The research focused on a well-established mouse model of drug-resistant temporal lobe epilepsy, in which kainic acid, a potent excitotoxin, is microinjected into the amygdala. This model is prized by epilepsy researchers because it recapitulates several defining features of the human condition, including unilateral hippocampal damage, spontaneous recurrent seizures, and a stubborn resistance to conventional anti-seizure medications. Two weeks after inducing status epilepticus, the prolonged seizure state that marks the transition from injury to chronic epilepsy, the researchers dissected the ipsilateral hippocampus, the side of the brain exposed to the initial insult, and prepared it for single-nucleus RNA sequencing.

Single-nucleus RNA-seq is a technique that reads out the gene expression profile of individual cell nuclei, allowing scientists to catalogue which genes are active in each of the thousands of distinct cell types that make up a tissue. Rather than averaging signals across a whole chunk of brain, which would bury cell-specific changes in noise, the method resolves the molecular fingerprint of every neuron, astrocyte, oligodendrocyte, microglial cell and endothelial cell separately. In this study, the team processed samples from epileptic and control mice on the 10X Genomics platform, ultimately sequencing 34,737 nuclei that together represented all the major cellular subtypes of the hippocampus. The resulting dataset constitutes what the authors describe as an atlas of transcriptomic change for this model, a reference map that other researchers can mine for years to come.

The first major finding was that gene dysregulation in epilepsy is not a uniform phenomenon but is sharply partitioned by both cell subtype and anatomical subfield. The hippocampus is organised into anatomically distinct regions, including the dentate gyrus and the CA1, CA2 and CA3 fields, each with its own circuitry and vulnerability. Neurons across the dentate gyrus, CA1 and CA3 all showed increases in activity-regulated genes, the immediate-early programmes that neurons deploy in response to strong stimulation. But beneath that shared signature, the subfields diverged dramatically. Dentate gyrus neurons displayed the greatest degree of differential gene expression of any neuronal population, and their altered genes were enriched for processes connected to synaptogenesis, synaptic plasticity and NMDA receptor signalling, the very molecular machinery that governs how connections between neurons are formed, strengthened and pruned.

That enrichment is significant because the dentate gyrus is widely regarded as a gatekeeper of the hippocampal circuit, filtering the flow of information from the entorhinal cortex into the rest of the hippocampus. In temporal lobe epilepsy, this gate is thought to fail, allowing hyperexcitable activity to propagate unchecked. The new data suggest that the failure is accompanied, and perhaps driven, by an extensive molecular programme of synaptic remodelling within dentate granule cells themselves. If the cells are actively rebuilding their synapses and recalibrating their NMDA receptor signalling two weeks after the initial insult, then the epileptic hippocampus is not passively deteriorating but is engaged in a maladaptive reconstruction, one that may lock in the hyperexcitable state rather than resolve it.

The CA3 and CA1 fields told different stories altogether. Transcriptional profiles from CA3 glutamatergic neurons pointed towards mechanical and injury responses, consistent with the particular vulnerability of this subfield to excitotoxic damage in seizure disorders. CA1 neurons, by contrast, carried signatures enriched for neuroinflammation and wound healing, suggesting that this region responds to the epileptic state less like injured wiring and more like tissue mounting a repair-and-defence programme. The implication is striking: within a structure measuring only a few millimetres, the same disease process produces at least three distinct cellular narratives, each defined by geography. Any therapy designed to treat the epileptic hippocampus as a single homogeneous target may therefore be addressing only one part of a much more heterogeneous problem.

Glial cells, the non-neuronal supporting cells of the brain, proved equally instructive. Among all glial populations, astrocytes showed the most extensive differential gene expression in epileptic mice. Their profiles revealed a mixed reactive state, simultaneously exhibiting pro-inflammatory and anti-inflammatory responses alongside altered metabolic signatures. Astrocytes are far more than passive scaffolding; they regulate neurotransmitter clearance, control local blood flow, supply metabolic substrates to neurons and help define the extracellular environment in which synaptic transmission occurs. The finding that epileptic astrocytes occupy a conflicted, dual-polarity reactive state hints at a cell type caught between containment and contribution, potentially both buffering the seizure disorder and facilitating it. Disentangling those two roles is now an explicit target for future work.

Perhaps the most forward-looking component of the study was its cell-to-cell communication analysis, which used the gene expression data to predict how signalling conversations between cell types change in epilepsy. The analysis predicted extensive remodelling of hippocampal signalling across cell subtypes, including alterations in glutamatergic transmission and, notably, changes in latrophilin-mediated ligand-receptor pairing between dentate gyrus and CA2 neurons. Latrophilins are adhesion G-protein-coupled receptors that help specify which neurons form synapses with which partners during development and plasticity. Evidence that this pairing system is reorganised in the epileptic hippocampus suggests that the disease may be physically rewiring the connectome, changing not just the strength of existing synapses but the very pattern of who talks to whom. That kind of structural reorganisation could help explain why drug-resistant epilepsy is so stable and so difficult to reverse once established.

The clinical stakes of this work are considerable. Roughly a third of people with epilepsy do not respond adequately to available anti-seizure medications, and temporal lobe epilepsy is among the most pharmacologically stubborn forms of the disorder. Current drugs largely suppress symptoms by damping neuronal excitability without addressing the underlying network adaptations that sustain the disease. By providing a cell-type-resolved catalogue of those adaptations, the new atlas offers a systematic way to identify targets for genuine disease modification, molecules that could interrupt the pathological rewiring rather than merely quiet the electrical storm. It also supplies potential biomarkers, gene signatures detectable in specific cell populations that could be used to track disease progression or treatment response in preclinical trials.

The study, led by Javier Villegas-Salmerón with Niamh M. C. Connolly and David C. Henshall as joint senior authors, was funded by Research Ireland through the Centre for Research Training in Genomics Data Science and the FutureNeuro Research Ireland Centre for Translational Brain Science, with additional support from the European Regional Development Fund and Science Foundation Ireland. The work was conducted under the appropriate EU and Irish animal research approvals. Its authors are careful to note that the data come from a mouse model at a single chronic time point, and that translating findings from sequenced nuclei to human patients will require further validation. Even so, the message of the atlas is hard to ignore: epilepsy is a disease of molecular geography, in which every neighbourhood of the hippocampus tells its own story of injury, inflammation and reconstruction. Reading those stories cell by cell may be the surest route yet towards therapies that do more than mute the symptoms of a brain that has rewired itself against its own interests.

Subject of Research: Single-nucleus transcriptomic profiling of hippocampal cell types in a mouse model of drug-resistant temporal lobe epilepsy

Article Title: Single-nucleus transcriptomic analysis reveals subfield-specific cell-to-cell synaptic reorganisation of the mouse hippocampus in focal temporal lobe epilepsy

Article References: Single-nucleus transcriptomic analysis reveals subfield-specific cell-to-cell synaptic reorganisation of the mouse hippocampus in focal temporal lobe epilepsy. (n.d.). https://doi.org/10.1186/s12967-026-08978-2

Image Credits: AI Generated

DOI: 10.1186/s12967-026-08978-2

Keywords: temporal lobe epilepsy, single-nucleus RNA-seq, hippocampus, kainic acid model, dentate gyrus, astrocytes, synaptic remodelling, latrophilin signalling, neuroinflammation, gene expression, CA1, CA3

GSK-3β has occupied a central place in Alzheimer’s research for decades. The enzyme is a serine/threonine kinase that phosphorylates a wide array of substrates, including the tau protein whose hyperphosphorylated tangles are a hallmark of the disease. In a mouse model engineered to overexpress GSK-3β, previous work had already documented a decrease in dendritic spine density in the dentate gyrus, the gateway through which cortical information enters the hippocampus. What remained unknown was how the rest of the trisynaptic circuit—the entorhinal cortex, CA3, and CA1—responds to elevated levels of this kinase. The new study, led by María Llorens-Martín and colleagues at the Centro de Biología Molecular Severo Ochoa in Madrid, set out to fill that gap.

To capture the fine structure of neurons, the researchers turned to a classical but technically demanding technique: intracellular injection of Lucifer Yellow, a fluorescent dye that fills individual neurons in fixed tissue and reveals their dendritic trees and spines in exquisite detail. Using this method, the team analyzed dendritic spine morphology and density on both apical and basal dendrites of pyramidal neurons in the entorhinal cortex, CA3, and CA1, comparing wild-type mice with mice overexpressing GSK-3β. Spines—the tiny protrusions studding dendrites where most excitatory synapses reside—come in distinct morphological classes, including mushroom, thin, and stubby forms, each thought to reflect different stages of synaptic maturity and stability. The head diameter and length of each spine type were quantified, alongside the overall density of spines.

The first striking result came from the wild-type animals themselves. Even in healthy brains, the study found intrinsic differences in spine density and in the distribution of spine types between apical and basal dendrites across the different regions of the trisynaptic circuit. This baseline regional heterogeneity matters, because it establishes that apical and basal dendrites— which receive different complements of afferent inputs—are not interchangeable substrates. Any pathological process acting on the circuit will therefore be superimposed on a landscape already patterned by region- and compartment-specific wiring.

When the researchers compared the GSK-3β-overexpressing mice to their wild-type littermates, a clear hierarchy of vulnerability emerged. The entorhinal cortex, despite being the region typically hit earliest by Alzheimer’s pathology in humans, showed only subtle morphological changes in this model, a finding the authors interpret as a form of partial structural resilience. The CA3 region, likewise, presented minimal alterations overall—although here the basal dendrites were more affected than their apical counterparts, a pattern the authors attribute to the differential inputs these two dendritic compartments receive. In sharp contrast, CA1 stood out as the most affected region of the entire circuit, a result consistent with the well-documented vulnerability of CA1 to Alzheimer’s disease pathology in both human patients and animal models.

Beyond spine shape, the study probed the functional architecture of the circuit by examining excitatory innervation. The researchers stained for vesicular glutamate transporter 1, or VGlut1, a marker of excitatory presynaptic boutons, and measured the percentage of area occupied by VGlut1-positive terminals around the dendritic compartments. In both CA1 and the basal dendrites of CA3, the GSK-3β-overexpressing mice showed a reduced percentage of area occupied by VGlut1-positive boutons, indicating a loss of excitatory innervation. Because excitatory drive is the currency of synaptic plasticity—the cellular substrate of learning and memory—this loss suggests that GSK-3β overexpression does not merely remodel the shape of spines but actively disrupts the connectivity needed for plasticity to occur.

The regional selectivity of these alterations carries significant implications for how scientists think about the progression of Alzheimer’s disease. Rather than a diffuse, homogeneous degeneration of the hippocampal formation, the data support a model in which specific subregions and even specific dendritic compartments are differentially susceptible to a single molecular insult. The vulnerability of CA1 is particularly noteworthy: this region serves as the major output hub of the hippocampus, relaying processed information back to the cortex. Structural compromise at this node, combined with lost excitatory innervation, could plausibly undermine the coherence of the entire memory circuit even while upstream regions such as the entorhinal cortex and CA3 appear comparatively preserved.

The study also underscores the value of apical–basal comparisons. In CA3, basal dendrites were more affected than apical dendrites, likely reflecting the different sources of input they receive—apical dendrites in CA3 are heavily targeted by perforant path fibers from the entorhinal cortex and associational inputs, whereas basal dendrites sample a different mix of local and long-range afferents. That GSK-3β overexpression left a compartment-specific fingerprint on the circuit suggests that the enzyme’s effects are mediated not only by intrinsic neuronal properties but also by the identity of the inputs each dendrite integrates. This level of resolution would have been impossible with bulk tissue measurements and highlights why single-cell anatomy remains indispensable in neuroscience.

Methodologically, the work relied on carefully characterized mouse cohorts, with the GSK-3β-overexpressing model validated by β-galactosidase and NeuN staining to confirm transgene expression and neuronal counts across the entorhinal cortex, CA3, and CA1. Excitatory and inhibitory balance was further assessed by quantifying GAD65-positive inhibitory boutons alongside VGlut1-positive excitatory terminals, allowing the team to compute ratios that capture the excitatory–inhibitory landscape around each dendritic compartment. Statistical comparisons were performed across regions, genotypes, and dendritic compartments, with sample sizes of four to five animals per group for the various analyses, lending statistical weight to the observed regional differences.

Taken together, the study paints a nuanced picture of GSK-3β as a driver of regionally selective synaptic deterioration within the memory circuit. By demonstrating that the entorhinal cortex retains partial structural resilience, that CA3 is largely spared except for its basal compartment, and that CA1 is the most affected node, the researchers provide a cellular framework for understanding why certain hippocampal areas fail early in Alzheimer’s disease while others endure. The loss of excitatory innervation in CA1 and basal CA3 further implicates disrupted synaptic plasticity as a downstream consequence of kinase overexpression. As the field continues to pursue GSK-3β as a therapeutic target, these findings caution that interventions will need to account for the striking regional and compartmental heterogeneity of the hippocampal circuit—and they offer a detailed anatomical benchmark against which future protective strategies can be measured.

Subject of Research: Regional dendritic spine and innervation changes caused by GSK-3β overexpression in the hippocampal trisynaptic circuit of a mouse model relevant to Alzheimer's disease.

Article Title: Regional differences in dendritic spine morphology and innervation of the trisynaptic circuit of a mouse model of GSK-3β overexpression

Article References: Alonso-Moreno, M. C., Terreros-Roncal, J., Rodríguez-Moreno, C. B., Ávila, J., & Llorens-Martín, M. (2026). Regional differences in dendritic spine morphology and innervation of the trisynaptic circuit of a mouse model of GSK-3β overexpression. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06304-z

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06304-z

Keywords: Alzheimer's disease, GSK-3β, dendritic spines, hippocampus, trisynaptic circuit, entorhinal cortex, CA1, CA3, pyramidal neurons, VGlut1, synaptic plasticity, mouse model