The Mechanisms and Functions of Synaptic Facilitation

Genetically encoded sensors illuminate in vivo detection for neurotransmission: Development, application, and optimization strategies

Limitations in existing tools have hindered neuroscientists from achieving a deeper understanding of complex behaviors and diseases. The recent development and optimization of genetically encoded sensors offer a powerful solution for investigating intricate dynamics such as calcium influx, membrane potential, and the release of neurotransmitters and neuromodulators. In contrast, traditional methods are constrained by insufficient spatial and/or temporal resolution, low sensitivity, and stringent application conditions. Genetically encoded sensors have gained widespread popularity due to their advantageous features, which stem from their genetic encoding and optical imaging capabilities. These include broad applicability, tissue specificity, and non-invasive operation. When combined with advanced microscopic techniques, optogenetics, and machine learning approaches, these sensors have become versatile tools for studying neuronal circuits in intact living systems, providing millisecond-scale temporal resolution and spatial resolution ranging from nanometers to micrometers. In this review, we highlight the advantages of genetically encoded sensors over traditional methods in the study of neurotransmission. We also discuss their recent advancements, diverse applications, and optimization strategies.

Auditory rate-induced facilitation of acoustic reflex thresholds in younger and middle-aged adults

OBJECTIVE

Acoustic reflex thresholds (ARTs) improve with an increase in click rates. The goal of this exploratory study was to compare the click-rate induced facilitation (cRIF) of ARTs across younger and middle-aged adults.

DESIGN

Cross-sectional.

STUDY SAMPLE

The younger adult group (18 to 27 years) included 16 women and 15 men. The middle-aged group (45 to 59 years) included 18 women and 12 men. ARTs were established at the click rates of 50 and 300/sec in each ear. The thresholds obtained at the rate of 300/sec were subtracted from those obtained at the rate of 50/sec to derive the cRIF.

RESULTS

A general linear repeated measures model was used by setting up the right and left RIF as repeated variables, sex and age as fixed factors, and right and left ear average hearing loss as covariates. This model revealed a medium-sized significant effect of age group [F (1,55) = 4.97; p = .030; Partial Eta Squared: .083], no effect of sex and ear, and no significant interactions.

CONCLUSIONS

The reduced cRIF of ARTs suggests a significant deterioration in temporal processing speed in the middle-aged group. Future studies to confirm these preliminary results will be helpful.

Neuromorphic Phototransistor with Biochemical Reconfigurability

Neuromorphic transistors with biochemical perception and reconfigurability are crucial for seamless human-robot interaction. However, existing hardware is limited by solid-state operation with electronic charge dynamics. Here, we present such a neuromorphic organic photoelectrochemical transistor (OPECT), in which two different biomolecules can be recognized and transduced into either excitatory or inhibitory signals, exhibiting bioswitchable positive and negative photoconductivity. By adjusting the biomolecular ratios, it further enables dynamic conversion between excitatory and inhibitory behaviors, as well as between paired-pulse facilitation and depression. By constructing a closed-loop neuromorphic biosensing-feedback system, a reconfigurable OPECT nerve is further developed to simulate the chemical-mediated dilation and contraction of a human pupil.

Optogenetics-Inspired Nanofluidic Artificial Dendrite with Spatiotemporal Integration Functions

Dendrites play an essential role in processing functions by facilitating the integration of spatial and temporal information in biological system. Nanofluidic memristors, which harness ions for signal transmission within electrolyte solutions, closely resemble biological neuronal ion channels and hold the potential for the development of biorealistic neuromorphic devices. Herein, inspired by the optogenetic technique that utilized light to tune the ions dynamic, an optical-controlled nanofluidic artificial dendrite by embedding layered graphene oxide (GO) within a polydimethylsiloxane (PDMS) elastomer is developed. Taking advantage of the confinement effect of ions in the nanochannel, it has demonstrated optically-modulated ionic currents, which can effectively replicate dendritic functions. The mechanism can be attributed to the migration of Na+ ions, driven by the electric potential difference light illumination. The dendritic spatial and temporal multiport integrations are realized, including the dendritic sublinear/superlinear integrations and spike-rate-dependent plasticity (SRDP). Moreover, the hand withdrawal reflex, as a crucial mode of neuroregulation governed by central nerve and brain control signals, is replicated in the nanofluidic dendrite-based neuromorphic system, capable of managing a range of withdrawal states of a mechanical arm. This work offers a new strategy for developing nanofluidic artificial dendrite and paves the way toward developing advanced neuromorphic sensorimotor systems.

Endogenous Recovery of Hippocampal Function Following Global Cerebral Ischemia in Juvenile Female Mice Is Influenced by Neuroinflammation and Circulating Sex Hormones

Cardiac arrest (CA)-induced global cerebral ischemia (GCI) in childhood often results in learning and memory deficits. We previously demonstrated in a murine CA and cardiopulmonary resuscitation (CA/CPR) mouse model that a cellular mechanism of learning and memory, long-term potentiation (LTP), is acutely impaired in the hippocampus of juvenile males, correlating with deficits in memory tasks. However, little is known regarding plasticity impairments in juvenile females. We performed CA/CPR in juvenile (P21-25) female mice and used slice electrophysiology and hippocampal-dependent behavior to assess hippocampal function. LTP and contextual fear were impaired 7 days after GCI and endogenously recovered by 30 days. LTP remained impaired at 30 days in ovariectomized females, suggesting the surge in gonadal sex hormones during puberty mediates endogenous recovery. Unlike juvenile males, recovery of LTP in juvenile females was not associated with BDNF expression. NanoString transcriptional analysis revealed a potential role of neuroinflammatory processes, and specifically Cd68 pathways, in LTP impairment and hormone-dependent recovery. This was confirmed with staining that revealed increased Cd68 expression in microglia within the hippocampus. We were able to restore LTP in ovariectomized females with chronic and acute PPT administration, implicating estrogen receptor alpha in recovery mechanisms. This study supports a mechanism of endogenous LTP recovery after GCI in juvenile female mice, which differs mechanistically from juvenile males and does not occur in adults of either sex.

Faecal Microbiota Transplantation Modulates Morphine Addictive-Like Behaviours Through Hippocampal Metaplasticity

The microbiota-gut-brain axis has been implicated in the pathology of substance use disorders (SUDs). In light of the brain's capability to reorganize itself in response to intrinsic and extrinsic stimuli, opioid-induced dysbiosis is likely to contribute to addictive behaviour through modulating neuroplasticity. In this study, a faecal microbiota transplantation (FMT) from a saline-donor was performed on morphine-treated rats to evaluate the effects of gut microbiota on morphine-induced metaplasticity and addictive behaviours. Male Wistar rats were treated with subcutaneous injections of 10 mg/kg morphine sulphate every 12 h for 9 days in an effort to induce dependence. The withdrawal syndrome was precipitated by injecting naloxone (1.5 mg/kg, ip) after the final dose of morphine. The tolerance was induced by repeated morphine injections over a period of 7 days (10 mg/kg, once a day, ip). FMT was applied daily through gavage of processed faeces 1 week before and during the morphine treatment. Field potential recordings (i.e., fEPSP) were carried out to assess short-term and long-term synaptic plasticity in the CA1 area of the hippocampus following Schaffer-collateral stimulation. Animals subjected to FMT exhibited significant reductions in naloxone-precipitated withdrawal syndrome (one-way ANOVA, p < 0.05). Tolerance to the analgesic effects of morphine was not affected by FMT (two-way ANOVA, p > 0.05). Following high-frequency stimulation (HFS) to induce long-term potentiation (LTP), a greater fEPSP slope was observed in morphine-treated animals (unpaired t test, p < 0.05). FMT from saline-donor rats diminished morphine-induced augmented LTP (unpaired t test, p < 0.05). These results highlighted the alleviating effects of FMT from saline-donors on morphine-induced metaplasticity and dependence potentially by modulating the dysbiosis of gut microbiota.

In-Sensor Computing with Visual-Tactile Perception Enabled by Mechano-Optical Artificial Synapse

In-sensor computing paradigm holds the promise of realizing rapid and low-power signal processing. Constructing crossmodal in-sensor computing systems to emulate human sensory and recognition capabilities has been a persistent pursuit for developing humanoid robotics. Here, an artificial mechano-optical synapse is reported to implement in-sensor dynamic computing with visual-tactile perception. By employing mechanoluminescence (ML) material, direct conversion of the mechanical signals into light emission is achieved and the light is transported to an adjacent photostimulated luminescence (PSL) layer without pre- and post-irradiation. The PSL layer acts as a photon reservoir as well as a processing unit for achieving in-memory computing. The approach based on ML coupled with PSL material is different from traditional circuit-constrained methods, enabling remote operation and easy accessibility. Individual and synergistic plasticity are elaborately investigated under force and light pulses, including paired-pulse facilitation, learning behavior, and short-term and long-term memory. A multisensory neural network is built for processing the obtained handwritten patterns with a tablet consisting of the device, achieving a recognition accuracy of up to 92.5%. Moreover, material identification has been explored based on visual-tactile sensing, with an accuracy rate of 98.6%. This work provides a promising strategy to construct in-sensor computing systems with crossmodal integration and recognition.

VIP-to-SST Cell Circuit Motif Shows Differential Short-Term Plasticity across Sensory Areas of Mouse Cortex

Inhibition of GABAergic interneurons has been found to critically fine-tune the excitation-inhibition balance of the cortex. Inhibition is mediated by many connectivity motifs formed by GABAergic neurons. One such motif is the inhibition of somatostatin (SST)-expressing neurons by vasoactive intestinal polypeptide (VIP)-expressing neurons. We studied the synaptic properties of layer (L) 2/3 VIP cells onto L4 SST cells in somatosensory (S1) and visual (V1) cortices of mice of either sex using paired whole-cell patch-clamp recordings, followed by morphological reconstructions. We identified strong differences in the morphological features of L4 SST cells, wherein cells in S1 fell into the non-Martinotti cell (nMC) subclass, while in V1 presented with Martinotti cell (MC)-like features. Approximately 40-45% of tested SST cells were inhibited by VIP cells in both cortices. While unitary connectivity properties of the VIP-to-nMC and VIP-to-MC motifs were comparable, we observed stark differences in short-term plasticity. During high-frequency stimulation of both motifs, some connections showed short-term facilitation while others showed a stable response, with a fraction of VIP-to-nMC connections showing short-term depression. We thus provide evidence that VIP cells target morphological subclasses of SST cells differentially, forming cell-type-specific inhibitory motifs.

Distinct roles of PV and Sst interneurons in visually induced gamma oscillations

Gamma-frequency oscillations are a hallmark of active information processing and are generated by interactions between excitatory and inhibitory neurons. To examine the contribution of distinct inhibitory interneurons to visually induced gamma oscillations, we recorded from optogenetically identified PV+ (parvalbumin) and Sst+ (somatostatin) interneurons in mouse primary visual cortex (V1). PV and Sst inhibitory interneurons exhibited distinct correlations to gamma oscillations. PV cells were strongly phase locked, while Sst cells were weakly phase locked, except for narrow-waveform Sst cells. PV cells fired at a substantially earlier phase in the gamma cycle (≈6 ms) than Sst cells. PV cells fired shortly after the onset of tightly synchronized burst events in excitatory cells, while Sst interneurons fired after subsequent burst spikes or single spikes. These findings indicate a main role of PV interneurons in synchronizing network activity and suggest that PV and Sst interneurons control the excitability of somatic and dendritic neural compartments with precise time delays coordinated by gamma oscillations.

A Self-Driven Ga2O3 Memristor Synapse for Humanoid Robot Learning

In recent years, the rapid development of brain-inspired neuromorphic systems has created an imperative demand for artificial photonic synapses that operate with low power consumption. In this study, a self-driven memristor synapse based on gallium oxide (Ga2O3) nanowires is proposed and demonstrated successfully. This memristor synapse is capable of emulating a range of functionalities of biological synapses when exposed to 255 nm light stimulation. These functionalities encompass peak time-dependent plasticity, pulse facilitation, and memory learning capabilities. It exhibits an ultrahigh paired-pulse facilitation index of 158, indicating exceptional learning performance. The transition from short-term memory to long-term memory can be attributed to the remarkable relearning capabilities. Furthermore, the potential applications of the memristor synapse is showcased through the successful manipulation of a humanoid intelligent robot. Upon establishing artificial intelligence (AI) systems, the control commands originating from the synaptic device can drive the humanoid robot to perform various actions. Based on the memristor synapses, the autonomous feedback system of the humanoid robot facilitates a good collaboration between robotic actions and bio-inspired light perception. Therefore, this research opens up an effective way to advance the development of neuromorphic computing technologies, AI systems, and intelligent robots that demand ultra-low energy consumption.

Delta opioid receptors engage multiple signaling cascades to differentially modulate prefrontal GABA release with input and target specificity

Opioids regulate circuits associated with motivation and reward across the brain. Of the opioid receptor types, delta opioid receptors (DORs) appear to have a unique role in regulating the activity of circuits related to reward without liability for abuse. In neocortex, DORs are expressed primarily in interneurons, including parvalbumin- and somatostatin-expressing interneurons that inhibit somatic and dendritic compartments of excitatory pyramidal cells, respectively. But how DORs regulate transmission from these key interneuron classes is unclear. We found that DORs regulate inhibition from these interneuron classes using different G-protein signaling pathways that both converge on presynaptic calcium channels but regulate distinct aspects of calcium channel function. This imposes different temporal filtering effects, via short-term plasticity, that depend on how calcium channels are regulated. Thus, DORs engage differential signaling cascades to regulate inhibition depending on the postsynaptic target compartment, with different effects on synaptic information transfer in somatic and dendritic domains.

Surface Argon Plasma Treatment Enabled Broadband Optoelectronic Synapses Based on Large-Scale Epitaxial GaSe/GaN Heterojunctions

Creating and tuning charge trapping states by introducing atomic-scale defects are crucial for the optoelectronic synapses that parallelize sensing, processing, and memorizing of optical signals in a single device, which is essential for bioinspired neuromorphic computing. Herein, a mild Ar-plasma treatment approach to enable synaptic behavior in 2D semiconductor devices has been proposed and demonstrated in large-scale epitaxial GaSe/GaN heterostructures. The GaSe films were epitaxially grown on a GaN substrate by physical vapor deposition in an ultrahigh vacuum environment, while the devices were fabricated in situ using a shadow mask-assisted electrode deposition technique. A tailored mild Ar-plasma treatment on the GaSe films has been employed to create atomic-scale defects, which provide charge trapping states in the band gap without making morphological damage, as confirmed by the Raman spectra, scanning electron microscopy, and photoluminescence characterizations. Optoelectronic transport measurement under pulsed illumination of varying wavelengths reveals broadband photoresponse and significantly prolonged response time (×103) that give rise to the superior performance of the synaptic devices. This has been proven by the simulation of classic synaptic behaviors of adaptive pain perception and associative learning. Our work provides an efficient approach to facilitate optoelectronic synaptic behaviors in 2D semiconductor devices.

Synaptic Dysregulation Drives Hyperexcitability in Pyramidal Neurons Surrounding Freeze-Induced Neocortical Malformations in Rats

Focal cortical dysplasia (FCD) is a leading cause of drug-resistant epilepsy; however, the mechanisms underlying hyperexcitability in the affected cortical regions remain poorly understood. In this study, we employed a freeze-induced neocortical malformation model in rats to investigate the electrophysiological properties of pyramidal neurons surrounding the microgyrus and to evaluate changes in synaptic transmission. Using whole-cell patch-clamp recordings, we analyzed passive and active membrane properties, synaptic responses, and epileptiform activity in brain slices from rats with FCD and sham-operated controls. Our results revealed that while the intrinsic biophysical properties of neurons remained largely unchanged, the summation of excitatory and inhibitory inputs was significantly enhanced. Notably, the balance of inhibitory and excitatory synaptic currents was shifted toward excitation, making the perilesional cortex more susceptible to seizure generation. In a model of epileptiform activity induced by GABAA receptor blockade and reduced Mg2+ concentration, we observed early ictal activity originating in the microgyrus and spreading to adjacent regions. These findings demonstrate that synaptic perturbations, rather than alterations in intrinsic neuronal properties, are the primary drivers of hyperexcitability in this model. Our study highlights the importance of synaptic dysregulation in FCD-related epilepsy and suggests that targeting synaptic transmission may offer a promising therapeutic strategy for controlling seizures in patients with cortical malformations.

Endogenous recovery of hippocampal function following global cerebral ischemia in juvenile female mice is influenced by neuroinflammation and circulating sex hormones

Cardiac arrest-induced global cerebral ischemia (GCI) in childhood often results in learning and memory deficits. We previously demonstrated in a murine cardiac arrest and cardiopulmonary resuscitation (CA/CPR) mouse model that a cellular mechanism of learning and memory, long-term potentiation (LTP), is acutely impaired in the hippocampus of juvenile males, correlating with deficits in memory tasks. However, little is known regarding plasticity impairments in juvenile females. We performed CA/CPR in juvenile (P21-25) female mice and used slice electrophysiology and hippocampal dependent behavior to assess hippocampal function. LTP was and contextual fear were impaired 7-days after GCI and endogenously recovered by 30-days. LTP remained impaired at 30 days in ovariectomized females, suggesting the surge in gonadal sex hormones during puberty mediates endogenous recovery. Unlike juvenile males, recovery of LTP in juvenile females was not associated with BDNF expression. NanoString transcriptional analysis revealed a potential role of neuroinflammatory processes, and specifically Cd68 pathways, in LTP impairment and hormone-dependent recovery. We were able to restore LTP in ovariectomized females with chronic and acute PPT administration, implicating estrogen receptor alpha in recovery mechanisms. This study supports a mechanism of endogenous LTP recovery after GCI in juvenile female mice which differs mechanistically from juvenile males and does not occur in adults of either sex.

Input/Output Relationships for the Primary Hippocampal Circuit

The hippocampus is the most studied brain region, but little is known about signal throughput-the simplest, yet most essential of circuit operations-across its multiple stages from perforant path input to CA1 output. Using hippocampal slices derived from male mice, we have found that single-pulse lateral perforant path (LPP) stimulation produces a two-part CA1 response generated by LPP projections to CA3 ("direct path") and the dentate gyrus ("indirect path"). The latter, indirect path was far more potent in driving CA1 but did so only after a lengthy delay. Rather than operating as expected from the much-discussed trisynaptic circuit argument, the indirect path used the massive CA3 recurrent collateral system to trigger a high-frequency sequence of fEPSPs and spikes. The latter events promoted reliable signal transfer to CA1, but the mobilization time for the stereotyped, CA3 response resulted in surprisingly slow throughput. The circuit transmitted theta (5 Hz) but not gamma (50 Hz) frequency input, thus acting as a low-pass filter. It reliably transmitted short bursts of gamma input separated by the period of a theta wave-CA1 spiking output under these conditions closely resembled the input signal. In all, the primary hippocampal circuit does not behave as a linear, three-part system but instead uses novel filtering and amplification steps to shape throughput and restrict effective input to select patterns. We suggest that the operations described here constitute a default mode for processing cortical inputs with other types of functions being enabled by projections from outside the extended hippocampus.

The spinal premotor network driving scratching flexor and extensor alternation

Rhythmic motor behaviors are generated by neural networks termed central pattern generators (CPGs). Although locomotor CPGs have been extensively characterized, it remains unknown how the neuronal populations composing them interact to generate adaptive rhythms. We explored the non-linear cooperation dynamics among the three main populations of ipsilaterally projecting spinal CPG neurons - V1, V2a, V2b neurons - in scratch reflex rhythmogenesis. Ablation of all three neuronal subtypes reduced the oscillation frequency. Activation of excitatory V2a neurons enhanced the oscillation frequency, while activating inhibitory V1 neurons caused atonia. These findings required the development of a novel neuromechanical model that consists of flexor and extensor modules coupled via inhibition, in which rhythm in each module is generated by self-bursting excitatory populations and accelerated by intra-module inhibition. Inter-module inhibition coordinates the phases of flexor and extensor activity and slows the oscillations, while facilitation mechanisms in excitatory neurons explain the V2a activation-driven increase in frequency.

Minimal presynaptic protein machinery governing diverse kinetics of calcium-evoked neurotransmitter release

Neurotransmitters are released from synaptic vesicles with remarkable precision in response to presynaptic calcium influx but exhibit significant heterogeneity in exocytosis timing and efficacy based on the recent history of activity. This heterogeneity is critical for information transfer in the brain, yet its molecular basis remains poorly understood. Here, we employ a biochemically-defined fusion assay under physiologically relevant conditions to delineate the minimal protein machinery sufficient to account for various modes of calcium-triggered vesicle fusion dynamics. We find that Synaptotagmin-1, Synaptotagmin-7, and Complexin synergistically restrain SNARE complex assembly, thus preserving vesicles in a stably docked state at rest. Upon calcium activation, Synaptotagmin-1 induces rapid vesicle fusion, while Synaptotagmin-7 mediates delayed fusion. Competitive binding of Synaptotagmin-1 and Synaptotagmin-7 to the same SNAREs, coupled with differential rates of calcium-triggered fusion clamp reversal, govern the overall kinetics of vesicular fusion. Under conditions mimicking sustained neuronal activity, the Synaptotagmin-7 fusion clamp is destabilized by the elevated basal calcium concentration, thereby enhancing the synchronous component of fusion. These findings provide a direct demonstration that a small set of proteins is sufficient to account for how nerve terminals adapt and regulate the calcium-evoked neurotransmitter exocytosis process to support their specialized functions in the nervous system.

Differential effects of Phosphodiesterase 4A5 on cAMP-dependent forms of long-term potentiation

cAMP signalling is critical for memory consolidation and certain forms of long-term potentiation (LTP). Phosphodiesterases (PDEs), enzymes that degrade the second messengers cAMP and cGMP, are highly conserved during evolution and represent a unique set of drug targets, given the involvement of these enzymes in several pathophysiological states including brain disorders. The PDE4 family of cAMP-selective PDEs exert regulatory roles in memory and synaptic plasticity, but the specific roles of distinct PDE4 isoforms in these processes are poorly understood. Building on our previous work demonstrating that spatial and contextual memory deficits were caused by expressing selectively the long isoform of the PDE4A subfamily, PDE4A5, in hippocampal excitatory neurons, we now investigate the effects of PDE4A isoforms on different cAMP-dependent forms of LTP. We found that PDE4A5 impairs long-lasting LTP induced by theta burst stimulation (TBS) while sparing long-lasting LTP induced by spaced four-train stimulation (4 × 100 Hz). This effect requires the unique N-terminus of PDE4A5 and is specific to this long isoform. Targeted overexpression of PDE4A5 in area CA1 is sufficient to impair TBS-LTP, suggesting that cAMP levels in the postsynaptic neuron are critical for TBS-LTP. Our results shed light on the inherent differences among the PDE4A subfamily isoforms, emphasizing the importance of the long isoforms, which have a unique N-terminal region. Advancing our understanding of the function of specific PDE isoforms will pave the way for developing isoform-selective approaches to treat the cognitive deficits that are debilitating aspects of psychiatric, neurodevelopmental and neurodegenerative disorders. KEY POINTS: Hippocampal overexpression of PDE4A5, but not PDE4A1 or the N-terminus-truncated PDE4A5 (PDE4A5Δ4), selectively impairs long-term potentiation (LTP) induced by theta burst stimulation (TBS-LTP). Expression of PDE4A5 in area CA1 is sufficient to cause deficits in TBS-LTP. Hippocampal overexpression of the PDE4A isoforms PDE4A1 and PDE4A5 does not impair LTP induced by repeated tetanic stimulation at the CA3-CA1 synapses. These results suggest that PDE4A5, through its N-terminus, regulates cAMP pools that are critical for memory consolidation and expression of specific forms of long-lasting synaptic plasticity at CA3-CA1 synapses.

Synaptic Response of Fluidic Nanopores: The Connection of Potentiation with Hysteresis

Iontronic fluidic ionic/electronic components are emerging as promising elements for artificial brain-like computation systems. Nanopore ionic rectifiers can be operated as a synapse element, exhibiting conductance modulation in response to a train of voltage impulses, thus producing programmable resistive states. We propose a model that replicates hysteresis, rectification, and time domain response properties, based on conductance modulation between two conducting modes and a relaxation time of the state variable. We show that the kinetic effects observed in hysteresis loops govern the potentiation phenomena related to conductivity modulation. To illustrate the efficacy of the model, we apply it to replicate rectification, hysteresis and conductance modulation of two different experimental systems: a polymer membrane with conical pores, and a blind-hole nanoporous anodic alumina membrane with a barrier oxide layer. We show that the time transient analysis of the model develops the observed potentiation and depression phenomena of the synaptic properties.

Ultra-fast photoelectron transfer in bimetallic porphyrin optoelectrode for single neuron modulation

Shrinking the size of photoelectrodes into the nanoscale will enable the precise modulation of cellular and subcellular behaviors of a single neuron and neural circuits. However, compared to photovoltaic devices, the reduced size causes the compromised efficiencies. Here, we present a highly efficient nanoelectrode based on bimetallic zinc and gold porphyrin (ZnAuPN). Upon light excitation, we observe ultrafast energy transfer (~66 ps) and charge transfer (~0.5 ps) through the porphyrin ring, enabling 97% efficiency in separating and transferring photoinduced charges to single Au-atom centers. Leveraging these isolated Au atoms as stimulating electrode arrays, we achieve significant photocurrent injection in single neurons, triggering action potential with millisecond light pulses. Notably, Extracranial near-infrared light irradiation of the motor cortex induces neuronal firing and enhances mouse movement. These results show the potential of nanoscale optoelectrodes for high spatiotemporal modulation of neuronal networks without the need for gene transfection in optogenetics.

Breaking the burst: Unveiling mechanisms behind fragmented network bursts in patient-derived neurons

Fragmented network bursts (NBs) are observed as a phenotypic driver in many patient-derived neuronal networks on multi-electrode arrays (MEAs), but the pathophysiological mechanisms underlying this phenomenon are unknown. Here, we used our previously developed biophysically detailed in silico model to investigate these mechanisms. Fragmentation of NBs in our model simulations occurred only when the level of short-term synaptic depression (STD) was enhanced, suggesting that STD is a key player. Experimental validation with Dynasore, an STD enhancer, induced fragmented NBs in healthy neuronal networks in vitro. Additionally, we showed that strong asynchronous neurotransmitter release, NMDA currents, or short-term facilitation (STF) can support the emergence of multiple fragments in NBs by producing excitation that persists after high-frequency firing stops. Our results provide important insights into disease mechanisms and potential pharmaceutical targets for neurological disorders modeled using human induced pluripotent stem cell (hiPSC)-derived neurons.

Maternal fluoxetine impairs synaptic transmission and plasticity in the medial prefrontal cortex and alters the structure and function of dorsal raphe nucleus neurons in offspring mice

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are commonly prescribed to women during pregnancy and breastfeeding despite posing a risk of adverse cognitive outcomes and affective disorders for the child. The consequences of SSRI-induced excess of 5-HT during development for the brain neuromodulatory 5-HT system remain largely unexplored. In this study, an SSRI - fluoxetine (FLX) - was administered to C57BL/6 J mouse dams during pregnancy and lactation to assess its effects on the offspring. We found that maternal FLX decreased field potentials, impaired long-term potentiation, facilitated long-term depression and tended to increase the density of 5-HTergic fibers in the medial prefrontal cortex (mPFC) of female but not male adolescent offspring. These effects were accompanied by deteriorated performance in the temporal order memory task and reduced sucrose preference with no change in marble burying behavior in FLX-exposed female offspring. We also found that maternal FLX reduced the axodendritic tree complexity of 5-HT dorsal raphe nucleus (DRN) neurons in female but not male offspring, with no changes in the excitability of DRN neurons of either sex. While no effects of maternal FLX on inhibitory postsynaptic currents (sIPSCs) in DRN neurons were found, we observed a significant influence of FLX exposure on kinetics of spontaneous excitatory postsynaptic currents (sEPSCs) in DRN neurons. Finally, we report that no changes in field potentials and synaptic plasticity were evident in the mPFC of the offspring after maternal exposure during pregnancy and lactation to a new antidepressant, vortioxetine. These findings show that in contrast to the mPFC, long-term consequences of maternal FLX exposure on the structure and function of DRN 5-HT neurons are mild and suggest a sex-dependent, distinct sensitivity of cortical and brainstem neurons to FLX exposure in early life. Vortioxetine appears to exert fewer side effects with regards to the mPFC when compared with FLX.

The TrkC-PTPσ complex governs synapse maturation and anxiogenic avoidance via synaptic protein phosphorylation

The precise organization of pre- and postsynaptic terminals is crucial for normal synaptic function in the brain. In addition to its canonical role as a neurotrophin-3 receptor tyrosine kinase, postsynaptic TrkC promotes excitatory synapse organization through interaction with presynaptic receptor-type tyrosine phosphatase PTPσ. To isolate the synaptic organizer function of TrkC from its role as a neurotrophin-3 receptor, we generated mice carrying TrkC point mutations that selectively abolish PTPσ binding. The excitatory synapses in mutant mice had abnormal synaptic vesicle clustering and postsynaptic density elongation, more silent synapses, and fewer active synapses, which additionally exhibited enhanced basal transmission with impaired release probability. Alongside these phenotypes, we observed aberrant synaptic protein phosphorylation, but no differences in the neurotrophin signaling pathway. Consistent with reports linking these aberrantly phosphorylated proteins to neuropsychiatric disorders, mutant TrkC knock-in mice displayed impaired social responses and increased avoidance behavior. Thus, through its regulation of synaptic protein phosphorylation, the TrkC-PTPσ complex is crucial for the maturation, but not formation, of excitatory synapses in vivo.

Integration of distinct cortical inputs to primary and higher order inhibitory cells of the thalamus

The neocortex controls its own sensory input in part through top-down inhibitory mechanisms. Descending corticothalamic projections drive GABAergic neurons of the thalamic reticular nucleus (TRN), which govern thalamocortical cell activity via inhibition. Neurons in sensory TRN are organized into primary and higher order (HO) subpopulations, with separate intrathalamic connections and distinct genetic and functional properties. Here, we investigated top-down neocortical control over primary and HO neurons of somatosensory TRN. Projections from layer 6 of somatosensory cortex evoked stronger and more state-dependent activity in primary than in HO TRN, driven by more robust synaptic inputs and potent T-type calcium currents. However, HO TRN received additional, physiologically distinct, inputs from motor cortex and layer 5 of S1. Thus, in a departure from the canonical focused sensory layer 6 innervation characteristic of primary TRN, HO TRN integrates broadly from multiple corticothalamic systems, with unique state-dependence, extending the range of mechanisms for top-down control.

Neuromuscular Transmission in a Biological Context

Neuromuscular transmission is the process by which motor neurons activate muscle contraction and thus plays an essential role in generating the purposeful body movements that aid survival. While many features of this process are common throughout the Animal Kingdom, such as the release of transmitter in multimolecular "quanta," and the response to it by opening ligand-gated postsynaptic ion channels, there is also much diversity between and within species. Much of this diversity is associated with specialization for either slow, sustained movements such as maintain posture or fast but brief movements used during escape or prey capture. In invertebrates, with hydrostatic and exoskeletons, most motor neurons evoke graded depolarizations of the muscle which cause graded muscle contractions. By contrast, vertebrate motor neurons trigger action potentials in the muscle fibers which give rise to all-or-none contractions. The properties of neuromuscular transmission, in particular the intensity and persistence of transmitter release, reflect these differences. Neuromuscular transmission varies both between and within individual animals, which often have distinct tonic and phasic subsystems. Adaptive plasticity of neuromuscular transmission, on a range of time scales, occurs in many species. This article describes the main steps in neuromuscular transmission and how they vary in a number of "model" species, including C. elegans , Drosophila , zebrafish, mice, and humans. © 2024 American Physiological Society. Compr Physiol 14:5641-5702, 2024.

Short term plasticity at hippocampal mossy fiber synapses

Short-term synaptic plasticity refers to the regulation of synapses by their past activity on time scales of milliseconds to minutes. Hippocampal mossy fiber synapses onto CA3 pyramidal cells (Mf-CA3 synapses) are endowed with remarkable forms of short-term synaptic plasticity expressed as facilitation of synaptic release by a factor of up to ten-fold. Three main forms of short-term plasticity are distinguished: 1) Frequency facilitation, which includes low frequency facilitation and train facilitation, operating in the range of tens of milliseconds to several seconds; 2) Post-tetanic potentiation triggered by trains of high frequency stimulation, which lasts several minutes; 3) Finally, depolarization-induced potentiation of excitation, based on retrograde signaling, with an onset and offset of several minutes. Here we describe the proposed mechanisms for short-term plasticity, mainly based on the kinetics of presynaptic Ca2+ transients and the Ca2+ sensor synaptotagmin 7, on cAMP-dependent mechanisms and readily releasable vesicle pool, and on the regulation of presynaptic K+ channels. We then review evidence for a physiological function of short-term plasticity of Mf-CA3 synapses in information transfer between the dentate gyrus and CA3 in conditions of natural spiking, and discuss how short-term plasticity counteracts robust feedforward inhibition in a frequency-dependent manner. Although DG-CA3 connections have long been proposed to play a role in memory, direct evidence for an implication of short-term plasticity at Mf-CA3 synapses is mostly lacking. The mechanistic knowledge gained on short-term plasticity at Mf-CA3 synapses should help in designing future experiments to directly test how this evolutionary conserved feature controls hippocampal circuit function in behavioural conditions.

Information dynamics of in silico EEG Brain Waves: Insights into oscillations and functions

The relation between electroencephalography (EEG) rhythms, brain functions, and behavioral correlates is well-established. Some physiological mechanisms underlying rhythm generation are understood, enabling the replication of brain rhythms in silico. This offers a pathway to explore connections between neural oscillations and specific neuronal circuits, potentially yielding fundamental insights into the functional properties of brain waves. Information theory frameworks, such as Integrated Information Decomposition (Φ-ID), relate dynamical regimes with informational properties, providing deeper insights into neuronal dynamic functions. Here, we investigate wave emergence in an excitatory/inhibitory (E/I) balanced network of integrate and fire neurons with short-term synaptic plasticity. This model produces a diverse range of EEG-like rhythms, from low δ waves to high-frequency oscillations. Through Φ-ID, we analyze the network's information dynamics and its relation with different emergent rhythms, elucidating the system's suitability for functions such as robust information transfer, storage, and parallel operation. Furthermore, our study helps to identify regimes that may resemble pathological states due to poor informational properties and high randomness. We found, e.g., that in silico β and δ waves are associated with maximum information transfer in inhibitory and excitatory neuron populations, respectively, and that the coexistence of excitatory θ, α, and β waves is associated to information storage. Additionally, we observed that high-frequency oscillations can exhibit either high or poor informational properties, potentially shedding light on ongoing discussions regarding physiological versus pathological high-frequency oscillations. In summary, our study demonstrates that dynamical regimes with similar oscillations may exhibit vastly different information dynamics. Characterizing information dynamics within these regimes serves as a potent tool for gaining insights into the functions of complex neuronal networks. Finally, our findings suggest that the use of information dynamics in both model and experimental data analysis, could help discriminate between oscillations associated with cognitive functions and those linked to neuronal disorders.

Calcineurin inhibition prevents synaptic plasticity deficit induced by brain-derived tau oligomers

Compelling evidence suggests that cognitive decline in Alzheimer's disease is associated with the accumulation and aggregation of tau protein, with the most toxic aggregates being in the form of oligomers. This underscores the necessity for direct isolation and analysis of brain-derived tau oligomers from patients with Alzheimer's disease, potentially offering novel perspectives into tau toxicity. Alzheimer's brain-derived tau oligomers are potent inhibitors of synaptic plasticity; however, the involved mechanism is still not fully understood. We previously reported a significantly reduced incidence of Alzheimer's disease in ageing humans chronically treated with a Food and Drug Administration-approved calcineurin inhibitor, FK506 (tacrolimus), used as an immunosuppressant after solid organ transplant. Using a combination of electrophysiological and RNA-sequencing techniques, we provide here evidence that FK506 has the potential to block the acute toxic effect of brain-derived tau oligomers on synaptic plasticity, as well as to restore the levels of some key synaptic mRNAs. These results further support FK506 as a promising novel therapeutic strategy for the treatment of Alzheimer's disease.

Delta opioid receptors engage multiple signaling cascades to differentially modulate prefrontal GABA release with input and target specificity

Opioids regulate circuits associated with motivation and reward across the brain. Of the opioid receptor types, delta opioid receptors (DORs) appear to have a unique role in regulating the activity of circuits related to reward without a liability for abuse. In neocortex, DORs are expressed primarily in interneurons, including parvalbumin- and somatostatin-expressing interneurons that inhibit somatic and dendritic compartments of excitatory pyramidal cells, respectively. But how DORs regulate transmission from these key interneuron classes is unclear. We found that DORs regulate inhibition from these interneuron classes using different G-protein signaling pathways that both converge on presynaptic calcium channels, but regulate distinct aspects of calcium channel function. This imposes different temporal filtering effects, via short-term plasticity, that depend on how calcium channels are regulated. Thus, DORs engage differential signaling cascades to regulate inhibition depending on the postsynaptic target compartment, with different effects on synaptic information transfer in somatic and dendritic domains.

Non-canonical function of ADAM10 in presynaptic plasticity

A Disintegrin And Metalloproteinase 10 (ADAM10) plays a pivotal role in shaping neuronal networks by orchestrating the activity of numerous membrane proteins through the shedding of their extracellular domains. Despite its significance in the brain, the specific cellular localization of ADAM10 remains not well understood due to a lack of appropriate tools. Here, using a specific ADAM10 antibody suitable for immunostainings, we observed that ADAM10 is localized to presynapses and especially enriched at presynaptic vesicles of mossy fiber (MF)-CA3 synapses in the hippocampus. These synapses undergo pronounced frequency facilitation of neurotransmitter release, a process that play critical roles in information transfer and neural computation. We demonstrate, that in conditional ADAM10 knockout mice the ability of MF synapses to undergo this type of synaptic plasticity is greatly reduced. The loss of facilitation depends on the cytosolic domain of ADAM10 and association with the calcium sensor synaptotagmin 7 rather than ADAM10's proteolytic activity. Our findings unveil a new role of ADAM10 in the regulation of synaptic vesicle exocytosis.

Modulation of multisensory nociceptive neurons in monkey cortical area 7b and behavioral correlates

Wide-range thermoreceptive neurons (WRT-EN) in monkey cortical area 7b that encoded innocuous and nocuous cutaneous thermal and threatening visuosensory stimulation with high fidelity were studied to identify their multisensory integrative response properties. Emphasis was given to characterizing the spatial and temporal effects of threatening visuosensory input on the thermal stimulus-response properties of these multisensory nociceptive neurons. Threatening visuosensory stimulation was most efficacious in modulating thermal evoked responses when presented as a downward ("looming"), spatially congruent, approaching and closely proximal target in relation to the somatosensory receptive field. Both temporal alignment and misalignment of spatially aligned threatening visual and thermal stimulation significantly increased mean discharge frequencies above those evoked by thermal stimulation alone, particularly at near noxious (43°C) and mildly noxious (45°C) temperatures. The enhanced multisensory discharge frequencies were equivalent to the discharge frequency evoked by overtly noxious thermal stimulation alone at 47°C (monkey pain tolerance threshold). A significant increase in behavioral mean escape frequency with shorter escape latency was evoked by multisensory stimulation at near noxious temperature (43°C), which was equivalent to that evoked by noxious stimulation alone (47°C). The remarkable concordance of elevating both neural discharge and escape frequency from a nonnociceptive and prepain level by near noxious thermal stimulation to a nociceptive and pain level by multisensory visual and near noxious thermal stimulation and integration is an elegantly designed defensive neural mechanism that in effect lowers both nociceptive response and pain thresholds to preemptively engage nocifensive behavior and, consequently, avert impending and actual injurious noxious thermal stimulation.NEW & NOTEWORTHY Multisensory nociceptive neurons in cortical area 7b are engaged in integration of threatening visuosensory and a wide range of innocuous and nocuous somatosensory (thermoreceptive) inputs. The enhancement of neuronal activity and escape behavior in monkey by multisensory integration is consistent and supportive of human psychophysical studies. The spatial features of visuosensory stimulation in peripersonal space in relation to somatic stimulation in personal space are critical to multisensory integration, nociception, nocifensive behavior, and pain.

Dopamine biases decisions by limiting temporal integration

Motivations bias our responses to stimuli, producing behavioural outcomes that match our needs and goals. Here we describe a mechanism behind this phenomenon: adjusting the time over which stimulus-derived information is permitted to accumulate towards a decision. As a Drosophila copulation progresses, the male becomes less likely to continue mating through challenges1-3. We show that a set of copulation decision neurons (CDNs) flexibly integrates information about competing drives to mediate this decision. Early in mating, dopamine signalling restricts CDN integration time by potentiating Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation in response to stimulatory inputs, imposing a high threshold for changing behaviours. Later into mating, the timescale over which the CDNs integrate termination-promoting information expands, increasing the likelihood of switching behaviours. We suggest scalable windows of temporal integration at dedicated circuit nodes as a key but underappreciated variable in state-based decision-making.

Biomimetic Neuromorphic Sensory System via Electrolyte Gated Transistors

Biomimetic neuromorphic sensing systems, inspired by the structure and function of biological neural networks, represent a major advancement in the field of sensing technology and artificial intelligence. This review paper focuses on the development and application of electrolyte gated transistors (EGTs) as the core components (synapses and neuros) of these neuromorphic systems. EGTs offer unique advantages, including low operating voltage, high transconductance, and biocompatibility, making them ideal for integrating with sensors, interfacing with biological tissues, and mimicking neural processes. Major advances in the use of EGTs for neuromorphic sensory applications such as tactile sensors, visual neuromorphic systems, chemical neuromorphic systems, and multimode neuromorphic systems are carefully discussed. Furthermore, the challenges and future directions of the field are explored, highlighting the potential of EGT-based biomimetic systems to revolutionize neuromorphic prosthetics, robotics, and human-machine interfaces. Through a comprehensive analysis of the latest research, this review is intended to provide a detailed understanding of the current status and future prospects of biomimetic neuromorphic sensory systems via EGT sensing and integrated technologies.

The Lack of Synapsin Alters Presynaptic Plasticity at Hippocampal Mossy Fibers in Male Mice

Synapsins are highly abundant presynaptic proteins that play a crucial role in neurotransmission and plasticity via the clustering of synaptic vesicles. The synapsin III isoform is usually downregulated after development, but in hippocampal mossy fiber boutons, it persists in adulthood. Mossy fiber boutons express presynaptic forms of short- and long-term plasticity, which are thought to underlie different forms of learning. Previous research on synapsins at this synapse focused on synapsin isoforms I and II. Thus, a complete picture regarding the role of synapsins in mossy fiber plasticity is still missing. Here, we investigated presynaptic plasticity at hippocampal mossy fiber boutons by combining electrophysiological field recordings and transmission electron microscopy in a mouse model lacking all synapsin isoforms. We found decreased short-term plasticity, i.e., decreased facilitation and post-tetanic potentiation, but increased long-term potentiation in male synapsin triple knock-out (KO) mice. At the ultrastructural level, we observed more dispersed vesicles and a higher density of active zones in mossy fiber boutons from KO animals. Our results indicate that all synapsin isoforms are required for fine regulation of short- and long-term presynaptic plasticity at the mossy fiber synapse.

The 5-HT7 receptor antagonist SB 269970 ameliorates maternal fluoxetine exposure-induced impairment of synaptic plasticity in the prefrontal cortex of the offspring female mice

The use of a selective serotonin reuptake inhibitor fluoxetine in depression during pregnancy and the postpartum period might increase the risk of affective disorders and cognitive symptoms in progeny. In animal models, maternal exposure to fluoxetine throughout gestation and lactation negatively affects the behavior of the offspring. Little is known about the effects of maternal fluoxetine on synaptic transmission and plasticity in the offspring cerebral cortex. During pregnancy and lactation C57BL/6J mouse dams received fluoxetine (7.5 mg/kg/day) with drinking water. Female offspring mice received intraperitoneal injections of the selective 5-HT7 receptor antagonist SB 269970 (2.5 mg/kg) for 7 days. Whole-cell and field potential electrophysiological recordings were performed in the medial prefrontal cortex (mPFC) ex vivo brain slices. Perinatal exposure to fluoxetine resulted in decreased field potentials and impaired long-term potentiation (LTP) in layer II/III of the mPFC of female young adult offspring. Neither the intrinsic excitability nor spontaneous excitatory postsynaptic currents were altered in layer II/III mPFC pyramidal neurons. In mPFC slices obtained from fluoxetine-treated mice that were administered SB 269970 both field potentials and LTP magnitude were restored and did not differ from controls. Treatment of fluoxetine-exposed mice with a selective 5-HT7 receptor antagonist, SB 269970, normalizes synaptic transmission and restores the potential for plasticity in the mPFC of mice exposed in utero and postnatally to fluoxetine.

Impaired neurogenesis induced by fluoride via the Notch1 signaling and effects of carvacrol intervention

The negative regulation on neurogenesis has been implicated in fluoride neurotoxicity, while the evidence is limited. To explore whether fluoride interferes with neurogenesis via the Notch1 signaling and the potential alleviation effects of carvacrol (CAR), we conducted in vivo and in vitro experiments, as well as epidemiological analyses in this study. The results showed that urinary fluoride levels and circulating Notch1 levels were associated with IQ levels in boys. NaF-treated rats had fewer neurons, lower densities of dendritic spines, depressed neurogenesis, and impaired learning and memory abilities. In vitro experiments using undifferentiated PC12 cells mimicking neurogenesis revealed that NaF suppressed differentiation and neurite outgrowth. Besides, Notch1 signaling activation was detected in vivo and in vitro. The latter was confirmed using an in vitro model supplemented with DAPT, a potent Notch1 inhibitor. Furthermore, CAR supplementation negatively regulated NICD1 and Hes1 expressions and promoted hippocampal neurogenesis, thereby improving neurological functions in NaF-treated rats. These findings indicated that the inhibition of neurogenesis in hippocampi induced by fluoride via Notch1 signaling activation may be one of the underlying mechanisms of its neurotoxicity, and that CAR significantly alleviated the neurotoxicity of NaF via the Notch1 signaling.

Functional Dynamics and Selectivity of Two Parallel Corticocortical Pathways from Motor Cortex to Layer 5 Circuits in Somatosensory Cortex

In the rodent whisker system, active sensing and sensorimotor integration are mediated in part by the dynamic interactions between the motor cortex (M1) and somatosensory cortex (S1). However, understanding these dynamic interactions requires knowledge about the synapses and how specific neurons respond to their input. Here, we combined optogenetics, retrograde labeling, and electrophysiology to characterize the synaptic connections between M1 and layer 5 (L5) intratelencephalic (IT) and pyramidal tract (PT) neurons in S1 of mice (both sexes). We found that M1 synapses onto IT cells displayed modest short-term depression, whereas synapses onto PT neurons showed robust short-term facilitation. Despite M1 inputs to IT cells depressing, their slower kinetics resulted in summation and a response that increased during short trains. In contrast, summation was minimal in PT neurons due to the fast time course of their M1 responses. The functional consequences of this reduced summation, however, were outweighed by the strong facilitation at these M1 synapses, resulting in larger response amplitudes in PT neurons than IT cells during repetitive stimulation. To understand the impact of facilitating M1 inputs on PT output, we paired trains of inputs with single backpropagating action potentials, finding that repetitive M1 activation increased the probability of bursts in PT cells without impacting the time dependence of this coupling. Thus, there are two parallel but dynamically distinct systems of M1 synaptic excitation in L5 of S1, each defined by the short-term dynamics of its synapses, the class of postsynaptic neurons, and how the neurons respond to those inputs.

Anxiety-, and depression-like behavior following short-term finasteride administration is associated with impaired synaptic plasticity and cognitive behavior in male rats

Finasteride, a 5α-Reductase inhibitor, is used to treat male pattern baldness and benign prostatic hyperplasia. Several clinical studies show that chronic finasteride treatment induces persistent depression, suicidal thoughts and cognitive impairment and these symptoms are persistent even after its withdrawal. Previous results from our lab showed that repeated administration of finasteride for six days induces depression-like behavior. However, whether short-term finasteride administration induces anxiety-like behavior and memory impairment and alters synaptic plasticity are not known, which formed the basis of this study. Finasteride was administered to 2-2.5 months old male Wistar rats for six days and subjected to behavioral evaluation, biochemical estimation and synaptic plasticity assessment. Anxiety-like behavior was evaluated in the elevated plus maze (EPM), open field test (OFT), light/dark test (LDT), and novelty suppressed feeding test (NSFT), and learning and memory using novel object recognition test (NORT) and novel object location test (NOLT) and depression-like behavior in the sucrose preference test (SPT). Synaptic plasticity in the hippocampal Schaffer collateral-CA1 was evaluated using slice field potential recordings. Plasma corticosterone levels were estimated using ELISA. Finasteride administration induced anxiety-like behavior in the EPM, OFT, LDT and NSFT, and depression-like behavior in the SPT. Further, finasteride induced hippocampal dependent spatial learning and memory impairment in the NOLT. In addition, finasteride decreased basal synaptic plasticity and long-term potentiation (LTP) in the hippocampus. A trend of increased plasma corticosterone levels was observed following repeated finasteride administration. These results indicate the potential role of corticosterone and synaptic plasticity in finasteride-induced effects and further studies will pave way for the development of novel neurosteroid-based therapeutics in neuropsychiatric diseases.

Muscarinic Modulation of Synaptic Transmission and Short-Term Plasticity in the Dorsal and Ventral Hippocampus

Muscarinic neurotransmission is fundamentally involved in supporting several brain functions by modulating flow of information in brain neural circuits including the hippocampus which displays a remarkable functional segregation along its longitudinal axis. However, how muscarinic neuromodulation contributes to the functional segregation along the hippocampus remains unclear. In this study we show that the nonselective muscarinic receptor agonist carbachol similarly suppresses basal synaptic transmission in the dorsal and ventral CA1 hippocampal field, in a concentration-depended manner. Furthermore, using a ten-pulse stimulation train of varying frequency we found that carbachol changes the frequency filtering properties more in ventral than dorsal hippocampus by facilitating synaptic inputs at a wide range of input frequencies in the ventral compared with dorsal hippocampus. Using the M2 receptor antagonist gallamine and the M4 receptor antagonist tropicamide, we found that M2 receptors are involved in controlling basal synaptic transmission and short-term synaptic plasticity (STSP) in the ventral but not the dorsal hippocampus, while M4 receptors participate in modulating basal synaptic transmission and STSP in both segments of the hippocampus. These results were corroborated by the higher protein expression levels of M2 receptors in the ventral compared with dorsal hippocampus. We conclude that muscarinic transmission modulates excitatory synaptic transmission and short-term synaptic plasticity along the entire rat hippocampus by acting through M4 receptors and recruiting M2 receptors only in the ventral hippocampus. Furthermore, M4 receptors appear to exert a permissive role on the actions of M2 receptors on STSP in the ventral hippocampus. This dorsoventral differentiation of muscarinic modulation is expected to have important implications in information processing along the endogenous hippocampal circuitry.

Functional dynamics and selectivity of two parallel corticocortical pathways from motor cortex to layer 5 circuits in somatosensory cortex

In the rodent whisker system, active sensing and sensorimotor integration are mediated in part by the dynamic interactions between the motor cortex (M1) and somatosensory cortex (S1). However, understanding these dynamic interactions requires knowledge about the synapses and how specific neurons respond to their input. Here, we combined optogenetics, retrograde labeling, and electrophysiology to characterize the synaptic connections between M1 and layer 5 (L5) intratelencephalic (IT) and pyramidal tract (PT) neurons in S1 of mice (both sexes). We found that M1 synapses onto IT cells displayed modest short-term depression, whereas synapses onto PT neurons showed robust short-term facilitation. Despite M1 inputs to IT cells depressing, their slower kinetics resulted in summation and a response that increased during short trains. In contrast, summation was minimal in PT neurons due to the fast time course of their M1 responses. The functional consequences of this reduced summation, however, were outweighed by the strong facilitation at these M1 synapses, resulting in larger response amplitudes in PT neurons than IT cells during repetitive stimulation. To understand the impact of facilitating M1 inputs on PT output, we paired trains of inputs with single backpropagating action potentials, finding that repetitive M1 activation increased the probability of bursts in PT cells without impacting the time-dependence of this coupling. Thus, there are two parallel but dynamically distinct systems of M1 synaptic excitation in L5 of S1, each defined by the short-term dynamics of its synapses, the class of postsynaptic neurons, and how the neurons respond to those inputs.

Frequency-dependent dynamics of steady-state visual evoked potentials under sustained flicker stimulation

Steady-state visual evoked potentials (SSVEP) are electroencephalographic signals elicited when the brain is exposed to a visual stimulus with a steady frequency. We analyzed the temporal dynamics of SSVEP during sustained flicker stimulation at 5, 10, 15, 20 and 40 Hz. We found that the amplitudes of the responses were not stable over time. For a 5 Hz stimulus, the responses progressively increased, while, for higher flicker frequencies, the amplitude increased during the first few seconds and often showed a continuous decline afterward. We hypothesize that these two distinct sets of frequency-dependent SSVEP signal properties reflect the contribution of parvocellular and magnocellular visual pathways generating sustained and transient responses, respectively. These results may have important applications for SSVEP signals used in research and brain-computer interface technology and may contribute to a better understanding of the frequency-dependent temporal mechanisms involved in the processing of prolonged periodic visual stimuli.

A minimal presynaptic protein machinery mediating synchronous and asynchronous exocytosis and short-term plasticity

Neurotransmitters are released from synaptic vesicles with remarkable precision in response to presynaptic Ca2+ influx but exhibit significant heterogeneity in exocytosis timing and efficacy based on the recent history of activity. This heterogeneity is critical for information transfer in the brain, yet its molecular basis remains poorly understood. Here, we employ a biochemically-defined fusion assay under physiologically-relevant conditions to delineate the minimal protein machinery sufficient to account for different modes of Ca2+-triggered vesicle fusion and short-term facilitation. We find that Synaptotagmin-1, Synaptotagmin-7, and Complexin, synergistically restrain SNARE complex assembly, thus preserving vesicles in a stably docked state at rest. Upon Ca2+ activation, Synaptotagmin-1 induces rapid vesicle fusion, while Synaptotagmin-7 mediates delayed fusion. Competitive binding of Synaptotagmin-1 and Synaptotagmin-7 to the same SNAREs, coupled with differential rates of Ca2+-triggered fusion clamp reversal, govern the kinetics of vesicular fusion. Under conditions mimicking sustained neuronal activity, the Synaptotagmin-7 fusion clamp is destabilized by the elevated basal Ca2+ concentration, thereby enhancing the synchronous component of fusion. These findings provide a direct demonstration that a small set of proteins is sufficient to account for how nerve terminals adapt and regulate the Ca2+-evoked neurotransmitter exocytosis process to support their specialized functions in the nervous system.

Control of Munc13-1 Activity by Autoinhibitory Interactions Involving the Variable N-terminal Region

Regulation of neurotransmitter release during presynaptic plasticity underlies varied forms of information processing in the brain. Munc13s play essential roles in release via their conserved C-terminal region, which contains a MUN domain involved in SNARE complex assembly, and controls multiple presynaptic plasticity processes. Munc13s also have a variable N-terminal region, which in Munc13-1 includes a calmodulin binding (CaMb) domain involved in short-term plasticity and a C2A domain that forms an inhibitory homodimer. The C2A domain is activated by forming a heterodimer with the zinc-finger domain of αRIMs, providing a link to αRIM-dependent short- and long-term plasticity. However, it is unknown how the functions of the N- and C-terminal regions are integrated, in part because of the difficulty of purifying Munc13-1 fragments containing both regions. We describe for the first time the purification of a Munc13-1 fragment spanning its entire sequence except for a flexible region between the C2A and CaMb domains. We show that this fragment is much less active than the Munc13-1 C-terminal region in liposome fusion assays and that its activity is strongly enhanced by the RIM2α zinc-finger domain together with calmodulin. NMR experiments show that the C2A and CaMb domains bind to the MUN domain and that these interactions are relieved by the RIM2α ZF domain and calmodulin, respectively. These results suggest a model whereby Munc13-1 activity in promoting SNARE complex assembly and neurotransmitter release are inhibited by interactions of the C2A and CaMb domains with the MUN domain that are relieved by αRIMs and calmodulin.

Synergistic Effect of Electrical and Biochemical Stimulation on Human iPSC-Derived Neural Differentiation in a Microfluidic Electrode Array Chip

Neural differentiation is crucial for advancing our understanding of the nervous system and developing treatments for neurological disorders. The advanced methods and the ability to manipulate the alignment, proliferation, and differentiation of stem cells are essential for studying neuronal development and synaptic interactions. However, the utilization of human induced pluripotent stem cells (iPSCs) for disease modeling of neurodegenerative conditions may be constrained by the prolonged duration and uncontrolled cell differentiation required for functional neural cell differentiation. Here, we developed a microfluidic chip to enhance the differentiation and maturation of specific neural lineages by placing aligned microelectrodes on the glass surface to regulate the neural differentiation of human iPSCs. The utilization of electrical stimulation (ES) in conjunction with neurotrophic factors (NF) significantly enhanced the efficiency in generating functional neurons from human iPSCs. We also observed that the simultaneous application of NF and ES to human iPSCs promoted their differentiation and maturation into functional neurons while increasing synaptic interactions. Our research demonstrated the effect of combining NF and ES on human iPSC-derived neural differentiation.

At the Basis of Brain Malformations: Brain Plasticity, Developmental Neurobiology, and Considerations for Rehabilitation

From early age in the human brain occurs plasticity process that influences its development. The functioning of the brain is governed by its neuronal connectivity and the synaptic dynamics of these connections. A neuron, over thousands of synapses, can receive a large number of inputs and produce different outputs leading to the consolidation and integration of memory. Synaptic plasticity is the set of experience-dependent changes in neuronal pathways that support acquired habits. It is the ability of the nervous system to reshape connectivity between neurons, changing the functional and structural organization of neuronal circuits that allows us to adapt to the multiple and continuous changes in the environment and leading to processes such as cognitive development and the ability to learn. Synaptic plasticity is mainly due to short- and long-term mechanisms. Short-term synaptic plasticity refers to changes in synaptic strength that occurs very quickly (from one-thousandth of a second to 5 minutes) and are temporary and decay over minutes (maximum 30 minutes). Long-term synaptic plasticity is defined by a long-lasting, activity-dependent change in synaptic efficacy, last from hours up to a lifetime (from 30 minutes to weeks, months, and years) and is thought to constitute the basis of learning and memory. A significant difference occurs in the nature of the change; short-term plasticity adds only a functional change, whereas long-term plasticity causes not only functional but also structural changes. Aside from genetic factors and metabolic processes, brain development is mediated also by environmental factors. Interaction with the environment plays a key role in the development and growth of neural networks and neuroplasticity. Environmental interactions that can modify and increase the development of neural networks and intelligence in children are several and are herein discussed.

Ferroelectric 2D SnS2 Analog Synaptic FET

In this study, the development and characterization of 2D ferroelectric field-effect transistor (2D FeFET) devices are presented, utilizing nanoscale ferroelectric HfZrO2 (HZO) and 2D semiconductors. The fabricated device demonstrated multi-level data storage capabilities. It successfully emulated essential biological characteristics, including excitatory/inhibitory postsynaptic currents (EPSC/IPSC), Pair-Pulse Facilitation (PPF), and Spike-Timing Dependent Plasticity (STDP). Extensive endurance tests ensured robust stability (107 switching cycles, 105 s (extrapolated to 10 years)), excellent linearity, and high Gmax/Gmin ratio (>105), all of which are essential for realizing multi-level data states (>7-bit operation). Beyond mimicking synaptic functionalities, the device achieved a pattern recognition accuracy of ≈94% on the Modified National Institute of Standards and Technology (MNIST) handwritten dataset when incorporated into a neural network, demonstrating its potential as an effective component in neuromorphic systems. The successful implementation of the 2D FeFET device paves the way for the development of high-efficiency, ultralow-power neuromorphic hardware which is in sub-femtojoule (48 aJ/spike) and fast response (1 µs), which is 104 folds faster than human synapse (≈10 ms). The results of the research underline the potential of nanoscale ferroelectric and 2D materials in building the next generation of artificial intelligence technologies.

Synaptotagmin 7 docks synaptic vesicles to support facilitation and Doc2α-triggered asynchronous release

Despite decades of intense study, the molecular basis of asynchronous neurotransmitter release remains enigmatic. Synaptotagmin (syt) 7 and Doc2 have both been proposed as Ca2+ sensors that trigger this mode of exocytosis, but conflicting findings have led to controversy. Here, we demonstrate that at excitatory mouse hippocampal synapses, Doc2α is the major Ca2+ sensor for asynchronous release, while syt7 supports this process through activity-dependent docking of synaptic vesicles. In synapses lacking Doc2α, asynchronous release after single action potentials is strongly reduced, while deleting syt7 has no effect. However, in the absence of syt7, docked vesicles cannot be replenished on millisecond timescales. Consequently, both synchronous and asynchronous release depress from the second pulse onward during repetitive activity. By contrast, synapses lacking Doc2α have normal activity-dependent docking, but continue to exhibit decreased asynchronous release after multiple stimuli. Moreover, disruption of both Ca2+ sensors is non-additive. These findings result in a new model whereby syt7 drives activity-dependent docking, thus providing synaptic vesicles for synchronous (syt1) and asynchronous (Doc2 and other unidentified sensors) release during ongoing transmission.

Pre- versus Post-synaptic Forms of LTP in Two Branches of the Same Hippocampal Afferent

There has been considerable controversy about pre- versus postsynaptic expression of memory-related long-term potentiation (LTP), with corresponding disputes about underlying mechanisms. We report here an instance in male mice, in which both types of potentiation are expressed but in separate branches of the same hippocampal afferent. Induction of LTP in the dentate gyrus (DG) branch of the lateral perforant path (LPP) reduces paired-pulse facilitation, is blocked by antagonism of cannabinoid receptor type 1, and is not affected by suppression of postsynaptic actin polymerization. These observations are consistent with presynaptic expression. The opposite pattern of results was obtained in the LPP branch that innervates the distal dendrites of CA3: LTP did not reduce paired-pulse facilitation, was unaffected by the cannabinoid receptor blocker, and required postsynaptic actin filament assembly. Differences in the two LPP termination sites were also noted for frequency facilitation of synaptic responses, an effect that was reproduced in a two-step simulation by small adjustments to vesicle release dynamics. These results indicate that different types of glutamatergic neurons impose different forms of filtering and synaptic plasticity on their afferents. They also suggest that inputs are routed to, and encoded by, different sites within the hippocampus depending upon the pattern of activity arriving over the parent axon.

Molecular control of temporal integration matches decision-making to motivational state

Motivations bias our responses to stimuli, producing behavioral outcomes that match our needs and goals. We describe a mechanism behind this phenomenon: adjusting the time over which stimulus-derived information is permitted to accumulate toward a decision. As a Drosophila copulation progresses, the male becomes less likely to continue mating through challenges. We show that a set of Copulation Decision Neurons (CDNs) flexibly integrates information about competing drives to mediate this decision. Early in mating, dopamine signaling restricts CDN integration time by potentiating CaMKII activation in response to stimulatory inputs, imposing a high threshold for changing behaviors. Later into mating, the timescale over which the CDNs integrate termination-promoting information expands, increasing the likelihood of switching behaviors. We suggest scalable windows of temporal integration at dedicated circuit nodes as a key but underappreciated variable in state-based decision-making.

Receive, Retain and Retrieve: Psychological and Neurobiological Perspectives on Memory Retrieval

Memory and learning are interdependent processes that involve encoding, storage, and retrieval. Especially memory retrieval is a fundamental cognitive ability to recall memory traces and update stored memory with new information. For effective memory retrieval and learning, the memory must be stabilized from short-term memory to long-term memory. Hence, it is necessary to understand the process of memory retention and retrieval that enhances the process of learning. Though previous cognitive neuroscience research has focused on memory acquisition and storage, the neurobiological mechanisms underlying memory retrieval and its role in learning are less understood. Therefore, this article offers the viewpoint that memory retrieval is essential for selecting, reactivating, stabilizing, and storing information in long-term memory. In arguing how memories are retrieved, consolidated, transmitted, and strengthened for the long term, the article will examine the psychological and neurobiological aspects of memory and learning with synaptic plasticity, long-term potentiation, genetic transcription, and theta oscillation in the brain.