Exosomes, key mediators of intercellular transmission of pathogenic proteins, such as amyloid-beta and tau, significantly influence the progression and exacerbation of Alzheimer\'s disease (AD) pathology. Present in a variety of biological fluids, including cerebrospinal fluid, blood, saliva, and nasal lavage fluid (NLF), exosomes underscore their potential as integral mediators of AD pathology. By serving as vehicles for disease-specific molecules, exosomes could unveil valuable insights into disease identification and progression. This study emphasizes the imperative to investigate the impacts of exosomes on neural networks to enhance our comprehension of intracerebral neuronal communication and its implications for neurological disorders like AD. After harvesting exosomes derived from NLF of 5XFAD mice, we utilized a high-density multielectrode array (HD-MEA) system, the novel technology enabling concurrent recordings from thousands of neurons in primary cortical neuron cultures and organotypic hippocampal slices. The ensuing results revealed a surge in neuronal firing rates and disoriented neural connectivity, reflecting the effects provoked by pathological amyloid-beta oligomer treatment. The local field potentials in the exosome-treated hippocampal brain slices also exhibited aberrant rhythmicity, along with an elevated level of current source density. While this research is an initial exploration, it highlights the potential of exosomes in modulating neural networks under AD conditions and endorses the HD-MEA as an efficacious tool for exosome studies.

Two subtypes of group I metabotropic glutamate receptors (mGluRs), mGluR1 and mGluR5, participate in the regulation of cell excitability and synaptic plasticity in the central nervous system. They couple to the Gq/11 protein and release Ca2+ from the intracellular stores. In the marginal zone of the neonatal hippocampus, Cajal-Retzius (CR) cells, which control radial migration of neurons, express the subtype mGluR1. The adenosine A1 receptor (A1R) is also G-protein coupled and is extensively expressed in the central nervous system. The interactions among G-protein-coupled receptors have been predicted previously, however, there is insufficient evidence of functional interactions between naturally occurring receptors. In this study, potentiation of the mGluR1-mediated response by A1R activation was demonstrated in hippocampal CR cells. Fluorescence imaging revealed that the application of A1R agonists intensified mGluR1-induced elevation of intracellular Ca2+ concentration ([Ca2+]i). Activation of A1R did not change [Ca2+]i. The potentiated responses were independent of extracellular Ca2+ and prevented by the Gi inhibitor. The potentiation of mGluR1-induced [Ca2+]i. elevation was also enhanced by mGluR2/3 activation. These results suggest that mGluR1 and A1R cooperatively influence postnatal hippocampal development by facilitating Ca2+ mobilization in CR cells.

We present a novel closed-loop system designed to integrate biological and artificial neurons of the oscillatory type into a unified circuit. The system comprises an electronic circuit based on the FitzHugh-Nagumo model, which provides stimulation to living neurons in acute hippocampal mouse brain slices. The local field potentials generated by the living neurons trigger a transition in the FitzHugh-Nagumo circuit from an excitable state to an oscillatory mode, and in turn, the spikes produced by the electronic circuit synchronize with the living-neuron spikes. The key advantage of this hybrid electrobiological autogenerator lies in its capability to control biological neuron signals, which holds significant promise for diverse neuromorphic applications.

Zn2+ is an important contributor to ischemic brain injury, and recent studies support the hypothesis that mitochondria are key sites of its injurious effects. In murine hippocampal slices (both sexes) subjected to oxygen glucose deprivation (OGD), we found that Zn2+ accumulation and its entry into mitochondria precedes and contributes to the induction of acute neuronal death. In addition, if the ischemic episode is short (and sublethal), there is ongoing Zn2+ accumulation in CA1 mitochondria after OGD that may contribute to their delayed dysfunction. Using this slice model of sublethal OGD, we have examined Zn2+ contributions to the progression of changes evoked by OGD and occurring over 4-5 h. We detected progressive mitochondrial depolarization occurring from ∼2 h after ischemia, a large increase in spontaneous synaptic activity between 2 and 3 h, and mitochondrial swelling and fragmentation at 4 h. Blockade of the primary route for Zn2+ entry, the mitochondrial Ca2+ uniporter (with ruthenium red [RR]) or Zn2+ chelation shortly after OGD withdrawal substantially attenuated the mitochondrial depolarization and the changes in synaptic activity. RR also largely reversed the mitochondrial swelling. Finally, using an in vivo rat (male) asphyxial cardiac arrest model of transient global ischemia, we found that ∼8 min asphyxia induces considerable injury of CA1 neurons 4 h later that is associated with strong Zn2+ accumulation within many damaged mitochondria. These effects were substantially attenuated by infusion of RR on reperfusion. Our findings highlight mitochondrial Zn2+ accumulation after ischemia as a possible target for neuroprotective therapy.SIGNIFICANCE STATEMENT Brain ischemia is a leading cause of mortality and long-term disability that still lacks effective treatment. After transient ischemia, delayed death of neurons occurs in vulnerable brain regions. There is a critical need to understand mechanisms of this delayed neurodegeneration which can be targeted for neuroprotection. We found progressive and long-lasting mitochondrial Zn2+ accumulation to occur in highly vulnerable CA1 neurons after ischemia. Here we demonstrate that this Zn2+ accumulation contributes strongly to deleterious events occurring after ischemia, including mitochondrial dysfunction, swelling, and structural changes. We suggest that this mitochondrial Zn2+ entry may constitute a promising target for development of therapeutic interventions to be delivered after termination of an episode of transient global ischemia.

Cordycepin (known as 3-deoxyadenosine, CRD), a natural product from the valuable traditional Chinese medicine Cordyceps militaris, has been reported to improve cognitive function and modulate neuroprotective effects on the central nervous system (CNS). However, the modulating mechanisms of cordycepin on information processing in hippocampal CA1 pyramidal neurons are not fully understood. To clarify how cordycepin modulates synaptic responses of pyramidal neurons in rat hippocampal CA1 region, we conducted an electrophysiological experiment using whole-cell patch-clamp technique. The spontaneous and miniature excitatory postsynaptic currents (sEPSCs and mEPSCs, respectively) and the spontaneous and miniature inhibitory postsynaptic currents (sIPSCs and mIPSCs, respectively) recorded by this technique evaluated pure single or multi-synapse responses and enabled us to accurately quantify how cordycepin influenced the pre and postsynaptic aspects of synaptic transmission. The present results showed that cordycepin significantly decreased the frequency of both glutamatergic and GABAergic postsynaptic currents without affecting the amplitude, while these inhibitory effects were antagonized by the A1 adenosine receptor antagonist (DPCPX), but not the A2A (ZM 241385), A2B (MRS1754) and A3 (MRS1191) adenosine receptor antagonists. Taken together, our results suggested that cordycepin had a clear presynaptic effect on glutamatergic and GABAergic transmission, and provided novel evidence that cordycepin suppresses the synaptic transmission through the activation of A1AR.

Previously, we reported that prenatal exposure to 1-bromopropane (1-BP) causes the accumulation of bromide (Br-) in the brain of rat pups. Here, we aimed to investigate the effects of Br- accumulation in rat pups prenatally exposed to 1-BP vapor. Dam rats were exposed to 1-BP (400 or 700 ppm; 1-BP group) by inhalation, or to NaBr (20 mM; Br- group) in drinking water during gestation days 1-20. We also analyzed pentylenetetrazole (PTZ, 60 mg/kg, ip)-induced behavioral changes in pups prenatally exposed to 1-BP or Br- on postnatal day (PND) 14. PTZ-induced epileptic convulsions were inhibited in both 1-BP (700 ppm) and Br- groups. The inhibition of neuronal excitability induced by Br- was evaluated electrophysiologically using the hippocampal slices obtained from PND14-16 pups. PTZ (2 mM) failed to induce epileptiform discharge in the presence of 1.2 mM Br- in the slices obtained from the control group. However, it induced epileptiform discharge following the removal of Br-, by perfusing artificial cerebrospinal fluid into the slices obtained from the Br- group. Our results indicate that Br- accumulates in the brain of neonatal rat pups prenatally exposed to 1-BP vapor suppressed neuronal excitability.

Persistent acidosis occurs in ischemia and multiple neurological diseases. In previous studies, acidic stimulation leads to rapid increase in intracellular calcium in neurons. However, it remains largely unclear how a prolonged acidosis alters neuronal signaling. In our previous study, we found that GPR68-mediated PKC activities are protective against acidosis-induced injury in cortical slices. Here, we first asked whether the same principle holds true in organotypic hippocampal slices. Our data showed that 1-h pH 6 induced PKC phosphorylation in a GPR68-dependent manner. Go6983, a PKC inhibitor worsened acidosis-induced neuronal injury in wild type (WT) but had no effect in GPR68-/- slices. Next, to gain greater insights into acid signaling in brain tissue, we treated organotypic hippocampal slices with pH 6 for 1-h and performed a kinome profiling analysis by Western blot. Acidosis had little effect on cyclin-dependent kinase (CDK) or casein kinase 2 activity, two members of the CMGC family, or Ataxia telangiectasia mutated (ATM)/ATM and RAD3-related (ATR) activity, but reduced the phosphorylation of MAPK/CDK substrates. In contrast, acidosis induced the activation of CaMKIIα, PKA, and Akt. Besides these serine/threonine kinases, acidosis also induced tyrosine phosphorylation. Since GPR68 is widely expressed in brain neurons, we asked whether GPR68 contributes to acidosis-induced signaling. Deleting GPR68 had no effect on acidosis-induced CaMKII phosphorylation, attenuated that of phospho-Akt and phospho-PKA substrates, while abolishing acidosis-induced tyrosine phosphorylation. These data demonstrate that prolonged acidosis activates a network of signaling cascades, mediated by AGC kinases, CaMKII, and tyrosine kinases. GPR68 is the primary mediator for acidosis-induced activation of PKC and tyrosine phosphorylation, while both GPR68-dependent and -independent mechanisms contribute to the activation of PKA and Akt.

Alzheimer\'s disease (AD) is the most common cause of dementia in the aging population. Evidence implicates elevated soluble oligomeric Aβ as one of the primary triggers during the prodromic phase leading to AD, effected largely via hyperphosphorylation of the microtubule-associated protein tau. At low, physiological levels (pM-nM), however, oligomeric Aβ has been found to regulate synaptic plasticity as a neuromodulator. Through mutational analysis, we found a core hexapeptide sequence within the N-terminal domain of Aβ (N-Aβcore) accounting for its physiological activity, and subsequently found that the N-Aβcore peptide is neuroprotective. Here, we characterized the neuroprotective potential of the N-Aβcore against dysfunction of synaptic plasticity assessed in ex vivo hippocampal slices from 5xFAD APP/PS1 mice, specifically hippocampal long-term potentiation (LTP) and long-term depression (LTD). The N-Aβcore was shown to reverse impairment in synaptic plasticity in hippocampal slices from 5xFAD APP/PS1 model mice, both for LTP and LTD. The reversal by the N-Aβcore correlated with alleviation of downregulation of hippocampal AMPA-type glutamate receptors in preparations from 5xFAD mice. The action of the N-Aβcore depended upon a critical di-histidine sequence and involved the phosphoinositide-3 (PI3) kinase pathway via mTOR (mammalian target of rapamycin). Together, the present findings indicate that the non-toxic N-Aβcore hexapeptide is not only neuroprotective at the cellular level but is able to reverse synaptic dysfunction in AD-like models, specifically alterations in synaptic plasticity.

Excitotoxic Ca2+ accumulation contributes to ischemic neurodegeneration, and Ca2+ can enter the mitochondria through the mitochondrial calcium uniporter (MCU) to promote mitochondrial dysfunction. Yet, Ca2+-targeted therapies have met limited success. A growing body of evidence has highlighted the underappreciated importance of Zn2+, which also accumulates in neurons after ischemia and can induce mitochondrial dysfunction and cell death. While studies have indicated that Zn2+ can also enter the mitochondria through the MCU, the specificity of the pore\'s role in Zn2+-triggered injury is still debated. Present studies use recently available MCU knockout mice to examine how the deletion of this channel impacts deleterious effects of cytosolic Zn2+ loading. In cultured cortical neurons from MCU knockout mice, we find significantly reduced mitochondrial Zn2+ accumulation. Correspondingly, these neurons were protected from both acute and delayed Zn2+-triggered mitochondrial dysfunction, including mitochondrial reactive oxygen species generation, depolarization, swelling and inhibition of respiration. Furthermore, when toxic extramitochondrial effects of Ca2+ entry were moderated, both cultured neurons (exposed to Zn2+) and CA1 neurons of hippocampal slices (subjected to prolonged oxygen glucose deprivation to model ischemia) from MCU knockout mice displayed decreased neurodegeneration. Finally, to examine the therapeutic applicability of these findings, we added an MCU blocker after toxic Zn2+ exposure in wildtype neurons (to induce post-insult MCU blockade). This significantly attenuated the delayed evolution of both mitochondrial dysfunction and neurotoxicity. These data-combining both genetic and pharmacologic tools-support the hypothesis that Zn2+ entry through the MCU is a critical contributor to ischemic neurodegeneration that could be targeted for neuroprotection.

Fragile X syndrome (FXS) is caused by silencing of the FMR1 gene and consequent absence of its protein product, fragile X mental retardation protein (FMRP). FMRP is an RNA-binding protein that can suppress translation. The absence of FMRP leads to symptoms of FXS including intellectual disability and has been proposed to lead to abnormalities in synaptic plasticity. Synaptic plasticity, protein synthesis, and cellular growth pathways have been studied extensively in hippocampal slices from a mouse model of FXS (Fmr1 KO). Enhanced metabotropic glutamate receptor 5 (mGluR5)-dependent long-term depression (LTD), increased rates of protein synthesis, and effects on signaling molecules have been reported. These phenotypes were found under amino acid starvation, a condition that has widespread, powerful effects on activation and translation of proteins involved in regulating protein synthesis. We asked if this non-physiological condition could have effects on Fmr1 KO phenotypes reported in hippocampal slices. We performed hippocampal slice experiments in the presence and absence of amino acids. We measured rates of incorporation of a radiolabeled amino acid into protein to determine protein synthesis rates. By means of western blots, we assessed relative levels of total and phosphorylated forms of proteins involved in signaling pathways regulating translation. We measured evoked field potentials in area CA1 to assess the strength of the long-term depression response to mGluR activation. In the absence of amino acids, we replicate many of the reported findings in Fmr1 KO hippocampal slices, but in the more physiological condition of inclusion of amino acids in the medium, we did not find evidence of enhanced mGluR5-dependent LTD. Activation of mGluR5 increased protein synthesis in both wild type and Fmr1 KO. Moreover, mGluR5 activation increased eIF2α phosphorylation and decreased phosphorylation of p70S6k in slices from Fmr1 KO. We propose that the eIF2α response is a cellular attempt to compensate for the lack of regulation of translation by FMRP. Our findings call for a re-examination of the mGluR theory of FXS.