Achucarro Basque Center for Neuroscience

Parkinson’s disease (PD) is characterised by progressive dopaminergic neurodegeneration, alpha-synuclein (α-syn) aggregation, and neuroinflammation. Clinical and experimental studies suggest that sex influences disease onset, progression, and treatment response, yet its impact on α-syn-mediated pathology remains incompletely understood. In this study, we investigated sex-dependent progression of behavioural and neuropathological alterations in a mouse model overexpressing A53T α-syn. Male and female C57BL/6J mice received bilateral intranigral injections of adeno-associated viral vectors encoding mutant A53T α-syn or empty vectors. Motor performance was assessed at 60 and 120 days post-surgery using open field, wire hang, pole, and balance beam tasks complemented by automated behavioural analysis (DeepLabCut, SimBA). Brains were processed for immunohistochemical evaluation of α-syn accumulation, tyrosine hydroxylase (TH) expression, axonal integrity, and glial activation. A53T α-syn overexpression induced early subtle motor deficits primarily in males, accompanied by increased immobility on the balance beam despite preserved substantia nigra compacta neuron counts. By 120 days, striatal TH immunoreactivity was markedly reduced in α-syn mice. An integrated axonal degeneration index, combining TH optical density and swelling counts, revealed a faster progression of striatal axonopathy in males. Both sexes showed enhanced striatal astrogliosis, indicating α-syn-driven neuroinflammation independent of sex. These findings identify early axonal degeneration and reactive astrogliosis as key pathological events preceding neuronal loss in A53T α-syn mice. Importantly, the pronounced male vulnerability highlights sex as a critical biological variable in modelling PD progression and in developing precision-based neuroprotective strategies.

Emerging evidence links glial activation, particularly microglia, to Alzheimer's disease (AD) progression. While TSPO PET (positron emission tomography) imaging detects neuroinflammation, its limitations drive interest in alternative targets like the P2X7 receptor. Myelin loss, potentially tied to chronic inflammation, is increasingly recognized as a key hallmark in AD, though the timing and relationship between neuroinflammation and demyelination remain poorly understood. We conducted a longitudinal PET study from 4 to 22 months of age in TgF344-AD rats and wild-type controls to assess neuroinflammation with [18F]JNJ-64413739 (P2X7R) and [18F]DPA-714 (TSPO) only at 22 months, alongside myelin content using [18F]Florbetaben. Diffusion tensor imaging (DTI) was used to study variations on myelin structure in old AD and WT rats. In vitro studies, including autoradiography, immunofluorescence and staining were used to support the in vivo results. [18F]JNJ-64413739 PET showed increased P2X7 receptor expression in AD and control animals over time, while [18F]DPA-714 PET showed significant differences between groups at 22 months. [18F]Florbetaben PET showed different uptake in white matter rich areas between groups with observed demyelination in AD rats at 20 months in the brain stem, supported by diffusional MRI findings. In our study, P2X7R overexpression was attributed to aging rather than genotype effects, and no link was found to the observed demyelination in AD rats. Conversely, increased TSPO neuroinflammation in TgF344-AD rats correlated with myelin loss and the reported cognitive decline in this model. Our results support the use of the TgF344-AD model to study early AD pathology, focusing on neuroinflammation and white matter integrity.

Abstract Cortical states shape sensory processing, decision-making, and behavior, and are characterized by distinct patterns of neuronal oscillatory activity. Pharmacological agents can modulate these states and their underlying electrophysiological signatures. Modafinil is a widely used wake-promoting agent and cognitive enhancer, but its effects on cortical oscillations are not fully understood. In this study, we evaluated the effect of modafinil on cortical activity during wakefulness and subsequent sleep. Ten male Wistar rats were implanted with electrocorticographic electrodes and recorded following oral administration of modafinil or its vehicle. Our results show that modafinil increased wakefulness in a dose-dependent manner, with doses of 200 and 300 mg/kg producing prolonged wake episodes and reducing hypnogram complexity. During wakefulness, modafinil enhanced gamma-band power in anterior cortices, an effect primarily driven by increases in the aperiodic rather than oscillatory components. Although no sleep rebound was observed, subsequent NREM sleep exhibited increased delta power, particularly in anterior regions, indicating heightened sleep pressure. In conclusion, our findings demonstrate that modafinil-induced wakefulness is associated with an enhanced aperiodic gamma band component at the anterior cortices in the EEG. Furthermore, modafinil modulates sleep homeostasis by enhancing NREM sleep intensity rather than extending its duration.

ABSTRACTOligodendrocytes, traditionally recognized for their role in central nervous system myelination, have emerged during the last decades as key participants maintaining brain homeostasis in response to metabolic demands and stress. In addition, injury to myelin prompts a regenerative response that leads to the formation of new myelin sheaths. However, the signals regulating effective remyelination by oligodendrocytes are still not completely understood. Here, we report that oligodendrocytes can internalize exogenous myelin both in vitro and in vivo, which leads to an increase in oligodendroglial lineage progression. RNA sequencing reveals that myelin debris alters the oligodendrocyte transcriptional profile, leading to the suppression of immune‐related pathways and de novo cholesterol and fatty acid biosynthesis, while promoting lipid droplet formation for the storage and processing internalized myelin particles. In primary cultures, myelin exposure increases oligodendrocyte progenitor (OPC) proliferation and overall oligodendroglia lineage progression, accompanied by greater cellular complexity and a larger myelinated area per cell, without altering the relative OPC‐to‐mature oligodendrocyte ratio. Stereotaxic injection of fluorescent myelin into mouse cortex and zebrafish ventricles shows internalization by microglia and, to a lesser extent, by oligodendroglia. Notably, in the zebrafish model, ventricular injections of myelin also increase the number of ventral oligodendrocytes in the spinal cord, further supporting that myelin can promote lineage progression. These findings challenge the classical view that myelin debris intrinsically inhibits oligodendrocyte proliferation, suggesting instead that oligodendrocytes can use myelin to support self‐renewal and maturation across vertebrate species, acting as a trophic factor in the absence of pathological cues.

Translational challenges in neuroscience originate from species-specific differences that limit the generalizability of experimental findings. Comparative approaches can help distinguish conserved from species-specific mechanisms, but their application has been limited by the lack of molecular tools beyond traditional model organisms, complicating direct comparisons of conserved and divergent mechanisms of neural function. This gap is particularly evident for the dopaminergic system, a key regulator of motivated behaviors across species and the principal pharmacological target for current psychotherapies. Building on our recent development of comparative gene editing, we here present an adeno-associated virus-mediated CRISPR/Cas9 strategy to reduce in vivo dopamine receptors D1 and D2 levels across the rodent phylogeny. Using this approach, we achieved specific reduction of receptor levels in three rodent species (house mouse, prairie vole, and Syrian hamster), which we demonstrate with radioactive ligand binding assays. This toolkit expands the reach of comparative gene editing approaches, enabling functional investigation of the dopaminergic system across rodent species. Thereby, it supports comparative neuroscience by facilitating the identification of conserved versus species-specific neural mechanisms with enhanced translational potential.

We used transgenic mice expressing membrane-tagged green fluorescence protein in the oligodendrocyte precursor cells (OPCs), high-resolution imaging, and detailed quantitative morphometric analysis to investigate the geometrical principles that govern structural organization of OPCs in the mouse corpus callosum. Our major findings are: (1) During the first two months of postnatal life in mice, total length of all OPCs processes increases via elaboration of new branches from the existing processes rather than via the appearance of new processes; (2) New branches are preferentially added to more distal sites of OPCs processes; (3) The processes of OPCs show stronger preferential alignment with the posterior-anterior brain axis rather than with the lateral-medial or dorsal-ventral brain axes; at the same time, the processes of OPCs show stronger preferential alignment with the lateral-medial than with the dorsal-ventral brain axis. Our study is the first detailed comprehensive analysis of OPCs morphology comparable to those available for neurons. It helps understanding the geometrical principles that govern structural organization of OPCs. These principles are important when taking into account that OPCs receive synaptic input from neurons and are capable of synaptic integration. Arborization and structural organization of OPCs processes is expected to influence the travel of synaptic input from the processes (where synapses are located) to the cell soma (where synaptic inputs are integrated), in analogy to how it occurs in neurons. Hence, the integrated synaptic signal at the OPCs cell soma which is likely to influence development and behavior of OPCs will depend on the cell morphology.

ABSTRACT Parkinson’s disease (PD) is characterised by progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNc) and accumulation of misfolded α-synuclein (α-syn). Neuroinflammation also contributes to disease onset and progression. Notably, PD exhibits sexual dimorphism in clinical presentation and treatment response. This study investigated sex-specific behavioural and morphological changes in a mouse model overexpressing A53T α-syn. Male and female C57BL/6J mice received bilateral intranigral injections of adeno-associated viral vectors encoding mutant A53T α-syn or empty vectors. Motor function was assessed at 60 and 120 days post-surgery using open field, wire hang, pole, and balance beam tests. Brains were collected for immunohistochemical analyses of α-syn pathology, nigrostriatal integrity (tyrosine hydroxylase, TH), axonal degeneration, and neuroinflammation. α-Syn overexpression induced early, subtle motor deficits primarily in males, despite preserved SNc neuronal density. Automated analysis of balance beam walking behaviour (DeepLabCut, SimBA) revealed increased immobility and reduced walking time in α-syn males. At 120 days only, striatal TH levels were significantly reduced, driven by reductions in α-syn males. Although undetected at 60 days, an axonal degeneration index (combining striatal TH optical density and axonal swellings) revealed more advanced degeneration in α-syn males, suggesting faster disease progression. At both time points, α-syn mice showed increased striatal astrogliosis without sex differences, indicating α-syn-associated neuroinflammation. These findings support a PD model of early axonal degeneration and reactive astrogliosis preceding neuronal loss. The sex-specific behavioural and neuropathological patterns underscore the importance of incorporating sex as a biological variable in preclinical models and developing tailored therapeutic strategies.

Abstract Background: Neuroinflammation and myelin loss are hallmark features of Alzheimer’s disease (AD) associated with cognitive decline. Emerging evidence highlights the significant role of glial cell activation, particularly microglia, in driving neuroinflammation and disease progression. While translocator protein (TSPO) PET imaging is commonly used to detect neuroinflammation, limitations have prompted investigation into alternative targets such as the P2X7 receptor (P2X7R), which is upregulated during pathological conditions. Additionally, myelin loss has gained recognition as an important pathological feature in AD, potentially linked to chronic neuroinflammation. However, the temporal dynamics and interplay between neuroinflammation and myelin loss remain poorly understood in the context of AD. Methods: We conducted a longitudinal PET study from 4 to 22 months of age in TgF344-AD rats and wild-type controls to assess neuroinflammation with [18F]JNJ-64413739 (P2X7R) and [18F]DPA-714 (TSPO), alongside myelin content using [18F]Florbetaben. Diffusion tensor imaging (DTI) was used to study variations on myelin structure in old AD and WT rats. In vitro studies, including autoradiography, immunoflusorescence and staining were used to support the in vivo results. Results: [18F]JNJ-64413739 PET showed increased P2X7 receptor expression in AD and control animals over time, while [18F]DPA-714 PET showed significant differences between groups at 22 months. [18F]Florbetaben PET showed different uptake in white matter rich areas between groups with observed demyelination in AD rats at 20 months in the brain stem, supported by diffusional MRI findings. Conclusions: In our study, P2X7R overexpression was attributed to aging rather than genotype effects, and no link was found to the observed demyelination in AD rats. Conversely, increased TSPO neuroinflammation in TgF344-AD rats correlated with myelin loss and the reported cognitive decline in this model. Our results support the use of the TgF344-AD model to study early AD pathology, focusing on neuroinflammation and white matter integrity.

Abstract Negative symptoms in schizophrenia, particularly motivational deficits, pose significant challenges to treatment and recovery. Despite their profound impact on functional outcomes, these symptoms remain poorly understood and inadequately addressed by current interventions. The CHANSS (Characterising Negative Symptoms in Schizophrenia) study aims to dissect the cognitive mechanisms underlying motivational impairments by focusing on three interconnected domains: executive cognition, motivational cognition, and meta-cognition. This large, international, cross-sectional study recruits a heterogeneous sample of patients across illness stages (from first-episode psychosis to treatment-resistant schizophrenia) and uses a comprehensive cognitive battery, clinical scales, self-report measures, and computerised cognitive tasks. Four novel tasks assess key processes in motivated behaviour: option generation, reward-based decision-making, risk sensitivity, and performance self-evaluation. By incorporating control for secondary influences like depression, psychosis, sedation, and illness chronicity, the study seeks to identify distinct cognitive and behavioural subtypes within motivational dysfunction. CHANSS tests the hypothesis that specific patient profiles exhibit predominant impairments in one or more cognitive domains, which may differentially affect goal-directed behaviour. The study design allows exploration of hierarchical relationships between cognitive processes, such as how executive deficits may cascade to impair motivation and self-evaluation. Ultimately, CHANSS aims to advance mechanistic understanding of motivational deficits in schizophrenia and pave the way for personalised, targeted interventions. Its findings may inform future clinical trials and contribute to a shift away from one-size-fits-all approaches toward more effective, stratified treatment strategies in schizophrenia.

Pío Del Río Hortega (1882-1945) was a giant of modern neuroscience and perhaps the most impactful member of Cajal's School. His contributions to clarifying the structure of the nervous system were key to understanding the brain beyond neurons. He uncovered microglia and oligodendrocytes, the latter until then named mesoglia. Most importantly, the characterization of oligodendroglia subtypes he made has stood the omics revolution that added molecular details relevant to comprehend their biological properties. Astounding as it may seem on today's eyes, he postulated a century ago that oligodendrocytes provide trophic support to axons, an idea that is now beyond doubt and under scrutiny as dysfunction at the axon-myelin unit is key to neurodegeneration. Here, we revised recent key advancements in oligodendrocyte biology that shed light on Hortega's ideas a century ago.