Shank3 influences mammalian sleep development.

Sleep problems are prevalent in autism spectrum disorder (ASD), can be observed before diagnosis, and are associated with increased restricted and repetitive behaviors. Therefore, sleep abnormalities may be a core feature of the disorder, but the developmental trajectory remains unknown. Animal models provide a unique opportunity to understand sleep ontogenesis in ASD. Previously we showed that adult mice with a truncation in the high-confidence ASD gene Shank3 (Shank3∆C ) recapitulate the clinical sleep phenotype. In this study we used longitudinal electro-encephalographic (EEG) recordings to define, for the first time, changes in sleep from weaning to young adulthood in an ASD mouse model. We show that Shank3∆C male mice sleep less overall throughout their lifespan, have increased rapid eye movement (REM) sleep early in life despite significantly reduced non-rapid eye movement (NREM) sleep, and have abnormal responses to increased sleep pressure that emerge during a specific developmental period. We demonstrate that the ability to fall asleep quickly in response to sleep loss develops normally between 24 and 30 days in mice. However, mutants are unable to reduce sleep latency after periods of prolonged waking and maintain the same response to sleep loss regardless of age. This phenomenon seems independent of homeostatic NREM sleep slow-wave dynamics. Overall, our study recapitulates both preclinical models and clinical studies showing that reduced sleep is consistently associated with ASD and suggests that problems falling asleep may reflect abnormal development of sleep and arousal mechanisms.

A chemical-genetic investigation of BDNF-NtrkB signaling in mammalian sleep.

STUDY OBJECTIVES: The neurotrophin brain-derived neurotrophic factor (BDNF) is hypothesized to be a molecular mediator of mammalian sleep homeostasis. This hypothesis is supported by correlational findings and results obtained from pharmacology. BDNF binds with high affinity to the membrane-bound receptor Neurotrophin Tyrosine Kinase Receptor B (NtrkB), which triggers several intracellular signaling cascades. It is therefore possible that BDNF's role in sleep homeostasis is mediated via NtrkB. We examined this hypothesis using a chemical-genetic technique that allows for rapid and selective inhibition of NtrkB in vivo. METHODS: We used mutant mice bearing a point mutation in the NtrkB that allows for selective and reversible inactivation in the presence of a small binding molecule (1-NM-PP1). Using a crossover design, we determined the effects of NtrkB inhibition on baseline sleep architecture and sleep homeostasis. RESULTS: We find that NtrkB inhibition reduced rapid eye movement (REM) sleep time and changed state transitions but had no effect on sleep homeostasis. CONCLUSIONS: These findings suggest that BDNF-NtrkB receptor signaling has subtle roles in sleep architecture, but no role in sleep homeostasis.

A Role for Astroglial Calcium in Mammalian Sleep and Sleep Regulation.

Mammalian sleep expression and regulation have historically been thought to reflect the activity of neurons. Changes in other brain cells (glia) across the sleep-wake cycle and their role in sleep regulation are comparatively unexplored. We show that sleep and wakefulness are accompanied by state-dependent changes in astroglial activity. Using a miniature microscope in freely behaving mice and a two-photon microscope in head-fixed, unanesthetized mice, we show that astroglial calcium signals are highest in wake and lowest in sleep and are most pronounced in astroglial processes. We also find that astroglial calcium signals during non-rapid eye movement sleep change in proportion to sleep need. In contrast to neurons, astrocytes become less synchronized during non-rapid eye movement sleep after sleep deprivation at the network and single-cell level. Finally, we show that conditionally reducing intracellular calcium in astrocytes impairs the homeostatic response to sleep deprivation. Thus, astroglial calcium activity changes dynamically across vigilance states, is proportional to sleep need, and is a component of the sleep homeostat.

Shank3 modulates sleep and expression of circadian transcription factors.

Autism Spectrum Disorder (ASD) is the most prevalent neurodevelopmental disorder in the United States and often co-presents with sleep problems. Sleep problems in ASD predict the severity of ASD core diagnostic symptoms and have a considerable impact on the quality of life of caregivers. Little is known, however, about the underlying molecular mechanisms of sleep problems in ASD. We investigated the role of Shank3, a high confidence ASD gene candidate, in sleep architecture and regulation. We show that mice lacking exon 21 of Shank3 have problems falling asleep even when sleepy. Using RNA-seq we show that sleep deprivation increases the differences in prefrontal cortex gene expression between mutants and wild types, downregulating circadian transcription factors Per3, Bhlhe41, Hlf, Tef, and Nr1d1. Shank3 mutants also have trouble regulating wheel-running activity in constant darkness. Overall, our study shows that Shank3 is an important modulator of sleep and clock gene expression.

Distribution of orexin/hypocretin immunoreactivity in the brain of a male songbird, the house finch, Carpodacus mexicanus.

Previous research has shown orexin/hypocretin immunoreactive (orexin-ir) neurons in domesticated Galliformes. However, these findings may not be representative of other birds and these studies did not include a distribution of orexin-ir projections throughout the brain. The present study was carried out in a wild-caught passerine, the house finch, Carpodacus mexicanus, and includes a detailed description of orexin-ir neurons and their projections. Orexin A and B-ir neurons were located in a single population centered on the paraventricular nucleus of the hypothalamus extending into the lateral hypothalamic area, consistent with other studies in birds. Orexin A and B-ir fibers were similarly visible across the brain, with the highest density within the preoptic area, hypothalamus and thalamus. Orexin-ir projections extended from the paraventricular nucleus rostrally to the preoptic area, laterally towards the medial striatum, nidopallium, and dorsally along the lateral ventricle towards the mesopallium. Caudally, the highest densities of orexin-ir fibers were found along the third ventricle. The periaqueductal grey, substantia nigra pars compacta and the locus coeruleus also showed a high density of orexin-ir fibers. This study showed a detailed fiber distribution previously unreported in birds and showed that orexin-ir neurons were located in similar areas regardless of phylogeny or domestication in birds. The apparently conserved neural distribution of orexins suggests that these peptides play similar roles among birds. The widespread distribution of the projections in brain areas serving various roles indicates the potential involvement of these peptides in multiple behavioral and physiological functions.

Distribution of orexin/hypocretin immunoreactivity in the nervous system of the green Treefrog, Hyla cinerea.

We examined the distribution of orexin/hypocretin immunoreactive neurons and projections throughout the brain of the green treefrog (Hyla cinerea). Orexin A and B neurons were located in a single population centered on the suprachiasmatic nucleus. Orexin A and B fibers were visible across the brain, with the highest density within the preoptic area and hypothalamus. Our data suggest different distributions of orexin neurons but not projections between families of amphibians.

Disease and Degeneration of Aging Neural Systems that Integrate Sleep Drive and Circadian Oscillations.

Sleep/wake and circadian rest-activity rhythms become irregular with age. Typical outcomes include fragmented sleep during the night, advanced sleep phase syndrome and increased daytime sleepiness. These changes lead to a reduction in the quality of life due to cognitive impairments and emotional stress. More importantly, severely disrupted sleep and circadian rhythms have been associated with an increase in disease susceptibility. Additionally, many of the same brain areas affected by neurodegenerative diseases include the sleep and wake promoting systems. Any advances in our knowledge of these sleep/wake and circadian networks are necessary to target neural areas or connections for therapy. This review will discuss research that uses molecular, behavioral, genetic and anatomical methods to further our understanding of the interaction of these systems.