Tau pathology emerges early in Alzheimer's disease within entorhinal cortex layer II (ECII) and reaches hippocampal CA1, but how this circuit-level spread translates into sex-dependent vulnerability remains unclear. Using a circuit-defined model in which P301L human tau is expressed selectively in Wolframin-1 (Wfs1 + ) ECII neurons and propagates to CA1, we found that the extent and proximal-distal distribution of tau-positive CA1 neurons were comparable in males and females. Despite similar propagation, females exhibited broad hippocampal-dependent cognitive impairment (working memory, object recognition, fear acquisition, trace associative memory, and contextual fear memory), whereas males showed a selective deficit in trace associative memory. Consistent with these behavioral outcomes, CA1 pyramidal neurons in tau-propagated females displayed reduced excitability (slower action potential kinetics, reduced firing during depolarizing steps) and reduced spontaneous excitatory postsynaptic current (EPSC) amplitude, while males showed subtler intrinsic changes with altered EPSC kinetics. Bulk RNA sequencing of entorhinal cortex and CA1 revealed robust immune pathway engagement after tau propagation, with males showing a stronger Th1/Th2 and neuroinflammatory signature and CTLA4-associated signaling changes, whereas females showed prominent complement-phagosome pathway enrichment and a female-specific increase in Clec7a + microglia density in CA1. CD4 + T-cell infiltration into CA1 was detected in both sexes. Together, these results indicate that sex-specific neuroimmune programs, rather than differences in tau propagation load, shape CA1 electrophysiological dysfunction and the breadth of memory impairment following early entorhinal-to-hippocampal tau spread.

[This corrects the article DOI: 10.1371/journal.pone.0234394.].

Neuromuscular excitability is a vital body function, and Mg2+ is an essential regulatory cation for the function of excitable membranes. Loss of Mg2+ homeostasis disturbs fluxes of other cations across cell membranes, leading to pathophysiological electrogenesis, which can eventually cause vital threat to the patient. Chronic subclinical Mg2+ deficiency is an increasingly prevalent condition in the general population. It is associated with an elevated risk of cardiovascular, respiratory and neurological conditions and an increased mortality. Magnesium favours bronchodilation (by antagonizing Ca2+ channels on airway smooth muscle and inhibiting the release of endogenous bronchoconstrictors). Magnesium exerts antihypertensive effects by reducing peripheral vascular resistance (increasing endothelial NO and PgI2 release and inhibiting Ca2+ influx into vascular smooth muscle). Magnesium deficiency disturbs heart impulse generation and propagation by prolonging cell depolarization (due to Na+/K+ pump and Kir channel dysfunction) and dysregulating cardiac gap junctions, causing arrhythmias, while prolonged diastolic Ca2+ release (through leaky RyRs) disturbs cardiac excitation-contraction coupling, compromising diastolic relaxation and systolic contraction. In the brain, Mg2+ regulates the function of ion channels and neurotransmitters (blocks voltage-gated Ca2+ channel-mediated transmitter release, antagonizes NMDARs, activates GABAARs, suppresses nAChR ion current and modulates gap junction channels) and blocks ACh release at neuromuscular junctions. Magnesium exerts multiple therapeutic neuroactive effects (antiepileptic, antimigraine, analgesic, neuroprotective, antidepressant, anxiolytic, etc.). This review focuses on the effects of Mg2+ on excitable tissues in health and disease. As a natural membrane stabilizer, Mg2+ opposes the development of many conditions of hyperexcitability. Its beneficial recompensation and supplementation help treat hyperexcitability and should therefore be considered wherever needed.

Nano-sized titanium dioxide particles (TiO2 NPs) are a high-production volume nanomaterial widely used in the paints, cosmetics, food and photovoltaics industry. However, the potential carcinogenic effects of TiO2 NPs in the lung are still unclear despite the vast number of in vitro and in vivo studies investigating TiO2 NPs. Here, we systematically reviewed the existing in vitro and in vivo mechanistic evidence of TiO2 NP lung carcinogenicity using the ten key characteristics of carcinogens for identifying and classifying carcinogens. A total of 346 studies qualified for the quality and reliability assessment, of which 206 were considered good quality. Using a weight-of-evidence approach, these studies provided mainly moderate to high confidence for the biological endpoints regarding genotoxicity, oxidative stress and chronic inflammation. A limited number of studies investigated other endpoints important to carcinogenesis, relating to proliferation and transformation, epigenetic alterations and receptor-mediated effects. In summary, TiO2 NPs might possess the ability to induce chronic inflammation and oxidative stress, but it was challenging to compare the findings in the studies due to the wide variety of TiO2 NPs differing in their physicochemical characteristics, formulation, exposure scenarios/test systems, and experimental protocols. Given the limited number of high-quality and high-reliability studies identified within this review, there is a lack of good enough mechanistic evidence for TiO2 NP lung carcinogenicity. Future toxicology/carcinogenicity research must consider including positive controls, endotoxin testing (where necessary), statistical power analysis, and relevant biological endpoints, to improve the study quality and provide reliable data for evaluating TiO2 NP-induced lung carcinogenicity.

Astrocytes are an abundantly distributed population of glial cells in the central nervous system (CNS) that perform myriad functions in the normal and injured/diseased brain. Astrocytes exhibit heterogeneous phenotypes in response to various insults, a process known as astrocyte reactivity. The accuracy and precision of brain signaling are primarily based on interactions involving neurons, astrocytes, oligodendrocytes, microglia, pericytes, and dendritic cells within the CNS. Astrocytes have emerged as a critical entity within the brain because of their unique role in recycling neurotransmitters, actively modulating the ionic environment, regulating cholesterol and sphingolipid metabolism, and influencing cellular crosstalk in diverse neural injury conditions and neurodegenerative disorders. However, little is known about how an astrocyte functions in synapse formation, axon specification, neuroplasticity, neural homeostasis, neural network activity following dynamic surveillance, and CNS structure in neurological diseases. Interestingly, the tripartite synapse hypothesis came to light to fill some knowledge gaps that constitute an interaction of a subpopulation of astrocytes, neurons, and synapses. This review highlights astrocytes' role in health and neurological/neurodegenerative diseases arising from the omnidirectional signaling between astrocytes and neurons at the tripartite synapse. The review also recapitulates the disruption of the tripartite synapse with a focus on perturbations of the homeostatic astrocytic function as a key driver to modulate the molecular and physiological processes toward neurodegenerative diseases.

Occupational injuries and toxicant exposures lead to the development of neuroinflammation by activating distinct mechanistic signaling cascades that ultimately culminate in the disruption of neuronal function leading to neurological and neurodegenerative disorders. The entry of toxicants into the brain causes the subsequent activation of glial cells, a response known as 'reactive gliosis'. Reactive glial cells secrete a wide variety of signaling molecules in response to neuronal perturbations and thus play a crucial role in the progression and regulation of central nervous system (CNS) injury. In parallel, the roles of protein phosphorylation and cell signaling in eliciting neuroinflammation are evolving. However, there is limited understanding of the molecular underpinnings associated with toxicant- or occupational injury-mediated neuroinflammation, gliosis, and neurological outcomes. The activation of signaling molecules has biological significance, including the promotion or inhibition of disease mechanisms. Nevertheless, the regulatory mechanisms of synergism or antagonism among intracellular signaling pathways remain elusive. This review highlights the research focusing on the direct interaction between the immune system and the toxicant- or occupational injury-induced gliosis. Specifically, the role of occupational injuries, e.g., trips, slips, and falls resulting in traumatic brain injury, and occupational toxicants, e.g., volatile organic compounds, metals, and nanoparticles/nanomaterials in the development of neuroinflammation and neurological or neurodegenerative diseases are highlighted. Further, this review recapitulates the recent advancement related to the characterization of the molecular mechanisms comprising protein phosphorylation and cell signaling, culminating in neuroinflammation.

Glutathione is a remarkably functional molecule with diverse features, which include being an antioxidant, a regulator of DNA synthesis and repair, a protector of thiol groups in proteins, a stabilizer of cell membranes, and a detoxifier of xenobiotics. Glutathione exists in two states-oxidized and reduced. Under normal physiological conditions of cellular homeostasis, glutathione remains primarily in its reduced form. However, many metabolic pathways involve oxidization of glutathione, resulting in an imbalance in cellular homeostasis. Impairment of glutathione function in the brain is linked to loss of neurons during the aging process or as the result of neurological diseases such as Huntington's disease, Parkinson's disease, stroke, and Alzheimer's disease. The exact mechanisms through which glutathione regulates brain metabolism are not well understood. In this review, we will highlight the common signaling cascades that regulate glutathione in neurons and glia, its functions as a neuronal regulator in homeostasis and metabolism, and finally a mechanistic recapitulation of glutathione signaling. Together, these will put glutathione's role in normal aging and neurological disorders development into perspective.

Abnormally phosphorylated tau, an early neuropathologic marker of Alzheimer’s disease (AD), first occurs in the brain’s entorhinal cortex layer II (ECII) and then spreads to the CA1 field of the hippocampus. Animal models of tau propagation aiming to recapitulate this phenomenon mostly show tau transfer from ECII stellate neurons to the dentate gyrus, but tau pathology in the dentate gyrus does not appear until advanced stages of AD. Wolframin-1–expressing (Wfs1+) pyramidal neurons have been shown functionally to modulate hippocampal CA1 neurons in mice. Here, we report that Wfs1+ pyramidal neurons are conserved in the ECII of postmortem human brain tissue and that Wfs1 colocalized with abnormally phosphorylated tau in brains from individuals with early AD. Wfs1+ neuron–specific expression of human P301L mutant tau in mouse ECII resulted in transfer of tau to hippocampal CA1 pyramidal neurons, suggesting spread of tau pathology as observed in the early Braak stages of AD. In mice expressing human mutant tau specifically in the ECII brain region, electrophysiological recordings of CA1 pyramidal neurons showed reduced excitability. Multielectrode array recordings of optogenetically stimulated Wfs1+ ECII axons resulted in reduced CA1 neuronal firing. Chemogenetic activation of CA1 pyramidal neurons showed a reduction in c-fos+ cells in the CA1. Last, a fear conditioning task revealed deficits in trace and contextual memory in mice overexpressing human mutant tau in the ECII. This work demonstrates tau transfer from the ECII to CA1 in mouse brain and provides an early Braak stage preclinical model of AD.

AbstractBackgroundsTau‐containing extracellular vesicles (EVs) are transmissible and induce tau phosphorylation and conformational change in the recipient neurons. However, whether human brain‐derived EVs induce tau pathology has not yet been characterized in the mouse brain. Here, we assess the mechanisms of disease spread after intrahippocampal injection of human brain‐derived EVs into the aged mouse model.MethodsEV‐enriched fractions were isolated from unfixed frozen human brain samples from AD, prodromal AD (pAD), control (CTRL) cases, and tau knockout (TKO) mouse brains. Isolated EVs containing 300 pg of human total tau were sterotaxically injected into the right outer molecular layer of the dentate gyrus of 18 months‐old C57BL/6 female mice. 4.5 months after the injection, hippocampal slices were prepared for whole‐cell patch clamp recordings of CA1 pyramidal neurons were undertakent. Hippocampi were analyzed with immunohistochemistry using phosphorylated‐tau (p‐tau) epitopes including AT8. EVs were examined for protein composition by protein mass‐spectroscopy, the neuronal uptake in vitro, and structural analysis by the atomic force microscopy (AFM).ResultsSemiquantitative brain‐wide immunohistochemistry of p‐tau revealed that inoculation of AD or pAD‐EVs induced tau propagation throughout the hippocampus, including the dentate gyrus, CA3 and CA1 subregions. AT8 was localized primarily in GAD67+ GABAergic neurons in pAD and AD EVs groups, accompanied with reduced amplitude of inhibitory postsynaptic currents and Excitatory‐Inhibitory ratio in amplitube of postsynaptic currents in CA1 pyramidal neurons in pAD EVs. AFM analysis showed higher density of tau oligomers in both AD and pAD EVs while only AD EVs showed significantly higher neuronal uptake compared to CTRL EVs. Finally, proteomic analysis showed that AD EVs are enriched in disease and glia‐related molecules compared to CTRL EVs, which may contribute to their enhanced neuronal uptake.ConclusionsIntracranial injection of AD or pAD EVs induced p‐tau accumulation primarily in GABAergic neurons throughout the hippocampus, resulted in higher uptake by neurons, and tau oligomer conformation, indicating of their pathogenic potency as seeding factors. GABAergic neuronal dysfunction in the hippocampal neuronal circuitry reported in early AD brains could be attributed to specific EV mediated tau propagation in this cell type, a phenomenon meriting further investigation and validation.

AbstractBackgroundTau pathology correlates with cognitive impairment and is thought to propagate along neuroanatomical pathways. Tau accumulation is first observed in layer II of the entorhinal cortex (ECII), and then in CA1/2 of the hippocampus. The mechanism and nature of this propagation remains unclear and at present, no animal model recapitulates predominant tau propagation from ECII to CA1. Wolframin‐1‐immunoreactive (Wfs1+) neurons in the mouse ECII project to CA1 pyramidal neurons directly, or indirectly via interneurons in the S. lacunosum‐moleculare. We hypothesized that ECII Wfs1+ neurons mediate tau propagation to the CA1 pyramidal cells, making our model relevant for mimicking early stages of tau pathology in Alzheimer’s disease (AD).MethodTo specifically express mutant tau in Wfs1+ neurons, Wfs1‐Cre mice at 4‐6 months of age were injected with Cre‐inducible AAV2/6‐Flex‐P301Ltau expressing human P301L tau mutant or AAV2/6‐Flex‐Tdtomato in ECII, and euthanized at 4 weeks post‐injection for immunohistochemistry, electrophysiology and electron microscopy. To label and trace ECII‐CA1 connections, AAV9‐hSyn‐FLEX‐TVA‐P2A‐GFP‐2A‐oG and EnvA‐G‐deleted Rabies‐mCherry were injected into the CA1 pyramidal cells. The functional effects of tau on these connections were assessed by the multielectrode array to evaluate light‐evoked CA1 neuronal firing responses after the optogenetic stimulation of Wfs1+ ECII axons and also by measuring chemogenetic activation of CA1 pyramidal cells.ResultWfs1‐Cre mice injected in ECII with AAV2/6‐Flex‐P301Ltau exhibited significant human tau+ cells in the CA1 but not dentate gyrus at 4 weeks post‐injection. Monosynaptic tracing and electron microscopy revealed a direct synaptic connection between ECII Wfs1+ axons and CA1 pyramidal dendrites, and confirmed the presence of human tau in the pre‐ and post‐synaptic elements. Whole cell patch clamp recordings of CA1 pyramidal cells demonstrated reduction in measures of excitability. Optogenetic stimulation of Wfs1+ axons in the hippocampus coupled with multielectrode array‐recordings revealed a reduction in CA1 neuronal firing to light stimulation after AAV2/6‐Flex‐P301Ltau injection. Chemogenetic activation of CA1 neurons showed a reduction in c‐fos+ cells in CA1 after AAV2/6‐Flex‐P301Ltau injection compared to AAV2/6‐Flex‐Tdtomato controls.ConclusionExpression of P301Ltau in Wfs1+ neurons in the ECII induces the spread of human tau specifically to CA1 pyramidal neurons, which as a consequence exhibit several measures of neurophysiological impairment.

Functional recovery after cortical injury, such as stroke, is associated with neural circuit reorganization, but the underlying mechanisms and efficacy of therapeutic interventions promoting neural plasticity in primates are not well understood. Bone marrow mesenchymal stem cell-derived extracellular vesicles (MSC-EVs), which mediate cell-to-cell inflammatory and trophic signaling, are thought be viable therapeutic targets. We recently showed, in aged female rhesus monkeys, that systemic administration of MSC-EVs enhances recovery of function after injury of the primary motor cortex, likely through enhancing plasticity in perilesional motor and premotor cortices. Here, using in vitro whole-cell patch-clamp recording and intracellular filling in acute slices of ventral premotor cortex (vPMC) from rhesus monkeys (Macaca mulatta) of either sex, we demonstrate that MSC-EVs reduce injury-related physiological and morphologic changes in perilesional layer 3 pyramidal neurons. At 14-16 weeks after injury, vPMC neurons from both vehicle- and EV-treated lesioned monkeys exhibited significant hyperexcitability and predominance of inhibitory synaptic currents, compared with neurons from nonlesioned control brains. However, compared with vehicle-treated monkeys, neurons from EV-treated monkeys showed lower firing rates, greater spike frequency adaptation, and excitatory:inhibitory ratio. Further, EV treatment was associated with greater apical dendritic branching complexity, spine density, and inhibition, indicative of enhanced dendritic plasticity and filtering of signals integrated at the soma. Importantly, the degree of EV-mediated reduction of injury-related pathology in vPMC was significantly correlated with measures of behavioral recovery. These data show that EV treatment dampens injury-related hyperexcitability and restores excitatory:inhibitory balance in vPMC, thereby normalizing activity within cortical networks for motor function.SIGNIFICANCE STATEMENT Neuronal plasticity can facilitate recovery of function after cortical injury, but the underlying mechanisms and efficacy of therapeutic interventions promoting this plasticity in primates are not well understood. Our recent work has shown that intravenous infusions of mesenchymal-derived extracellular vesicles (EVs) that are involved in cell-to-cell inflammatory and trophic signaling can enhance recovery of motor function after injury in monkey primary motor cortex. This study shows that this EV-mediated enhancement of recovery is associated with amelioration of injury-related hyperexcitability and restoration of excitatory-inhibitory balance in perilesional ventral premotor cortex. These findings demonstrate the efficacy of mesenchymal EVs as a therapeutic to reduce injury-related pathologic changes in the physiology and structure of premotor pyramidal neurons and support recovery of function.

Extracellular vesicles are highly transmissible and play critical roles in the propagation of tau pathology, although the underlying mechanism remains elusive. Here, for the first time, we comprehensively characterized the physicochemical structure and pathogenic function of human brain-derived extracellular vesicles isolated from Alzheimer's disease, prodromal Alzheimer's disease, and non-demented control cases. Alzheimer's disease extracellular vesicles were significantly enriched in epitope-specific tau oligomers in comparison to prodromal Alzheimer's disease or control extracellular vesicles as determined by dot blot and atomic force microscopy. Alzheimer's disease extracellular vesicles were more efficiently internalized by murine cortical neurons, as well as more efficient in transferring and misfolding tau, than prodromal Alzheimer's disease and control extracellular vesicles in vitro. Strikingly, the inoculation of Alzheimer's disease or prodromal Alzheimer's disease extracellular vesicles containing only 300 pg of tau into the outer molecular layer of the dentate gyrus of 18-month-old C57BL/6 mice resulted in the accumulation of abnormally phosphorylated tau throughout the hippocampus by 4.5 months, whereas inoculation of an equal amount of tau from control extracellular vesicles, isolated tau oligomers, or fibrils from the same Alzheimer's disease donor showed little tau pathology. Furthermore, Alzheimer's disease extracellular vesicles induced misfolding of endogenous tau in both oligomeric and sarkosyl-insoluble forms in the hippocampal region. Unexpectedly, phosphorylated tau was primarily accumulated in glutamic acid decarboxylase 67 (GAD67) GABAergic interneurons and, to a lesser extent, glutamate receptor 2/3-positive excitatory mossy cells, showing preferential extracellular vesicle-mediated GABAergic interneuronal tau propagation. Whole-cell patch clamp recordings of CA1 pyramidal cells showed significant reduction in the amplitude of spontaneous inhibitory post-synaptic currents. This was accompanied by reductions in c-fos+ GAD67+ neurons and GAD67+ neuronal puncta surrounding pyramidal neurons in the CA1 region, confirming reduced GABAergic transmission in this region. Our study posits a novel mechanism for the spread of tau in hippocampal GABAergic interneurons via brain-derived extracellular vesicles and their subsequent neuronal dysfunction.

Extracellular vesicles (EVs) propagate tau pathology for Alzheimer’s disease (AD). How EV transmission influences AD are, nonetheless, poorly understood. To these ends, the physicochemical and molecular structure-function relationships of human brain-derived EVs, from AD and prodromal AD (pAD), were compared to non-demented controls (CTRL). AD EVs were shown to be significantly enriched in epitope-specific tau oligomers versus pAD or CTRL EVs assayed by dot-blot and atomic force microscopy tests. AD EVs were efficiently internalized by murine cortical neurons and transferred tau with higher aggregation potency than pAD and CTRL EVs. Strikingly, inoculation of tau-containing AD EVs into the outer molecular layer of the dentate gyrus induced tau propagation throughout the hippocampus. This was seen in 22 months-old C57BL/6 mice at 4.5 months post-injection by semiquantitative brain-wide immunohistochemistry tests with multiple anti-phospho-tau (p-tau) antibodies. Inoculation of the equal amount of tau from CTRL EVs or as oligomer or fibril-enriched fraction from the same AD donor showed little propagation. AD EVs induced tau accumulation in the hippocampus as oligomers or sarkosyl-insoluble proteins. Unexpectedly, p-tau cells were mostly GAD67 + GABAergic neurons and to a lesser extent, GluR2/3 + excitatory mossy cells, showing preferential EV-mediated GABAergic neuronal tau propagation. Whole-cell patch clamp recording of Cornu Ammonis (CA1) pyramidal cells showed significant reduction in the amplitude of spontaneous inhibitory post-synaptic currents. This was accompanied by reductions in c-fos + GAD67 + GABAergic neurons and GAD67 + GABAergic neuronal puncta surrounding pyramidal neurons in the CA1 region confirming reduced interneuronal projections. Our study posits a novel tau-associated pathological mechanism for brain-derived EVs.

In the BACHD mouse model of Huntington's disease (HD), deletion of the N17 domain of the Huntingtin gene (BACHDΔN17, Q97) has been reported to lead to nuclear accumulation of mHTT and exacerbation of motor deficits, neuroinflammation and striatal atrophy (Gu et al., 2015). Here we characterized the effect of N17 deletion on dorsolateral striatal medium spiny neurons (MSNs) in BACHDΔN17 (Q97) and BACWTΔN17 (Q31) mice by comparing them to MSNs in wildtype (WT) mice. Mice were characterized on a series of motor tasks and subsequently whole cell patch clamp recordings with simultaneous biocytin filling of MSNs in in vitro striatal slices from these mice were used to comprehensively assess their physiological and morphological features. Key findings include that: Q97 mice exhibit impaired gait and righting reflexes but normal tail suspension reflexes and normal coats while Q31 mice do not differ from WT; intrinsic membrane and action potential properties are altered -but differentially so- in MSNs from Q97 and from Q31 mice; excitatory and inhibitory synaptic currents exhibit higher amplitudes in Q31 but not Q97 MSNs, while excitatory synaptic currents occur at lower frequency in Q97 than in WT and Q31 MSNs; there is a reduced total dendritic length in Q31 -but not Q97- MSNs compared to WT, while spine density and number did not differ in MSNs in the three groups. The findings that Q31 MSNs differed from Q97 and WT neurons with regard to some physiological features and structurally suggest a novel role of the N17 domain in the function of WT Htt. The motor phenotype seen in Q97 mice was less robust than that reported in an earlier study (Gu et al., 2015), and the alterations to MSN physiological properties were largely consistent with changes reported previously in a number of other mouse models of HD. Together this study indicates that N17 plays a role in the modulation of the properties of MSNs in both mHtt and WT-Htt mice, but does not markedly exacerbate HD-like pathogenesis in the BACHD model.

We used voltage-clamp recordings from somatic outside-out macropatches to determine the amplitude and biophysical properties of putative Kv1-mediated currents in layer 5 pyramidal neurons (PNs) from mice expressing EGFP under the control of promoters for etv1 or glt. We then used whole cell current-clamp recordings and Kv1-specific peptide blockers to test the hypothesis that Kv1 channels differentially regulate action potential (AP) voltage threshold, repolarization rate, and width as well as rheobase and repetitive firing in these two PN types. We found that Kv1-mediated currents make up a similar percentage of whole cell K+ current in both cell types, and only minor biophysical differences were observed between PN types or between currents sensitive to different Kv1 blockers. Putative Kv1 currents contributed to AP voltage threshold in both PN types, but AP width and rate of repolarization were only affected in etv1 PNs. Kv1 currents regulate rheobase, delay to the first AP, and firing rate similarly in both cell types, but the frequency-current slope was much more sensitive to Kv1 block in etv1 PNs. In both cell types, Kv1 block shifted the current required to elicit an onset doublet of action potentials to lower currents. Spike frequency adaptation was also affected differently by Kv1 block in the two PN types. Thus, despite similar expression levels and minimal differences in biophysical properties, Kv1 channels differentially regulate APs and repetitive firing in etv1 and glt PNs. This may reflect differences in subcellular localization of channel subtypes or differences in the other K+ channels expressed. NEW & NOTEWORTHY In two types of genetically identified layer 5 pyramidal neurons, α-dendrotoxin blocked approximately all of the putative Kv1 current (on average). We used outside-out macropatches and whole cell recordings at 33°C to show that despite similar expression levels and minimal differences in biophysical properties, Kv1 channels differentially regulate action potentials and repetitive firing in etv1 and glt pyramidal neurons. This may reflect differences in subcellular localization of channel subtypes or differences in the other K+ channels expressed.

The paroxysmal depolarization shift (PDS) is a hallmark of epileptiform activities originating at cellular level.Given that the epileptiform activities are identical whether it is lower invertebrates or higher mammalian system, little is known about how the PDS generates, propagates, and terminates.Understanding the number, frequency, and timing of PDS can shed light on epileptiform research studies in details.Recent advances in K + channel research studies have witnessed that dysfunction in the repertoire of K + channel are widely implicated in numerous form of seizures.To understand the complexity of K + Channel and their roles in higher mammals, it is often necessary to explore the central nervous system of the simple invertebrate model system like leech Retzius nerve cells which is meant to exhibit lesser diversity in terms of K + channel populations.The present review highlights the non-synaptic nature of PDS arising from the suppression of the functions of Calcium-activated K + channel as a consequence of blockade of voltage-gated calcium channel, and unmasking the persistent sodium current leading to Na + -dependent PDS in the leech Retzius nerve cells.

The action potential (AP) is a fundamental feature of excitable cells that serves as the basis for long-distance signaling in the nervous system. There is considerable diversity in the appearance of APs and the underlying repolarization mechanisms in different neuronal types (reviewed in Bean BP. Nat Rev Neurosci 8: 451-465, 2007), including among pyramidal cell subtypes. In the present work, we used specific pharmacological blockers to test for contributions of K(v)1, K(v)2, or K(v)4 channels to repolarization of single APs in two genetically defined subpopulations of pyramidal cells in layer 5 of mouse somatosensory cortex (etv1 and glt) as well as pyramidal cells from layer 2/3. These three subtypes differ in AP properties (Groh A, Meyer HS, Schmidt EF, Heintz N, Sakmann B, Krieger P. Cereb Cortex 20: 826-836, 2010; Guan D, Armstrong WE, Foehring RC. J Neurophysiol 113: 2014-2032, 2015) as well as laminar position, morphology, and projection targets. We asked what the roles of K(v)1, K(v)2, and K(v)4 channels are in AP repolarization and whether the underlying mechanisms are pyramidal cell subtype dependent. We found that K(v)4 channels are critically involved in repolarizing neocortical pyramidal cells. There are also pyramidal cell subtype-specific differences in the role for K(v)1 channels. Only K(v)4 channels were involved in repolarizing the narrow APs of glt cells. In contrast, in etv1 cells and layer 2/3 cells, the broader APs are partially repolarized by K(v)1 channels in addition to K(v)4 channels. Consistent with their activation in the subthreshold range, K(v)1 channels also regulate AP voltage threshold in all pyramidal cell subtypes.

The effects of Mg2+ on Ni(2+)-induced epileptiform bursting activity and input membrane resistance during this activity of leech Retzius neurons were examined using intracellular recordings. To induce epileptiform activity, 3 mmol/l NiCl2 was added into superfusing Ringer (Ri) saline. To test for dose-dependence of the effects of Mg2+ on the induced epileptiform activity, MgCl2 was added in concentrations from 1 mmol/l to 20 mmol/l Mg2+ to the Ni(2+)-containing Ri saline. Input membrane resistance (IMR) was measured in standard Ri, Ni2+ Ri and 20 mmol/l Mg2+Ni2+ Ri saline. Superfusion with Ni2+ Ri induced epileptiform bursting activity characterized by generation of paroxysmal depolarization shifts (PDSs). Parameters of epileptiform activity including PDS frequency, PDS duration, PDS amplitude and the number of spikes/PDS were measured. Magnesium suppressed Ni(2+)-induced epileptiform activity, significantly reducing values of all parameters observed in a concentration-dependent manner. The highest concentration applied of 20 mmol/l Mg2+ completely eliminated epileptiform activity. To test for the effect of Mg2+ on membrane conductance during bursting, IMR was measured. Magnesium significantly increased IMR during bursting suppression.

The amino acid beta-N-methylamino-L-alanine (L-BMAA) has been associated with the amyotrophic lateral sclerosis/parkinsonism-dementia complex in three distinct western Pacific populations. The putative neurotoxin is produced by cyanobacteria, which live symbiotically in the roots of cycad trees. L-BMAA was thought to be a threat only to those few populations whose diet and medicines rely heavily on cycad seeds. However, the recent discovery that cyanobacteria from diverse terrestrial, freshwater, and saltwater ecosystems around the world produce the toxin requires a reassessment of whether it poses a larger health threat. Therefore, it is proposed that monitoring L-BMAA levels in cyanobacteria-contaminated water supplies might be prudent.