Brain Expression, Physiological Regulation and Role in Motivation and Associative Learning of Peroxisome Proliferator-activated Receptor γ.

Like other members of the superfamily of nuclear receptors, the peroxisome proliferator-activated receptor γ (PPARγ), is a ligand-activated transcription factor known for its insulin-sensitizing actions in the periphery. Despite only sparse evidence for PPARγ in the CNS, many reports suggest direct PPARγ-mediated actions in the brain. This study aimed to (i) map PPARγ expression in rodent brain areas, involved in the regulation of cognitive, motivational, and emotional functions, (ii) examine the regulation of central PPARγ by physiological variables (age, sex, obesity); (iii) chemotypically identify PPARγ-expressing cells in the frontal cortex (FC) and hippocampus (HP); (iv) study whether activation of PPARγ by pioglitazone (Pio) in FC and HP cells can induce target gene expression; and (v) demonstrate the impact of activated PPARγ on learning behavior and motivation. Immunoreactive PPARγ was detectable in specific sub-nuclei/subfields of the FC, HP, nucleus accumbens, amygdala, hypothalamus, thalamus, and granular layers of the cerebellum. PPARγ protein levels were upregulated during aging and in high fat diet-induced obesity. PPARγ mRNA expression was upregulated in the amygdala of females (but not males) that were made obese. Neural precursor cells, mature neurons, and astrocytes in primary FC and HP cultures were shown to express PPARγ. Pioglitazone dose-dependently upregulated PPARγ target genes in manner that was specific to the origin (FC or HP) of the cultures. Lastly, administration of Pio impaired motivation and associative learning. Collectively, we provide evidence for the presence of regulatable PPARγ in the brain and demonstrate their participation the regulation of key behaviors.

Reciprocal Lateral Hypothalamic and Raphe GABAergic Projections Promote Wakefulness.

The lateral hypothalamus (LH), together with multiple neuromodulatory systems of the brain, such as the dorsal raphe nucleus (DR), is implicated in arousal, yet interactions between these systems are just beginning to be explored. Using a combination of viral tracing, circuit mapping, electrophysiological recordings from identified neurons, and combinatorial optogenetics in mice, we show that GABAergic neurons in the LH selectively inhibit GABAergic neurons in the DR, resulting in increased firing of a substantial fraction of its neurons that ultimately promotes arousal. These DRGABA neurons are wake active and project to multiple brain areas involved in the control of arousal, including the LH, where their specific activation potently influences local network activity leading to arousal from sleep. Our results show how mutual inhibitory projections between the LH and the DR promote wakefulness and suggest a complex arousal control by intimate interactions between long-range connections and local circuit dynamics.SIGNIFICANCE STATEMENT: Multiple brain systems including the lateral hypothalamus and raphe serotonergic system are involved in the regulation of the sleep/wake cycle, yet the interaction between these systems have remained elusive. Here we show that mutual disinhibition mediated by long range inhibitory projections between these brain areas can promote wakefulness. The main importance of this work relies in revealing the interaction between a brain area involved in autonomic regulation and another in controlling higher brain functions including reward, patience, mood and sensory coding.

Psycho-social factors associated with mental resilience in the Corona lockdown.

The SARS-CoV-2 pandemic is not only a threat to physical health but is also having severe impacts on mental health. Although increases in stress-related symptomatology and other adverse psycho-social outcomes, as well as their most important risk factors have been described, hardly anything is known about potential protective factors. Resilience refers to the maintenance of mental health despite adversity. To gain mechanistic insights about the relationship between described psycho-social resilience factors and resilience specifically in the current crisis, we assessed resilience factors, exposure to Corona crisis-specific and general stressors, as well as internalizing symptoms in a cross-sectional online survey conducted in 24 languages during the most intense phase of the lockdown in Europe (22 March to 19 April) in a convenience sample of N = 15,970 adults. Resilience, as an outcome, was conceptualized as good mental health despite stressor exposure and measured as the inverse residual between actual and predicted symptom total score. Preregistered hypotheses (osf.io/r6btn) were tested with multiple regression models and mediation analyses. Results confirmed our primary hypothesis that positive appraisal style (PAS) is positively associated with resilience (p < 0.0001). The resilience factor PAS also partly mediated the positive association between perceived social support and resilience, and its association with resilience was in turn partly mediated by the ability to easily recover from stress (both p < 0.0001). In comparison with other resilience factors, good stress response recovery and positive appraisal specifically of the consequences of the Corona crisis were the strongest factors. Preregistered exploratory subgroup analyses (osf.io/thka9) showed that all tested resilience factors generalize across major socio-demographic categories. This research identifies modifiable protective factors that can be targeted by public mental health efforts in this and in future pandemics.

REM sleep stabilizes hypothalamic representation of feeding behavior.

During rapid eye movement (REM) sleep, behavioral unresponsiveness contrasts strongly with intense brain-wide neural network dynamics. Yet, the physiological functions of this cellular activation remain unclear. Using in vivo calcium imaging in freely behaving mice, we found that inhibitory neurons in the lateral hypothalamus (LHvgat) show unique activity patterns during feeding that are reactivated during REM, but not non-REM, sleep. REM sleep-specific optogenetic silencing of LHvgat cells induced a reorganization of these activity patterns during subsequent feeding behaviors accompanied by decreased food intake. Our findings provide evidence for a role for REM sleep in the maintenance of cellular representations of feeding behavior.

Blunted leptin sensitivity during hedonic overeating can be reinstated by activating galanin 2 receptors (Gal2R) in the lateral hypothalamus.

AIM: Since foods with high hedonic value are often consumed in excess of energetic needs, this study was designed to identify the mechanisms that may counter anorexigenic signalling in the presence of hedonic foods in lean animals. METHODS: Mice, in different states of satiety (fed/fasted, or fed/fasted and treated with ghrelin or leptin, respectively), were allowed to choose between high-fat/high-sucrose and standard foods. Intake of each food type and the activity of hypothalamic neuropetidergic neurons that regulate appetite were monitored. In some cases, food choice was monitored in leptin-injected fasted mice that received microinjections of galanin receptor agonists into the lateral hypothalamus. RESULTS: Appetite-stimulating orexin neurons in the lateral hypothalamus are rapidly activated when lean, satiated mice consume a highly palatable food (PF); such activation (upregulated c-Fos expression) occurred even after administration of the anorexigenic hormone leptin and despite intact leptin signalling in the hypothalamus. The ability of leptin to restrain PF eating is restored when a galanin receptor 2 (Gal2R) agonist is injected into the lateral hypothalamus. CONCLUSION: Hedonically-loaded foods interrupt the inhibitory actions of leptin on orexin neurons and interfere with the homeostatic control of feeding. Overeating of palatable foods can be curtailed in lean animals by activating Gal2R in the lateral hypothalamus.

Update on nonpharmacological interventions in parasomnias.

Parasomnias are abnormal behaviors that occur during sleep and can be associated, in particular during adulthood, with impaired sleep quality, daytime dysfunction, and occasionally with violent and harmful nocturnal behaviors. In these cases, therapies are often considered. Longterm pharmacological treatments are not always well tolerated and often have limited efficacy. Therefore, behavioral approaches remain an important treatment option for several types of parasomnias. However, the evidence-based approaches are limited. In the current review, we highlight results from various nonpharmacological techniques on different types of parasomnias and provide a glimpse into the future of nonpharmacological treatments in this field.

Restoring Serotonergic Homeostasis in the Lateral Hypothalamus Rescues Sleep Disturbances Induced by Early-Life Obesity.

Early-life obesity predisposes to obesity in adulthood, a condition with broad medical implications including sleep disorders, which can exacerbate metabolic disturbances and disrupt cognitive and affective behaviors. In this study, we examined the long-term impact of transient peripubertal diet-induced obesity (ppDIO, induced between 4 and 10 weeks of age) on sleep-wake behavior in male mice. EEG and EMG recordings revealed that ppDIO increases sleep during the active phase but reduces resting-phase sleep quality. This impaired sleep phenotype persisted for up to 1 year, although animals were returned to a non-obesiogenic diet from postnatal week 11 onwards. To better understand the mechanisms responsible for the ppDIO-induced alterations in sleep, we focused on the lateral hypothalamus (LH). Mice exposed to ppDIO did not show altered mRNA expression levels of orexin and melanin-concentrating hormone, two peptides that are important for sleep-wake behavior and food intake. Conversely, the LH of ppDIO-exposed mice had reduced contents of serotonin (5-hydroxytryptamine, 5-HT), a neurotransmitter involved in both sleep-wake and satiety regulation. Interestingly, an acute peripheral injection of the satiety-signaling peptide YY 3-36 increased 5-HT turnover in the LH and ameliorated the ppDIO-induced sleep disturbances, suggesting the therapeutic potential of this peptide. These findings provide new insights into how sleep-wake behavior is programmed during early life and how peripheral and central signals are integrated to coordinate sleep.SIGNIFICANCE STATEMENT Adult physiology and behavior are strongly influenced by dynamic reorganization of the brain during puberty. The present work shows that obesity during puberty leads to persistently dysregulated patterns of sleep and wakefulness by blunting serotonergic signaling in the lateral hypothalamus. It also shows that pharmacological mimicry of satiety with peptide YY3-36 can reverse this neurochemical imbalance and acutely restore sleep composition. These findings add insight into how innate behaviors such as feeding and sleep are integrated and suggest a novel mechanism through which diet-induced obesity during puberty imposes its long-lasting effects on sleep-wake behavior.

Heart rate variability and cordance in rapid eye movement sleep as biomarkers of depression and treatment response.

OBJECTIVES: The relevance of rapid eye movement (REM) sleep in affective disorders originates from its well-known abnormalities in depressed patients, who display disinhibition of REM sleep reflected by increased frequency of rapid eye movements (REM density). In this study we examined whether heart rate variability (HRV) and prefrontal theta cordance, both derived from REM sleep, could represent biomarkers of antidepressant treatment response. METHODS: In an open-label, case-control design, thirty-three in-patients (21 females) with a depressive episode were treated with various antidepressants for four weeks. Response to treatment was defined as a ≥50% reduction of HAM-D score at the end of the fourth week. Sleep EEG was recorded after the first and the fourth week of medication. HRV was derived from 3-min artifact-free electrocardiogram segments during REM sleep. Cordance was computed for prefrontal EEG channels in the theta frequency band during tonic REM sleep. RESULTS: HRV during REM sleep was decreased in depressed patients at week four as compared to controls (high effect size; Cohen's d > 1), and showed a negative correlation with REM density in both, healthy subjects and patients at week four. Further, the fourteen responders had significantly higher prefrontal theta cordance as compared to the nineteen non-responders after the first week of antidepressant medication; in contrast, HRV at week one did not discriminate between responders and non-responders. CONCLUSIONS: Our data suggest that HRV in REM sleep categorizes healthy subjects and depressed patients, whereas REM sleep-derived prefrontal cordance may predict the response to antidepressant treatment in depressed patients.

Definition of a critical spatiotemporal window within which primary cilia control midbrain dopaminergic neurogenesis.

Midbrain dopaminergic (mDA) neurons are generated in the ventral midbrain floor plate depending on Sonic Hedgehog (SHH) signaling for induction. Primary cilia transduce canonical SHH signals. Loss of intraflagellar transport protein IFT88, essential for ciliary function, disrupts SHH signaling in the ventral midbrain and results in the reduction in mDA progenitors and neurons. We investigate whether conditional inactivation of the kinesin motor protein KIF3A recapitulates phenotypes observed in conditional Ift88 mutants. Conditional Kif3a inactivation reduced the mDA progenitor domain size, but did not result in mDA neuron reduction, most likely because of a delayed loss of cilia and delayed inactivation of SHH signaling. We thereby define a precise spatiotemporal window within which primary cilia-dependent SHH signaling determines mDA fate.

Primary cilia are critical for Sonic hedgehog-mediated dopaminergic neurogenesis in the embryonic midbrain.

Midbrain dopaminergic (mDA) neurons modulate various motor and cognitive functions, and their dysfunction or degeneration has been implicated in several psychiatric diseases. Both Sonic Hedgehog (Shh) and Wnt signaling pathways have been shown to be essential for normal development of mDA neurons. Primary cilia are critical for the development of a number of structures in the brain by serving as a hub for essential developmental signaling cascades, but their role in the generation of mDA neurons has not been examined. We analyzed mutant mouse lines deficient in the intraflagellar transport protein IFT88, which is critical for primary cilia function. Conditional inactivation of Ift88 in the midbrain after E9.0 results in progressive loss of primary cilia, a decreased size of the mDA progenitor domain, and a reduction in mDA neurons. We identified Shh signaling as the primary cause of these defects, since conditional inactivation of the Shh signaling pathway after E9.0, through genetic ablation of Gli2 and Gli3 in the midbrain, results in a phenotype basically identical to the one seen in Ift88 conditional mutants. Moreover, the expansion of the mDA progenitor domain observed when Shh signaling is constitutively activated does not occur in absence of Ift88. In contrast, clusters of Shh-responding progenitors are maintained in the ventral midbrain of the hypomorphic Ift88 mouse mutant, cobblestone. Despite the residual Shh signaling, the integrity of the mDA progenitor domain is severely disturbed, and consequently very few mDA neurons are generated in cobblestone mutants. Our results identify for the first time a crucial role of primary cilia in the induction of mDA progenitors, define a narrow time window in which Shh-mediated signaling is dependent upon normal primary cilia function for this purpose, and suggest that later Wnt signaling-dependent events act independently of primary cilia.

Cordance derived from REM sleep EEG as a biomarker for treatment response in depression--a naturalistic study after antidepressant medication.

OBJECTIVE: To evaluate whether prefrontal cordance in theta frequency band derived from REM sleep EEG after the first week of antidepressant medication could characterize the treatment response after 4 weeks of therapy in depressed patients. METHOD: 20 in-patients (15 females, 5 males) with a depressive episode and 20 healthy matched controls were recruited into 4-week, open label, case-control study. Patients were treated with various antidepressants. No significant differences in age (responders (mean ± SD): 45 ± 22) years; non-responders: 49 ± 12 years), medication or Hamilton Depression Rating Scale (HAM-D) score (responders: 23.8 ± 4.5; non-responders 24.5 ± 7.6) at inclusion into the study were found between responders and non-responders. Response to treatment was defined as a ≥50% reduction of HAM-D score at the end of four weeks of active medication. Sleep EEG of patients was recorded after the first and the fourth week of medication. Cordance was computed for prefrontal EEG channels in theta frequency band during tonic REM sleep. RESULTS: The group of 8 responders had significantly higher prefrontal theta cordance in relation to the group of 12 non-responders after the first week of antidepressant medication. This finding was significant also when controlling for age, gender and number of previous depressive episodes (F1,15 = 6.025, P = .027). Furthermore, prefrontal cordance of all patients showed significant positive correlation (r = 0.52; P = .019) with the improvement of HAM-D score between the inclusion week and fourth week of medication. CONCLUSIONS: The results suggest that prefrontal cordance derived from REM sleep EEG could provide a biomarker for the response to antidepressant treatment in depressed patients.

SCOPRISM: a new algorithm for automatic sleep scoring in mice.

BACKGROUND: Scoring of wake-sleep states by trained investigators is a time-consuming task in many sleep experiments. We aimed to validate SCOPRISM, a new open-source algorithm for sleep scoring based on automatic graphical clustering of epoch distribution. METHODS: We recorded sleep and blood pressure signals of 36 orexin-deficient, 7 leptin knock-out, and 43 wild-type control mice in the PRISM laboratory. Additional groups of mice (n=14) and rats (n=6) recorded in independent labs were used to validate the algorithm across laboratories. RESULTS: The overall accuracy, specificity and sensitivity values of SCOPRISM (97%, 95%, and 94%, respectively) on PRISM lab data were similar to those calculated between human scorers (98%, 98%, and 94%, respectively). Using SCOPRISM, we replicated the main sleep and sleep-dependent cardiovascular findings of our previous studies. Finally, the cross-laboratory analyses showed that the SCOPRISM algorithm performed well on mouse and rat data. COMPARISON WITH EXISTING METHODS: SCOPRISM performed similarly or even better than recently reported algorithms. SCOPRISM is a very simple algorithm, extensively (cross)validated and with the possibility to evaluate its efficacy following a quick and easy visual flow chart. CONCLUSIONS: We validated SCOPRISM, a new, automated and open-source algorithm for sleep scoring on a large population of mice, including different mutant strains and on subgroups of mice and rats recorded by independent labs. This algorithm should help accelerate basic research on sleep and integrative physiology in rodents.

Ghrelin increases slow wave sleep and stage 2 sleep and decreases stage 1 sleep and REM sleep in elderly men but does not affect sleep in elderly women.

Ghrelin increases non-REM sleep and decreases REM sleep in young men but does not affect sleep in young women. In both sexes, ghrelin stimulates the activity of the somatotropic and the hypothalamic-pituitary-adrenal (HPA) axis, as indicated by increased growth hormone (GH) and cortisol plasma levels. These two endocrine axes are crucially involved in sleep regulation. As various endocrine effects are age-dependent, aim was to study ghrelin's effect on sleep and secretion of GH and cortisol in elderly humans. Sleep-EEGs (2300-0700 h) and secretion profiles of GH and cortisol (2000-0700 h) were determined in 10 elderly men (64.0+/-2.2 years) and 10 elderly, postmenopausal women (63.0+/-2.9 years) twice, receiving 50 microg ghrelin or placebo at 2200, 2300, 0000, and 0100 h, in this single-blind, randomized, cross-over study. In men, ghrelin compared to placebo was associated with significantly more stage 2 sleep (placebo: 183.3+/-6.1; ghrelin: 221.0+/-12.2 min), slow wave sleep (placebo: 33.4+/-5.1; ghrelin: 44.3+/-7.7 min) and non-REM sleep (placebo: 272.6+/-12.8; ghrelin: 318.2+/-11.0 min). Stage 1 sleep (placebo: 56.9+/-8.7; ghrelin: 50.9+/-7.6 min) and REM sleep (placebo: 71.9+/-9.1; ghrelin: 52.5+/-5.9 min) were significantly reduced. Furthermore, delta power in men was significantly higher and alpha power and beta power were significantly lower after ghrelin than after placebo injection during the first half of night. In women, no effects on sleep were observed. In both sexes, ghrelin caused comparable increases and secretion patterns of GH and cortisol. In conclusion, ghrelin affects sleep in elderly men but not women resembling findings in young subjects.