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Frontiers in Cellular Neuroscience 2024Insulin-like growth factor-1 (IGF-1) is a polypeptide hormone with a ubiquitous distribution in numerous tissues and with various functions in both neuronal and...
Insulin-like growth factor-1 (IGF-1) is a polypeptide hormone with a ubiquitous distribution in numerous tissues and with various functions in both neuronal and non-neuronal cells. IGF-1 provides trophic support for many neurons of both the central and peripheral nervous systems. In the central nervous system (CNS), IGF-1R signaling regulates brain development, increases neuronal firing and modulates synaptic transmission. IGF-1 and IGF-IR are not only expressed in CNS neurons but also in sensory dorsal root ganglion (DRG) nociceptive neurons that convey pain signals. DRG nociceptive neurons express a variety of receptors and ion channels that are essential players of neuronal excitability, notably the ligand-gated cation channel TRPV1 and the voltage-gated M-type K channel, which, respectively, triggers and dampens sensory neuron excitability. Although many lines of evidence suggest that IGF-IR signaling contributes to pain sensitivity, its possible modulation of TRPV1 and M-type K channel remains largely unexplored. In this study, we examined the impact of IGF-1R signaling on DRG neuron excitability and its modulation of TRPV1 and M-type K channel activities in cultured rat DRG neurons. Acute application of IGF-1 to DRG neurons triggered hyper-excitability by inducing spontaneous firing or by increasing the frequency of spikes evoked by depolarizing current injection. These effects were prevented by the IGF-1R antagonist NVP-AEW541 and by the PI3Kinase blocker wortmannin. Surprisingly, acute exposure to IGF-1 profoundly inhibited both the TRPV1 current and the spike burst evoked by capsaicin. The Src kinase inhibitor PP2 potently depressed the capsaicin-evoked spike burst but did not alter the IGF-1 inhibition of the hyperexcitability triggered by capsaicin. Chronic IGF-1 treatment (24 h) reduced the spike firing evoked by depolarizing current injection and upregulated the M-current density. In contrast, chronic IGF-1 markedly increased the spike burst evoked by capsaicin. In all, our data suggest that IGF-1 exerts complex effects on DRG neuron excitability as revealed by its dual and opposite actions upon acute and chronic exposures.
PubMed: 38919332
DOI: 10.3389/fncel.2024.1391858 -
Neurochemical Research Jun 2024Neuropsychiatric and neurological disorders pose a significant global health burden, highlighting the need for innovative therapeutic approaches. Fingolimod (FTY720), a... (Review)
Review
Neuropsychiatric and neurological disorders pose a significant global health burden, highlighting the need for innovative therapeutic approaches. Fingolimod (FTY720), a common drug to treat multiple sclerosis, has shown promising efficacy against various neuropsychiatric and neurological disorders. Fingolimod exerts its neuroprotective effects by targeting multiple cellular and molecular processes, such as apoptosis, oxidative stress, neuroinflammation, and autophagy. By modulating Sphingosine-1-Phosphate Receptor activity, a key regulator of immune cell trafficking and neuronal function, it also affects synaptic activity and strengthens memory formation. In the hippocampus, fingolimod decreases glutamate levels and increases GABA levels, suggesting a potential role in modulating synaptic transmission and neuronal excitability. Taken together, fingolimod has emerged as a promising neuroprotective agent for neuropsychiatric and neurological disorders. Its broad spectrum of cellular and molecular effects, including the modulation of apoptosis, oxidative stress, neuroinflammation, autophagy, and synaptic plasticity, provides a comprehensive therapeutic approach for these debilitating conditions. Further research is warranted to fully elucidate the mechanisms of action of fingolimod and optimize its use in the treatment of neuropsychiatric and neurological disorders.
PubMed: 38918332
DOI: 10.1007/s11064-024-04199-5 -
Fluorescence lifetime imaging of AMPA receptor endocytosis in living neurons: effects of Aβ and PP1.Frontiers in Molecular Neuroscience 2024The relative amount of AMPA receptors expressed at the surface of neurons can be measured using superecliptic pHluorin (SEP) labeling at their N-terminus. However, the...
The relative amount of AMPA receptors expressed at the surface of neurons can be measured using superecliptic pHluorin (SEP) labeling at their N-terminus. However, the high signal variability resulting from protein overexpression in neurons and the low signal observed in intracellular vesicles make quantitative characterization of receptor trafficking difficult. Here, we establish a real-time live-cell assay of AMPAR trafficking based on fluorescence lifetime imaging (FLIM), which allows for simultaneous visualization of both surface and intracellular receptors. Using this assay, we found that elevating amyloid-beta (Aβ) levels leads to a strong increase in intracellular GluA1 and GluA2-containing receptors, indicating that Aβ triggers the endocytosis of these AMPARs. In APP/PS1 Alzheimer's disease model mouse neurons, FLIM revealed strikingly different AMPAR trafficking properties for GluA1- and GluA3-containing receptors, suggesting that chronic Aβ exposure triggered the loss of both surface and intracellular GluA3-containing receptors. Interestingly, overexpression of protein phosphatase 1 (PP1) also resulted in GluA1 endocytosis as well as depressed synaptic transmission, confirming the important role of phosphorylation in regulating AMPAR trafficking. This new approach allows for the quantitative measurement of extracellular pH, small changes in receptor trafficking, as well as simultaneous measurement of surface and internalized AMPARs in living neurons, and could therefore be applied to several different studies in the future.
PubMed: 38915938
DOI: 10.3389/fnmol.2024.1409401 -
BioRxiv : the Preprint Server For... Jun 2024Prosapip1 is a brain-specific protein localized to the postsynaptic density, where it promotes dendritic spine maturation in primary hippocampal neurons. However,...
Prosapip1 is a brain-specific protein localized to the postsynaptic density, where it promotes dendritic spine maturation in primary hippocampal neurons. However, nothing is known about the role of Prosapip1 . To examine this, we utilized the Cre-loxP system to develop a Prosapip1 neuronal knockout mouse. We found that Prosapip1 controls the synaptic localization of its binding partner SPAR, along with PSD-95 and the GluN2B subunit of the NMDA receptor (NMDAR) in the dorsal hippocampus (dHP). We next sought to identify the potential contribution of Prosapip1 to the activity and function of the NMDAR and found that Prosapip1 plays an important role in NMDAR-mediated transmission and long-term potentiation (LTP) in the CA1 region of the dHP. As LTP is the cellular hallmark of learning and memory, we examined the consequences of neuronal knockout of Prosapip1 on dHP-dependent memory. We found that global or dHP-specific neuronal knockout of Prosapip1 caused a deficit in learning and memory whereas developmental, locomotor, and anxiety phenotypes were normal. Taken together, Prosapip1 in the dHP promotes the proper localization of synaptic proteins which, in turn, facilitates LTP driving recognition, social, and spatial learning and memory.
PubMed: 38915579
DOI: 10.1101/2024.06.13.597459 -
BioRxiv : the Preprint Server For... Jun 2024Dependence is a hallmark of alcohol use disorder characterized by excessive alcohol intake and withdrawal symptoms. The central nucleus of the amygdala (CeA) is a key...
Dependence is a hallmark of alcohol use disorder characterized by excessive alcohol intake and withdrawal symptoms. The central nucleus of the amygdala (CeA) is a key brain structure underlying the synaptic and behavioral consequences of ethanol dependence. While accumulating evidence suggests that astrocytes regulate synaptic transmission and behavior, there is a limited understanding of the role astrocytes play in ethanol dependence. The present study used a combination of viral labeling, super resolution confocal microscopy, 3D image analysis, and slice electrophysiology to determine the effects of chronic intermittent ethanol (CIE) exposure on astrocyte plasticity in the CeA. During withdrawal from CIE exposure, we observed increased GABA transmission, an upregulation in astrocytic GAT3 levels, and an increased proximity of astrocyte processes near CeA synapses. Furthermore, GAT3 levels and synaptic proximity were positively associated with voluntary ethanol drinking in dependent rats. Slice electrophysiology confirmed that the upregulation in astrocytic GAT3 levels was functional, as CIE exposure unmasked a GAT3-sensitive tonic GABA current in the CeA. A causal role for astrocytic GAT3 in ethanol dependence was assessed using viral-mediated GAT3 overexpression and knockdown approaches. However, GAT3 knockdown or overexpression had no effect on somatic withdrawal symptoms, dependence-escalated ethanol intake, aversion-resistant drinking, or post-dependent ethanol drinking in male or female rats. Moreover, intra-CeA pharmacological inhibition of GAT3 also did not alter dependent ethanol drinking. Together, these findings indicate that ethanol dependence induces GABAergic dysregulation and astrocyte plasticity in the CeA. However, astrocytic GAT3 does not appear necessary for the drinking related phenotypes associated with dependence.
PubMed: 38915577
DOI: 10.1101/2024.06.11.598470 -
Acta Pharmacologica Sinica Jun 2024Methamphetamine (METH), an abused psychostimulant, impairs cognition through prolonged or even single-dose exposure, but animal experiments have shown contradictory...
Methamphetamine (METH), an abused psychostimulant, impairs cognition through prolonged or even single-dose exposure, but animal experiments have shown contradictory effects on memory deficits. In this study we investigated the effects and underlying mechanisms of single-dose METH administration on the retrieval of object recognition memory (ORM) in mice. We showed that single-dose METH administration (2 mg/kg, i.p.) significantly impaired ORM retrieval in mice. Fiber photometry recording in METH-treated mice revealed that the activity of prelimbic cortex glutamatergic neurons (PrL) was significantly reduced during ORM retrieval. Chemogenetic activation of PrL or glutamatergic projections from ventral CA1 to PrL (vCA1-PrL) rescued ORM retrieval impairment. Fiber photometry recording revealed that dopamine (DA) levels in PrL of METH-treated mice were significantly increased, and micro-infusion of the D2 receptor (D2R) antagonist sulpiride (0.25 μg/side) into PrL rescued ORM retrieval impairment. Whole-cell recordings in brain slices containing the PrL revealed that PrL intrinsic excitability and basal glutamatergic synaptic transmission were significantly reduced in METH-treated mice, and the decrease in intrinsic excitability was reversed by micro-infusion of Sulpiride into PrL in METH-treated mice. Thus, the impaired ORM retrieval caused by single-dose METH administration may be attributed to reduced PrL activity, possibly due to excessive DA activity on D2R. Selective activation of PrL or vCA1-PrL may serve as a potential therapeutic strategy for METH-induced cognitive dysfunction.
PubMed: 38914676
DOI: 10.1038/s41401-024-01321-9 -
Neuroscience Letters Jun 2024To investigate the precise mechanism of xenon (Xe), pharmacologically isolated AMPA/KA and NMDA receptor-mediated spontaneous (s) and evoked (e) excitatory postsynaptic...
To investigate the precise mechanism of xenon (Xe), pharmacologically isolated AMPA/KA and NMDA receptor-mediated spontaneous (s) and evoked (e) excitatory postsynaptic currents (s/eEPSC and s/eEPSC) were recorded from mechanically isolated single spinal sacral dorsal commissural nucleus (SDCN) neurons attached with glutamatergic nerve endings (boutons) using conventional whole-cell patch-clamp technique. We analysed kinetic properties of both s/eEPSC and s/eEPSC by focal single- and/or paired-pulse electrical stimulation to compare them. The s/eEPSC showed smaller amplitude, slower rise time, and slower 1/e decay time constant (τ) than those of s/eEPSC. We previously examined how Xe modulates s/eEPSC, therefore, examined the effects on s/eEPSC in the present study. Xe decreased the frequency and amplitude of sEPSC, and decreased the amplitude but increased the failure rate and paired-pulse ratio of eEPSC without affecting their τ. It was concluded that Xe might suppress NMDA receptor-mediated synaptic transmission via both presynaptic and postsynaptic mechanisms.
PubMed: 38914276
DOI: 10.1016/j.neulet.2024.137885 -
Journal of Visualized Experiments : JoVE Jun 2024Retinal organoids (ROs) are a three-dimensional culture system mimicking human retinal features that have differentiated from induced pluripotent stem cells (iPSCs)...
Retinal organoids (ROs) are a three-dimensional culture system mimicking human retinal features that have differentiated from induced pluripotent stem cells (iPSCs) under specific conditions. Synapse development and maturation in ROs have been studied immunocytochemically and functionally. However, the direct evidence of the synaptic contact ultrastructure is limited, containing both special ribbon synapses and conventional chemical synapses. Transmission electron microscopy (TEM) is characterized by high resolution and a respectable history elucidating retinal development and synapse maturation in humans and various species. It is a powerful tool to explore synaptic structure in ROs and is widely used in the research field of ROs. Therefore, to better explore the structure of RO synaptic contacts at the nanoscale and obtain high-quality microscopic evidence, we developed a simple and repeatable method of RO TEM sample preparation. This paper describes the protocol, reagents used, and detailed steps, including RO fixation preparation, post fixation, embedding, and visualization.
Topics: Organoids; Retina; Microscopy, Electron, Transmission; Humans; Induced Pluripotent Stem Cells; Animals; Synapses
PubMed: 38912821
DOI: 10.3791/66590 -
Frontiers in Immunology 2024Secondary progressive multiple sclerosis (SPMS) is defined by the irreversible accumulation of disability following a relapsing-remitting MS (RRMS) course. Despite...
BACKGROUND
Secondary progressive multiple sclerosis (SPMS) is defined by the irreversible accumulation of disability following a relapsing-remitting MS (RRMS) course. Despite treatments advances, a reliable tool able to capture the transition from RRMS to SPMS is lacking. A T cell chimeric MS model demonstrated that T cells derived from relapsing patients exacerbate excitatory transmission of central neurons, a synaptotoxic event absent during remitting stages. We hypothesized the re-emergence of T cell synaptotoxicity during SPMS and investigated the synaptoprotective effects of siponimod, a sphingosine 1-phosphate receptor (S1PR) modulator, known to reduce grey matter damage in SPMS patients.
METHODS
Data from healthy controls (HC), SPMS patients, and siponimod-treated SPMS patients were collected. Chimeric experiments were performed incubating human T cells on murine cortico-striatal slices, and recording spontaneous glutamatergic activity from striatal neurons. Homologous chimeric experiments were executed incubating EAE mice T cells with siponimod and specific S1PR agonists or antagonists to identify the receptor involved in siponimod-mediated synaptic recovery.
RESULTS
SPMS patient-derived T cells significantly increased the striatal excitatory synaptic transmission (n=40 synapses) compared to HC T cells (n=55 synapses), mimicking the glutamatergic alterations observed in active RRMS-T cells. Siponimod treatment rescued SPMS T cells synaptotoxicity (n=51 synapses). Homologous chimeric experiments highlighted S1P5R involvement in the siponimod's protective effects.
CONCLUSION
Transition from RRMS to SPMS involves the reappearance of T cell-mediated synaptotoxicity. Siponimod counteracts T cell-induced excitotoxicity, emphasizing the significance of inflammatory synaptopathy in progressive MS and its potential as a promising pharmacological target.
Topics: Humans; Animals; Mice; Female; Multiple Sclerosis, Chronic Progressive; T-Lymphocytes; Azetidines; Benzyl Compounds; Male; Adult; Synapses; Middle Aged; Encephalomyelitis, Autoimmune, Experimental; Sphingosine 1 Phosphate Receptor Modulators; Mice, Inbred C57BL; Sphingosine-1-Phosphate Receptors; Synaptic Transmission; Neurons
PubMed: 38911847
DOI: 10.3389/fimmu.2024.1416133 -
Frontiers in Genetics 2024Visna/Maedi virus (VMV) is lentiviral disease of sheep responsible for severe production losses. Multiple genomic regions associated with infection were reported...
Visna/Maedi virus (VMV) is lentiviral disease of sheep responsible for severe production losses. Multiple genomic regions associated with infection were reported indicating genetic complexity. In this study, a combined genome-wide approach using a high-density SNP array has been performed, comparing VMV-infected ( = 78) and non-infected ( = 66) individuals of the Valle del Belice breed. The serological tests showed a seroprevalence of 26%. The comparison among results from different approaches (GWAS, Fisher's exact test and the F analysis) revealed two association signals: on OAR03 close to the gene and on OAR05 close to the gene. To the best of our knowledge, there has been no previous association between these genes and lentiviral infection in any species. The gene plays a role in pain response, synaptic transmission, and receptor clustering, while is involved in the development of immune-related disorders. The results highlighted new aspects of the genetic complexity related to the resistance/susceptibility to VMV in sheep, confirming that studies on different breeds can lead to different results. The ideal approach for validation of the markers identified in our study is to use samples from a population independent from the discovery population with the same phenotype used in the discovery stage.
PubMed: 38911298
DOI: 10.3389/fgene.2024.1376883