect the percent time spent in NREM sleep when compared to vehicle in both NTg and TgCRND8. (<b>B)</b> At 2 mg/kg, treatment with Prazosin significantly increases the time spent in NREM sleep in comparison to vehicle in NTg mice only. The observed increase in NREM sleep in NTg following treatment with 2 mg/kg prazosin differed significantly from time spent in NREM sleep following treatment with 2 mg/kg in TgCRND8. (<b>C)</b> At 5 mg/kg, prazosin significantly increases time spent in NREM sleep in both NTg and TgCRND8 mice. Error bars represent SEM. NTg vehicle n = 11, NTg 1, 2 and 5 mg/kg n = 8, Tg vehicle n = 11, Tg 1 and 2 mg/kg n = 9, Tg 5 mg/kg n = 6. Fig <b>5A</b>, <b>5B</b> and <b>5C</b> were analyzed by individual two-way ANOVAs comparing each prazosin dose to vehicle, followed by Tukey’s post-hoc or simple effects analysis where appropriate, * <i>P</i><0.05, ** <i>P</i><0.01, *** <i>P</i><0.001.</p