Biology subjects

Soares-Cunha, C.

Publications and source records attributed to Soares-Cunha, C..

14 recordsLinked to original sources

bioRxiv2026

Hippocampal astrocytes contribute to encoding context-specific aversive stimuli to regulate fear-related behavior

In contextual fear conditioning, subjects learn to associate a neutral environment with an aversive stimulus and exhibit fear responses to that context, signaling danger. Neuronal activity in hippocampal-amygdala circuits has been shown extensively to underlie the conditioning and recall of contextual fear memories, yet the direct contribution of astrocytes to integrating stimulus and contextual information in this task remains unknown. In this study, we monitor astrocyte activity in real time in the hippocampus and simultaneously during performance in the contextual fear conditioning task. We find that shock-evoked astrocyte responses during conditioning predict the magnitude of freezing during recall in a context-specific manner. Importantly, astrocytic Ca2+ activity progressively precedes freezing onset specifically in the shock-associated context, indicating that hippocampal astrocytes contribute to encoding context-specific shock information. This work reveals an unprecedented contribution of astrocytes to the encoding of context-related information about aversive stimuli in fear-related behavior.

neuroscience↗

bioRxiv2026

Valence-specific ensembles in the laterodorsal tegmentum encode salient stimuli and modulate motivated behavior

The laterodorsal tegmentum (LDT) is a brainstem hub that integrates sensory and motivational signals to regulate adaptive behavior. While LDT neurons are known to modulate reward and aversion, whether salient stimuli recruit distinct neuronal ensembles within this structure remains unknown. Here, combined cell-type-specific calcium imaging, activity-dependent genetic tagging (TRAP2), and optogenetic reactivation to investigate how rewarding and aversive stimuli recruit and functionally define LDT neurons. Notably, single exposures to cocaine or shock in TRAP2;Ai14 mice labeled spatially and neurochemically distinct ensembles, with minimal overlap. We used fiber photometry and TRAP2 system to tag active neuronal ensembles in the LDT during cocaine (coca-LDT) and foot shock (shock-LDT) exposure, expressing GCaMP8m (green) in these neurons and, simultaneously, sRGECO (red) in the whole LDT. Our results demonstrate coca-LDT activation by physical aversive events and valenced odours, with reduced activity in response to rewarding liquids. Shock-LDT showed activation by physical aversive events, odours, and shock-predictive cues. Additionally, optogenetic reactivation of cocaine-TRAPed ensembles in a two-choice operant task biased action selection toward stimulation-paired responses, whereas shock-TRAPed ensemble activation did not drive avoidance. These findings identify functionally segregated LDT ensembles recruited by opposing motivational stimuli and reveal a causal role for reward-activated brainstem ensembles in shaping behavior. This functional segregation may contribute to the brains ability to differentiate stimulus types and, to some extent, valence experiences. Our results may provide evidence on how the LDT influences decision-making processes in addiction and anxiety disorders, potentially paving the way for novel therapeutic approaches.

neuroscience↗

bioRxiv2026

Dissociable neuronal substrates for positive and negative valence stimuli in the nucleus accumbens

The nucleus accumbens (NAc) responds to both natural and artificial rewards and to aversive stimuli; however, it remains unclear whether these opposing valence signals engage distinct neuronal ensembles. Here we used Fos-CreERT2-based activity-dependent tagging to label NAc neuronal ensembles activated by cocaine or foot shock. We found that cocaine ensemble consisted predominantly of dopamine D1 receptor-expressing medium spiny neurons (D1-MSNs), whereas foot shock ensemble similarly recruited D1- and D2-MSNs. One-photon calcium imaging in freely moving mice revealed that acute cocaine primarily excited D1-MSNs while inhibiting the majority of D2-MSNs, whereas foot shock induced excitatory responses in both types of MSNs. Optogenetic reactivation of the cocaine-ensemble elicited a strong behavioural preference, whereas reactivation of the shock-ensemble produced no significant behavioural effect. Together, these findings demonstrate that cocaine recruits a functionally specific NAc ensemble distinct from that recruited by shock, providing mechanistic insight into the valence-specific neuronal substrates underlying reward and aversion processing.

neuroscience↗

bioRxiv2026

The loss of Tau in the adult brain triggers neuroplastic, epigenetic and behavioral deficits

INTRODUCTIONAccumulation of pathological Tau precipitates neuronal malfunction in Alzheimers disease (AD). However, the impact of loss of normal Tau function in the adult brain, independently of Tau aggregates, remains unclarified. METHODSWe used a mouse model with conditional mapt knocking-down in forebrain of 5-7 months old animals (cTau-KO), a virus-driven selective Tau knockdown in wild-types (WT) and Tau re-expression approaches, accompanied by neurostructural, epigenetic, proteomic, electrophysiological, neurochemical and behavioral analyses. RESULTSLoss of Tau in the adult brain of cTau-KOs triggers neuronal atrophy and malfunction, epigenetic as well cognitive and mood deficits. Importantly, these perturbations were confirmed by selective Tau loss in WT adult brain and reverted by Tau re-expression or pharmacologically-induced epigenetic correction in cTau-KOs. DISCUSSIONOur findings highlight the contribution of loss of normal Tau function in the adult brain malfunction that could be relevant in diverse brain pathologies beyond AD, associated to Tau and its dysfunction.

neuroscience↗

bioRxiv2025

iPSC derived MSC secretome activates distinct neuroprotective pathways in a preclinical model of Parkinsons disease

Parkinsons disease (PD) is characterized by a progressive loss of dopaminergic neurons, which current therapies fail to address. Mesenchymal stem cells (MSCs) secretome holds promising therapeutic potential; however, the gold standard source - bone marrow (BM) - face scalability limitations. Induced pluripotent stem cells (iPSCs)-derived MSCs (iMSCs) are a rejuvenated and clinically attractive source, yet the effects of their secretome have not been studied in PD. Here, we directly compare the effects of BM-MSCs and iMSCs secretome in a 6-OHDA rat model. Despite few differences in secretome composition, both improved motor function and partially ameliorated anhedonia, but only iMSCs secretome significantly preserved dopaminergic neurons. Proteomic analysis revealed that BM-MSCs secretome activates antioxidant and proteostasis pathways, whereas iMSCs secretome activate broader pro-survival and regenerative pathways, including NRF2-mediated oxidative stress response and mTOR. In addition, iMSC-secretome treatment modulated glutamatergic and GABAergic neurotransmission, suggesting restoration of synaptic homeostasis beyond dopaminergic preservation. These findings demonstrate that iMSCs secretome exerts robust neuroprotective effects and shed light on the mechanisms underlying this scalable and clinically translatable therapy for PD.

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bioRxiv2025

hpGRISZ: a high-performance fluorescent biosensor for in vivo imaging of synaptic zinc dynamics

Despite the crucial role of synaptic Zn2+ in neurotransmission and neural processing, direct in vivo measurement of Zn2+ transients has remained challenging due to the limited responsiveness of existing fluorescent indicators. Here we report hpGRISZ (high-performance green indicator for synaptic Zn2+), an ultraresponsive turn-on green fluorescent biosensor engineered through iterative linker optimization, mutagenesis, and directed evolution. hpGRISZ exhibits exceptional brightness, thermostability, and a large fluorescence response (F/F0 {approx} 25) with micromolar affinity suitable for detecting extracellular synaptic Zn2+ release. We comprehensively characterized hpGRISZ in vitro, in mammalian cells, and in vivo. A membrane-anchored version of hpGRISZ traffics robustly to the cell surface under physiological conditions, where it retains strong responsiveness and supports wide-field, two-photon, and fiber photometry recordings in awake mice. These assays revealed synaptic Zn2+ dynamics across distinct brain regions and neuronal circuits. Together, our findings establish hpGRISZ as a powerful tool for dissecting zinc signaling in neural circuits and as a prototype for next-generation genetically encoded biosensors for in vivo imaging.

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bioRxiv2024

Dynamic representation of appetitive and aversive stimuli in nucleus accumbens shell D1- and D2-medium spiny neurons

The nucleus accumbens (NAc) is a key brain region for motivated behaviors, yet how distinct neuronal populations encode appetitive or aversive stimuli remains undetermined. Using microendoscopic calcium imaging, we tracked NAc shell D1- or D2-medium spiny neurons (MSNs) activity during exposure to stimuli of opposing valence and associative learning. Despite drift in individual neurons coding, both D1- and D2-population activity was sufficient to discriminate opposing valence unconditioned stimuli, but not predictive cues. Notably, D1- and D2-MSNs were similarly co-recruited during appetitive and aversive conditioning, supporting a concurrent role in associative learning. Conversely, when contingencies changed, there was an asymmetric response in the NAc, with more pronounced changes in the activity of D2-MSNs. Optogenetic manipulation of D2-MSNs provided causal evidence of the necessity of this population in the extinction of aversive associations. Our results reveal how NAc shell neurons encode valence, Pavlovian associations and their extinction, and unveil new mechanisms underlying motivated behaviors.

neuroscience↗

bioRxiv2023

Nucleus accumbens neurons dynamically encode positive and aversive associative learning

To survive, individuals must learn to associate cues in the environment with emotionally relevant outcomes. This association is partially mediated by the nucleus accumbens (NAc), a key brain region of the reward circuit that is mainly composed by GABAergic medium spiny neurons (MSNs), that express either dopamine receptor D1 or D2. Recent studies showed that both populations can drive reward and aversion, however, the activity of these neurons during appetitive and aversive Pavlovian conditioning remains to be determined. Here, we investigated the relevance of D1- and D2-neurons in Pavlovian associations, by measuring calcium transients with fiber photometry during appetitive and aversive Pavlovian tasks. Sucrose was used as a positive unconditioned stimulus (US) and foot shock was used as a negative US. We show that during appetitive Pavlovian conditioning, D1- and D2-neurons exhibit a general decrease in activity in response to CS and to US across learning, with dynamic, and partially overlapping, activity responses to CS and US. During the aversive Pavlovian conditioning, D1- and D2-neurons showed an increase in the activity in response to the CS and to the US (shock). Our data supports a synchronous role for D1- and D2-neurons in appetitive and aversion processing.

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bioRxiv2023

Impact of prenatal synthetic glucocorticoid exposure on the adolescent brain

Synthetic Glucocorticoids (sGC) are commonly prescribed in preterm risk pregnancies in order to improve fetal organ maturation. This administration greatly reduces perinatal and neonatal mortality and respiratory distress syndrome associated with prematurity, but preclinical evidence warns for an adverse effect of sGC in the developing brain. In this work we evaluated the long-term effects of prenatal exposure to sGC in the brain of 17 years-old adolescents using multimodal MRI. From 4607 birth registrations from Hospital de Braga - Portugal, we selected participants that were born with similar gestational age, but that were either exposed during pregnancy to sGC (n=21) or non-exposed (n=24). After obtaining a detailed clinical history, participants were subjected to an extensive neuropsychological evaluation, followed by structural and functional MRI. No differences were found in the performance on neuropsychological tests between sGC-exposed and non-exposed participants. Moreover, no differences were found in regional brain volumes. However, the sGC-exposed group presented reduced functional connectivity at rest in a network involving primarily sub-cortical, cerebellar and frontal nodes in comparison to the non-exposed group, even after controlling for confounding factors such as gestational age at birth, birth weight, and sex. Our results suggest that prenatal sGC-exposed adolescents present no significant deviations in neuropsychological performance in the dimensions that we evaluated, although they presented altered functional connectivity, highlighting the need for additional studies to understand the impact of these changes in brain functioning and in behavior. HighlightsPrenatal synthetic glucocorticoid exposure does not lead to structural changes in the adolescent brain. Adolescents prenatally exposed to synthetic glucocorticoids present altered resting state network.

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bioRxiv2022

Involvement of nucleus accumbens D2-MSN projections to the ventral pallidum in anxious-like behavior

The nucleus accumbens (NAc) is a crucial brain region for emotionally-relevant behaviors. The NAc is mainly composed of medium spiny neurons (MSN) expressing either dopamine receptor D1 (D1-MSNs) or D2 (D2-MSNs). D1-MSNs project to the ventral tegmental area (VTA) and ventral pallidum (VP), while D2-MSNs project only to the VP. In this work, we selectively manipulated D1-MSN projections to the VP and VTA, and D2-MSN projections to the VP during classical anxiety behavioral paradigms in naive mice. We found that optogenetic activation of D1-MSN to VP or VTA did not trigger significant anxious-like behaviors. Interestingly, optical activation of D2-MSN-VP projections significantly increased anxious-like behavior in all of the tests performed. This phenotype was associated with a decrease in the activity of VP putative GABAergic neurons. Importantly, pre-treating D2-MSN-VP animals with the GABA modulator diazepam prevented the optically-triggered anxious-like behavior. Overall, our results suggest that D2-MSN-VP projections contribute for the development of anxious-like behavior, through modulation of GABAergic activity in the VP.

neuroscience↗

bioRxiv2021

Constitutive AP2gamma deficiency reduces postnatal hippocampal neurogenesis and induces behavioral deficits in juvenile mice that persist during adulthood

The transcription factor activating protein two gamma (AP2{gamma}) is an important regulator of neurogenesis both during embryonic development as well as in the postnatal brain, but its role for neurophysiology and behavior at distinct postnatal periods is still unclear. In this work, we explored the neurogenic, behavioral, and functional impact of a constitutive AP2{gamma} heterozygous deletion in mice from early postnatal development until adulthood. Constitutive AP2{gamma} heterozygous deletion in mice caused a reduction of hippocampal transient amplifying progenitors (TAPs) in the postnatal brain, inducing significant impairments on hippocampal-dependent emotional- and cognitive-behavioral tasks including anxiety-like behavior and cognitive deficits, typically associated with an intact neurogenic activity. Moreover, AP2{gamma} deficiency impairs dorsal hippocampus-to-prefrontal cortex functional connectivity. We observed a progressive and cumulative impact of constitutive AP2{gamma} deficiency on the hippocampal glutamatergic neurogenic process, as well as alterations on limbic-cortical connectivity, together with impairments on emotional and cognitive behaviors from juvenile to adult periods. Collectively, the results herein presented demonstrate the importance of AP2{gamma} in the generation of glutamatergic neurons in the postnatal brain and its impact on behavioral performance.

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bioRxiv2020

Distinct role of nucleus accumbens D2-MSN projections to ventral pallidum in different phases of motivated behavior

The nucleus accumbens (NAc) is a key region in motivated behaviors. NAc medium spiny neurons (MSNs) are divided into those expressing dopamine receptor D1 or D2. Classically, D1- and D2-MSNs have been described as having opposing roles in reinforcement but recent evidence suggests a more complex role for D2-MSNs. Here we show that optogenetic modulation of D2-MSN to ventral pallidum (VP) projections during different stages of motivated behavior has contrasting effects in motivation. Activation of D2-MSN-VP projections during a reward-predicting cue results in increased motivational drive, whereas activation at reward delivery results in decreased motivation; optical inhibition has the opposite behavioral effect. In addition, in a free choice instrumental task, animals prefer the lever that originates one pellet in opposition to pellet plus D2-MSN-VP optogenetic activation, and vice versa for optogenetic inhibition. In summary, D2-MSN-VP projections play different (and even opposing) roles in distinct phases of motivated behavior.

neuroscience↗

bioRxiv2018

Criticality between cortical states

Since the first measurements of neuronal avalanches [1], the critical brain hypothesis has gained traction [2]. However, if the brain is critical, what is the phase transition? For several decades it has been known that the cerebral cortex operates in a diversity of regimes [3], ranging from highly synchronous states (e.g. slow wave sleep [4], with higher spiking variability) to desynchronized states (e.g. alert waking [5], with lower spiking variability). Here, using independent signatures of criticality, we show that a phase transition occurs in an intermediate value of spiking variability. The critical exponents point to a universality class different from mean-field directed percolation (MF-DP). Importantly, as the cortex hovers around this critical point [6], it follows a linear relation between the avalanche exponents that encompasses previous experimental results from different setups [7, 8] and is reproduced by a model.

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bioRxiv2018

Endo-lysosomal sorting and degradation of Tau mediates glucocorticoid-driven hippocampalmalfunction

Emerging studies implicate Tau as an essential mediator of neuronal atrophy and cognitive impairment in Alzheimers disease (AD), yet the factors that precipitate Tau dysfunction in AD are poorly understood. Chronic environmental stress and elevated glucocorticoids (GC), the major stress hormones, are associated with increased risk of AD, and have been shown to trigger intracellular Tau accumulation and downstream Tau-dependent neuronal dysfunction. However, the mechanisms through which stress and GC disrupt Tau clearance and degradation in neurons remain unclear. Here, we demonstrate that Tau undergoes degradation via endolysosomal sorting in a pathway requiring the small GTPase Rab35 and the endosomal sorting complex required for transport (ESCRT) machinery. Furthermore, we find that GC impair Tau degradation by decreasing Rab35 levels, and that AAV-mediated expression of Rab35 in the hippocampus rescues GC-induced Tau accumulation and related neurostructural deficits. These studies indicate that the Rab35/ESCRT pathway is essential for Tau clearance and part of the mechanism through which GC precipitate brain pathology.

neuroscience↗