Biology subjects

Lledo, P.-M.

Publications and source records attributed to Lledo, P.-M..

13 recordsLinked to original sources

bioRxiv2026

Olfactory learning potentiates long-range cortical GABAergic inputs onto adult-born neurons.

Adult neurogenesis in the olfactory bulb (OB) contributes to structural and functional plasticity, influencing olfactory perception, learning, and memory. Adult-born granule cells (abGCs) exhibit unique morphological, electrophysiological, and synaptic properties compared to their neonatally born counterparts, suggesting a specialized role in olfactory processing. In the OB, such processing relies both on sensory inputs from the olfactory epithelium as well as top-down cortical feedback, which encompass both glutamatergic and GABAergic projections from the olfactory cortex back to the OB. While abGCs are known to integrate both bottom-up sensory inputs and top-down cortical projections, the specific connectivity and functional influence of cortical GABAergic inputs on abGCs remain largely unexplored. In this study, we investigated whether activity of cortical GABAergic projections is modulated by olfactory learning, how they impact olfactory behavior and whether these connections selectively influence mature abGCs. Using in vivo fiber photometry following odor-reward associative conditioning, we found odor- and reward-dependent activity of cortical GABAergic projections during learning session. Furthermore, their functional role was revealed using optogenetic activation which impaired both the acquisition and the reversal of an odor-reward association. Ex vivo patch-clamp recordings demonstrated that olfactory learning potentiates cortical GABAergic inputs specifically onto abGCs, and morphological analysis confirmed that learning increases the number of cortical GABAergic synapses. These findings highlight a novel mechanism by which top-down inhibitory control from the olfactory cortex selectively targets abGC activity during olfactory learning. Our results provide new insights into the functional specialization of abGCs and their role in adaptive olfactory behaviors.

neuroscience↗

bioRxiv2024

Cerebral Venous Blood Flow Regulates Brain Fluid Clearance via Dural Lymphatics

The vascular system regulates brain clearance through arterial blood flow and lymphatic drainage of cerebrospinal fluid (CSF). Idiopathic intracranial hypertension (IIH), characterized by elevated intracranial pressure and dural venous sinus stenoses, can be treated by restoring venous blood flow via venous stenting, suggesting a role for venous blood flow in brain fluid clearance. Using magnetic resonance imaging (MRI) in IIH patients and healthy controls, we identified that dural venous stenoses in IIH were associated with impaired lymphatic drainage, perivenous fluid retention, and brain fluid accumulation. To investigate this further, we developed a mouse model with bilateral jugular vein ligation (JVL), which recapitulated key human findings, including intracranial hypertension, calvarial lymphatic regression, and brain swelling due to impaired clearance. To further dissect the respective roles of dural lymphatics and venous blood flow in brain clearance, we performed JVL in mice with dural lymphatic depletion. These mice exhibited spontaneous elevated intracranial pressure, but JVL did not further exacerbate this effect. Moreover, the synchronous restoration of brain clearance and dural lymphatics observed in mice after JVL was absent in lymphatic-deficient mice.Transcriptomic analyses revealed that lymphatic remodeling induced by JVL was driven by VEGF-C signaling between dural mesenchymal and lymphatic endothelial cells. These findings establish the dural venous sinuses as a critical platform where venous blood flow interacts with mesenchymal cells to preserve dural lymphatic integrity and function, essential for brain fluid clearance.

neuroscience↗

bioRxiv2024

Dissecting the contribution of vagal subcircuits in sepsis-induced brain dysfunctions.

Sepsis, a life-threatening syndrome caused by a dysregulated host response to infection, induces a range of acute effects on the brain, including sickness behaviour and sepsis-associated encephalopathy. In addition, sepsis can lead to durable changes in neuronal circuits, resulting in long-term impairments such as post-traumatic stress disorder (PTSD). These brain dysfunctions are not directly caused by brain infection but result from peripheral inflammatory signals relayed to the brain via neural and humoral pathways. The vagal complex in the brainstem, composed of the nucleus of the solitary tract (NTS) and the area postrema, plays a crucial role in sensing and relaying these signals. Notably, the activation of the vagal complex triggers neurovegetative, neuroendocrine, and behavioural responses to infection. Chronic electrical vagus nerve stimulation has been used clinically to treat various brain disorders and is being investigated for its potential to alleviate inflammation and immune diseases through the anti-inflammatory reflex. However, a deeper understanding of the involvement of the vagus nerve and downstream brain circuits in sepsis-induced brain activation and dysfunction is needed to optimize therapeutic strategies. To investigate the role of the vagal complex in sepsis-induced brain dysfunction, various techniques were employed to manipulate vagus nerve activity and downstream circuits in a rodent model of sepsis by caecal ligation and puncture. Subdiaphragmatic vagotomy and pharmacogenetic manipulation of NTS and nodose (i.e. vagus sensory neurons) were implemented, revealing that vagotomy effectively reduced acute brain activation, inflammatory responses, and sickness behaviour triggered by sepsis. Additionally, transient activation of NTS neurons had a significant impact on inflammatory responses, sickness behaviour, and long-term PTSD-like consequences. This study underscores the complex interplay among the vagus nerve, brain circuits, and systemic inflammation during sepsis, emphasizing the critical importance of understanding these interactions in the development of targeted therapeutic interventions.

neuroscience↗

bioRxiv2023

Basolateral amygdala circuits supporting negative emotional bias in a mouse model for depression

Negative emotional bias is an essential hallmark of depression reflected by negative shift in hedonic valence assignment to emotional stimuli. Pleasant cues become less attractive and unpleasant ones more aversive. Given the crucial role of amygdala in valence coding, we hypothesize that specific basolateral amygdala (BLA) circuits alterations might support negative emotional bias associated with depressive states. Using a translational assay, we evaluate odor valence assignment in an animal model for depression chronically administered by corticosterone (CORT). We show spontaneous negative bias in depressive-like mice that attribute more negative valences for both attractive and aversive odors, mimicking thus the bias observed in depressed bipolar patients. Combining CTB and rabies-based tracing with ex vivo measurements of neuronal activity and chemogenetics experiments, we find that the CORT treatment reduces BLA-to-nucleus accumbens (NAc) neuronal activity and increases BLA-to-central amygdala activity, circuits respectively known to be involved in positive and negative valence encoding. Alterations in presynaptic connectivity of BLA-projecting neurons accompany these activity shifts. Interestingly, inputs from the paraventricular thalamus nucleus (PVT) towards BLA-to-NAc neurons are reduced in CORT-treated mice. Finally, chemogenetically activating the BLA-to-NAc circuit attenuates the negative bias in CORT-treated mice as well as the depressive-like phenotype, similarly than Fluoxetine antidepressant treatment. Altogether, we demonstrate that depressive states are associated with negative emotional bias both in human and mice. This bias is supported by activity shifts of specific BLA circuits along with durable presynaptic connectivity changes, but it could be alleviated by antidepressant drug or activity manipulation of altered BLA circuit.

neuroscience↗

bioRxiv2022

Neuroinvasion and anosmia are independent phenomena upon infection with SARS-CoV-2 and its variants

SUMMARYAnosmia was identified as a hallmark of COVID-19 early in the pandemic, however, with the emergence of variants of concern, the clinical profile induced by SARS-CoV-2 infection has changed, with anosmia being less frequent. Here, we assessed the clinical, olfactory and neuroinflammatory conditions of golden hamsters infected with the original Wuhan SARS-CoV-2 strain, its isogenic ORF7-deletion mutant and three variants: Gamma, Delta, and Omicron/BA.1. We show that infected animals developed a variant-dependent clinical disease including anosmia, and that the ORF7 of SARS-CoV-2 contributes to the induction of olfactory dysfunction. Conversely, all SARS- CoV-2 variants were found to be neuroinvasive, regardless of the clinical presentation they induce. Taken together, this confirms that neuroinvasion and anosmia are independent phenomena upon SARS-CoV-2 infection. Using newly generated nanoluciferase-expressing SARS-CoV-2, we validated the olfactory pathway as a major entry point into the brain in vivo and demonstrated in vitro that SARS-CoV-2 travels retrogradely and anterogradely along axons in microfluidic neuron-epithelial networks. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=151 HEIGHT=200 SRC="FIGDIR/small/505985v2_ufig1.gif" ALT="Figure 1"> View larger version (58K): org.highwire.dtl.DTLVardef@8225ceorg.highwire.dtl.DTLVardef@80342aorg.highwire.dtl.DTLVardef@e0dfd1org.highwire.dtl.DTLVardef@1861e13_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

Age-associated gut microbiota impairs hippocampus-dependent memory in a vagus dependent manner

Aging is known to be associated with hippocampus-dependent memory decline, but the underlying causes of the age-related memory impairment remain yet highly debated. Here we showed that fecal microbiota transplantation (FMT) from aged, but not young, animal donors in young mice is sufficient to trigger profound hippocampal alterations including astrogliosis, decreased adult neurogenesis, decreased novelty-induced neuronal activation and impairment in hippocampus-dependent memory. Furthermore, similar alterations were reported when mice were subjected to an FMT from aged human donors. To decipher the mechanisms involved in mediating these microbiota-induced effects on brain function, we mapped the vagus nerve (VN)-related neuronal activity patterns and report that aged-mice FM transplanted animals showed a reduction in neuronal activity in the ascending VN output brain structure, both in basal condition and following VN stimulation. Targeted pharmacogenetic manipulation of VN-ascending neurons demonstrated that the decrease in vagal activity is detrimental to hippocampal functions. In contrast, increasing vagal ascending activity alleviated the adverse effects of aged mice FMT on hippocampal functions, and had a pro-mnesic effect in aged mice. Thus, pharmacogenetic VN stimulation is a potential therapeutic strategy to lessen microbiota-dependent age-associated impairments in hippocampal functions. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=168 SRC="FIGDIR/small/428594v3_ufig1.gif" ALT="Figure 1"> View larger version (32K): org.highwire.dtl.DTLVardef@8e668borg.highwire.dtl.DTLVardef@ee5d18org.highwire.dtl.DTLVardef@1220a87org.highwire.dtl.DTLVardef@1e12fe7_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2021

Interneuron activity-structural plasticity association is driven by context-dependent sensory experience

Neuronal dendritic spine dynamics provide a plasticity mechanism for altering brain circuit connectivity to integrate new information for learning and memory. Previous in vivo studies in the olfactory bulb (OB) showed that regional increases in activity caused localized spine stability, at a population level, yet how activity affects spine dynamics at an individual neuron level remains unknown. In this study, we tracked in vivo the correlation between an individual neurons activity and its dendritic spine dynamics of OB granule cell (GC) interneurons. Odor experience caused a consistent correlation between individual GC activity and spine stability. Dissecting the components of the OB circuit showed that increased principal cell (MC) activity was sufficient to drive this correlation, whereas cell-autonomously driven GC activity had no effect. A mathematical model was able to replicate the GC activity-spine stability correlation and showed MC output having improved odor discriminability while retaining odor memory. These results reveal that GC spine plasticity provides a sufficient network mechanism to decorrelate odors and maintain a memory trace.

neuroscience↗

bioRxiv2020

Long-range GABAergic projections contribute to cortical feedback control of sensory processing.

Cortical sensory areas send excitatory projections back to earlier stage of sensory processing. Here, we uncover for the first time the existence of a corticofugal inhibitory feedback between two sensory areas, paralleling the well-documented excitatory feedback. In the olfactory system, we reveal that a subpopulation of GABAergic neurons in the anterior olfactory nucleus and anterior piriform cortex target the olfactory bulb. These long-range inhibitory inputs synapse with both local and output olfactory bulb neurons, mitral and tufted cells. Optogenetic stimulation coupled to in vivo imaging and network modeling showed that activation these inhibitory inputs drives a net subtractive inhibition of both spontaneous and odor-evoked activity in local as well as mitral and tufted cells. Further, cortical GABAergic feedback stimulation enhanced separation of population odor responses in tufted cells, but not mitral cells. Targeted pharmacogenetic silencing of cortical GABAergic axon terminals in the OB impaired discrimination of similar odor mixtures. We propose here that cortical GABAergic feedback represents a new circuit motif in sensory systems, involved in refining sensory processing and perception.

neuroscience↗

bioRxiv2020

Anti-COVID-19 efficacy of ivermectin in the golden hamster

The devastating coronavirus disease 2019 (COVID-19) pandemic, due to SARS-CoV-2, has caused more than 47 million confirmed cases and more than 1.2 million human deaths around the globe1, and most of the severe cases of COVID-19 in humans are associated with neurological symptoms such as anosmia and ageusia, and uncontrolled inflammatory immune response2-5. Among therapeutic options6-8, the use of the anti-parasitic drug ivermectin (IVM), has been proposed, given its possible anti-SARS-CoV-2 activity9. Ivermectin is a positive allosteric modulator of the -7 nicotinic acetylcholine receptor10, which has been suggested to represent a target for the control of Covid-19 infection11, with a potential immunomodulatory activity12. We assessed the effects of IVM in SARS-CoV-2-intranasally-inoculated golden Syrian hamsters. Even though ivermectin had no effect on viral load, SARS-Cov-2-associated pathology was greatly attenuated. IVM had a sex-dependent and compartmentalized immunomodulatory effect, preventing clinical deterioration and reducing olfactory deficit in infected animals. Importantly, ivermectin dramatically reduced the Il-6/Il-10 ratio in lung tissue, which likely accounts for the more favorable clinical presentation in treated animals. Our data support IVM as a promising anti-COVID-19 drug candidate.

immunology↗

bioRxiv2020

COVID-19-associated olfactory dysfunction reveals SARS-CoV-2 neuroinvasion and persistence in the olfactory system

While recent investigations have revealed viral, inflammatory and vascular factors involved in SARS-CoV-2 lung pathogenesis, the pathophysiology of neurological disorders in COVID-19 remains poorly understood. Yet, olfactory and taste dysfunction are rather common in COVID-19, especially in pauci-symptomatic patients which constitutes the most frequent clinical manifestation of the infection. We conducted a virologic, molecular, and cellular study of the olfactory system from COVID-19 patients presenting acute loss of smell, and report evidence that the olfactory epithelium represents a highly significant infection site where multiple cell types, including olfactory sensory neurons, support cells and immune cells, are infected. Viral replication in the olfactory epithelium is associated with local inflammation. Furthermore, we show that SARS-CoV-2 induces acute anosmia and ageusia in golden Syrian hamsters, both lasting as long as the virus remains in the olfactory epithelium and the olfactory bulb. Finally, olfactory mucosa sampling in COVID-19 patients presenting with persistent loss of smell reveals the presence of virus transcripts and of SARS-CoV-2-infected cells, together with protracted inflammation. Viral persistence in the olfactory epithelium therefore provides a potential mechanism for prolonged or relapsing symptoms of COVID-19, such as loss of smell, which should be considered for optimal medical management and future therapeutic strategies.

neuroscience↗

bioRxiv2020

SARS-CoV-2 infection damages airway motile cilia and impairs mucociliary clearance

Understanding how SARS-CoV-2 spreads within the respiratory tract is important to define the parameters controlling the severity of COVID-19. We examined the functional and structural consequences of SARS-CoV-2 infection in a reconstituted human bronchial epithelium model. SARS-CoV-2 replication caused a transient decrease in epithelial barrier function and disruption of tight junctions, though viral particle crossing remained limited. Rather, SARS-CoV-2 replication led to a rapid loss of the ciliary layer, characterized at the ultrastructural level by axoneme loss and misorientation of remaining basal bodies. The motile cilia function was compromised, as measured in a mucociliary clearance assay. Epithelial defense mechanisms, including basal cell mobilization and interferon-lambda induction, ramped up only after the initiation of cilia damage. Analysis of SARS-CoV-2 infection in Syrian hamsters further demonstrated the loss of motile cilia in vivo. This study identifies cilia damage as a pathogenic mechanism that could facilitate SARS-CoV-2 spread to the deeper lung parenchyma.

microbiology↗

bioRxiv2019

The impact of gut microbiota on depressive-like behaviors and adult hippocampal neurogenesis requires the endocannabinoid system

Depression is the leading cause of disability worldwide. Recent observations have revealed an association between mood disorders and alterations of the intestinal microbiota, but causality remains yet to be established. Here, using unpredictable chronic mild stress (UCMS) as a mouse model of depression, we show that the UCMS mice display phenotypic alterations -- characterized by an altered gut microbiota composition, a reduced adult hippocampal neurogenesis and a depressive-like behaviors -- which could be transferred from UCMS donors to naive recipient mice by fecal microbiota transplantation. The cellular and behavioral alterations observed in recipient mice were accompanied by a decrease in the endocannabinoid (eCB) signaling due to lower peripheral levels of fatty acid precursors of eCB ligands. The adverse effects of UCMS-transferred microbiota on adult neurogenesis and behavior in naive recipient mice were alleviated by selectively enhancing the central eCB tone or by adding arachidonic acid, a fatty acid precursor of eCB ligands, to the diet. In the gut of both UCMS donors and recipients, the microbiota composition was characterized by a relative decrease in Lactobacilli abundance, and complementation of the UCMS recipient microbiota with a strain of the Lactobacilli genus was sufficient to restore normal eCB brain levels, hippocampal neurogenesis and to alleviate depressive-like behaviors. Our findings provide a mechanistic scenario for how chronic stress, diet and gut microbiota dysbiosis generate a pathological feed-forward loop that contributes to despair behavior via the central eCB system.

neuroscience↗

bioRxiv2019

Gut microbiota requires vagus nerve integrity to promote depression

Chronic stress constitutes one of the strongest risk factors for depression and can disrupt various aspects of homeostasis, including gut microbiota composition. We found that stress-induced changes in gut microbiota promote depression and decrease adult hippocampal neurogenesis upon transfer to antibiotic-treated recipient mice. Subdiaphragmatic vagotomy abrogated the microbiota-induced effects on behavior and neurogenesis, suggesting that gut microbiota can influence brain plasticity and behavior through vagal afferents.

neuroscience↗