Discovery of a novel piperazine derivative, cmp2: a selective TRPC6 activator suitable for treatment of synaptic deficiency in Alzheimer's disease hippocampal neurons.

Alzheimer disease (AD) is characterized by progressive loss of memory. Synaptic loss is now the best correlate of cognitive dysfunction in patients with Alzheimer's disease. Thus, restoration or limitation of synapse loss is a promising strategy for pharmacotherapy of AD. N-N substituted piperazines are widely used chemical compounds for drug interventions to treat different illnesses including CNS diseases such as drug abuse, mental and anxiety disorders. Piperazine derivatives are small molecules that are usually well tolerated and cross blood brain barrier (BBB). Thus, disubstituted piperazines are good tools for searching and developing novel disease-modifying drugs. Previously, we have determined the piperazine derivative, 51164, as an activator of TRPC6 in dendritic spines. We have demonstrated synaptoprotective properties of 51164 in AD mouse models. However, 51164 was not able to cross BBB. Within the current study, we identified a novel piperazine derivative, cmp2, that is structurally similar to 51164 but is able to cross BBB. Cmp2 binds central part of monomeric TRPC6 in similar way as hypeforin does. Cmp2 selectively activates TRPC6 but not structurally related TRPC3 and TRPC7. Novel piperazine derivative exhibits synaptoprotective properties in culture and slices and penetrates the BBB. In vivo study indicated cmp2 (10 mg/kg I.P.) reversed deficits in synaptic plasticity in the 5xFAD mice. Thus, we suggest that cmp2 is a novel lead compound for drug development. The mechanism of cmp2 action is based on selective TRPC6 stimulation and it is expected to treat synaptic deficiency in hippocampal neurons.

THE EFFECTS OF HYDROCORTISONE ON SYNAPTIC PROCESSES IN PARKINSON'S DISEASE UNDERLYING THE POTENTIAL THERAPEUTIC STRATEGIES.

The study was carried out electrophysiological effects of hydrocortisone for protection on the prelimbic cortex (PrL) neurons in rats, particularly in response to high-frequency stimulation (HFS) of the Caudate-Putamen nuclear complex (CPu) on the models of Parkinson's disease (PD). The study involved 19 rats of the Albino line, each weighing 250 gr. The rats were divided into three experimental groups: intact, rotenone model of Parkinson's disease (PD), and rats with PD but treated with hydrocortisone for protection. Extracellular recording was conducted to measure the impulse activity of single neurons in the prelimbic cortex (PrL) particularly in response to high-frequency stimulation (HFS) of the Caudate-Putamen nuclear complex (CPu) on the models of PD and PD treated with hydrocortisone for protection. In rats with the PD model, there was a decrease in post-stimulus synaptic depressor tetanic effects compared to the norm. This means that the ability of synapses to depress their activity after stimulation was reduced in PD. Conversely, excitatory effects increased in PD rats compared to the norm. This indicates an increase in the excitatory response of neurons in the PD model. When hydrocortisone was applied in PD rats, the frequency of impulse activity dropped sharply, even falling below the levels observed in the normal condition. This indicates that hydrocortisone treatment mitigated the heightened neural activity induced by PD, possibly returning it to a more normal state. Overall, these findings suggest that PD alters synaptic responses and neural activity in the PrL, and hydrocortisone treatment seems to reverse some of these effects.

Dexamethasone as an emerging environmental pollutant: Disruption of cholesterol-dependent synaptogenesis in the hippocampus and subsequent neurobehavioral impacts in offspring.

When fetuses are exposed to abnormally high levels of glucocorticoids in utero, irreversible damage to neuronal synaptogenesis occurs, leading to long-term cognitive and emotional behavioral abnormalities after birth. In this study, we investigated how maternal exposure to a novel environmental pollutant-synthetic glucocorticoid dexamethasone-affects offspring cognitive and emotional behaviors enduringly. We noted that offspring subjected to maternal dexamethasone exposure (MDE) displayed cognitive and emotional neurobehavioral deficits beginning in infancy, and these impairments persisted into adulthood. The principal mechanism involves MDE-induced damage to hippocampal neuronal synapse formation in the offspring, primarily due to a cholesterol deficiency which destabilizes neuronal membranes, thereby affecting normal synapse formation and ultimately leading to cognitive and emotional deficiencies. Specifically, we demonstrated abnormal activation of glucocorticoid receptors in hippocampal astroglial cells of MDE offspring, which triggers changes in the miR-450a-3p/HAT1/ABCG1 signaling axis, causing impaired cholesterol efflux in astroglial cells and insufficient cholesterol supply to neurons, further impairing synaptogenesis. This research not only underscores the significant impact of prenatal environmental pollutants on long-term health outcomes in offspring but also broadens our understanding of how prenatal exposure to glucocorticoids affects brain development in the progeny, providing new insights for interventions in neurodevelopmental and psychiatric disorders of fetal origin.

Quantitative proteomics combined independent PRM analysis reveals the mitochondrial and synaptic mechanism underlying norisoboldine's antidepressant effects.

Major depressive disorder (MDD) is a common disease affecting 300 million people worldwide. The existing drugs are ineffective for approximately 30% of patients, so it is urgent to develop new antidepressant drugs with novel mechanisms. Here, we found that norisoboldine (NOR) showed an antidepressant efficacy in the chronic social defeat stress (CSDS) depression model in the tail suspension, forced swimming, and sucrose consumption tests. We then utilized the drug-treated CSDS mice paradigm to segregate and gain differential protein groups of CSDS versus CON (CSDSCON), imipramine (IMI)-treated versus CSDS (IMICSDS), and NOR-treated versus CSDS (NORCSDS) from the prefrontal cortex. These protein expression alterations were first analyzed by ANOVA with p < 0.05. The protein cluster 1 and cluster 3, in which the pattern of protein levels similar to the mood pattern, showed enrichment in functions and localizations related to mitochondrion, ribosome and synapses. Further GO analysis of the common proteins for NORCSDS groups and NORIMI groups supported the findings from ANOVA analysis. We employed Protein-Protein interaction (PPI) analysis to examine the proteins of NORCSDS and NORIMI, revealing an enrichment of the proteins associated with the mitochondrial ribosomal and synaptic functions. Further independent analysis using parallel reaction monitoring (PRM) revealed that Cox7c, Mrp142, Naa30, Ighm, Apoa4, Ssu72, Mrps30, Apoh, Acbd5, and Cdv3, exhibited regulation in the NOR-treated group to support the homeostasis of mitochondrial functions. Additionally, Dcx, Arid1b, Rnf112, and Fam3c, were also observed to undergo modulation in the NOR-treated groups to support the synaptic formation and functions. These findings suggest that the proteins involved in depression treatment exert effects in strengthen the mitochondrial and synaptic functions in the mice PFC. Western blot analysis supported the data that the levels of Mrpl42, Cox7c, Naa30, Rnf112, Dcx Apoa4, Apoh and Fam3c were altered in the CSDS mice, and rescued by NOR treatment, supporting the PRM data. NOR treatment also rescued the NLRP3 inflammasome activation in CSDS mice. In summary, the current proteomic research conducted on the prefrontal cortex has provided valuable insights into the specific and shared molecular mechanisms underlying pathophysiology and treatment to CSDS-induced depression, shedding light on the therapeutic effects of Norisoboldine.

Brain-to-heart cholinergic synapse-calcium signaling mediates ischemic stroke-induced atrial fibrillation.

Background: Stroke-related cardiovascular diseases have attracted considerable attention, with atrial fibrillation (AF) being among the most frequent complications. Despite increasing clinical evidence, experimental models of stroke-induced AF are still lacking, hindering mechanistic discoveries and the development of adequate therapeutics targeting this stroke-heart syndrome (SHS). This study aims to create a rat model of ischemic stroke-induced AF (ISIAF) and to explore the efficacy and mechanism of Wenxin Keli (WK), an antiarrhythmic Chinese medicine. Method: The middle cerebral artery occlusion/reperfusion model was adapted to create subacute brain ischemia in rats with normal cardiac function. Invasive electrophysiologic studies and ex vivo optical mapping were performed to evaluate the altered electrophysiological parameters and Ca2+ handling properties. RNA-seq analysis, RT-PCR, and immunohistochemistry (IHC) with immunofluorescence (IF) were employed to assess the SHS model and elucidate the mechanisms of ISIAF and the effects of WK. UPLC/Q-TOF-MS, molecular docking, and whole-cell patch recordings were used to identify the active components of WK for SHS. Results: Ischemic stroke aggravated atrial electrical instability, altered action potential duration (APD), Ca2+ transient duration (CaT), conduction heterogeneity, and spatially discordant alternans in SHS rat hearts. These abnormalities were alleviated by WK. RNA-seq analysis revealed that M3-mediated cholinergic synapse signaling and L-type calcium channel (LTCCs)-mediated Ca2+ signaling play prominent roles in ISIAF development and its reversal by WK. UPLC/Q-TOF-MS analysis identified 19 WK components as the main components in plasma after WK treatment. Molecular docking screening identified Dioscin as the major active component of WK. WK and Dioscin reduced ICa-L in a concentration-dependent manner with a half-maximal inhibitory concentration of 24.254 ± 2.051 mg/mL and 8.666 ± 0.777 µmol/L, respectively. Conclusion: This study established an experimental model of ISIAF capable of characterizing clinically relevant atrial electrophysiological changes post-cerebral ischemia. Molecular mechanistic studies revealed that the cholinergic-calcium signaling pathway is central to this brain-heart syndrome. Ischemic stroke-induced atrial fibrillation is partially reversible by the Chinese medicine Wenxin Keli, which acts via regulation of the cholinergic-calcium signaling pathway, with its active component Dioscin directly binding to IKM3 and inhibiting ICa-L.

Role of Hippocampal Glutamatergic Synaptic Alterations in Sevoflurane-Induced Cognitive Dysfunction in Aged Mice.

AIMS: Perioperative neurocognitive disorders (PND), including postoperative delirium (POD) and postoperative cognitive dysfunction (POCD), are common following anesthesia and surgery in older patients and significantly increase morbidity and mortality. However, the underlying mechanism of PND is unclear. Our study aims to analyze the differentially expressed genes (DEGs) in excitatory neurons and investigate the role of hippocampal glutamatergic synaptic alterations in sevoflurane-induced cognitive dysfunction in aged mice. METHODS: We performed single-nucleus RNA sequencing (snRNA-seq) technology to examine the alterations of excitatory neurons in hippocampus induced by sevoflurane in aged mice. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis of DEGs were performed in excitatory neurons. At last, immunofluorescence staining was used to validate sevoflurane-induced alternation of glutamatergic synapses in the hippocampus of aged mice. RESULTS: This study demonstrates that DEGs in excitatory neurons are associated with reduction of glutamatergic synapses and cognitive dysfunction. After immunofluorescence staining validation, we also confirmed that sevoflurane anesthesia decreased the density of glutamatergic synapses in the hippocampus of aged mice. CONCLUSIONS: Our findings demonstrated a key role of hippocampal glutamatergic synaptic alterations in sevoflurane-induced cognitive dysfunction in aged mice.

Autophagy defects at weaning impair complement-dependent synaptic pruning and induce behavior deficits.

Autophagy is crucial for synaptic plasticity and the architecture of dendritic spines. However, the role of autophagy in schizophrenia (SCZ) and the mechanisms through which it affects synaptic function remain unclear. In this study, we identified 995 single nucleotide polymorphisms (SNPs) across 19 autophagy-related genes that are associated with SCZ. Gene Set Enrichment Analysis (GSEA) of data from the Gene Expression Omnibus public database revealed defective autophagy in patients with SCZ. Using a maternal immune activation (MIA) rat model, we observed that autophagy was downregulated during the weaning period, and early-life activation of autophagy with rapamycin restored abnormal behaviors and electrophysiological deficits in adult rats. Additionally, inhibition of autophagy with 3-Methyladenine (3-MA) during the weaning period resulted in aberrant behaviors, abnormal electrophysiology, increased spine density, and reduced microglia-mediated synaptic pruning. Furthermore, 3-MA treatment significantly decreased the expression and synaptosomal content of complement, impaired the recognition of C3b and CR3, indicating that autophagy deficiency disrupts complement-mediated synaptic pruning. Our findings provide evidence for a significant association between SCZ and defective autophagy, highlighting a previously underappreciated role of autophagy in regulating the synaptic and behavioral deficits induced by MIA.

Cannabinol (CBN) Influences the Ion Channels and Synaptic-Related Genes in NSC-34 Cell Line: A Transcriptomic Study.

Neurological disorders such as Alzheimer's, Parkinson's, amyotrophic lateral sclerosis, and schizophrenia are associated with altered neuronal excitability, resulting from dysfunctions in the molecular architecture and physiological regulation of ion channels and synaptic transmission. Ion channels and synapses are regarded as suitable therapeutic targets in modern pharmacology. Cannabinoids have received great attention as an original therapeutic approach for their effects on human health due to their ability to modulate the neurotransmitter release through interaction with the endocannabinoid system. In our study, we explored the effect of cannabinol (CBN) through next-generation sequencing analysis of NSC-34 cell physiology. Our findings revealed that CBN strongly influences the ontologies related to ion channels and synapse activity at all doses tested. Specifically, the genes coding for calcium and potassium voltage-gated channel subunits, and the glutamatergic and GABAergic receptors (Cacna1b, Cacna1h, Cacng8, Kcnc3, Kcnd1, Kcnd2, Kcnj4, Grik5, Grik1, Slc17a7, Gabra5), were up-regulated. Conversely, the genes involved into serotoninergic and cholinergic pathways (Htr3a, Htr3b, Htr1b, Chrna3, Chrnb2, Chrnb4), were down-regulated. These findings highlight the influence of CBN in the expression of genes involved into ion influx and synaptic transmission.

Ketamine reverses chronic corticosterone-induced behavioral deficits and hippocampal synaptic dysfunction by regulating eIF4E/BDNF signaling.

Major depressive disorder (MDD) is a debilitating illness with a high global burden. While Ketamine, an N-methyl-D-aspartate (NMDA) receptor antagonist, offers rapid-acting antidepressant effects, its mechanism remains incompletely understood. Recent research suggests that dysregulation of mRNA translation via the Eukaryotic initiation factor 4E (eIF4E) pathway might contribute to depression pathophysiology. This study investigates whether Ketamine modulates eIF4E signaling in the hippocampus during its antidepressant action. Herein, adult male mice were exposed to Corticosterone, a well-established model for anxiety and depression, followed by behavioral testing and biochemical analysis. Corticosterone induced depression-like symptoms and disrupted synaptic function, including reduced TrkB/BDNF and eIF4E/MNK1/p-eIF2α/ubiquitin signaling. Ketamine treatment reversed these deficits. Notably, the eIF4E/MNK1 signaling inhibitor, eFT508, blocked Ketamine's antidepressant effect, leading to a return of depression-like phenotype and impaired synaptic signaling. Importantly, these effects were reversed by 7,8-DHF, a BDNF/TrkB signaling agonist. Mice treated with Corticosterone, Ketamine, and eFT508 and subsequently exposed to 7,8-DHF displayed normalized depression-like behaviors and restored synaptic signaling, including increased eIF4E phosphorylation and MNK1 expression. Besides, 7,8-DHF treatment enhanced p-eIF2α levels compared to the eFT508-treated group. These findings suggest that Ketamine exerts its antidepressant action through the regulation of the eIF4E/BDNF signaling pathway in the hippocampus. This study provides novel insights into the molecular mechanisms underlying Ketamine's therapeutic effects and highlights the potential of targeting this pathway for future MDD treatment strategies.

Neonatal anesthesia with remimazolam Reduces the expression of synaptic proteins and increases depressive behavior in adult mice.

The demand for pediatric anesthesia has risen in decades, raising concerns about the neurotoxic potential of anesthetics like remimazolam, which may impact neurodevelopment and later cognitive function. This study utilized a neonatal mouse model to assess remimazolam's neurodevelopmental effects. Results indicate that remimazolam-exposed mice displayed cognitive impairment and depressive behaviors in adulthood. Acute reductions in synaptic protein expression post-anesthesia were observed, along with long-term decreases in hippocampal choline acetyltransferase levels, reduced dendritic spine density in the CA1 region, and microglial proliferation. Collectively, these findings suggest that remimazolam can induce neurotoxicity and neuroinflammation, leading to synaptic dysfunction and associated cognitive and behavioral deficits.

Wnt Signaling Modulators Exhibit Neuroprotective Effects via Combating Astrogliosis and Balancing Synaptic Density at Early and Late Stage Temporal Lobe Epilepsy.

Temporal Lobe Epilepsy (TLE) is a severe neurological condition characterized by recurrent seizures that often do not respond well to available anti-seizure medications. TLE has been associated with epileptogenesis, a process that starts during the latent period following a neurologic insult and is followed by chronic phase. Recent research has linked canonical Wnt signaling to the pathophysiology of epileptogenesis and TLE. Our previous study demonstrated differential regulation of canonical Wnt signaling during early and late stage post status epilepticus (SE) induction. Building on these findings, our current study utilized Wnt modulators: GSK-3ß inhibitor 6-bromoindirubin-3'-oxime (6-Bio) and disheveled inhibitor niclosamide and investigated their impact on canonical Wnt signaling during the early (30 days) and later stages (60 days) following SE induction. We assessed several parameters, including seizure frequency, astrogliosis, synaptic density, and neuronal counts in hippocampal tissue. We used immunohistochemistry and Nissl staining to evaluate gliosis, synaptic density, and neuronal counts in micro-dissected hippocampi. Western blotting was used to examine the expression of proteins involved in canonical Wnt/ß-catenin signaling, and real-time PCR was conducted to analyze their relative mRNA expression. Wnt modulators, 6-Bio and Niclosamide were found to reduce seizure frequency and various other parameters including behavioral parameters, hippocampal morphology, astrogliosis and synaptic density at different stages of TLE.

Transcriptome Profiling of Phenylalanine-Treated Human Neuronal Model: Spotlight on Neurite Impairment and Synaptic Connectivity.

Phenylketonuria (PKU) is the most common inherited disorder of amino acid metabolism, characterized by high levels of phenylalanine (Phe) in the blood and brain, leading to cognitive impairment without treatment. Nevertheless, Phe-mediated brain dysfunction is not fully understood. The objective of this study was to address gene expression alterations due to excessive Phe exposure in the human neuronal model and provide molecular advances in PKU pathophysiology. Hence, we performed NT2/D1 differentiation in culture, and, for the first time, we used Phe-treated NT2-derived neurons (NT2/N) as a novel model for Phe-mediated neuronal impairment. NT2/N were treated with 1.25 mM, 2.5 mM, 5 mM, 10 mM, and 30 mM Phe and subjected to whole-mRNA short-read sequencing. Differentially expressed genes (DEGs) were analyzed and enrichment analysis was performed. Under three different Phe concentrations (2.5 mM, 5 mM, and 10 mM), DEGs pointed to the PREX1, LRP4, CDC42BPG, GPR50, PRMT8, RASGRF2, and CDH6 genes, placing them in the context of PKU for the first time. Enriched processes included dendrite and axon impairment, synaptic transmission, and membrane assembly. In contrast to these groups, the 30 mM Phe treatment group clearly represented the neurotoxicity of Phe, exhibiting enrichment in apoptotic pathways. In conclusion, we established NT2/N as a novel model for Phe-mediated neuronal dysfunction and outlined the Phe-induced gene expression changes resulting in neurite impairment and altered synaptic connectivity.

[Protective effect and mechanism of Zuogui Jiangtang Jieyu Formula on damage to hippocampal synaptic microenvironment in rats with diabetes-related depression based on microglia-neuron crosstalk signal CD300f/TLR4].

This study aims to reveal the protective effect and mechanism of Zuogui Jiangtang Jieyu Formula on the damage to hippo-campal synaptic microenvironment in rats with diabetes-related depression(DD) via regulating microglia immune receptor molecule-like family member f(CD300f)/Toll-like receptor 4(TLR4) signal. Firstly, the model of DD rats was established by a two-week high-fat diet+STZ injection+chronic mild and unpredictable stress plus isolation for 28 days. The rats were randomly divided into normal group, model group, CD300f blocker(CLM1, 2 µg·kg~(-1)) group, CD300f agonist(Fcγ, 5 µg·kg~(-1)) group, positive drug(0.18 g·kg~(-1) metformin+1.8 mg·kg~(-1) fluoxetine) group, and high-dose and low-dose(20.52 and 10.26 g·kg~(-1)) Zuogui Jiangtang Jieyu Formula groups. Depression-like behavior of rats was evaluated by open field and forced swimming experiments. The levels of blood glucose and insulin were detected by biochemical analysis. The levels of tumor necrosis factor α(TNF-α), interleukin-1ß(IL-1ß), indoleamine 2, 3-dioxygenase(IDO), 5-hydroxytryptamine(5-HT), and dopamine(DA) in the hippocampus were detected by enzyme-linked immunosorbent assay. The changes in the synaptic ultrastructure in hippocampal neurons of rats were observed by transmission electron microscopy. The protein expressions of CD300f, TLR4, synaptophysin(SYN), and postsynaptic density protein 95(PSD-95) in microglial cells of the hippocampus were detected by immunofluorescence and Western blot. The results indicated that compared with that in the normal group, the total movement distance in open field experiments was reduced in the model group, and the immobility time in forced swimming experiments increased, with an elevated insulin level in serum, as well as TNF-α, IL-1ß, and IDO levels in the hippocampus. The 5-HT and DA levels in the hippocampus were reduced. In addition, the CD300f expression was down-regulated in microglial cells of the hippocampus, and the TLR4 expression was up-regulated. Moreover, the expression of synapse-related proteins SYN and PSD-95 in hippocampal neurons decreased, and the synaptic ultrastructure of hippocampal neurons was significantly damaged. Compared with the model group, the CD300f blocker and agonist aggravated and alleviated the above abnormal changes, respectively. High-dose and low-dose Zuogui Jiangtang Jieyu Formula could significantly improve the above depression-like beha-vior in rats, inhibit the abnormal increase of TNF-α, IL-1ß, and IDO and the decrease of 5-HT and DA, effectively increase the expression of CD300f in microglial cells, and decrease the expression of TLR4. They could up-regulate the protein expression of presyna-ptic membrane SYN and postsynaptic membrane PSD-95 in hippocampal neurons and finally improve the damage to the hippocampal synaptic microenvironment. In conclusion, this research confirmed that Zuogui Jiangtang Jieyu Formula effectively alleviated the depression-like behavior and inhibited inflammatory activation of microglial cells in the hippocampus of rats with DD, and the mechanism might be related to the regulation of CD300f/TLR4 signal to alleviate the damage to hippocampal synaptic microenvironment.

Impaired Hippocampal Long-Term Potentiation and Memory Deficits upon Haploinsufficiency of MDGA1 Can Be Rescued by Acute Administration of D-Cycloserine.

The maintenance of proper brain function relies heavily on the balance of excitatory and inhibitory neural circuits, governed in part by synaptic adhesion molecules. Among these, MDGA1 (MAM domain-containing glycosylphosphatidylinositol anchor 1) acts as a suppressor of synapse formation by interfering with Neuroligin-mediated interactions, crucial for maintaining the excitatory-inhibitory (E/I) balance. Mdga1-/- mice exhibit selectively enhanced inhibitory synapse formation in their hippocampal pyramidal neurons, leading to impaired hippocampal long-term potentiation (LTP) and hippocampus-dependent learning and memory function; however, it has not been fully investigated yet if the reduction in MDGA1 protein levels would alter brain function. Here, we examined the behavioral and synaptic consequences of reduced MDGA1 protein levels in Mdga1+/- mice. As observed in Mdga1-/- mice, Mdga1+/- mice exhibited significant deficits in hippocampus-dependent learning and memory tasks, such as the Morris water maze and contextual fear-conditioning tests, along with a significant deficit in the long-term potentiation (LTP) in hippocampal Schaffer collateral CA1 synapses. The acute administration of D-cycloserine, a co-agonist of NMDAR (N-methyl-d-aspartate receptor), significantly ameliorated memory impairments and restored LTP deficits specifically in Mdga1+/- mice, while having no such effect on Mdga1-/- mice. These results highlight the critical role of MDGA1 in regulating inhibitory synapse formation and maintaining the E/I balance for proper cognitive function. These findings may also suggest potential therapeutic strategies targeting the E/I imbalance to alleviate cognitive deficits associated with neuropsychiatric disorders.

µ-Opioid Receptor Modulation of the Glutamatergic/GABAergic Midbrain Inputs to the Mouse Dorsal Hippocampus.

We used virus-mediated anterograde and retrograde tracing, optogenetic modulation, immunostaining, in situ hybridization, and patch-clamp recordings in acute brain slices to study the release mechanism and µ-opioid modulation of the dual glutamatergic/GABAergic inputs from the ventral tegmental area and supramammillary nucleus to the granule cells of the dorsal hippocampus of male and female mice. In keeping with previous reports showing that the two transmitters are released by separate active zones within the same terminals, we found that the short-term plasticity and pharmacological modulation of the glutamatergic and GABAergic currents are indistinguishable. We further found that glutamate and GABA release at these synapses are both virtually completely mediated by N- and P/Q-type calcium channels. We then investigated µ-opioid modulation of these synapses and found that activation of µ-opioid receptors (MORs) strongly inhibits the glutamate and GABA release, mostly through inhibition of presynaptic N-type channels. However, the modulation by MORs of these dual synapses is complex, as it likely includes also a disinhibition due to downmodulation of local GABAergic interneurons which make direct axo-axonic contacts with the dual glutamatergic/GABAergic terminals. We discuss how this opioid modulation may enhance LTP at the perforant path inputs, potentially contributing to reinforce memories of drug-associated contexts.

Mitigation of synaptic and memory impairments via F-actin stabilization in Alzheimer's disease.

BACKGROUND: Synaptic dysfunction, characterized by synapse loss and structural alterations, emerges as a prominent correlate of cognitive decline in Alzheimer's disease (AD). Actin cytoskeleton, which serves as the structural backbone of synaptic architecture, is observed to be lost from synapses in AD. Actin cytoskeleton loss compromises synaptic integrity, affecting glutamatergic receptor levels, neurotransmission, and synaptic strength. Understanding these molecular changes is crucial for developing interventions targeting synaptic dysfunction, potentially mitigating cognitive decline in AD. METHODS: In this study, we investigated the synaptic actin interactome using mass spectrometry in a mouse model of AD, APP/PS1. Our objective was to explore how alterations in synaptic actin dynamics, particularly the interaction between PSD-95 and actin, contribute to synaptic and cognitive impairment in AD. To assess the impact of restoring F-actin levels on synaptic and cognitive functions in APP/PS1 mice, we administered F-actin stabilizing agent, jasplakinolide. Behavioral deficits in the mice were evaluated using the contextual fear conditioning paradigm. We utilized primary neuronal cultures to study the synaptic levels of AMPA and NMDA receptors and the dynamics of PSD-95 actin association. Furthermore, we analyzed postmortem brain tissue samples from subjects with no cognitive impairment (NCI), mild cognitive impairment (MCI), and Alzheimer's dementia (AD) to determine the association between PSD-95 and actin. RESULTS: We found a significant reduction in PSD-95-actin association in synaptosomes from middle-aged APP/PS1 mice compared to wild-type (WT) mice. Treatment with jasplakinolide, an actin stabilizer, reversed deficits in memory recall, restored PSD-95-actin association, and increased synaptic F-actin levels in APP/PS1 mice. Additionally, actin stabilization led to elevated synaptic levels of AMPA and NMDA receptors, enhanced dendritic spine density, suggesting improved neurotransmission and synaptic strength in primary cortical neurons from APP/PS1 mice. Furthermore, analysis of postmortem human tissue with NCI, MCI and AD subjects revealed disrupted PSD-95-actin interactions, underscoring the clinical relevance of our preclinical studies. CONCLUSION: Our study elucidates disrupted PSD-95 actin interactions across different models, highlighting potential therapeutic targets for AD. Stabilizing F-actin restores synaptic integrity and ameliorates cognitive deficits in APP/PS1 mice, suggesting that targeting synaptic actin regulation could be a promising therapeutic strategy to mitigate cognitive decline in AD.

A small TAT-TrkB peptide prevents BDNF receptor cleavage and restores synaptic physiology in Alzheimer's disease.

In Alzheimer's disease (AD), amyloid ß (Aß)-triggered cleavage of TrkB-FL impairs brain-derived neurotrophic factor (BDNF) signaling, thereby compromising neuronal survival, differentiation, and synaptic transmission and plasticity. Using cerebrospinal fluid and postmortem human brain samples, we show that TrkB-FL cleavage occurs from the early stages of the disease and increases as a function of pathology severity. To explore the therapeutic potential of this disease mechanism, we designed small TAT-fused peptides and screened their ability to prevent TrkB-FL receptor cleavage. Among these, a TAT-TrkB peptide with a lysine-lysine linker prevented TrkB-FL cleavage both in vitro and in vivo and rescued synaptic deficits induced by oligomeric Aß in hippocampal slices. Furthermore, this TAT-TrkB peptide improved the cognitive performance, ameliorated synaptic plasticity deficits and prevented Tau pathology progression in vivo in the 5XFAD mouse model of AD. No evidence of liver or kidney toxicity was found. We provide proof-of-concept evidence for the efficacy and safety of this therapeutic strategy and anticipate that this TAT-TrkB peptide has the potential to be a disease-modifying drug that can prevent and/or reverse cognitive deficits in patients with AD.

Nogo-A-mediated constraints on activity-dependent synaptic plasticity and associativity in rat hippocampal CA2 synapses.

Hippocampal area CA2 has garnered attention in recent times owing to its significant involvement in social memory and distinctive plasticity characteristics. Research has revealed that the CA2 region demonstrates a remarkable resistance to plasticity, particularly in the Schaffer Collateral (SC)-CA2 pathway. In this study we investigated the role of Nogo-A, a well-known axon growth inhibitor and more recently discovered plasticity regulator, in modulating plasticity within the CA2 region. The findings demonstrate that blocking Nogo-A in male rat hippocampal slices facilitates the establishment of both short-term and long-term plasticity in the SC-CA2 pathway, while having no impact on the Entorhinal Cortical (EC)-CA2 pathway. Additionally, the study reveals that inhibiting Nogo-A enables association between the SC and EC pathways. Mechanistically, we confirm that Nogo-A operates through its well-known co-receptor, p75 neurotrophin receptor (p75NTR), and its downstream signaling factor such as Rho-associated protein kinase (ROCK), as their inhibition also allows plasticity induction in the SC-CA2 pathway. Additionally, the induction of long-term depression (LTD) in both the EC and SC-CA2 pathways led to persistent LTD, which was not affected by Nogo-A inhibition. Our study demonstrates the involvement of Nogo-A mediated signaling mechanisms in limiting synaptic plasticity within the CA2 region.

Amitriptyline protects afferent synapses in the cochlea against excitotoxic trauma in vitro.

Afferent synapses between inner hair cells (IHCs) and the type I spiral ganglion neurons (SGNs) in the cochlea provide over 95% of sensory signals for auditory perception in the brain. However, these afferent synapses are particularly vulnerable to damage, for example from excitotoxicity, and exposure to noise in the environment which often leads to noise-induced cochlear synaptopathy (NICS). In this study, we simulated excitotoxic trauma by incubating kainic acid, a non-desensitizing agonist for AMPA type glutamate receptors on cultured cochleae. The possible protective effects of amitriptyline against NICS were examined. We found that, in IHCs, amitriptyline reversed the decrease of Ca2+ current and exocytosis caused by excitotoxic trauma. In SGNs, amitriptyline promoted the recovery of neurite loss caused by excitotoxic trauma. Furthermore, we found that the protective effects of amitriptyline are likely mediated by suppressing apoptosis factors that were upregulated during excitotoxic trauma. In conclusion, our results suggest that amitriptyline could protect afferent synapses in the cochlea from NICS, making it a potential drug candidate for hearing protection.

Insulin restores retinal ganglion cell functional connectivity and promotes visual recovery in glaucoma.

Dendrite pathology and synaptic loss result in neural circuit dysfunction, a common feature of neurodegenerative diseases. There is a lack of strategies that target dendritic and synaptic regeneration to promote neurorecovery. We show that daily human recombinant insulin eye drops stimulate retinal ganglion cell (RGC) dendrite and synapse regeneration during ocular hypertension, a risk factor to develop glaucoma. We demonstrate that the ribosomal protein p70S6 kinase (S6K) is essential for insulin-dependent dendritic regrowth. Furthermore, S6K phosphorylation of the stress-activated protein kinase-interacting protein 1 (SIN1), a link between the mammalian target of rapamycin complexes 1 and 2 (mTORC1/2), is required for insulin-induced dendritic regeneration. Using two-photon microscopy live retinal imaging, we show that insulin rescues single-RGC light-evoked calcium (Ca2+) dynamics. We further demonstrate that insulin enhances neuronal survival and retina-brain connectivity leading to improved optomotor reflex-elicited behaviors. Our data support that insulin is a compelling pro-regenerative strategy with potential clinical implications for the treatment and management of glaucoma.