Hippocampal GABAergic interneurons and memory

An overview of extracellular field potentials: Different potentiation and measurable components, interpretations, and hippocampal synaptic activity models

The hippocampus and some other brain regions are critically involved in synaptic plasticity. Electrophysiological recordings using extracellular field potentials (EFPs) reveal diverse synaptic activity within the hippocampus, including input/output functions (reflecting neural excitability), paired-pulse responses (reflecting short-term plasticity), and long-term potentiation (reflecting long-term plasticity). EFP techniques offer various measurable components for assessing multiple neural functions. These include fEPSP slope, amplitude, and area under curve (AUC), as well as latency (fEPSP onset or peak after stimulation), width at half amplitude, fiber volley, decay time, time-course (fEPSP rise and decay time constants; tau), initial slope/initial area and -/late area derived from a fEPSP waveform sample. Each of these parameters is separately evaluated and provides distinct electrophysiological interpretations. Despite the rich data offered by EFP techniques, many studies adopt a limited approach, focusing solely on fEPSP slope, amplitude, and occasionally AUC, thereby neglecting the potential insights provided by other parameters. Given the inherent variability of fEPSP components within a single recording and timeframe, a comprehensive analysis of synaptic activity within a specific hippocampal region is necessary for obtaining the full spectrum of fEPSP-related data. Researchers should consider the potential influence of additional factors contributing to the variability of synaptic activity magnitude. A detailed analysis considering different parts of extracellular fEPSP recordings and their properties is crucial for a deeper understanding of synaptic activity changes within the brain. Therefore, this review aims to provide a comprehensive overview of diverse forms of hippocampal synaptic activity, measurable components of EFP recordings, and their corresponding interpretations.

Spatio-temporal organization of network activity patterns in the hippocampus

Understanding how coordinated neural networks support brain functions remains a central goal in neuroscience. The hippocampus, with its layered architecture and structured inputs to diverse cell populations, is a tractable model for dissecting operating microcircuits through the analysis of electrophysiological signatures. We investigated hippocampal network patterns in behaving mice by developing a low-dimensional embedding of local field potentials recorded along the CA1-to-dentate gyrus axis. This embedding revealed layer-specific gamma profiles reflecting spatially organized rhythms and their associated principal cell-interneuron firing motifs. Moreover, firing behaviors along the CA1 radial axis distinguished between deep and superficial principal cells, as well as between interneurons from the pyramidal, radiatum, and lacunosum-moleculare layers. These findings provide a comprehensive map of spatiotemporal activity patterns underlying hippocampal network functions.

Protective effects of anthocyanins on the nervous system injury caused by fluoride-induced endoplasmic reticulum stress in rats

Long-term fluoride exposure can produce neurotoxicity. Anthocyanins, as antioxidants, have a certain protective effect in nerve damage. This study aimed to investigate the protective role of anthocyanins in fluoride-induced neurological damage due to endoplasmic reticulum stress (ERS). Using a fluoride-exposed Wistar rat model, we assessed learning memory capacity and pathologic and ultrastructural injury. The level of oxidative stress (OS) in vivo was detected by colorimetric method, the level of ERS was analyzed by immunohistochemistry, and the apoptosis of neuronal cells was observed by TUNEL staining. The results showed that fluoride exposure could decrease the learning and memory ability in rats, and led to histopathological and ultrastructural damage in the hippocampal CA1, CA3 and cortical regions. Fluoride exposure-induced OS in vivo, which further activates ERS, which was manifested by increased levels of ERS-related proteins GRP78, Caspase 12, and Caspase 3 in hippocampal CA1, CA3, and cortical regions, and eventually led to a significant increase in neuronal apoptosis rate. Notably, after anthocyanins treatment, pathological and ultrastructural damage was restored, the level of OS and ERS were significantly restored, and the apoptosis rate of neuronal cells was significantly reduced. In summary, as nutritional interventions, anthocyanins exert a protective role in fluoride-induced neurological injury.

Whole-brain mapping of basal forebrain cholinergic neurons reveals a long-range reciprocal input-output loop between distinct subtypes

Basal forebrain cholinergic neurons (BFCNs) influence cognition and emotion through specific acetylcholine release in various brain regions, including the prefrontal cortices and basolateral amygdala (BLA). Acetylcholine release is controlled by distinct BFCN subtypes, modulated by excitatory and inhibitory inputs. However, the organization of the whole-brain input-output networks of these subtypes remains unclear. Here, we identified two distinct BFCN subtypes-BFCN→ACA and BFCN→BLA-innervating the anterior cingulate cortex (ACA) and BLA, each with unique distributions, electrophysiological properties, and projection patterns. Combining rabies-virus-assisted mapping and triple-plex RNAscope hybridization, we characterized their whole-brain input networks, identifying unique excitatory and shared inhibitory inputs for these subtypes. Moreover, our results reveal a long-range reciprocal input-output loop: BFCN→ACA neurons target the isocortex, their shared excitatory-input source, whereas BFCN→BLA neurons target shared inhibitory-input sources such as the striatum and pallidum, thus enabling dynamic interactions among these BFCN subtypes. Our study deepens understanding of cholinergic modulation in cognition and emotion and provides insights into their functional interactions.

Hippocampal Interneurons Shape Spatial Coding Alterations in Neurological Disorders

Hippocampal interneurons (INs) play a fundamental role in regulating neural oscillations, modulating excitatory circuits, and shaping spatial representation. While historically overshadowed by excitatory pyramidal cells in spatial coding research, recent advances have demonstrated that inhibitory INs not only coordinate network dynamics but also contribute directly to spatial information processing. This review aims to provide a novel integrative perspective on how distinct IN subtypes participate in spatial coding and how their dysfunction contributes to cognitive deficits in neurological disorders such as epilepsy, Alzheimer's disease (AD), traumatic brain injury (TBI), and cerebral hypoxia-ischemia. We synthesize recent findings demonstrating that different IN classes-including parvalbumin (PV)-, somatostatin (SST)-, cholecystokinin (CCK)-, and calretinin (CR)-expressing neurons-exhibit spatially selective activity, challenging traditional views of spatial representation, and influence memory consolidation through network-level interactions. By leveraging cutting-edge techniques such as in vivo calcium imaging and optogenetics, new evidence suggests that INs encode spatial information with a level of specificity previously attributed only to pyramidal cells. Furthermore, we investigate the impact of inhibitory circuit dysfunction in neurological disorders, examining how disruptions in interneuronal activity lead to impaired theta-gamma coupling, altered sharp wave ripples, and destabilized place cell representations, ultimately resulting in spatial memory deficits. This review advances the field by shifting the focus from pyramidal-centered models to a more nuanced understanding of the hippocampal network, emphasizing the active role of INs in spatial coding. By highlighting the translational potential of targeting inhibitory circuits for therapeutic interventions, we propose novel strategies for restoring hippocampal network function in neurological conditions. Readers will gain a comprehensive understanding of the emerging role of INs in spatial representation and the critical implications of their dysfunction, paving the way for future research on interneuron-targeted treatments for cognitive disorders.

Neuroprotective Effects of Qi Jing Wan and Its Active Ingredient Diosgenin Against Cognitive Impairment in Plateau Hypoxia

Background/Objectives: High-altitude environments have a significant detrimental impact on the cognitive functions of the brain. Qi Jing Wan (QJW), a traditional herbal formula composed of Angelica sinensis, Astragalus membranaceus, and Rhizoma Polygonati Odorati, has demonstrated potential efficacy in treating cognitive disorders. However, its effects on cognitive dysfunction in plateau hypoxic environments remain unclear. Methods: In this study, acute and chronic plateau cognitive impairment mouse models were constructed to investigate the preventive and therapeutic effects of QJW and its significant active ingredient, diosgenin (Dio). Behavioral experiments were conducted to assess learning and memory in mice. Morphological changes in hippocampal neurons and synapses were assessed, and microglial activation and inflammatory factor levels were measured to evaluate brain damage. Potential active ingredients capable of crossing the blood-brain barrier were identified through chemical composition analysis and network database screening, followed by validation in animal and brain organoid experiments. Transcriptomics analysis, immunofluorescence staining, and molecular docking techniques were employed to explore the underlying mechanisms. Results: QJW significantly enhanced learning and memory abilities in plateau model mice, reduced structural damage to hippocampal neurons, restored NeuN expression, inhibited inflammatory factor levels and microglial activation, and improved hippocampal synaptic damage. Transcriptomics analysis revealed that Dio alleviated hypoxic brain damage and protected cognitive function by regulating the expression of PDE4C. Conclusions: These findings indicate that QJW and its significant active ingredient Dio effectively mitigate hypoxic brain injury and prevent cognitive impairment in high-altitude environments.

Brain mechanisms underlying the inhibitory control of thought

Controlling action and thought requires the capacity to stop mental processes. Over the past two decades, evidence has grown that a domain-general inhibitory control mechanism supported by the right lateral prefrontal cortex achieves these functions. However, current views of the neural mechanisms of inhibitory control derive largely from research into the stopping of action. Whereas action stopping is a convenient empirical model, it does not invoke thought inhibition and cannot be used to identify the unique features of this process. Here, we review research that addresses how organisms stop a key process that drives thoughts: memory retrieval. This work has shown that retrieval stopping shares right dorsolateral and ventrolateral prefrontal mechanisms with action stopping, consistent with a domain-general inhibitory control mechanism, but also recruits a distinct fronto-temporal pathway that determines the success of mental control. As part of this pathway, GABAergic inhibition within the hippocampus influences the efficacy of prefrontal control over thought. These unique elements of mental control suggest that hippocampal disinhibition is a transdiagnostic factor underlying intrusive thinking, linking the fronto-temporal control pathway to preclinical models of psychiatric disorders and fear extinction. We suggest that retrieval-stopping deficits may underlie the intrusive thinking that is common across many psychiatric disorders.

Cathodal weak direct current decreases epileptic excitability with reduced neuronal activity and enhanced delta oscillations

Seizures are manifestations of hyperexcitability in the brain. Non-invasive weak current stimulation, delivered through cathodal transcranial direct current stimulation (ctDCS), has emerged to treat refractory epilepsy and seizures, although the cellular-to-populational electrophysiological mechanisms remain unclear. Using the ctDCS in vivo model, we investigate how neural excitability is modulated through weak direct currents by analysing the local field potential (LFP) and extracellular unit spike recordings before, during and after ctDCS versus sham stimulation. In rats with kainic acid (KA)-induced acute hippocampal seizures, ctDCS reduced seizure excitability by decreasing the number and amplitude of epileptic spikes in LFP and enhancing delta (δ) power. We identified unit spikes of putative excitatory neurons in CA1 stratum pyramidale based on waveform sorting and validated via optogenetic inhibitions which increased aberrantly in seizure animals. Notably, cathodal stimulation significantly reduced these unit spikes, whereas anodal stimulation exhibited the opposite effect, showing polarity-specific and current strength-dependent responses. The reduced unit spikes after ctDCS coupled to δ oscillations with an increased coupling strength. These effects occurred during stimulation and lasted 90 min post-stimulation, accompanied by inhibitory short-term synaptic plasticity changes shown in paired-pulse stimulation after ctDCS. Consistently, neuronal activations measured by c-Fos significantly decreased after ctDCS, particularly in CaMKII+-excitatory neurons while increased in GAD+-inhibitory neurons. In conclusion, epileptic excitability was alleviated with cathodal weak direct current stimulation by diminishing excitatory neuronal activity and enhancing endogenous δ oscillations through strengthened coupling between unit spikes and δ waves, along with inhibitory plasticity changes, highlighting the potential implications to treat brain disorders characterized by hyperexcitability. KEY POINTS: Electric fields generated by transcranial weak electric current stimulation were measured at CA1, showing polarity-specific and current strength-dependent modulation of unit spike activity. Polyspike epileptiform discharges were observed in rats with kainic acid (KA)-induced hippocampal seizures. Cathodal transcranial direct current stimulation (ctDCS) reduced the number and amplitude of the epileptic spikes in local field potentials (LFPs) while increased δ oscillations. Neuronal unit spikes aberrantly increased in seizures and coupled with epileptiform discharges. ctDCS reduced excitatory neuronal firings at CA1 and strengthened the coupling between unit spikes and δ waves. Neuronal activations, measured by c-Fos, decreased in CaMKII+-excitatory neurons while increased in GAD+-inhibitory neurons after ctDCS. These effects on LFP and unit spikes lasted up to 90 min post-stimulation. Inhibitory short-term plasticity changes detected through paired-pulse stimulation underpin the enduring effects of ctDCS on seizures.

Inflammation in Schizophrenia: The Role of Disordered Oscillatory Mechanisms

Schizophrenia is a chronic, debilitating disorder with diverse symptomatology, including disorganised cognition and behaviour. Despite considerable research effort, we have only a limited understanding of the underlying brain dysfunction. A significant proportion of individuals with schizophrenia exhibit high levels of inflammation, and inflammation associated with maternal immune system activation is a risk factor for the disorder. In this review, we outline the potential role of inflammation in the disorder, with a particular focus on how cytokine release might affect the development and function of GABAergic interneurons. One consequence of this change in inhibitory control is a disruption in oscillatory processes in the brain. These changes disrupt the spatial and temporal synchrony of neural activity in the brain, which, by disturbing representations of time and space, may underlie some of the disorganisation symptoms observed in the disorder.

The effect of traumatic brain injury on learning and memory: A synaptic focus

Deficits in learning and memory are some of the most commonly reported symptoms following a traumatic brain injury (TBI). We will examine whether the neural basis of these deficits stems from alterations to bidirectional synaptic plasticity within the hippocampus. Although the CA1 subregion of the hippocampus has been a focus of TBI research, the dentate gyrus should also be given attention as it exhibits a unique ability for adult neurogenesis, a process highly susceptible to TBI-induced damage. This review examines our current understanding of how TBI results in deficits in synaptic plasticity, as well as how TBI-induced changes in endocannabinoid (eCB) systems may drive these changes. Through the synthesis and amalgamation of existing data, we propose a possible mechanism for eCB-mediated recovery in synaptic plasticity deficits. This hypothesis is based on the plausible roles of CB1 receptors in regulating inhibitory tone, influencing astrocytes and microglia, and modulating glutamate release. Dysregulation of the eCBs may be responsible for deficits in synaptic plasticity and learning following TBI. Taken together, the existing evidence indicates eCBs may contribute to TBI manifestation, pathogenesis, and recovery, but it also suggests there may be a therapeutic role for the eCB system in TBI.

A cortical-hippocampal communication undergoes rebalancing after new learning

The brain's ability to consolidate a wide range of memories while maintaining their distinctiveness across experiences remains poorly understood. Sharp-wave ripples, neural oscillations that occur predominantly within CA1 of the hippocampus during immobility and sleep, have been shown to play a critical role in the consolidation process. More recently, evidence has uncovered functional heterogeneity of pyramidal neurons within distinct sublayers of CA1 that display unique properties during ripples, potentially contributing to memory specificity. Despite this, it remains unclear exactly how ripples shift the activity of CA1 neuronal populations to accommodate the consolidation of specific memories and how sublayer differences manifest. Here, we studied interactions between the anterior cingulate cortex (ACC) and CA1 neurons during ripples and discovered a reorganization of their communication following learning. Notably, this reorganization appeared specifically for CA1 superficial (CA1sup) sublayer neurons. Utilizing a generalized linear model decoder, we demonstrate the pre-existence of ACC-to-CA1sup communication, which is suppressed during new learning and subsequent sleep suggesting that ACC activity may reallocate the contribution of CA1sup neurons during memory acquisition and consolidation. Further supporting this notion, we found that optogenetic stimulations of the ACC preferentially suppressed CA1sup interneurons while activating a unique subset of CA1 interneurons. Overall, these findings highlight a possible role of the ACC in rebalancing CA1 neuronal populations' contribution to ripple contents surrounding learning.

Preoperative Sleep Deprivation Exacerbates Anesthesia/Surgery-induced Abnormal GABAergic Neurotransmission and Neuronal Damage in the Hippocampus in Aged Mice

Older adults with anesthesia and surgery often suffer from postoperative cognitive dysfunction (POCD), which puts a heavy burden on rehabilitation. Preoperative sleep disorder, a common phenomenon in elderly anesthesia patients, is closely associated with POCD, but the underlying mechanism is still not fully understood. Hippocampal gamma-aminobutyric acid (GABA)ergic neurotransmission has been reported to play an important role in sleep disorder and cognitive impairment. The aim of this study was to elucidate the effect of preoperative acute sleep deprivation (SD) on anesthesia/surgery-induced POCD and the potential mechanism of hippocampal GABAergic neurotransmission. In the aged (18-20-month-old) male mice, we used a rotating rod to deprive sleep for 24 h and induced a POCD model using sevoflurane exposure combined with laparotomy exploration. A sequential set of behavioral tests, including open field test (OFT), Y-maze, and novel object recognition (NOR), was conducted to assess cognitive performances. In vivo magnetic resonance imaging (MRI) technique was used to observe hippocampal axonal microstructural changes. The levels of GABAergic neurotransmitter markers glutamic acid decarboxylase (GAD) 67, vesicular GABA transporter (VGAT), GABA transporter (GAT)-1, and GABA in the hippocampus were detected with enzyme-linked immunosorbent assay (ELISA). The reactivity of GABAergic neurons and neuronal damage in different subregions of the hippocampus were observed by immunofluorescence and Nissl staining, respectively. Compared the anesthesia/surgery (A/S) mice, 24-h SD combined with A/S induced shorter stay time in the central area of the open field, less the percent of novel arm preference in the Y maze, and lower recognition index in the NOR, as well as significantly enhanced hippocampal GABAergic neurotransmission, decreased hippocampal axonal integrity and density, and increased GAD67 reactivity and reduced the number of neurons in hippocampal CA1. Preoperative 24-h SD exacerbated anesthesia/surgery-induced POCD in aged mice, with the cumulative effect of abnormal GABAergic neurotransmission and neuronal damage in the hippocampus.

Interneuron migration impairment and brain region-specific DNA damage response following irradiation during early neurogenesis in mice

Embryonic DNA damage resulting from DNA repair deficiencies or exposure to ionizing radiation during early neurogenesis can lead to neurodevelopmental disorders, including microcephaly. This has been linked to an excessive DNA damage response in dorsal neural progenitor cells (NPCs), resulting in p53-dependent apoptosis and premature neuronal differentiation which culminates in depletion of the NPC pool. However, the effect of DNA damage on ventral forebrain NPCs, the origin of interneurons, remains unclear. In this study, we investigated the sequelae of irradiation of mouse fetuses at an early timepoint of forebrain neurogenesis. We focused on the neocortex (NCX) and medial ganglionic eminence (MGE), key regions for developing dorsal and ventral NPCs, respectively. Although both regions showed a typical p53-mediated DNA damage response consisting of cell cycle arrest, DNA repair and apoptosis, NCX cells displayed prolonged cell cycle arrest, while MGE cells exhibited more sustained apoptosis. Moreover, irradiation reduced the migration speed of interneurons in acute living brain slices and MGE explants, the latter indicating a cell-intrinsic component in the defect. RNA sequencing and protein analyses revealed disruptions in actin and microtubule cytoskeletal-related cellular machinery, particularly in MGE cells. Despite massive acute apoptosis and an obvious interneuron migration defect, prenatally irradiated animals did not show increased sensitivity to pentylenetetrazole-induced seizures, nor was there a reduction in cortical interneurons in young adult mice. This suggests a high plasticity of the developing brain to acute insults during early neurogenesis. Overall, our findings indicate that embryonic DNA damage induces region-specific responses, potentially linked to neurodevelopmental disorders.

GABAergic Progenitor Cell Graft Rescues Cognitive Deficits in Fragile X Syndrome Mice

Fragile X syndrome (FXS) is an inherited neurodevelopmental disorder characterized by a range of clinical manifestations with no effective treatment strategy to date. Here, transplantation of GABAergic precursor cells from the medial ganglionic eminence (MGE) is demonstrated to significantly improve cognitive performance in Fmr1 knockout (KO) mice. Within the hippocampus of Fmr1-KO mice, MGE-derived cells from wild-type donor mice survive, migrate, differentiate into functionally mature interneurons, and form inhibitory synaptic connections with host pyramidal neurons. MGE cell transplantation restores Ras-PKB signaling in pyramidal neurons, enhances AMPA receptor trafficking, rescues synaptic plasticity, and corrects abnormal hippocampal neural oscillations. These findings highlight the potential of GABAergic precursor cell transplantation as a promising therapeutic strategy for FXS.

The Suprapyramidal and Infrapyramidal Blades of the Dentate Gyrus Exhibit Different GluN Subunit Content and Dissimilar Frequency-Dependent Synaptic Plasticity In Vivo

The entorhinal cortex sends afferent information to the hippocampus by means of the perforant path (PP). The PP input to the dentate gyrus (DG) terminates in the suprapyramidal (sDG) and infrapyramidal (iDG) blades. Different electrophysiological stimulation patterns of the PP can generate hippocampal synaptic plasticity. Whether frequency-dependent synaptic plasticity differs in the sDG and iDG is unclear. Here, we compared medial PP-DG responses in freely behaving adult rats and found that synaptic plasticity in the sDG is broadly frequency dependent, whereby long-term depression (LTD, > 24 h) is induced with stimulation at 1 Hz, short-term depression (< 2 h) is triggered by 5 or 10 Hz, and long-term potentiation (LTP) of increasing magnitudes is induced by 200 and 400 Hz stimulation, respectively. By contrast, although the iDG expresses STD following 5 or 10 Hz stimulation, LTD induced by 1 Hz is weaker, LTP is not induced by 200 Hz and LTP induced by 400 Hz stimulation is significantly smaller in magnitude than LTP induced in sDG. Furthermore, the stimulus-response relationship of iDG is suppressed compared to sDG. These differences may arise from differences in granule cell properties, or the complement of NMDA receptors. Patch clamp recordings, in vitro, revealed reduced firing frequencies in response to high currents, and different action potential thresholds in iDG compared to sDG. Assessment of the expression of GluN subunits revealed significantly lower expression levels of GluN1, GluN2A, and GluN2B in the middle molecular layer of iDG compared to sDG. Taken together, these data indicate that synaptic plasticity in the iDG is weaker, less persistent and less responsive to afferent frequencies than synaptic plasticity in sDG. Effects may be mediated by weaker NMDA receptor expression and differences in neuronal responses in iDG versus sDG. These characteristics may explain reported differences in experience-dependent information processing in the suprapyramidal and infrapyramidal blades of the DG.

Deep Learning-Based Ion Channel Kinetics Analysis for Automated Patch Clamp Recording

The patch clamp technique is a fundamental tool for investigating ion channel dynamics and electrophysiological properties. This study proposes the first artificial intelligence framework for characterizing multiple ion channel kinetics of whole-cell recordings. The framework integrates machine learning for anomaly detection and deep learning for multi-class classification. The anomaly detection excludes recordings that are incompatible with ion channel behavior. The multi-class classification combined a 1D convolutional neural network, bidirectional long short-term memory, and an attention mechanism to capture the spatiotemporal patterns of the recordings. The framework achieves an accuracy of 97.58% in classifying 124 test datasets into six categories based on ion channel kinetics. The utility of the novel framework is demonstrated in two applications: Alzheimer's disease drug screening and nanomatrix-induced neuronal differentiation. In drug screening, the framework illustrates the inhibitory effects of memantine on endogenous channels, and antagonistic interactions among potassium, magnesium, and calcium ion channels. For nanomatrix-induced differentiation, the classifier indicates the effects of differentiation conditions on sodium and potassium channels associated with action potentials, validating the functional properties of differentiated neurons for Parkinson's disease treatment. The proposed framework is promising for enhancing the efficiency and accuracy of ion channel kinetics analysis in electrophysiological research.

Platelets tune fear memory in mice

Several lines of evidence have shown that platelet-derived factors are key molecules in brain-body communication in pathological conditions. Here, we identify platelets as key actors in the modulation of fear behaviors in mice through the control of inhibitory neurotransmission and plasticity in the hippocampus. Interfering with platelet number or activation reduces hippocampal serotonin (5-HT) and modulates fear learning and memory in mice, and this effect is reversed by serotonin replacement by serotonin precursor (5-HTP)/benserazide. In addition, we unravel that natural killer (NK) cells participate in this mechanism, regulating interleukin-13 (IL-13) levels in the gut, with effects on serotonin production by enterochromaffin cells and uptake by platelets. Both NK cells and platelet depletion reduce the activation of hippocampal inhibitory neurons and increase the long-term potentiation of synaptic transmission. Understanding the role of platelets in the modulation of neuro-immune interactions offers additional tools for the definition of the molecular and cellular elements involved in the growing field of brain-body communication.

Spatiotemporal analysis of gene expression in the human dentate gyrus reveals age-associated changes in cellular maturation and neuroinflammation

The dentate gyrus of the hippocampus is important for many cognitive functions, including learning, memory, and mood. Here, we present transcriptome-wide spatial gene expression maps of the human dentate gyrus and investigate age-associated changes across the lifespan. Genes associated with neurogenesis and the extracellular matrix are enriched in infants and decline throughout development and maturation. Following infancy, inhibitory neuron markers increase, and cellular proliferation markers decrease. We also identify spatio-molecular signatures that support existing evidence for protracted maturation of granule cells during adulthood and age-associated increases in neuroinflammation-related gene expression. Our findings support the notion that the hippocampal neurogenic niche undergoes major changes following infancy and identify molecular regulators of brain aging in glial- and neuropil-enriched tissue.

Supralinear dendritic integration in murine dendrite-targeting interneurons

Non-linear summation of synaptic inputs to the dendrites of pyramidal neurons has been proposed to increase the computation capacity of neurons through coincidence detection, signal amplification, and additional logic operations such as XOR. Supralinear dendritic integration has been documented extensively in principal neurons, mediated by several voltage-dependent conductances. It has also been reported in parvalbumin-positive hippocampal basket cells, in dendrites innervated by feedback excitatory synapses. Whether other interneurons, which support feed-forward or feedback inhibition of principal neuron dendrites, also exhibit local non-linear integration of synaptic excitation is not known. Here, we use patch-clamp electrophysiology, and two-photon calcium imaging and glutamate uncaging, to show that supralinear dendritic integration of near-synchronous spatially clustered glutamate-receptor mediated depolarization occurs in NDNF-positive neurogliaform cells and oriens-lacunosum moleculare interneurons in the mouse hippocampus. Supralinear summation was detected via recordings of somatic depolarizations elicited by uncaging of glutamate on dendritic fragments, and, in neurogliaform cells, by concurrent imaging of dendritic calcium transients. Supralinearity was abolished by blocking NMDA receptors (NMDARs) but resisted blockade of voltage-gated sodium channels. Blocking L-type calcium channels abolished supralinear calcium signalling but only had a minor effect on voltage supralinearity. Dendritic boosting of spatially clustered synaptic signals argues for previously unappreciated computational complexity in dendrite-projecting inhibitory cells of the hippocampus.

Interneuronal modulations as a functional switch for cortical computations: mechanisms and implication for disease

Understanding cortical inhibition and its diverse roles remains a key challenge in neurophysiological research. Traditionally, inhibition has been recognized for controlling the stability and rhythmicity of network dynamics, or refining the spatiotemporal properties of cortical representations. In this perspective, we propose that specific types of interneurons may play a complementary role, by modulating the computational properties of neural networks. We review experimental and theoretical evidence, mainly from rodent sensory cortices, that supports this view. Additionally, we explore how dysfunctions in these interneurons may disrupt the network's ability to switch between computational modes, impacting the flexibility of cortical processing and potentially contributing to various neurodevelopmental and psychiatric disorders.

The lactate metabolism and protein lactylation in epilepsy

Protein lactylation is a new form of post-translational modification that has recently been proposed. Lactoyl groups, derived mainly from the glycolytic product lactate, have been linked to protein lactylation in brain tissue, which has been shown to correlate with increased neuronal excitability. Ischemic stroke may promote neuronal glycolysis, leading to lactate accumulation in brain tissue. This accumulation of lactate accumulation may heighten neuronal excitability by upregulating protein lactylation levels, potentially triggering post-stroke epilepsy. Although current clinical treatments for seizures have advanced significantly, approximately 30% of patients with epilepsy remain unresponsive to medication, and the prevalence of epilepsy continues to rise. This study explores the mechanisms of epilepsy-associated neuronal death mediated by lactate metabolism and protein lactylation. This study also examines the potential for histone deacetylase inhibitors to alleviate seizures by modifying lactylation levels, thereby offering fresh perspectives for future research into the pathogenesis and clinical treatment of epilepsy.

Multi-region processing during sleep for memory and cognition

Over the past decades, the understanding of sleep has evolved to be a fundamental physiological mechanism integral to the processing of different types of memory rather than just being a passive brain state. The cyclic sleep substates, namely, rapid eye movement (REM) sleep and non-REM (NREM) sleep, exhibit distinct yet complementary oscillatory patterns that form inter-regional networks between different brain regions crucial to learning, memory consolidation, and memory retrieval. Technical advancements in imaging and manipulation approaches have provided deeper understanding of memory formation processes on multi-scales including brain-wide, synaptic, and molecular levels. The present review provides a short background and outlines the current state of research and future perspectives in understanding the role of sleep and its substates in memory processing from both humans and rodents, with a focus on cross-regional brain communication, oscillation coupling, offline reactivations, and engram studies. Moreover, we briefly discuss how sleep contributes to other higher-order cognitive functions.

Vagus nerve stimulation: a physical therapy with promising potential for central nervous system disorders

The diseases of the central nervous system (CNS) often cause irreversible damage to the human body and have a poor prognosis, posing a significant threat to human health. They have brought enormous burdens to society and healthcare systems. However, due to the complexity of their causes and mechanisms, effective treatment methods are still lacking. Vagus nerve stimulation (VNS), as a physical therapy, has been utilized in the treatment of various diseases. VNS has shown promising outcomes in some CNS diseases and has been approved by the Food and Drug Administration (FDA) in the United States for epilepsy and depression. Moreover, it has demonstrated significant potential in the treatment of stroke, consciousness disorders, and Alzheimer's disease. Nevertheless, the exact efficacy of VNS, its beneficiaries, and its mechanisms of action remain unclear. This article discusses the current clinical evidence supporting the efficacy of VNS in CNS diseases, providing updates on the progress, potential, and potential mechanisms of action of VNS in producing effects on CNS diseases.

The neuronal Golgi in neural circuit formation and reorganization

The Golgi apparatus is a central hub in the intracellular secretory pathway. By positioning in the specific intracellular region and transporting materials to spatially restricted compartments, the Golgi apparatus contributes to the cell polarity establishment and morphological specification in diverse cell types. In neurons, the Golgi apparatus mediates several essential steps of initial neural circuit formation during early brain development, such as axon-dendrite polarization, neuronal migration, primary dendrite specification, and dendritic arbor elaboration. Moreover, neuronal activity-dependent remodeling of the Golgi structure enables morphological changes in neurons, which provides the cellular basis of circuit reorganization during postnatal critical period. In this review, I summarize recent findings illustrating the unique Golgi positioning and its developmental dynamics in various types of neurons. I also discuss the upstream regulators for the Golgi positioning in neurons, and functional roles of the Golgi in neural circuit formation and reorganization. Elucidating how Golgi apparatus sculpts neuronal connectivity would deepen our understanding of the cellular/molecular basis of neural circuit development and plasticity.

Longitudinal autophagy profiling of the mammalian brain reveals sustained mitophagy throughout healthy aging

Mitophagy neutralizes mitochondrial damage, thereby preventing cellular dysfunction and apoptosis. Defects in mitophagy have been strongly implicated in age-related neurodegenerative disorders such as Parkinson's and Alzheimer's disease. While mitophagy decreases throughout the lifespan of short-lived model organisms, it remains unknown whether such a decline occurs in the aging mammalian brain-a question of fundamental importance for understanding cell type- and region-specific susceptibility to neurodegeneration. Here, we define the longitudinal dynamics of basal mitophagy and macroautophagy across neuronal and non-neuronal cell types within the intact aging mouse brain in vivo. Quantitative profiling of reporter mouse cohorts from young to geriatric ages reveals cell- and tissue-specific alterations in mitophagy and macroautophagy between distinct subregions and cell populations, including dopaminergic neurons, cerebellar Purkinje cells, astrocytes, microglia and interneurons. We also find that healthy aging is hallmarked by the dynamic accumulation of differentially acidified lysosomes in several neural cell subsets. Our findings argue against any widespread age-related decline in mitophagic activity, instead demonstrating dynamic fluctuations in mitophagy across the aging trajectory, with strong implications for ongoing theragnostic development.

Ventral hippocampal interneurons govern extinction and relapse of contextual associations

Contextual memories are critical for survival but must be extinguished when new conditions render them nonproductive. By most accounts, extinction forms a new memory that competes with the original association for control over behavior, but the underlying circuit mechanisms remain largely enigmatic. Here, we demonstrate that extinction of contextual fear conditioning recruits somatostatin interneurons (SST-INs) in the ventral hippocampus. Correspondingly, real-time activity of SST-INs correlates with transitions between immobility and movement, signaling exit from defensive freezing bouts. Optogenetic manipulation of SST-INs but not parvalbumin interneurons (PV-INs) elicits bidirectional changes in freezing that are specific to the context in which extinction was acquired. Finally, similar effects were obtained following extinction of sucrose-based appetitive conditioning, in which SST-IN inhibition triggers relapse to reward seeking. These data suggest that ventral hippocampal SST-INs play a fundamental role in extinction that is independent of affective valence and may be related to their disruption of spontaneous emotional responses.

Unraveling the role of cholecystokinin in epilepsy: Mechanistic insight into neuroplasticity

Epilepsy is a disorder characterized by an imbalance between excitability and inhibition, leading to uncontrolled hyperexcitability of neurons in the central nervous system. Despite the prevalence of epileptic seizures, the underlying mechanisms driving this hyperexcitability remain poorly understood. This review article aims to enhance our understanding of the mechanisms of epilepsy, with a specific focus on the role of cholecystokinin (CCK) in this debilitating disease. We will begin with an introduction to the topic, followed by an examination of the role of GABAergic neurons and the synaptic plasticity mechanisms associated with seizures. As we delve deeper, we will elucidate how CCK and its receptors contribute to seizure behavior. Finally, we will discuss the CCK-dependent synaptic plasticity mechanisms and highlight their potential implications in seizure activity. Through a comprehensive examination of these aspects, this review provides valuable insights into the involvement of CCK and its receptors in epilepsy. By improving our understanding of the mechanisms underlying this condition, particularly the role of CCK, we aim to contribute to the development of more effective treatment strategies.

Unveiling mitochondria as central components driving cognitive decline in alzheimer's disease through cross-transcriptomic analysis of hippocampus and entorhinal cortex microarray datasets

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by symptoms such as memory loss and impaired learning. This study conducted a cross-transcriptomic analysis of AD using existing microarray datasets from the hippocampus (HC) and entorhinal cortex (EC), comparing them with age-matched non-AD controls. Both of these brain regions are critical for learning and memory processing and are vulnerable areas that exhibit abnormalities in early AD. The cross-transcriptomic analysis identified 564 significantly differentially expressed genes in HC and 479 in EC. Among these, 151 genes were significantly differentially expressed in both tissues, with functions related to synaptic vesicle clustering, synaptic vesicle exocytosis/endocytosis, mitochondrial ATP synthesis, hydrogen ion transmembrane transport, and structural constituent of cytoskeleton, suggesting a potential association between cognitive decline in AD, synaptic vesicle dynamics, dysregulation of cytoskeleton organization, and mitochondrial dysfunction. Further gene ontology analysis specific to the HC revealed the gene ontology enrichment in aerobic respiration, synaptic vesicle cycle, and oxidative phosphorylation. The enrichment analysis in CA1 of HC revealed differentiation in gene expression related to mitochondrial membrane functions involved in bioenergetics, mitochondrial electron transport, and biological processes associated with microtubule-based process, while analysis in the EC region showed enrichment in synaptic vesicle dynamics which is associated with neurotransmitter release and the regulation of postsynaptic membrane potential and synaptic transmission of GABAergic and glutamatergic synapse. Protein-protein interaction analysis highlighted central hub proteins predominantly expressed in mitochondria, involved in regulation of oxidative stress and ATP synthesis. These hub proteins interact not only within the mitochondria but also with proteins in the vesicular membrane and neuronal cytoskeleton, indicating a central role of mitochondria. This finding underscores the association between clinical symptoms and mitochondrial dysregulation of synaptic vesicle dynamics, cytoskeleton organization, and mitochondrial processes in both the HC and EC of AD. Therefore, targeting these dysregulated pathways could provide promising therapeutic targets aimed at cognitive decline and memory impairment in early AD stages.

Targeted sonogenetic modulation of GABAergic interneurons in the hippocampal CA1 region in status epilepticus

Rationale: Sonogenetics is an advanced ultrasound-based neurostimulation approach for targeting neurons in specific brain regions. However, the role of sonogenetics in treating status epilepticus (SE) remains unclear. Here, we aimed to investigate the effects of ultrasound neurostimulation and MscL-G22S (a mechanosensitive ion channel that mediates Ca2+ influx)-mediated sonogenetics (MG-SOG) in a mouse model of kainic acid (KA)-induced SE. Methods: For MG-SOG, a Cre-dependent AAV expressing MscL-G22S was injected into parvalbumin (PV)-cre and somatostatin (SST)-cre mice to induce the expression of MscL-G22S-EGFP in PV interneurons (PV-INs) and SST interneurons (SST-INs), respectively; mice were stimulated with continuous pulses of ultrasound stimulation during the latency of generalized seizures (GSs), the latency to SE, in SE model mice. We performed calcium fiber photometry, patch-clamp recording, local field potential recording, and SE monitoring to investigate the role of MG-SOG in treating SE. Results: First, we observed obvious neuronal activation in the hippocampal CA1 region in SE model mice. Both excitatory neurons (ENs) and GABAergic interneurons (GABA-INs) in the CA1 region were activated in SE model mice; however, the inhibitory effect of GABA-INs on ENs seemed to be insufficient to reduce EN excitability despite the increased activation of GABA-INs in SE model mice. Thus, we speculated that MG-SOG-induced activation of GABA-INs, mainly SST-INs and PV-INs, in the CA1 region may protect against SE. We found that MG-SOG-mediated PV-IN activation in the CA1 region ameliorated SE and changed SE-related electrophysiological abnormalities in the CA1 region; however, MG-SOG-induced SST-IN activation in the CA1 region did not ameliorate SE. Conclusions: MG-SOG-mediated activation of PV-INs had a positive effect on relieving SE. Our work may promote the development of sonogenetic neurostimulation techniques for treating SE.

Stimulation of an entorhinal-hippocampal extinction circuit facilitates fear extinction in a post-traumatic stress disorder model

Effective psychotherapy of post-traumatic stress disorder (PTSD) remains challenging owing to the fragile nature of fear extinction, for which the ventral hippocampal CA1 (vCA1) region is considered as a central hub. However, neither the core pathway nor the cellular mechanisms involved in implementing extinction are known. Here, we unveil a direct pathway, where layer 2a fan cells in the lateral entorhinal cortex (LEC) target parvalbumin-expressing interneurons (PV-INs) in the vCA1 region to propel low-gamma-band synchronization of the LEC-vCA1 activity during extinction learning. Bidirectional manipulations of either hippocampal PV-INs or LEC fan cells sufficed for fear extinction. Gamma entrainment of vCA1 by deep brain stimulation (DBS) or noninvasive transcranial alternating current stimulation (tACS) of LEC persistently enhanced the PV-IN activity in vCA1, thereby promoting fear extinction. These results demonstrate that the LEC-vCA1 pathway forms a top-down motif to empower low-gamma-band oscillations that facilitate fear extinction. Finally, application of low-gamma DBS and tACS to a mouse model with persistent PTSD showed potent efficacy, suggesting that the dedicated LEC-vCA1 pathway can be stimulated for therapy to remove traumatic memory trace.

Impaired Hippocampal Long-Term Potentiation and Memory Deficits upon Haploinsufficiency of MDGA1 Can Be Rescued by Acute Administration of D-Cycloserine

The maintenance of proper brain function relies heavily on the balance of excitatory and inhibitory neural circuits, governed in part by synaptic adhesion molecules. Among these, MDGA1 (MAM domain-containing glycosylphosphatidylinositol anchor 1) acts as a suppressor of synapse formation by interfering with Neuroligin-mediated interactions, crucial for maintaining the excitatory-inhibitory (E/I) balance. Mdga1-/- mice exhibit selectively enhanced inhibitory synapse formation in their hippocampal pyramidal neurons, leading to impaired hippocampal long-term potentiation (LTP) and hippocampus-dependent learning and memory function; however, it has not been fully investigated yet if the reduction in MDGA1 protein levels would alter brain function. Here, we examined the behavioral and synaptic consequences of reduced MDGA1 protein levels in Mdga1+/- mice. As observed in Mdga1-/- mice, Mdga1+/- mice exhibited significant deficits in hippocampus-dependent learning and memory tasks, such as the Morris water maze and contextual fear-conditioning tests, along with a significant deficit in the long-term potentiation (LTP) in hippocampal Schaffer collateral CA1 synapses. The acute administration of D-cycloserine, a co-agonist of NMDAR (N-methyl-d-aspartate receptor), significantly ameliorated memory impairments and restored LTP deficits specifically in Mdga1+/- mice, while having no such effect on Mdga1-/- mice. These results highlight the critical role of MDGA1 in regulating inhibitory synapse formation and maintaining the E/I balance for proper cognitive function. These findings may also suggest potential therapeutic strategies targeting the E/I imbalance to alleviate cognitive deficits associated with neuropsychiatric disorders.

NECAB1-3, parvalbumin, calbindin, and calretinin in the hippocampus of the European mole

Many calcium-binding proteins are expressed in a region-and cell-type specific manner in the mammalian hippocampus. Neuronal calcium-binding proteins (NECABs) are also expressed in hippocampal neurons, but few species have been investigated, with partly controversial findings. We here describe NECAB1, NECAB2 and NECAB3 as well as parvalbumin, calbindin, and calretinin in the European mole, and compare staining patterns of these proteins with those in mouse and other species. While subtle differences are present, NECAB staining in the European mole was generally similar to those in mouse. Common to European moles, mice, and other species we investigated, large hilar polymorphic cells, likely to represent mossy cells, were positive for all three NECABs. NECAB1 and 2 are suitable as markers for these cells along the entire septotemporal axis of the hippocampus. In the European mole, parvalbumin, calbindin and calretinin showed traits that have been described in other species before, albeit in a unique combination. In summary, we provide the first description of distribution of these proteins in the hippocampus of the European mole. This subterranean, insectivorous, and solitary living species belongs to the Order of Eulipotyphla. Despite many similarities with other subterranean species from the rodent order in terms of lifestyle, its hippocampus is cytoarchitecturally much more elaborated than in, e.g., mole-rats. It remains an open question if the hippocampal structure of the European mole reflects evolutionary constraints or ecology. Our descriptive study highlights the diversity in hippocampal cytoarchitecture even in small mammalian species.

Spontaneously Hypertensive Rats Present Exacerbated Focal Stroke Behavioral Outcomes

This study aimed to analyze the effects of systemic arterial hypertension (SAH) in a model of permanent ischemic stroke (focal ischemia due to thermocoagulation of pial vessels) on sensorimotor function (cylinder test and patch removal test), behavioral tasks (novelty habituation memory open field task) and cerebral infarct size in adult male spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY) for 42 days after the occurrence of a stroke. We observed that the stroke caused asymmetry in the front paws and delayed adhesive removal. These effects were spontaneously reduced in WKY rats, but not in SHR. Short- and long-term novelty habituation memories were abolished by stroke in WYK and SHR. On the 3rd day after stroke, the size of the focal cerebral infarct was the same in WKY and SHR. However, on the 7th day, the infarct size decreased in WKY rats, but not SHR. These results suggested that SAH impairment of sensorimotor recovery in rats subjected to cerebral ischemia could be related to augmented focal cerebral infarct size. Moreover, the behavioral tasks used in this study were unaffected by Systemic Arterial Hypertension. Our results highlight the need for animal models of comorbidities in stroke research.

Estrogenic regulation of hippocampal inhibitory system across lifespan

Estrogens produced in peripheral tissues and locally in the brain are potent neuromodulators. The function of the hippocampus, a brain region essential for episodic memory and spatial navigation, relies on the activity of ensembles of excitatory neurons whose activity is temporally and spatially coordinated by a wide diversity of inhibitory neurons (INs) types. Over the last years, we have accumulated evidence that indicates that estrogens regulate the function of hippocampal INs through different mechanisms, including transcriptional regulation and rapid nongenomic signaling. Here, we argue that the well-documented influence of estrogens on episodic memory may be related to the actions of local and peripheral estrogens on the heterogenous populations of hippocampal INs. We discuss how physiological changes in peripheral sex hormone levels throughout lifespan may interact with local brain sources to regulate IN function at different stages of life, from early hippocampal development to the aging brain. We conclude that considering INs as mediators of sex hormone actions in the hippocampus across the healthy life span will benefit our understanding of sex-biased neurodevelopmental disorders and physiological aging.

Learning, Fast and Slow: Single- and Many-Shot Learning in the Hippocampus

The hippocampus is critical for memory and spatial navigation. The ability to map novel environments, as well as more abstract conceptual relationships, is fundamental to the cognitive flexibility that humans and other animals require to survive in a dynamic world. In this review, we survey recent advances in our understanding of how this flexibility is implemented anatomically and functionally by hippocampal circuitry, during both active exploration (online) and rest (offline). We discuss the advantages and limitations of spike timing-dependent plasticity and the more recently discovered behavioral timescale synaptic plasticity in supporting distinct learning modes in the hippocampus. Finally, we suggest complementary roles for these plasticity types in explaining many-shot and single-shot learning in the hippocampus and discuss how these rules could work together to support the learning of cognitive maps.

The Neuroprotective Effect of Neural Cell Adhesion Molecule L1 in the Hippocampus of Aged Alzheimer's Disease Model Mice

Alzheimer's disease (AD) is a severe neurodegenerative disorder and the most common form of dementia, causing the loss of cognitive function. Our previous study has shown, using a doubly mutated mouse model of AD (APP/PS1), that the neural adhesion molecule L1 directly binds amyloid peptides and decreases plaque load and gliosis when injected as an adeno-associated virus construct (AAV-L1) into APP/PS1 mice. In this study, we microinjected AAV-L1, using a Hamilton syringe, directly into the 3-month-old APP/PS1 mouse hippocampus and waited for a year until significant neurodegeneration developed. We stereologically counted the principal neurons and parvalbumin-positive interneurons in the hippocampus, estimated the density of inhibitory synapses around principal cells, and compared the AAV-L1 injection models with control injections of green fluorescent protein (AAV-GFP) and the wild-type hippocampus. Our results show that there is a significant loss of granule cells in the dentate gyrus of the APP/PS1 mice, which was improved by AAV-L1 injection, compared with the AAV-GFP controls (p < 0.05). There is also a generalized loss of parvalbumin-positive interneurons in the hippocampus of APP/PS1 mice, which is ameliorated by AAV-L1 injection, compared with the AAV-GFP controls (p < 0.05). Additionally, AAV-L1 injection promotes the survival of inhibitory synapses around the principal cells compared with AAV-GFP controls in all three hippocampal subfields (p < 0.01). Our results indicate that L1 promotes neuronal survival and protects the synapses in an AD mouse model, which could have therapeutic implications.

Autism-associated neuroligin 3 deficiency in medial septum causes social deficits and sleep loss in mice

Patients with autism spectrum disorder (ASD) frequently experience sleep disturbance. Genetic mutations in the neuroligin 3 (NLG3) gene are highly correlative with ASD and sleep disturbance. However, the cellular and neural circuit bases of this correlation remain elusive. Here, we found that the conditional knockout of Nlg3 (Nlg3-CKO) in the medial septum (MS) impairs social memory and reduces sleep. Nlg3 CKO in the MS caused hyperactivity of MSGABA neurons during social avoidance and wakefulness. Activation of MSGABA neurons induced social memory deficits and sleep loss in C57BL/6J mice. In contrast, inactivation of these neurons ameliorated social memory deficits and sleep loss in Nlg3-CKO mice. Sleep deprivation led to social memory deficits, while social isolation caused sleep loss, both resulting in a reduction in NLG3 expression and an increase in activity of GABAergic neurons in the MS from C57BL/6J mice. Furthermore, MSGABA-innervated CA2 neurons specifically regulated social memory without impacting sleep, whereas MSGABA-innervating neurons in the preoptic area selectively controlled sleep without affecting social behavior. Together, these findings demonstrate that the hyperactive MSGABA neurons impair social memory and disrupt sleep resulting from Nlg3 CKO in the MS, and achieve the modality specificity through their divergent downstream targets.

Role of adaptor protein complexes in generating functionally distinct synaptic vesicle pools

The synaptic vesicle (SV) cycle ensures the release of neurotransmitters and the replenishment of SVs to sustain neuronal activity. Multiple endocytosis and sorting pathways contribute to the recapture of the SV membrane and proteins after fusion. Adaptor protein (AP) complexes are among the critical components of the SV retrieval machinery. The canonical clathrin adaptor AP2 ensures the replenishment of most SVs across many neuronal populations. An alternative AP1/AP3-dependent process mediates the formation of a subset of SVs that differ from AP2 vesicles in molecular composition and respond preferentially during higher frequency firing. Furthermore, recent studies show that vesicular transporters for different neurotransmitters depend to a different extent on the AP3 pathway and this affects the release properties of the respective neurotransmitters. This review focuses on the current understanding of the AP-dependent molecular and functional diversity among SVs. We also discuss the contribution of these pathways to the regulation of neurotransmitter release across neuronal populations.

Parvalbumin interneuron cell-to-network plasticity: mechanisms and therapeutic avenues

Alzheimer's disease (AD) and schizophrenia (SCZ) represent two major neuropathological conditions with a high disease burden. Despite their distinct etiologies, patients suffering from AD or SCZ share a common burden of disrupted memory functions unattended by current therapies. Recent preclinical analyses highlight cell-type-specific contributions of parvalbumin interneurons (PVIs), particularly the plasticity of their cellular excitability, towards intact neuronal network function (cell-to-network plasticity) and memory performance. Here we argue that deficits of PVI cell-to-network plasticity may underlie memory deficits in AD and SCZ, and we explore two therapeutic avenues: the targeting of PVI-specific neuromodulation, including by neuropeptides, and the recruitment of network synchrony in the gamma frequency range (40 Hz) by external stimulation. We finally propose that these approaches be merged under consideration of recent insights into human brain physiology.

Salidroside directly activates HSC70, revealing a new role for HSC70 in BDNF signalling and neurogenesis after cerebral ischemia

Salidroside, a principal bioactive component of Rhodiola crenulata, is neuroprotective across a wide time window in stroke models. We investigated whether salidroside induced neurogenesis after cerebral ischemia and aimed to identify its primary molecular targets. Rats, subjected to transient 2 h of middle cerebral artery occlusion (MCAO), received intraperitoneal vehicle or salidroside ± intracerebroventricular HSC70 inhibitor VER155008 or TrkB inhibitor ANA-12 for up to 7 days. MRI, behavioural tests, immunofluorescent staining and western blotting measured effects of salidroside. Reverse virtual docking and enzymatic assays assessed interaction of salidroside with purified recombinant HSC70. Salidroside dose-dependently decreased cerebral infarct volumes and neurological deficits, with maximal effects by 50 mg/kg/day. This dose also improved performance in beam balance and Morris water maze tests. Salidroside significantly increased BrdU+/nestin+, BrdU+/DCX+, BrdU+/NeuN+, BrdU-/NeuN+ and BDNF+ cells in the peri-infarct cortex, with less effect in striatum and no significant effect in the subventricular zone. Salidroside was predicted to bind with HSC70. Salidroside dose-dependently increased HSC70 ATPase and HSC70-dependent luciferase activities, but it did not activate HSP70. HSC70 immunoreactivity concentrated in the peri-infarct cortex and was unchanged by salidroside. However, VER155008 prevented salidroside-dependent increases of neurogenesis, BrdU-/NeuN+ cells and BDNF+ cells in peri-infarct cortex. Salidroside also increased BDNF protein and p-TrkB/TrkB ratio in ischemic brain, changes prevented by VER155008 and ANA-12, respectively. Additionally, ANA-12 blocked salidroside-dependent neurogenesis and increased BrdU-/NeuN+ cells in the peri-infarct cortex. Salidroside directly activates HSC70, thereby stimulating neurogenesis and neuroprotection via BDNF/TrkB signalling after MCAO. Salidroside and similar activators of HSC70 might provide clinical therapies for ischemic stroke.

The Role of Tenascin-C on the Structural Plasticity of Perineuronal Nets and Synaptic Expression in the Hippocampus of Male Mice

Neuronal plasticity is a crucial mechanism for an adapting nervous system to change. It is shown to be regulated by perineuronal nets (PNNs), the condensed forms of the extracellular matrix (ECM) around neuronal bodies. By assessing the changes in the number, intensity, and structure of PNNs, the ultrastructure of the PNN mesh, and the expression of inhibitory and excitatory synaptic inputs on these neurons, we aimed to clarify the role of an ECM glycoprotein, tenascin-C (TnC), in the dorsal hippocampus. To enhance neuronal plasticity, TnC-deficient (TnC-/-) and wild-type (TnC+/+) young adult male mice were reared in an enriched environment (EE) for 8 weeks. Deletion of TnC in TnC-/- mice showed an ultrastructural reduction of the PNN mesh and an increased inhibitory input in the dentate gyrus (DG), and an increase in the number of PNNs with a rise in the inhibitory input in the CA2 region. EE induced an increased inhibitory input in the CA2, CA3, and DG regions; in DG, the change was also followed by an increased intensity of PNNs. No changes in PNNs or synaptic expression were found in the CA1 region. We conclude that the DG and CA2 regions emerged as focal points of alterations in PNNs and synaptogenesis with EE as mediated by TnC.

GABAergic interneuron diversity and organization are crucial for the generation of human-specific functional neural networks in cerebral organoids

This mini review investigates the importance of GABAergic interneurons for the network function of human-induced pluripotent stem cells (hiPSC)-derived brain organoids. The presented evidence suggests that the abundance, diversity and three-dimensional cortical organization of GABAergic interneurons are the primary elements responsible for the creation of synchronous neuronal firing patterns. Without intricate inhibition, coupled oscillatory patterns cannot reach a sufficient complexity to transfer spatiotemporal information constituting physiological network function. Furthermore, human-specific brain network function seems to be mediated by a more complex and interconnected inhibitory structure that remains developmentally flexible for a longer period when compared to rodents. This suggests that several characteristics of human brain networks cannot be captured by rodent models, emphasizing the need for model systems like organoids that adequately mimic physiological human brain function in vitro.

Hippocampal Lactate-Infusion Enhances Spatial Memory Correlated with Monocarboxylate Transporter 2 and Lactylation

Lactate has emerged as a key player in regulating neural functions and cognitive processes. Beyond its function as an energy substrate and signal molecule, recent research has revealed lactate to serve as an epigenetic regulator in the brain. However, the molecular mechanisms by which lactate regulates spatial memory and its role in the prevention of cognitive disorders remain unclear. Herein, we injected L-lactate (10 μmol/kg/d for 6 d) into the mouse's hippocampus, followed by the Morris water maze (MWM) test and molecular analyses. Improved spatial memory performances were observed in mice injected with lactate. Besides, lactate upregulated the expression of synaptic proteins post-synaptic density 95 (PSD95), synaptophysin (SYP), and growth associated protein 43 (GAP43) in hippocampal tissues and HT22 cells, suggesting a potential role in synaptic transmission and memory formation. The facilitative role of monocarboxylate transporter 2 (MCT2), a neuron-specific lactate transporter, in this process was confirmed, as MCT2 antagonists attenuated the lactate-induced upregulation of synaptic proteins. Moreover, lactate induced protein lactylation, a post-translational modification, which could be suppressed by MCT2 inhibition. RNA sequencing of lactated-injected hippocampal tissues revealed a comprehensive gene expression profile influenced by lactate, with significant changes in genes associated with transcriptional progress. These data demonstrate that hippocampal lactate injection enhances spatial memory in mice, potentially through the upregulation of synaptic proteins and induction of protein lactylation, with MCT2 playing a crucial role in these processes. Our findings shed light on the multi-faceted role of lactate in neural function and memory regulation, opening new avenues for therapeutic interventions targeting cognitive disorders.

Ventral hippocampal cholecystokinin interneurons gate contextual reward memory

Associating contexts with rewards depends on hippocampal circuits, with local inhibitory interneurons positioned to play an important role in shaping activity. Here, we demonstrate that the encoding of context-reward memory requires a ventral hippocampus (vHPC) to nucleus accumbens (NAc) circuit that is gated by cholecystokinin (CCK) interneurons. In a sucrose conditioned place preference (CPP) task, optogenetically inhibiting vHPC-NAc terminals impaired the acquisition of place preference. Transsynaptic rabies tracing revealed vHPC-NAc neurons were monosynaptically innervated by CCK interneurons. Using intersectional genetic targeting of CCK interneurons, ex vivo optogenetic activation of CCK interneurons increased GABAergic transmission onto vHPC-NAc neurons, while in vivo optogenetic inhibition of CCK interneurons increased cFos in these projection neurons. Notably, CCK interneuron inhibition during sucrose CPP learning increased time spent in the sucrose-associated location, suggesting enhanced place-reward memory. Our findings reveal a previously unknown hippocampal microcircuit crucial for modulating the strength of contextual reward learning.

Meta-Analysis in Transgenic Alzheimer's Disease Mouse Models Reveals Opposite Brain Network Effects of Amyloid-β and Phosphorylated Tau Proteins

Background

Cognitive deficits observed in Alzheimer's disease (AD) patients have been correlated with altered hippocampal activity. Although the mechanism remains under extensive study, neurofibrillary tangles and amyloid plaques have been proposed as responsible for brain activity alterations. Aiming to unveil the mechanism, researchers have developed several transgenic models of AD. Nevertheless, the variability in hippocampal oscillatory alterations found in different genetic backgrounds and ages remains unclear.

Objective

To assess the oscillatory alterations in relation to animal developmental age and protein inclusion, amyloid-β (Aβ) load, and abnormally phosphorylated tau (pTau), we reviewed and analyzed the published data on peak power, frequency, and quantification of theta-gamma cross-frequency coupling (modulation index values).

Methods

To ensure that the search was as current as possible, a systematic review was conducted to locate and abstract all studies published from January 2000 to February 2023 that involved in vivo hippocampal local field potential recording in transgenic mouse models of AD.

Results

The presence of Aβ was associated with electrophysiological alterations that are mainly reflected in power increases, frequency decreases, and lower modulation index values. Concomitantly, pTau accumulation was associated with electrophysiological alterations that are mainly reflected in power decreases, frequency decreases, and no significant alterations in modulation index values.

Conclusions

In this study, we showed that electrophysiological parameters are altered from prodromal stages to the late stages of pathology. Thus, we found that Aβ deposition is associated with brain network hyperexcitability, whereas pTau deposition mainly leads to brain network hypoexcitability in transgenic models.

Ventral hippocampal interneurons govern extinction and relapse of contextual associations

Contextual associations are critical for survival but must be extinguished when new conditions render them nonproductive. By most accounts, extinction forms a new memory that competes with the original association for control over behavior, but the mechanisms underlying this competition remain largely enigmatic. Here we find the retrieval of contextual fear conditioning and extinction yield contrasting patterns of activity in prefrontal cortex and ventral hippocampus. Within ventral CA1, activation of somatostatin-expressing interneurons (SST-INs) occurs preferentially during extinction retrieval and correlates with differences in input synaptic transmission. Optogenetic manipulation of these cells but not parvalbumin interneurons (PV-INs) elicits bidirectional changes in fear expression following extinction, and the ability of SST-INs to gate fear is specific to the context in which extinction was acquired. A similar pattern of results was obtained following reward-based extinction. These data show that ventral hippocampal SST-INs are critical for extinguishing prior associations and thereby gate relapse of both aversive and appetitive responses.