Biology subjects

Vassalli, A.

Publications and source records attributed to Vassalli, A..

6 recordsLinked to original sources

bioRxiv2025

Divergent modulation of dopaminergic neurons by hypocretin/orexin receptors-1 and -2 shapes dopaminergic cell activity and socio-emotional behavior

BACKGROUNDMany neuropsychiatric disorders involve dysregulation of the dopaminergic (DA) input to the forebrain. Of particular relevance are DA projections stemming from the midbrain ventral tegmental area (VTA). A key neuromodulatory influence onto DAVTA neurons arises from lateral hypothalamic area hypocretin/orexin (OX) neurons. Despite being a major input, the differential action of orexin peptides A and B (OXA and OXB) on orexin receptors 1 and 2 in DA cells is poorly understood. We recently identified profoundly divergent functions of OX1R vs OX2R in DA cells in regulating sleep/wake architecture, brain oscillations and cognitive behaviors. OX2R, but not OX1R, loss dramatically increased time in EEG theta-rich (alert) wakefulness, reward-driven learning and attentional skills, but impaired inhibitory control. METHODSUsing genetically engineered mice whose DA cells selectively lack OX input via Hcrtr1 (DAOx1R-KO) or Hcrtr2 (DAOx2R-KO), we assessed intrinsic excitability and electrophysiological responses of DAVTA neurons and evaluated behavioral phenotypes across multiple domains. RESULTSWe uncover previously unrecognized effects of OX peptides on DAVTA cell response. In WT and control mice, we show that while OXA enhances, OXB diminishes DAVTA neuronal excitability. OX1R-deficient DA cells lose OXA responding and OX2R-deficient DA cells lose OXB responding. DA Ox1R loss generates anxiety-like behavior and context-dependent hyperactivity. In contrast, OX2R loss decreases sociability and, despite exhibiting enhanced reward-driven learning, mice show highly compromised aversion-driven learning. CONCLUSIONSWe evidence strikingly distinct functions of OX1R vs OX2R signaling in modulating the intrinsic excitability of DAVTA neurons and influencing DA-related behaviors. These data implicate OX[->]DA signaling pathways in neuropsychiatric endophenotypes relevant to obsessive-compulsive, attention-deficit/hyperactivity, and autism spectrum disorders, and raise important considerations for the development of OXR-targeted therapeutics.

neuroscience↗

bioRxiv2025

Solriamfetol enhances alertness and cognitive performance in mice

Solriamfetol [(R)-2-amino-3-phenylpropylcarbamate hydrochloride], a phenylalanine derivative initially developed as potential antidepressant, was shown by our group in 2009 to have potent, dose-dependent wake-promoting activity in mice. Solriamfetol (Sunosi(R)) is used since 2019 to counteract excessive daytime sleepiness (EDS) in patients with narcolepsy and obstructive sleep apnea (OSA). It has several advantages over other stimulants, notably that it is not associated with strong psychomotor activity, does not induce behavioral stereotypies and anxiety-related behaviors, in contrast to amphetamines and modafinil. Its mode-of-action remains incompletely solved. It was reported to act as dual dopamine-and-noradrenaline-reuptake-inhibitor (DNRI), and more recently, to have TAAR1 agonist activity. In our early mouse study, we showed that, at 150 mg/kg, Solriamfetol induces a state of wakefulness featuring a dramatic upregulation of EEG gamma activity, a cognitive biomarker, and the expression of genes implicated in neural plasticity, learning and memory. Besides being prescribed to treat EDS, central nervous system stimulants are commonly used as smart drugs to enhance cognition in normal individuals. Therefore, based on Solriamfetols ability to potently induce wakefulness, EEG and molecular markers of learning and memory, we aimed to determine whether it could improve the cognitive performance of wild-type mice. Because at doses of 50-150 mg/kg, Solriamfetol induced an alert waking state associated with low mobility, thus precluding behavioral testing, we used lower doses (1-3 mg/kg) to assess cognition in a battery of tests evaluating short- or long-term memory and spatial navigation. We found that compared to saline, Solriamfetol 3 mg/kg consistently improves sustained attention for a novel object, as well as spatial memory. Next, to determine the brain activity correlates of enhanced cognition, we performed EEG/EMG recording while the mice performed the novel object recognition (NOR) task. Power spectral density (PSD) analysis revealed that 3 mg/kg Solriamfetol reduced EEG delta (an index of sleepiness) during exposure to a novel context, and enhanced EEG fast-gamma (an index of mental concentration) during execution of the NOR task. Taken together, our data demonstrate that low-dose Solriamfetol improves memory and attentional performance in wild-type mice.

animal behavior and cognition↗

bioRxiv2024

Sex-Specific Roles of Hypocretin Receptor Signaling in CRF Neurons on Alcohol Drinking, Anxiety, and BNST Neuronal Excitability

Alcohol use disorder (AUD) is characterized by compulsive alcohol consumption and negative emotional states during withdrawal, often perpetuating a cycle of addiction through arousal dysfunction. The hypocretin/orexin (Hcrt) neuropeptide system, a key regulator of arousal, has been implicated in these processes, particularly in its interactions with corticotropin-releasing factor (CRF) neurons within the bed nucleus of the stria terminalis (BNST). We investigated the role of Hcrt receptor signaling in CRF neurons in modulating alcohol intake, anxiety behaviors, and BNST excitability, with a focus on sex-specific differences. Using CRF-specific genetic deletion of HcrtR1 and/or HcrtR2 receptors in mice, we found that deletion of HcrtR1 significantly reduced alcohol intake, with sex-specific effects on BNST excitability. CRF-specific HcrtR2 deletion, while not affecting alcohol consumption, decreased baseline anxiety-like behaviors in males relative to females. Moreover, the double deletion of both Hcrt receptors from CRF neurons led to reduced alcohol drinking in males and dampened anxiety behaviors and BNST excitability in both sexes during protracted withdrawal. These findings suggest that Hcrt signaling in CRF neurons plays a critical role in the persistence of excessive alcohol consumption and the development of negative affective states, with distinct contributions from HcrtR1 and HcrtR2. The observed sex-specific differences underscore the need for tailored therapeutic approaches targeting the Hcrt system in the treatment of AUD.

neuroscience↗

bioRxiv2022

Orexin action on the dopaminergic system modulates theta during REM sleep and wakefulness

Both dopaminergic (DA) and orexinergic (OX) systems establish brain-wide neuromodulatory circuits that profoundly influence brain states and behavioral outputs. To unravel their interactions, we inactivated OX-to-DA neurotransmission by selective disruption of HcrtR1/OxR1, or HcrtR2/OxR2, or both receptors, in DA neurons. Chronic loss of OXR2 in DA neurons (OxR2Dat-CKO mice) dramatically increased electrocorticographic (EcoG) theta rhythms in wakefulness and REM sleep. Episode duration and total times spent in active wakefulness and REMS were prolonged, and theta/fast-gamma wave coupling was enhanced in both states. Increased theta in OxR2DatCKO mice baseline wake was accompanied by diminished infra-theta and increased fast-gamma activities, i.e. the mice exhibited signs of constitutive electrocortical hyperarousal, albeit uncoupled with locomotor activity. These effects were not seen in OxR1-ablated dopaminergic mutants, which tended to show opposite phenotypes, resembling those caused by the loss of both receptors. Our data establish a clear, genetically-defined link between monosynaptic orexin-to-dopaminergic connectivity and the power of theta oscillations, with a differential role of OXR2 in cross-frequency wave coupling and attentional processes.

neuroscience↗

bioRxiv2021

Narcolepsy with cataplexy is caused by epigenetic silencing of hypocretin neurons

Narcolepsy with cataplexy is a chronic sleep disorder characterized by hypocretin deficiency. The condition is believed to result from autoimmune destruction of hypocretin (HCRT) neurons, although direct evidence is lacking and mere Hcrt gene inactivation causes full-blown narcolepsy in mice. Here we show that the expression of another hypothalamic neuropeptide, QRFP, is lost in mouse models with HCRT cell-ablation, but tends to be even increased in Hcrt gene knockout mice, suggesting that QRFP expression can be used as a proxy for the presence or absence of HCRT neurons. Similar to Hcrt knockout mice, narcolepsy patients show intact hypothalamic QRFP expression, and cerebrospinal fluid levels of QRFP peptide are increased, suggesting their HCRT neurons are intact. We show that the human HCRT gene promoter is methylation-sensitive in vitro, and is hypermethylated in the hypothalamus of patients selectively at a putative PAX5:ETS1 binding site within the proximal HCRT promoter. Ets1-KO mice display downregulated Hcrt expression, while pax5-ets1 knockdown in zebrafish causes decreased hcrt expression, decreased activity and sleep fragmentation, similar to narcolepsy patients. Our results suggest that HCRT neurons are alive, but epigenetically silenced, in the hypothalamus of narcolepsy patients, opening the possibility to reverse or cure narcolepsy.

neuroscience↗

bioRxiv2017

Altered allostatic regulation of wakefulness and slow-wave-sleep spectral quality in mice with hypocretin (orexin) receptor 1 inactivation in noradrenergic cells

Noradrenaline (NA) and hypocretins/orexins (HCRT), and their receptors, dynamically modulate the circuits that configure behavioral states, and their associated oscillatory activities. Salient stimuli activate spiking of locus coeruleus noradrenergic (NALC) cells, inducing NA release and brain-wide noradrenergic signalling, thus resetting network activity, and mediating an orienting response. Hypothalamic HCRT neurons provide one of the densest input to NALC cells. To functionally address the HCRT-to-NA connection, we selectively disrupted the Hcrtr1 gene in NA neurons, and analyzed resulting (Hcrtr1Dbh-CKO) mice, and their control littermates electrocortical response in several contexts of enhanced arousal. Under enforced wakefulness (EW), or after cage change (CC), Hcrtr1Dbh-CKO mice exhibited a weakened ability to lower infra-{theta} frequencies (1-7 Hz), and mount a robust, narrow-bandwidth, high-frequency {theta} rhythm (~8.5 Hz). A fast-{gamma} (55-80 Hz) response, whose dynamics closely parallelled {theta}, also diminished, while {beta}/slow-{gamma} activity (15-45 Hz) increased. Furthermore, EW-associated locomotion was lower. Surprisingly, nestbuilding-associated wakefulness, inversely, featured enhanced {theta} and fast-{gamma} activities. Thus HCRT-to-NA signalling may fine-tune arousal, up in alarming conditions, and down during self-motivated, goal-driven behaviors. Lastly, slow-wave-sleep following EW and CC, but not nestbuilding, was severely deficient in slow-{delta} waves (0.75-2.25 Hz), suggesting that HCRT-to-NA signalling regulates the slow-{delta} rebound characterizing sleep after stress-associated arousal.

neuroscience↗