Frontiers in Synaptic Neuroscience最新文献

In vitro maintained human brain slices provide a unique experimental platform for investigating rhythmic neuronal network activity, bridging the gap between animal models and clinical studies. A wide range of spontaneous and induced oscillatory activities has been described in human brain slices. However, their occurrence and characteristics are strongly shaped by methodological determinants spanning tissue origin, slice preparation, recording conditions, and induction strategies. This has been shown to have a profound impact on the reproducibility and interpretation of oscillatory dynamics. This review synthesizes current evidence on rhythmic network activity in acute human brain slices, with a particular emphasis on how methodological determinants interact with intrinsic circuit properties to generate oscillatory dynamics. We discuss how different experimental manipulations influence oscillation frequency, stability, and spatial organization. We further examine the cellular and circuit mechanisms underlying rhythmic activity, highlighting the roles of excitatory-inhibitory balance, synaptic dynamics, neuromodulatory influences, and distinct interneuron populations. Finally, we consider how oscillatory patterns differ across disease contexts, particularly epilepsy and tumor-associated cortex, and discuss the translational value and limitations of human brain slices for linking microcircuit mechanisms to pathological and functional brain states.

Introduction: Programmed axon degeneration significantly affects neural connectivity, however, the underlying mechanisms remain poorly understood, particularly in cortical regions. Sterile Alpha and TIR motif-containing protein 1 (SARM1) is a known regulator of axon degeneration in the peripheral nervous system, but its role in cortical axon plasticity, particularly during injury conditions, remains unclear. This study examined the role of SARM1 in synaptic connectivity and remodelling in the adult sensory-motor cortex under normal physiological conditions and following acute axonal injury.

Methods: Adult male Thy1-GFP-M mice (3-12 months) expressing EGFP in excitatory neurons were also either wild-type (WT-GFP) or null for SARM1 (SARM1KO-GFP). Using in vivo multiphoton microscopy, long cortical axon segments (~335 μm ± 140 μm), with terminaux and en passant synaptic boutons in the upper layers of the cortical neuropil, were repeatedly imaged at 48-h intervals to assess axon morphology, synaptic density, and synaptic turnover in the presence and absence of SARM1.

Results: Without injury, axon morphology, synaptic density, and turnover were similar between WT and SARM1KO groups, suggesting that SARM1 is not necessary for maintaining baseline cortical synaptic connectivity. Following axotomy by laser lesion, the non-degenerating proximal axon (still connected to the soma) showed significant changes in synaptic plasticity, with an increased rate of loss of synapses.

Discussion: Our findings suggest that SARM1 plays no role in the remodelling of synapses in the proximal axon after an acute axonal injury.

Introduction: Group I metabotropic glutamate receptors (mGluRs) play a critical role in regulating neuronal excitability, synaptic strength, and cortical network activity. Although their physiological functions and involvement in neurological disorders are well established, direct experimental evidence for their role in human cortical neurons remains limited.

Methods: We investigated the effects of group I mGluR activation on excitatory synaptic transmission in the human supragranular cortex using paired whole-cell patch-clamp recordings from synaptically connected pyramidal cells and interneurons in acute slices of human neocortex resected during neurosurgery.

Results: Activation of mGluRs with the agonist (S)-3,5-dihydroxyphenylglycine (DHPG) altered excitatory synaptic efficacy in an interneuron subtype-dependent manner. Specifically, we observed acute enhancement of excitatory postsynaptic current (EPSC) amplitudes in 54% of fast-spiking interneurons and in 15% of non-fast-spiking interneuron types. Applying the same experimental protocol in slices from Wistar rats resulted in a similar increase in synaptic strength in fast-spiking interneurons. However, paired-pulse ratio analysis showed species-dependent differences, which may reflect distinct contributions of pre- and postsynaptic factors to the observed modulation.

Discussion: Together, these results demonstrate that acute modulation of pyramidal cell-fast-spiking interneuron synapses via group I mGluRs is conserved between human and rodent neocortex, while pointing to species-specific underlying mechanisms. Moreover, mGluR-mediated modulation exhibits cell-type specificity in human cortical circuits. Collectively, these findings provide direct functional evidence for group I mGluR-dependent synaptic regulation in the human cortex and highlight important species- and cell-type-specific differences that should be considered when extrapolating rodent data to human cortical physiology and disease mechanisms.

Understanding the sophisticated cognitive abilities of the human brain requires understanding its cellular and synaptic components. While rodent studies provide foundational knowledge, recent research using freshly resected human neocortical and hippocampal tissue has revealed unanticipated distinctive cellular characteristics. These properties, identified through in vitro electrophysiology, anatomical reconstructions, and computational modeling, have profound implications for physiological processes and modulatory responses. Here we highlight and review a selection of key unique features of human neurons. Human layer 2/3 pyramidal cells exhibit exceptionally low specific membrane capacitance and distinctive ion channel kinetics. Moreover, human pyramidal-to-pyramidal connections display species-specific synaptic dynamics, recovering from short-term depression much faster than in rodents. We also highlight that human pyramidal neurons exhibit more elaborate dendritic trees, particularly perisomatic branching, and faster, more stable Action Potentials (AP) dynamics. Interestingly, these features allow higher-bandwidth information transfer, reflecting enhanced computational power. All these cell-level differences directly impact how circuits process information and respond to pharmacological interventions. Increasingly, drugs targeting ion channels or synaptic mechanisms are used but often display different efficacy or kinetics in human neurons compared to rodents, reflecting underlying biophysical disparities. Consequently, leveraging human brain tissue is key as it allows for the identification of human-specific drug targets and a more accurate understanding of disease mechanisms. This review highlights these crucial cellular distinctions and underscores the importance of exploiting resected human brain tissue for advancing central nervous system therapeutics.

Introduction: In pyramidal neurons, backpropagating action potentials (bAPs) activate voltage-gated calcium channels (VGCCs), producing compartment-specific dendritic Ca²⁺ transients. While extensively characterized in rodent models, little is known about the spatial properties and channel-specific contributions of bAP-induced Ca²⁺ signals in human cortical neurons.

Methods: We used simultaneous whole-cell patch-clamp recordings and two-photon Ca²⁺ imaging in acute human cortical slices to characterize bAP-evoked Ca²⁺ transients along the apical dendrites of layer 2/3 pyramidal neurons.

Results: We found that Ca²⁺ signal amplitudes followed a non-linear spatial profile, increasing proximally and peaking between 50-100 µm from the soma before declining in more distal regions. Oblique dendrites exhibited significantly higher Ca²⁺ amplitudes compared to the primary apical branches. Morphological parameters, such as dendritic diameter, spine density, and branching, were correlated with the spatial profile of Ca²⁺ transients to the peak of the calcium signal profile. Pharmacological blockade of VGCCs revealed that major channel subtypes (L-, N-, R-, and T-type) contribute to dendritic Ca²⁺ influx, with distinct spatial effects. In particular, N-type channel blockade produced the largest attenuation in the medial dendritic segments, while T-type channel inhibition affected all regions.

Discussion: These findings highlight spatial heterogeneity and channel-specific contributions to dendritic Ca²⁺ signaling in human neocortical neurons and underscore the influence of dendritic morphology on signal propagation.

The umbrella of synaptic plasticity includes associative, activity-dependent alterations in synaptic strength that are thought to underlie learning and memory, and negative feedback that stabilizes network activity, termed Hebbian and homeostatic plasticity, respectively. These forms of plasticity respond to activity oppositely, and on different spatial and temporal scales. However, despite these fundamental differences, many similar molecular mechanisms are engaged by each form of plasticity to alter synaptic strength. Here, we review molecular mechanisms involved in homeostatic plasticity and compare their involvement in Hebbian plasticity. We focus on synaptic scaling, long-term potentiation, and long-term depression, which are mediated by regulation of post-synaptic amino-3-hydroxyl-5-methyl-4-isoxazole-propionate-type glutamate receptor (AMPARs) accumulation. Addressing synaptic scaffolding, intracellular signaling, cell-adhesion, and secreted factors, we identify mechanisms that appear to be convergent, differentially engaged, and divergent that uniquely regulate homeostatic scaling. These comparisons identify clear gaps to be addressed by future studies that aim to parse the contributions of Hebbian and homeostatic plasticity to regulate AMPAR function.

Homo sapiens has evolved a large and complex neocortex that underlies advanced cognitive capabilities. Neural computation, however, is inherently energy-intensive, and evolutionary pressures have shaped mechanisms that optimize both computational performance and energy efficiency in the human brain. Fast-spiking interneurons, particularly basket cells, are among the most active neuron types in the neocortex, where they play a key role in coordinating time and space in the activity of neuronal networks, but their high activity levels require high metabolic resources. Because the human neocortex is significantly larger than that of rodents-and contains a higher proportion of inhibitory interneurons relative to pyramidal cells-this expansion may have created evolutionary pressure to reduce the energetic cost of fast-spiking neurons. Compared with rodents, human fast-spiking neurons exhibit adaptations that appear to lower energy expenditure while preserving rapid and precise inhibition. One such adaptation is increased input resistance, which allows both excitation and inhibition to occur with reduced transmembrane ion currents, thereby decreasing the energy required to maintain ionic gradients across the plasma membrane. Since higher input resistance also slows down membrane potential changes, these cells show secondary adaptations that maintain rapid electrical signaling. Additional modifications-such as optimized ion channel composition in soma and axon initial segment, enhanced axon myelination, simplified structure of dendritic tree, and multivesicular synapses-further improve electrical signaling and are likely to reduce metabolic demand, collectively reducing ATP consumption in the neuronal network. By integrating cellular and synaptic perspectives, this review highlights how fast-spiking neurons in the human neocortex have evolved differently from those in rodents to balance energy efficiency while maintaining computational power, providing insight into the metabolic constraints of the human brain.

Alzheimer's disease is a progressive neurodegenerative disorder marked by cognitive decline, accumulation of amyloid-β plaques and neurofibrillary tangles, synaptic dysfunction, and mitochondrial impairment. Despite multiple therapeutic strategies, currently available treatments only provide symptomatic relief without halting disease progression. Emerging evidence implicates mitochondrial dysfunction-including oxidative stress, impaired calcium signaling, mitophagy deficits, disrupted proteostasis, and electron transport chain abnormalities, as central to AD pathogenesis. These dysfunctions contribute to synaptic degeneration, increased reactive oxygen species, and neuronal death. This review consolidates current knowledge on the mechanistic pathways of mitochondrial impairment in AD and their downstream effects on neuronal health. We also explore the therapeutic potential of multitarget approaches, including agents targeting Aβ and tau pathology, oxidative stress mitigation, mitochondrial quality control, and synaptic restoration. By integrating evidence from recent preclinical and clinical studies, this work highlights mitochondrial homeostasis as a promising frontier for disease-modifying therapies in AD.

Synapses are the highly specialized connection sites between neurons enabling the establishment of complex neuronal networks. As highly plastic structures, synapses collocate both the transmission and storage of information, which is an essential prerequisite for learning and memory. Since synaptic deficits are associated with degenerative and neuropsychiatric diseases, it is essential to understand the mechanisms of synaptic plasticity. Throughout evolution, the human brain has developed distinct characteristics, such as supragranular expansion and enhanced long-range connectivity, suggesting an evolutionary specialization of synapses. Recent collaborative research, employing slice preparations obtained from neurosurgical resections of the human neocortex, has significantly advanced our understanding of the unique structural and functional properties of the human neocortex. This review investigates findings derived from diverse experimental methodologies, highlighting specific synaptic features. Focusing on synapses in supragranular layers, we discuss the distinctive synaptic structure, function, and mechanisms of plasticity that contribute to the unique circuitry of the adult human brain. Additionally, we outline emerging directions of research aimed at further elucidating the functionality of human cortical networks.

Understanding how synaptic interactions lead to circuit dynamics for neural computation requires experimental tools that can both observe and perturb neuronal activity across spatial and temporal scales. Microelectrode arrays (MEAs) provide scalable access to population spiking activity, yet they lack the spatial resolution and molecular specificity to precisely dissect synaptic mechanisms. In contrast, recent advances in optogenetic actuators, genetically encoded calcium and voltage indicators, and patterned photostimulation have transformed in vitro research, enabling all-optical interrogation of synaptic plasticity, functional connectivity, and emergent network dynamics. Further progress in transparent MEAs and hybrid optical-electrical systems has bridged the divide between electrophysiology and optical control, allowing simultaneous, bidirectional interaction with biological neural networks (BNNs) and real-time feedback modulation of activity patterns. Together, these multimodal in vitro platforms provide unprecedented experimental access to how local interactions shape global network behavior. Beyond technical integration, they establish a foundation for studying biological computation, linking mechanistic understanding of synaptic processes with their computational outcomes. This mini-review summarizes the progression from conventional MEA-based electrophysiology, through all-optical interrogation, to integrated multimodal frameworks that unite the strengths of both modalities.