Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy and is associated with a variety of structural and psychological alterations. Recently, there has been renewed interest in using brain tissue resected during epilepsy surgery, in particular `non-epileptic¿ brain samples with normal histology that can be found alongside epileptic tissue in the same epileptic patients ¿ with the aim being to study the normal human brain organization using a variety of methods. An important limitation is that different medical characteristics of the patients may modify the brain tissue. Thus, to better determine how `normal¿ the resected tissue is, it is fundamental to know certain clinical, anatomical and psychological characteristics of the patients. Unfortunately, this information is frequently not fully available for the patient from which the resected tissue has been obtained ¿ or is not fully appreciated by the neuroscientists analyzing the brain samples, who are not necessarily experts in epilepsy. In order to present the full picture of TLE in a way that would be accessible to multiple communities (e.g., basic researchers in neuroscience, neurologists, neurosurgeons and psychologists), we have reviewed 34 TLE patients, who were selected due to the availability of detailed clinical, anatomical, and psychological information for each of the patients. Our aim was to convey the full complexity of the disorder, its putative anatomical substrates, and the wide range of individual variability, with a view toward: (1) emphasizing the importance of considering critical patient information when using brain samples for basic research and (2) gaining a better understanding of normal and abnormal brain functioning. In agreement with a large number of previous reports, this study (1) reinforces the notion of substantial individual variability among epileptic patients, and (2) highlights the common but overlooked psychopathological alterations that occur even in patients who become ¿seizure-free¿ after surgery. The first point is based on pre- and post-surgical comparisons of patients with hippocampal sclerosis and patients with normal-looking hippocampus in neuropsychological evaluations. The second emerges from our extensive battery of personality and projective tests, in a two-way comparison of these two types of patients with regard to pre- and post-surgical performance., This work was supported by grants from the following entities: Grant PID2021-127924NB-I00 funded by MCIN/AEI/10.13039/501100011033; Centro de Investigación en Red sobre Enfermedades Neurodegenerativas (CIBERNED, CB06/05/0066); and CSIC Interdisciplinary Thematic Platform (PTI) Cajal Blue Brain (PTI-BLUEBRAIN; Spain). RA was supported by ANDIA grant #0011-3947-2021-000023 from the Gobierno de Navarra.

Perisomatic GABAergic innervation in the cerebral cortex is carried out mostly by basket and chandelier cells, which differentially participate in the control of pyramidal cell action potential output and synchronization. These cells establish multiple synapses with the cell body (and proximal dendrites) and the axon initial segment (AIS) of pyramidal neurons, respectively. Using multiple immunofluorescence, confocal microscopy and 3D quantification techniques, we have estimated the number and density of GABAergic boutons on the cell body and AIS of pyramidal neurons located through cortical layers of the human and mouse neocortex. The results revealed, in both species, that there is clear variability across layers regarding the density and number of perisomatic GABAergic boutons. We found a positive linear correlation between the surface area of the soma, or the AIS, and the number of GABAergic terminals in apposition to these 2 neuronal domains. Furthermore, the density of perisomatic GABAergic boutons was higher in the human cortex than in the mouse. These results suggest a selectivity for the GABAergic innervation of the cell body and AIS that might be related to the different functional attributes of the microcircuits in which neurons from different layers are involved in both human and mouse., CB06/05/0066/Centro de Investigación en Red sobre Enfermedades Neurodegenerativas
PID2021-127924NB-I00/MCIN

The principal aim of the present work was to chemically characterize the population of neurons labeled for the calcium binding protein secretagogin (SCGN) in the human frontal and temporal cortices (Brodmann’s area 10 and 21, respectively). Both cortical regions are involved in many high cognitive functions that are especially well developed (or unique) in humans, but with different functional roles. The pattern of SCGN immunostaining was rather similar in BA10 and BA21, with all the labeled neurons displaying a non-pyramidal morphology (interneurons). Although SCGN cells were present throughout all layers, they were more frequently observed in layers II, III and IV, whereas in layer I they were found only occasionally. We examined the degree of colocalization of SCGN with parvalbumin (PV) and calretinin (CR), as well as with nitric oxide synthase (nNOS; the enzyme responsible for the synthesis of nitric oxide by neurons) by triple immunostaining. We looked for possible similarities or differences in the coexpression patterns of SCGN with PV, CR and nNOS between BA10 and BA21 throughout the different cortical layers (I–VI). The percentage of colocalization was estimated by counting the number of all labeled cells through columns (1,100–1,400 μm wide) across the entire thickness of the cortex (from the pial surface to the white matter) in 50 μm-thick sections. Several hundred neurons were examined in both cortical regions. We found that SCGN cells include multiple neurochemical subtypes, whose abundance varies according to the cortical area and layer. The present results further highlight the regional specialization of cortical neurons and underline the importance of performing additional experiments to characterize the subpopulation of SCGN cells in the human cerebral cortex in greater detail., This work was supported by the following Grants: PGC2018-094307-B-I00 and PID2021-127924NB-I00 (to JD) funded by MCIN/AEI/10.13039/501100011033, CSIC Interdisciplinary Thematic Platform – Cajal Blue Brain (PTI-BLUEBRAIN; Spain) and the European Union’s Horizon 2020 Framework Programme for Research and Innovation under Specific grant agreements no. 785907 (Human Brain Project SGA2) and no. 945539 (Human Brain Project SGA3).

descripción no proporcionada por scopus, This work was supported by grant PID2021-127924NB-I00 funded by MCIN/AEI/10.13039/501100011033.

The purinergic ATP-gated P2X7 receptor (P2X7R) is increasingly recognized to contribute to pathological neuroinflammation and brain hyperexcitability. P2X7R expression has been shown to be increased in the brain, including both microglia and neurons, in experimental models of epilepsy and patients. To date, the cell type-specific downstream effects of P2X7Rs during seizures remain, however, incompletely understood., This work was supported by funding from Science Foundation Ireland (17/CDA/4708, SFI Centre for Research Training in Genomics Data Science under Grant number 18/CRT/6214 and co-funded under the European Regional Development Fund and by FutureNeuro industry partners 16/RC/3948, 18/RI/5792, 21/RC/10294_P2); from the H2020 Marie Skłodowska-Curie Actions Individual Fellowship (796600), from Irish Research Council Postdoctoral Fellowships (GOIPD/2020/806 and GOIPD/2020/865) from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement (No. 766124), the Agencia Estatal de Investigación (Spain) PID2021-127924NB-I00 (funded by MCIN/AEI/10.13039/501100011033) and National Natural Science Foundation of China (31970550). Fondazione Cariverona -Bando Ricerca e Sviluppo 2022 -ID52251-2022.0087. Excellence Project 2023-2027 of the Department of Neuroscience, Biomedicine and Movement Sciences of the University of Verona, funded by the Italian Ministry of University and Research., Peer reviewed

The search for biomarkers for the early diagnosis of neurodegenerative diseases is a growing area. Numerous investigations are exploring minimally invasive and cost-effective biomarkers, with the detection of phosphorylated Tau (pTau) protein emerging as one of the most promising fields. pTau is the main component of the paired helical filaments found in the brains of Alzheimer’s disease cases and serves as a precursor in the formation of neurofibrillary tangles (NFTs). Recent research has revealed that analysis of p-Tau181, p-Tau217 and p-Tau231 in blood may be an option for detecting the preclinical stage of Alzheimer’s disease. In this study, we have analyzed the values of pTau 181 in the serum of Syrian hamsters during hibernation. Naturally, over the course of hibernation, these animals exhibit a reversible accumulation of pTau in the brain tissue, which rapidly disappears upon awakening. A biosensing system based on the interferometric optical detection method was used to measure the concentration of pTau181 protein in serum samples from Syrian hamsters. This method eliminates the matrix effect and amplifies the signal obtained by using silicon dioxide nanoparticles (SiO NPs) biofunctionalized with the αpTau181 antibody. Our results indicate a substantial increase in the serum concentration of pTau in threonine-181 during hibernation, which disappears completely 2–3 h after awakening. Investigating the mechanism by which pTau protein appears in the blood non-pathologically may enhance current diagnostic techniques. Furthermore, since this process is reversible, and no tangles are detected in the brains of hibernating hamsters, additional analysis may contribute to the discovery of improved biomarkers. Additionally, exploring drugs targeting pTau to prevent the formation of tangles or studying the outcomes of any pTau-targeted treatment could be valuable., FUSP-PPC-19-264E8B2F/Universidad San Pablo - CEU
PID2021-127924NB-I00/MCIN/AEI/10.13039/501100011033; CSIC Interdisciplinary Thematic Platform - Cajal Blue Brain (PTI-BLUEBRAIN; Spain)
CB06/05/0066/CIBERNED, ISCIII
SOL-00116599/Center for the Development of Industrial Technology (CDTI)
IND2019/IND-17207/Spanish Ministry of Economy and Competitiveness project TEC2017-84846-R, Madrid Regional

Functional and structural studies investigating macroscopic connectivity in the human cerebral cortex suggest that high-order associative regions exhibit greater connectivity compared to primary ones. However, the synaptic organization of these brain regions remains unexplored. In the present work, we conducted volume electron microscopy to investigate the synaptic organization of the human brain obtained at autopsy. Specifically, we examined layer III of Brodmann areas 17, 3b, and 4, as representative areas of primary visual, somatosensorial, and motor cortex. Additionally, we conducted comparative analyses with our previous datasets of layer III from temporopolar and anterior cingulate associative cortical regions (Brodmann areas 24, 38, and 21). 9,690 synaptic junctions were 3D reconstructed, showing that certain synaptic characteristics are specific to particular regions. The number of synapses per volume, the proportion of the postsynaptic targets, and the synaptic size may distinguish one region from another, regardless of whether they are associative or primary cortex. By contrast, other synaptic characteristics were common to all analyzed regions, such as the proportion of excitatory and inhibitory synapses, their shapes, their spatial distribution, and a higher proportion of synapses located on dendritic spines. The present results provide further insights into the synaptic organization of the human cerebral cortex., PID2021-127924NB-I00
MCIN/AEI/10.13039/501100011033
CSIC Interdisciplinary Thematic Platform-Cajal Blue Brain
PRE2019-089228/MCIN/AEI/10.13039/501100011033

The brain contains thousands of millions of synapses, exhibiting diverse structural, molecular, and functional characteristics. However, synapses can be classified into two primary morphological types: Gray’s type I and type II, corresponding to Colonnier’s asymmetric (AS) and symmetric (SS) synapses, respectively. AS and SS have a thick and thin postsynaptic density, respectively. In the cerebral cortex, since most AS are excitatory (glutamatergic), and SS are inhibitory (GABAergic), determining the distribution, size, density, and proportion of the two major cortical types of synapses is critical, not only to better understand synaptic organization in terms of connectivity, but also from a functional perspective. However, several technical challenges complicate the study of synapses. Potassium ferrocyanide has been utilized in recent volume electron microscope studies to enhance electron density in cellular membranes. However, identifying synaptic junctions, especially SS, becomes more challenging as the postsynaptic densities become thinner with increasing concentrations of potassium ferrocyanide. Here we describe a protocol employing Focused Ion Beam Milling and Scanning Electron Microscopy for studying brain tissue. The focus is on the unequivocal identification of AS and SS types. To validate SS observed using this protocol as GABAergic, experiments with immunocytochemistry for the vesicular GABA transporter were conducted on fixed mouse brain tissue sections. This material was processed with different concentrations of potassium ferrocyanide, aiming to determine its optimal concentration. We demonstrate that using a low concentration of potassium ferrocyanide (0.1%) improves membrane visualization while allowing unequivocal identification of synapses as AS or SS., The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. This work was supported by the following Grants: PID2021-127924NB-I00 funded by MCIN/AEI/10.13039/501100011033; CSIC Interdisciplinary Thematic Platform - Cajal Blue Brain (PTI-BLUEBRAIN; Spain); and CIBERNED, ISCIII, CB06/05/0066. Research Fellowships funded by MCIN/AEI/10.13039/501100011033 for NC-A. (PRE2019-089228) and SP-A. (FPU19/00007).

The highly complex structure of the brain requires an approach that can unravel its connectivity. Using volume electron microscopy and a dedicated software we can trace and measure all nerve fibers present within different samples of brain tissue. With this software tool, individual dendrites and axons are traced, obtaining a simplified “skeleton” of each fiber, which is linked to its corresponding synaptic contacts. The result is an intricate meshwork of axons and dendrites interconnected by a cloud of synaptic junctions. To test this methodology, we apply it to the stratum radiatum of the hippocampus and layers 1 and 3 of the somatosensory cortex of the mouse. We find that nerve fibers are densely packed in the neuropil, reaching up to 9 kilometers per cubic mm. We obtain the number of synapses, the number and lengths of dendrites and axons, the linear densities of synapses established by dendrites and axons, and their location on dendritic spines and shafts. The quantitative data obtained through this method enable us to identify subtle traits and differences in the synaptic organization of the samples, which might have been overlooked in a qualitative analysis., We would like to thank Ana I. Garcia for technical assistance and Nick Guthrie for his excellent editorial assistance. This work was supported by the following Grants: PID2021-127924NB-I00 funded by MCIN/AEI/10.13039/501100011033; CSIC Interdisciplinary Thematic Platform - Cajal Blue Brain (PTI-BLUEBRAIN; Spain); CIBERNED, ISCIII, CB06/05/0066 and; the European Union’s Horizon 2020 Framework Programme for Research and Innovation under Specific Grant Agreements No. 785907 (Human Brain Project SGA2) and No. 945539 (Human Brain Project SGA3).

Significant progress has been made with regard to understanding how the adult brain responds after a stroke. However, a large number of patients continue to suffer lifelong disabilities without adequate treatment. In the present study, we have analyzed possible microanatomical alterations in the contralesional hippocampus from the ischemic stroke mouse model tMCAo 12-14 weeks after transient middle cerebral artery occlusion. After individually injecting Lucifer yellow into pyramidal neurons from the CA1 field of the hippocampus, we performed a detailed three-dimensional analysis of the neuronal complexity, dendritic spine density, and morphology. We found that, in both apical (stratum radiatum) and basal (stratum oriens) arbors, CA1 pyramidal neurons in the contralesional hippocampus of tMCAo mice have a significantly higher neuronal complexity, as well as reduced spine density and alterations in spine volume and spine length. Our results show that when the ipsilateral hippocampus is dramatically damaged, the contralesional hippocampus exhibits several statistically significant selective alterations. However, these alterations are not as significant as expected, which may help to explain the recovery of hippocampal function after stroke. Further anatomical and physiological studies are necessary to better understand the modifications in the "intact" contralesional lesioned brain regions, which are probably fundamental to recover functions after stroke., This work was supported by the following entities:Network of European Funding for NeuroscienceResearch (ERA-NET NEURON, PCI2018-092874); PID2021-127924NB-I00 (to Javier DeFelipe) and IJCI-2016-27658 (to Paula Merino-Serrais) funded by MCIN/AEI/10.13039/501100011033; and CIBER de Enfermedades Neurodegenerativas, Instituto de Salud Carlos III (CIBERNED, CB06/05/0066). Sergio Plaza-Alonso was awarded a research fellowship from the Spanish Ministry of Universities (contract FPU19/00007). Thiswork was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy within the framework of the Munich Cluster for Systems Neurology (EXC 2145 SyNergy—ID390857198) to Nikolaus Plesnila.

Knowledge about empathy is part of the study of artistic expressions, among which stand out works of personalities such as the Renaissance polymath Leonardo da Vinci, who was concerned with the connection between science and art during his creative research full of imagination and sensitivity to nature and human anatomy. The word empathy emerged among critics of German art as the term einfühlung, which was used within the aesthetic bias by philosophers and art historians. It emphasized the idea that a viewer perceiving an object could establish a link between it and themselves, projecting the object ‘into themselves’. That is, the artwork could be experienced by the observer as if the viewer belonged predominantly to the object, in such a way that its characteristics could be actually felt through the expression of emotions, feelings and thoughts. This analysis of art appreciation required a great deal of knowledge and contemplation of nature, as understood by the German Romanticists, who had enormous admiration for da Vinci and his universal and systematic mind—a mind which reacted against formalisms, building his intellectual and sensory systems based on both his observation of nature and his own criteria. In particular, the art of painting for Leonardo was a way to demonstrate a mental discourse, just as the most important aspect of human portraits is to represent—in gestures and facial expressions—the states of mind and emotions. These are facts that German Romanticists tried to explain as the relationship between empathy and a work of art. The present manuscript aims to describe empathy from an artistic view, considering the roots of this word in German Romanticism; to comment about Leonardo da Vinci and the expression of art in the Renaissance; and, finally, to discuss the expression of his art in relation to empathy., The author(s) declare financial support was received for the research, authorship, and/or publication of this article. This work was supported by the following grants: PID2021-127924NB-I00 (to JD) funded by MCIN/AEI/10.13039/501100011033.

Intracranial potentials are used as functional biomarkers of neural networks. As potentials spread away from the source populations, they become mixed in the recordings. In humans, interindividual differences in the gyral architecture of the cortex pose an additional challenge, as functional areas vary in location and extent. We used source separation techniques to disentangle mixing potentials obtained by exploratory deep arrays implanted in epileptic patients of either sex to gain access to the number, location, relative contribution, and dynamics of coactive sources. The unique spatial profiles of separated generators made it possible to discern dozens of independent cortical areas for each patient, whose stability maintained even during seizure, enabling the follow up of activity for days and across states. Through matching these profiles to MRI, we associated each with limited portions of sulci and gyri and determined the local or remote origin of the corresponding sources. We also plotted source-specific 3D coverage across arrays. In average, individual recording sites are contributed to by 3-5 local and distant generators from areas up to several centimeters apart. During seizure, 13-85% of generators were involved, and a few appeared anew. Significant bias in location assignment using raw potentials is revealed, including numerous false positives when determining the site of origin of a seizure. This is not amended by bipolar montage, which introduce additional errors of its own. In this way, source disentangling reveals the multisource nature and far intracranial spread of potentials in humans, while efficiently addressing patient-specific anatomofunctional cortical divergence., This work was supported by the Spanish Ministerio de Ciencia e Innovación (MICIN) grants PID2019-111587RB-I00, PID2022-137801NB-I00 (O.H.), and PID2021-127924NB-I00 (J.F.), the Agencia Estatal de Evaluación, Next Generation EU grant PDC2021-121103-I00 (O.H.), MCIN/AEI/10.13039/501100011033 (J.F.), and CSIC Interdisciplinary Thematic Platform - Cajal Blue Brain (PTI-BLUEBRAIN; Spain). We thank participants for their contributions to research, and Nick Guthrie for his helpful comments and excellent editorial assistance. AGN thanks Fundación Iniciativa para las Neurociencias (FINCE) for continuing support., Peer reviewed

Significant progress has been made with regard to understanding how the adult brain responds after a stroke. However, a large number of patients continue to suffer lifelong disabilities without adequate treatment. In the present study, we have analyzed possible microanatomical alterations in the contralesional hippocampus from the ischemic stroke mouse model tMCAo 12-14 weeks after transient middle cerebral artery occlusion. After individually injecting Lucifer yellow into pyramidal neurons from the CA1 field of the hippocampus, we performed a detailed three-dimensional analysis of the neuronal complexity, dendritic spine density, and morphology. We found that, in both apical (stratum radiatum) and basal (stratum oriens) arbors, CA1 pyramidal neurons in the contralesional hippocampus of tMCAo mice have a significantly higher neuronal complexity, as well as reduced spine density and alterations in spine volume and spine length. Our results show that when the ipsilateral hippocampus is dramatically damaged, the contralesional hippocampus exhibits several statistically significant selective alterations. However, these alterations are not as significant as expected, which may help to explain the recovery of hippocampal function after stroke. Further anatomical and physiological studies are necessary to better understand the modifications in the "intact" contralesional lesioned brain regions, which are probably fundamental to recover functions after stroke., CB06/05/0066/Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas
390857198/Deutsche Forschungsgemeinschaft
PCI2018-092874/ERA-NET NEURON
IJCI-2016-27658/MCIN/AEI/10.13039/501100011033
PID2021-127924NB-I00/MCIN/AEI/10.13039/501100011033
FPU19/00007/Spanish Ministry of Universities, Peer reviewed

Tau has a wide variety of essential functions in the brain, but this protein also plays a determining role in the development of Alzheimer's disease (AD) and other neurodegenerative diseases called tauopathies. This is due to its abnormal aggregation and the subsequent formation of neurofibrillary tangles. Tau hyperphosphorylation appears to be a critical step in its transformation into an aggregated protein. However, the exact process, including the cellular events that trigger it, remains unclear. In this study, we employed immunocytochemistry assays on hippocampal sections from AD cases and from tauopathy cases (Braak stage III) with no evidence of cognitive decline, and the P301S mouse model to investigate the colocalization patterns of Tau phosphorylated (p) at specific residues (S202-T205, S214, and T231) within the proline-rich region. Our results show pyramidal neurons in the hippocampus of P301S mice in which Tau is intensely phosphorylated at residues S202 and T205 (recognized by the AT8 antibody), but with no detectable phosphorylation at S214 or T231. These non-colocalizing neurons displayed intensely labeled aggregated pTau deposits distributed through the soma and dendritic processes. However, most of the hippocampal pyramidal neurons are labeled with pTauS214 or pTauT231 antibodies and typically showed a homogeneous and diffuse pTau distribution (not aggregated). This different labeling likely reflects a Tau conformational step, potentially related to the transition from a diffuse tau phosphorylation phenotype (Type 2) into an NFT-like or Type 1 phenotype. We further observed that dendrites of CA3 pyramidal cells are intensely labeled with pTau214 in the stratum lucidum, but not with AT8 or pTauT231. By contrast, analysis of tissue from AD patients or other human tauopathy cases (Braak stage III) with no evidence of cognitive decline revealed extensive colocalization with both antibody combinations in CA1. The complete or mature tangle development may follow a different mechanism in the P301S mouse model or may require more time to achieve the maturity state found in AD cases. Further studies would be necessary to address this question., This work was supported by a grant from Fundación Universitaria San Pablo CEU-Banco Santander to GLE (FUSP-PPC-19-264E8B2F) and from the following grants to JDF: PID2021-127924NB-I00 funded by MCIN/ AEI/10.13039/501100011033; CSIC Interdisciplinary Thematic Platform - Cajal Blue Brain (PTI-BLUEBRAIN; Spain); and CIBERNED, ISCIII, CB06/05/0066. Work in the laboratory of JA is funded by grants from MCIN/AEI/10.13039/501100011033/FEDER, UE (PID2021- 123859OB-100). Work in the laboratory of FH is funded by grants from the Spanish Ministry of Economy and Competitiveness (Ministerio de Economía, Industria y Competitividad, Gobierno de España, PID2020- 113204GB-I00)., Peer reviewed

Alzheimer’s disease (AD) is the most common neurodegenerative disorder in the elderly. Recent efforts have centered on understanding early events that trigger AD, aiming to facilitate early diagnosis and intervention for improved patient outcomes. The traditional histopathological features observed in AD encompass the extracellular accumulation of amyloid-beta protein and the intracellular abnormal phosphorylation of Tau protein (pTau). However, elucidating how these pathological hallmarks ultimately contribute to cognitive deficits remains a complex challenge. While AD is commonly conceptualized as a disorder characterized by synaptic failure, substantial knowledge gaps persist regarding the mechanisms underlying the onset and progression of the disease, underscoring the need for novel and more effective therapeutic approaches. In this context, the impairment of GABAergic paravalbumin (PV+) neurons has been proposed as a crucial factor contributing to neuronal network dysfunction and cognitive decline in AD. The presence of pTau in pyramidal neurons is directly linked to their impairment in AD; however, the effect of pTau in PV+ neurons remains unclear. In this present study, we analyzed the existence of PV+ neurons containing pTau using immunocytochemistry in the hippocampal formation and entorhinal cortex of human samples from diagnosed AD cases and individuals without neurological or psychiatric disorders. Two pTau isoforms, pTau and pTau, corresponding to early and late stages of AD respectively, were examined. Our findings indicate that most PV+ neurons across the hippocampal formation and entorhinal cortex did not contain pTau in either group cases. Interestingly, while AD cases diagnosed with dementia exhibited a higher number of pTau+ neurons, the majority of PV+/pTau+ neurons were found in individuals with no neurological alterations. This suggests that the presence of pTau in PV+ neurons does not directly correlate with the overall abundance of pTau+ neurons. Given that PV+ neuron impairment is a key pathogenic mechanism in AD and is associated with cognitive decline, understanding the changes in PV+ neurons during AD progression could provide critical insights into the alterations of neuronal circuits underlying the disease., The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported by the following grants: PID2021-127924NB-I00 funded by MCIN/AEI/10.13039/501100011033; and the Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED, CB06/05/0066, Spain). S.P.A. was awarded a research fellowship from the Spanish Ministry of Universities (contract FPU19/00007).

The organizational principles that distinguish the human brain from other species have been a long-standing enigma in neuroscience. Focusing on the uniquely evolved human cortical layers 2 and 3, we computationally reconstruct the cortical architecture for mice and humans. Human neurons form highly complex networks demonstrated by their increased number and simplex dimension compared to mice. This is surprising because human pyramidal cells are much sparser. The number and size of neurons cannot account for this increased network complexity, suggesting that another morphological property is a key determinant of network connectivity. The topological comparison of the dendritic structure reveals higher perisomatic density in human pyramidal cells. We quantitatively show that this neuronal structural property directly impacts network complexity, including the formation of a rich subnetwork structure. Therefore, greater dendritic complexity, a defining attribute of human pyramidal cells, may provide the human cortex with enhanced computational capacity and cognitive flexibility., The authors thank Daniela Egas-Santader for her useful contributions to the topological analysis of the networks. We also thank the visualization team of the Blue Brain Project for figure editing. This study was supported by funding to the Blue Brain Project, a research center of the École polytechnique fédérale de Lausanne (EPFL), from the Swiss government’s ETH Board of the Swiss Federal Institutes of Technology. H.D.M. and C.d.K. were supported by grant awards U01MH114812 (H.D.M.) and UM1MH130981-01 (H.D.M. and C.d.K.) from the National Institute of Mental Health, grant no. 945539 (Human Brain Project SGA3, H.D.M.) from the European Union’s Horizon 2020 Framework Programme for Research and Innovation, NWO Gravitation program BRAINSCAPES: A Roadmap from Neurogenetics to Neurobiology (NWO: 024.004.012, H.D.M.), ERC AdG ‘fasthumanneuron’ 101093198 (H.D.M), and an NWO Open Competition grant (ENW-M2, project OCENW.M20.285, C.d.K.). R.S. was supported by Swiss National Science Foundation (IZLSZ3_148803, IZLIZ3_200297, IZLCZ0_206045, 31003A_138526) and Synapsis Foundation (2020-PI02). J.D.F. and R.B.P. were supported by Grant: PID2021-127924NB-I00 funded by Ministerio de Ciencia e Innovación/Agencia Estatal de Investigació (MCIN/AEI/10.13039/501100011033). I.S. was supported by grants from the ONR (3013007336), the NIH, and the Gatsby Charitable Foundation.

Dendritic spines of pyramidal neurons are the targets of most excitatory synapses in the cerebral cortex, and dendritic spine morphology directly reflects their function. However, there are scarce data available regarding both the detailed morphology of these structures for the human cerebral cortex and the extent to which they differ in comparison with other species. Thus, in the present study, we used intracellular injections of Lucifer yellow to reconstruct—in three dimensions—the morphology of basal dendritic spines from pyramidal cells in the human and mouse CA1 hippocampal region and compared these spines with those of the human temporal and cingular cortex. We found that human hippocampal dendrites show lower spine density, larger volume, and longer length of dendritic spines than mouse CA1 spines. Furthermore, human hippocampal dendrites show higher spine density, smaller spine volume, and shorter length compared to dendritic spines from the human temporal and cingular cortex. This morphological diversity suggests an equally large variability of synaptic strength and learning rules across these brain regions in humans and between humans and mice. Nevertheless, a balance between size and density was found in all cases, which may be a cortical rule maintained across cortical areas and species., We would like to thank Ana García for her technical assistance and Nick Guthrie for his helpful editorial assistance. This work was supported by grants from the following entities: Grant PID2021-127924NB-I00 funded by MCIN/AEI/10.13039/501100011033; Centro de Investigación en Red sobre Enfermedades Neurodegenerativas (CIBERNED, CB06/05/0066); CSIC Interdisciplinary Thematic Platform (PTI) Cajal Blue Brain (PTIBLUEBRAIN;Spain).

Dysfunction of the basal ganglia is implicated in a wide range of neurological and psychiatric disorders. Our understanding of the operation of the basal ganglia is largely derived on data from studies conducted on mice, which are frequently used as model organisms for various clinical conditions. The striatum, the largest compartment of the basal ganglia, consists of 90-95% striatal projection neurons (SPNs). It is therefore crucial to establish if human and mouse SPNs have distinct or similar properties, as this has implications for the relevance of mouse models for understanding the human striatum. To address this, we compared the general organization of the somato-dendritic tree of SPNs, the dimensions of the dendrites, the density and size of spines (spine surface area), and ion channel subtypes in human and mouse SPNs. Our findings reveal that human SPNs are significantly larger, but otherwise the organisation of the dendritic tree (dendrogram) with an average of approximately 5 primary dendrites, is similar in both species. Additionally in both humans and mice, over 90% of the spines are located on the terminal branches of each dendrite. Human spines are somewhat larger (4.3 versus 3.1 μm2) and the terminal dendrites have a uniform diameter in both humans and mice, although somewhat broader in the latter (1.0 versus 0.6 μm). The composition of ion channels is also largely conserved. These data have been used to simulate human SPNs building on our previous detailed simulation of mouse SPNs. We conclude that the human SPNs essentially appear as enlarged versions of the mouse SPNs. This similarity suggests that both species process information in a comparable manner, supporting the relevance of mouse models for studying the human striatum., This study was supported by the Spanish Ministry of Science and Innovation (PID2021-127924NB-I00 funded by MCIN/AEI/10.13039/501100011033) to RBP and JDF, by CIBERNED, ISCIII, CB06/05/0066 to JDF, by the Swedish Research Council (VR-M-2021-01995, VR-M-2024-01995, VR-M-2020-01652), EU/Horizon 2020 no. 945539 (HBP SGA3) and no. 101147319 (EBRAINS 2.0 Project) to SG and AK, the European Union’s Research and Innovation Program Horizon Europe under grant agreement no. 101137289 (the Virtual Brain Twin Project), the Swedish e-Science Research Centre (SeRC), Science for Life Laboratory and KTH Digital Futures to AK, by the Spanish Ministry of Science, Innovation and Universities (PID-2021-122766OB-100, PDC2021-121421-I00, PDC2022-133765-I00), CIBERNED/ISCIII (CB06/05/0010), and The Autonomous Community of Madrid (P2022/BMD-7230) to AIR and AC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Alzheimer’s disease (AD) is the most common neurodegenerative disorder in the elderly. Recent efforts have centered on understanding early events that trigger AD, aiming to facilitate early diagnosis and intervention for improved patient outcomes. The traditional histopathological features observed in AD encompass the extracellular accumulation of amyloid-beta protein and the intracellular abnormal phosphorylation of Tau protein (pTau). However, elucidating how these pathological hallmarks ultimately contribute to cognitive deficits remains a complex challenge. While AD is commonly conceptualized as a disorder characterized by synaptic failure, substantial knowledge gaps persist regarding the mechanisms underlying the onset and progression of the disease, underscoring the need for novel and more effective therapeutic approaches. In this context, the impairment of GABAergic paravalbumin (PV+) neurons has been proposed as a crucial factor contributing to neuronal network dysfunction and cognitive decline in AD. The presence of pTau in pyramidal neurons is directly linked to their impairment in AD; however, the effect of pTau in PV+ neurons remains unclear. In this present study, we analyzed the existence of PV+ neurons containing pTau using immunocytochemistry in the hippocampal formation and entorhinal cortex of human samples from diagnosed AD cases and individuals without neurological or psychiatric disorders. Two pTau isoforms, pTau and pTau, corresponding to early and late stages of AD respectively, were examined. Our findings indicate that most PV+ neurons across the hippocampal formation and entorhinal cortex did not contain pTau in either group cases. Interestingly, while AD cases diagnosed with dementia exhibited a higher number of pTau+ neurons, the majority of PV+/pTau+ neurons were found in individuals with no neurological alterations. This suggests that the presence of pTau in PV+ neurons does not directly correlate with the overall abundance of pTau+ neurons. Given that PV+ neuron impairment is a key pathogenic mechanism in AD and is associated with cognitive decline, understanding the changes in PV+ neurons during AD progression could provide critical insights into the alterations of neuronal circuits underlying the disease., The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported by the following grants: PID2021-127924NB-I00 funded by MCIN/AEI/10.13039/501100011033; and the Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED, CB06/05/0066, Spain). S.P.A. was awarded a research fellowship from the Spanish Ministry of Universities (contract FPU19/00007).

This article explores the historical progression of studying neuronal connections, beginning with nineteenth-century advancements in light microscopy and histological techniques. Early methods were limited in terms of their capacity to trace neuronal connections, but a breakthrough came with Camillo Golgi's "black reaction" staining method, later refined and extensively used by Santiago Ramón y Cajal. Cajal's observations supported the Neuron Theory, which proposed that neurons communicate via specialized points of contact, contradicting the prevailing Reticular Theory of a continuous neural network, which was supported by Golgi. This contrast is particularly intriguing because, although Golgi and Cajal used the same black reaction technique and similar microscopes, their interpretations of the microscopic world diverged significantly. An important consequence of the Neuron Theory was Cajal's Law of Dynamic Polarization, which proposed that neurons generally consist of three functionally distinct regions: a receptor apparatus (dendrites and soma), an emission apparatus (axon), and a distribution apparatus (terminal axonal arborization). He applied this principle across various parts of the nervous system and to different neuron types, enabling the generation of the first detailed circuit diagrams of the brain. Cajal's observations, concepts, and theories had a profound impact-not only on researchers of his time, but also on modern neuroscience. This article reflects on the early studies of neuronal connections, highlighting the scientific climate in which Golgi and Cajal initiated their groundbreaking research., Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature. This work was supported by the grant PID2021-127924NB-I00, funded by MCIN/AEI/https:// doi. org/ 10. 13039/ 50110 00110 33., Peer reviewed

Santiago Ramón y Cajal’s pioneering work laid the foundations for modern neuroscience and continues to impact the development of artificial intelligence, particularly deep learning. His neuron theory, the principle of dynamic polarization, and his insights into brain plasticity and network organization have significantly influenced both our understanding of the nervous system and the design of artificial neural networks. This article reviews Cajal’s key contributions, explores their role in the evolution of AI, and emphasizes the enduring links between neuroscience and machine learning in the digital era., The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported by grants PID2021-127924NB-I00 (JD) and PID2022-137801NB-I00 (OH), both funded by MCIN/AEI/10.13039/501100011033, and by the VIRTUAL BRAIN TWIN project (HORIZON-HLTH-2023-TOOL-05-03, MG-L).

Santiago Ramón y Cajal’s pioneering work laid the foundations for modern neuroscience and continues to impact the development of artificial intelligence, particularly deep learning. His neuron theory, the principle of dynamic polarization, and his insights into brain plasticity and network organization have significantly influenced both our understanding of the nervous system and the design of artificial neural networks. This article reviews Cajal’s key contributions, explores their role in the evolution of AI, and emphasizes the enduring links between neuroscience and machine learning in the digital era., The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported by grants PID2021-127924NB-I00 (JD) and PID2022-137801NB-I00 (OH), both funded by MCIN/AEI/10.13039/501100011033, and by the VIRTUAL BRAIN TWIN project (HORIZON-HLTH-2023-TOOL-05-03, MG-L).

Santiago Ramón y Cajal’s pioneering work laid the foundations for modern neuroscience and continues to impact the development of artificial intelligence, particularly deep learning. His neuron theory, the principle of dynamic polarization, and his insights into brain plasticity and network organization have significantly influenced both our understanding of the nervous system and the design of artificial neural networks. This article reviews Cajal’s key contributions, explores their role in the evolution of AI, and emphasizes the enduring links between neuroscience and machine learning in the digital era., The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported by grants PID2021-127924NB-I00 (JD) and PID2022-137801NB-I00 (OH), both funded by MCIN/AEI/10.13039/501100011033, and by the VIRTUAL BRAIN TWIN project (HORIZON-HLTH-2023-TOOL-05-03, MG-L).

Santiago Ramón y Cajal’s pioneering work laid the foundations for modern neuroscience and continues to impact the development of artificial intelligence, particularly deep learning. His neuron theory, the principle of dynamic polarization, and his insights into brain plasticity and network organization have significantly influenced both our understanding of the nervous system and the design of artificial neural networks. This article reviews Cajal’s key contributions, explores their role in the evolution of AI, and emphasizes the enduring links between neuroscience and machine learning in the digital era., The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported by grants PID2021-127924NB-I00 (JD) and PID2022-137801NB-I00 (OH), both funded by MCIN/AEI/10.13039/501100011033, and by the VIRTUAL BRAIN TWIN project (HORIZON-HLTH-2023-TOOL-05-03, MG-L).

Santiago Ramón y Cajal’s pioneering work laid the foundations for modern neuroscience and continues to impact the development of artificial intelligence, particularly deep learning. His neuron theory, the principle of dynamic polarization, and his insights into brain plasticity and network organization have significantly influenced both our understanding of the nervous system and the design of artificial neural networks. This article reviews Cajal’s key contributions, explores their role in the evolution of AI, and emphasizes the enduring links between neuroscience and machine learning in the digital era., The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported by grants PID2021-127924NB-I00 (JD) and PID2022-137801NB-I00 (OH), both funded by MCIN/AEI/10.13039/501100011033, and by the VIRTUAL BRAIN TWIN project (HORIZON-HLTH-2023-TOOL-05-03, MG-L).

Perisomatic GABAergic innervation in the cerebral cortex is carried out mostly by basket and chandelier cells, which differentially participate in the control of pyramidal cell action potential output and synchronization. These cells establish multiple synapses with the cell body (and proximal dendrites) and the axon initial segment (AIS) of pyramidal neurons, respectively. Using multiple immunofluorescence, confocal microscopy and 3D quantification techniques, we have estimated the number and density of GABAergic boutons on the cell body and AIS of pyramidal neurons located through cortical layers of the human and mouse neocortex. The results revealed, in both species, that there is clear variability across layers regarding the density and number of perisomatic GABAergic boutons. We found a positive linear correlation between the surface area of the soma, or the AIS, and the number of GABAergic terminals in apposition to these 2 neuronal domains. Furthermore, the density of perisomatic GABAergic boutons was higher in the human cortex than in the mouse. These results suggest a selectivity for the GABAergic innervation of the cell body and AIS that might be related to the different functional attributes of the microcircuits in which neurons from different layers are involved in both human and mouse.

Dysfunction of the basal ganglia is implicated in a wide range of neurological and psychiatric disorders. Our understanding of the operation of the basal ganglia is largely derived on data from studies conducted on mice, which are frequently used as model organisms for various clinical conditions. The striatum, the largest compartment of the basal ganglia, consists of 90-95% striatal projection neurons (SPNs). It is therefore crucial to establish if human and mouse SPNs have distinct or similar properties, as this has implications for the relevance of mouse models for understanding the human striatum. To address this, we compared the general organization of the somato-dendritic tree of SPNs, the dimensions of the dendrites, the density and size of spines (spine surface area), and ion channel subtypes in human and mouse SPNs. Our findings reveal that human SPNs are significantly larger, but otherwise the organisation of the dendritic tree (dendrogram) with an average of approximately 5 primary dendrites, is similar in both species. Additionally in both humans and mice, over 90% of the spines are located on the terminal branches of each dendrite. Human spines are somewhat larger (4.3 versus 3.1 μm2) and the terminal dendrites have a uniform diameter in both humans and mice, although somewhat broader in the latter (1.0 versus 0.6 μm). The composition of ion channels is also largely conserved. These data have been used to simulate human SPNs building on our previous detailed simulation of mouse SPNs. We conclude that the human SPNs essentially appear as enlarged versions of the mouse SPNs. This similarity suggests that both species process information in a comparable manner, supporting the relevance of mouse models for studying the human striatum.

Background: The purinergic ATP-gated P2X7 receptor (P2X7R) is increasingly recognized to contribute to pathological neuroinflammation and brain hyperexcitability. P2X7R expression has been shown to be increased in the brain, including both microglia and neurons, in experimental models of epilepsy and patients. To date, the cell type-specific downstream effects of P2X7Rs during seizures remain, however, incompletely understood. Methods: Effects of P2X7R signaling on seizures and epilepsy were analyzed in induced seizure models using male mice including the kainic acid model of status epilepticus and pentylenetetrazole model and in male and female mice in a genetic model of Dravet syndrome. RNA sequencing was used to analyze P2X7R downstream signaling during seizures. To investigate the cell type-specific role of the P2X7R during seizures and epilepsy, we generated mice lacking exon 2 of the P2rx7 gene in either microglia (P2rx7:Cx3cr1-Cre) or neurons (P2rx7:Thy-1-Cre). To investigate the protective potential of overexpressing P2X7R in GABAergic interneurons, P2X7Rs were overexpressed using adeno-associated virus transduction under the mDlx promoter. Results: RNA sequencing of hippocampal tissue from wild-type and P2X7R knock-out mice identified both glial and neuronal genes, in particular genes involved in GABAergic signaling, under the control of the P2X7R following seizures. Mice with deleted P2rx7 in microglia displayed less severe acute seizures and developed a milder form of epilepsy, and microglia displayed an anti-inflammatory molecular profile. In contrast, mice lacking P2rx7 in neurons showed a more severe seizure phenotype when compared to epileptic wild-type mice. Analysis of single-cell expression data revealed that human P2RX7 expression is elevated in the hippocampus of patients with temporal lobe epilepsy in excitatory and inhibitory neurons. Functional studies determined that GABAergic interneurons display increased responses to P2X7R activation in experimental epilepsy. Finally, we show that viral transduction of P2X7R in GABAergic interneurons protects against evoked and spontaneous seizures in experimental temporal lobe epilepsy and in mice lacking Scn1a, a model of Dravet syndrome. Conclusions: Our results suggest a dual and opposing action of P2X7R in epilepsy and suggest P2X7R overexpression in GABAergic interneurons as a novel therapeutic strategy for acquired and, possibly, genetic forms of epilepsy.