Dopamine neuron degeneration in the Ventral Tegmental Area causes hippocampal hyperexcitability in experimental Alzheimer's Disease

Unveiling the Therapeutic Potential of Banxia Xiexin Decoction in Alzheimer's Disease: Insights From Network Pharmacology and Experimental Validation

Background

Alzheimer's disease (AD) is associated with various pathological states for which there is no effective treatment. First documented in the Eastern Han Dynasty's medical classic, "Treatise on Febrile and Miscellaneous Diseases" (200-210 Anno Domini), Banxia Xiexin Decoction (BXD) stands as a quintessential approach to treating spleen ailments. Recent studies have shown BXD's effectiveness in mitigating memory impairment associated with AD. Yet, the precise mechanisms underlying BXD's action against AD require further exploration.

Aim of the Study

To explore the important components of BXD in exerting anti-AD effects and the underlying molecular mechanisms using network pharmacology, metabolomics analysis, and in vitro and in vivo validation strategies. Initially, candidates for BXD's application in AD therapy were identified through extensive database searches, followed by an analysis of protein-protein interactions (PPI). To elucidate BXD's therapeutic pathways in AD, we engaged in Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) assessments. Further, we delved into BXD's primary constituents through ultra-high-pressure liquid chromatography coupled with Q Exactive mass spectrometry and molecular docking techniques. Finally, AD-associated Aβ42-SY5Y cells and APPswe/PS1dE9 (APP/PS1) transgenic mice models were utilized to further determine the activity and mechanisms of BXD through various molecular or phenotypic assays and metabolomics analysis.

Results

Our findings identified the PI3K/Akt signaling pathways as central to BXD's effects. Using in vitro and in vivo models, we found the activity of BXD against AD to be mediated by the suppression of neuroinflammation and apoptosis, accompanied by activation of the PI3K/Akt pathway. Finally, we observed robust changes in metabolite levels in the plasma of BXD-treated APP/PS1 mice.

Conclusion

Through systematic data analysis and experimental validation, the therapeutic advantages and fundamental molecular mechanisms of BXD in treating AD were revealed. These findings underscore the promising prospects and compelling potential of BXD, which targets the PI3K/Akt signaling pathway and inflammation, apoptosis, as a therapeutic strategy for improving AD.

Pharmacological reduction of reverse-translated hippocampal hyperactivity in mouse: relevance for psychosis

Hippocampal hyperactivity (HH) is a potential biomarker in schizophrenia psychosis, which also appears in several other brain disorders, compromising specificity. We hypothesized that the reversal of HH in an established, reverse-translational animal preparation, coupled with a behavioral marker of psychosis may be a predictor of antipsychotic efficacy of a medication. We used a chemogenetic reverse-translational mouse preparation relevant to schizophrenia psychosis which shows HH and aberrant psychosis-relevant behaviors, specifically disrupted social recognition memory (SRM). Mice with and without HH were treated with three drugs; two known antipsychotics and one HH-reducing anticonvulsant, to assess their effects on both HH and SRM performance. All animals received one of the four treatments: vehicle (N = 15-24), haloperidol (N = 8-15), xanomeline (N = 8-13) or levetiracetam (N = 6-15) and were subsequently tested for baseline c-Fos protein expression within the hippocampal subfields (CA3 and CA1) as a measure of neuronal activity, or tested with the SRM task as a measure of social memory. All three drugs acutely reduced baseline HH compared to vehicle treatment. Subacute administration of haloperidol or xanomeline, the two drugs known to have antipsychotic activity, but not levetiracetam, normalized the SRM behavior to control levels. These results suggest that the reversal of HH alone cannot be a predictor of antipsychotic efficacy of an experimental drug and HH as a biomarker could benefit from a more sensitive readout approach.

The complex relationship between gut microbiota and Alzheimer's disease: A systematic review

Alzheimer's disease (AD) is a progressive, degenerative disorder of the central nervous system. Despite extensive research conducted on this disorder, its precise pathogenesis remains unclear. In recent years, the microbiota-gut-brain axis has attracted considerable attention within the field of AD. The gut microbiota communicates bidirectionally with the central nervous system through the gut-brain axis, and alterations in its structure and function can influence the progression of AD. Consequently, regulating the gut microbiota to mitigate the progression of AD has emerged as a novel therapeutic approach. Currently, numerous studies concentrate on the intrinsic relationship between the microbiota-gut-brain axis and AD. In this paper, we summarize the multifaceted role of the gut microbiota in AD and present detailed therapeutic strategies targeting the gut microbiota, including the treatment of AD with Traditional Chinese Medicine (TCM), which has garnered increasing attention in recent years. Finally, we discuss potential therapeutic strategies for modulating the gut microbiota to alleviate the progression of AD, the current challenges in this area of research, and provide an outlook on future research directions in this field.

Dual-channel nano-carbon-liquid/liquid junction electrodes for multi-modal analysis: redox-active (dopamine) and non-redox-active (acetylcholine)

We present here a dual-channel nanoelectrode to detect both redox-active and non-redox-active analytes. The dual-channel nanoelectrode was developed from theta nanopipette. We developed one channel of the theta nanopipette to be a carbon nanoelectrode and the other channel to be a nano interface between two immiscible electrolyte solutions (nanoITIES) electrode, producing a nano-carbon-ITIES platform. The carbon nanoelectrode channel was developed by carbon deposition via pyrolysis followed by focused ion beam milling to measure redox-active analytes. The nanoITIES electrode channel was developed to detect non-redox-active analytes. The nano-carbon-ITIES electrodes were characterized using electrochemistry, scanning electron microscopy and transmission electron microscopy. Dopamine (a redox-active analyte) and acetylcholine (a non-redox-active analyte) were measured on the dual-channel nano-carbon-ITIES platform using the carbon nanoelectrode and the nanoITIES electrode, respectively. Using cyclic voltammetry, the diffusion-limited current of dopamine and acetylcholine detection on the nano-carbon-ITIES electrode increased linearly with increasing their concentrations. Using chronoamperometry (current versus time), we showed that the nano-carbon-ITIES electrode detected acetylcholine and dopamine at the same time. The introduced first-ever dual-functional nano-carbon-ITIES electrodes expand the current literature in multi-channel electrodes for multi-purpose analysis, which is an emerging area of research. Developing the analytical capability for the simultaneous detection of acetylcholine and dopamine is a critical step towards understanding diseases and disorders where both dopamine and acetylcholine are involved.

Repeated exposure to novelty promotes resilience against the amyloid-beta effect through dopaminergic stimulation

RATIONALE

The accumulation of beta-amyloid peptide (Aβ) in the forebrain leads to cognitive dysfunction and neurodegeneration in Alzheimer's disease. Studies have shown that individuals with a consistently cognitively active lifestyle are less vulnerable to Aβ toxicity. Recent research has demonstrated that intrahippocampal Aβ can impact catecholaminergic release and spatial memory. Interestingly, exposure to novelty stimuli has been found to stimulate the release of catecholamines in the hippocampus. However, it remains uncertain whether repeated enhancing catecholamine activity can effectively alleviate cognitive impairment in individuals with Alzheimer's disease.

OBJECTIVES

Our primary aim was to investigate whether repeated exposure to novelty could enable cognitive resilience against Aβ. This protection could be achieved by modulating catecholaminergic activity within the hippocampus.

METHODS

To investigate this hypothesis, we subjected mice to three different conditions-standard housing (SH), repeated novelty (Nov), or daily social interaction (Soc) for one month. We then infused saline solution (SS) or Aβ (Aβ1-42) oligomers intrahippocampally and measured spatial memory retrieval in a Morris Water Maze (MWM). Stereological analysis and extracellular baseline dopamine levels using in vivo microdialysis were assessed in independent groups of mice.

RESULTS

The mice that received Aβ1-42 intrahippocampal infusions and remained in SH or Soc conditions showed impaired spatial memory retrieval. In contrast, animals subjected to the Nov protocol demonstrated remarkable resilience, showing strong spatial memory expression even after Aβ1-42 intrahippocampal infusion. The stereological analysis indicated that the Aβ1-42 infusion reduced the tyrosine hydroxylase axonal length in SH or Soc mice compared to the Nov group. Accordingly, the hippocampal extracellular dopamine levels increased significantly in the Nov groups.

CONCLUSIONS

These compelling results demonstrate the potential for repeated novelty exposure to strengthen the dopaminergic system and mitigate the toxic effects of Aβ1-42. They also highlight new and promising therapeutic avenues for treating and preventing AD, especially in its early stages.

Entorhinal cortex-hippocampal circuit connectivity in health and disease

The entorhinal cortex (EC) and hippocampal (HC) connectivity is the main source of episodic memory formation and consolidation. The entorhinal-hippocampal (EC-HC) connection is classified as canonically glutamatergic and, more recently, has been characterized as a non-canonical GABAergic connection. Recent evidence shows that both EC and HC receive inputs from dopaminergic, cholinergic, and noradrenergic projections that modulate the mnemonic processes linked to the encoding and consolidation of memories. In the present review, we address the latest findings on the EC-HC connectivity and the role of neuromodulations during the mnemonic mechanisms of encoding and consolidation of memories and highlight the value of the cross-species approach to unravel the underlying cellular mechanisms known. Furthermore, we discuss how EC-HC connectivity early neurodegeneration may contribute to the dysfunction of episodic memories observed in aging and Alzheimer's disease (AD). Finally, we described how exercise may be a fundamental tool to prevent or decrease neurodegeneration.

Gut microbiota metabolites: potential therapeutic targets for Alzheimer's disease?

Background

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive decline in cognitive function, which significantly increases pain and social burden. However, few therapeutic interventions are effective in preventing or mitigating the progression of AD. An increasing number of recent studies support the hypothesis that the gut microbiome and its metabolites may be associated with upstream regulators of AD pathology.

Methods

In this review, we comprehensively explore the potential mechanisms and currently available interventions targeting the microbiome for the improvement of AD. Our discussion is structured around modern research advancements in AD, the bidirectional communication between the gut and brain, the multi-target regulatory effects of microbial metabolites on AD, and therapeutic strategies aimed at modulating gut microbiota to manage AD.

Results

The gut microbiota plays a crucial role in the pathogenesis of AD through continuous bidirectional communication via the microbiota-gut-brain axis. Among these, microbial metabolites such as lipids, amino acids, bile acids and neurotransmitters, especially sphingolipids and phospholipids, may serve as central components of the gut-brain axis, regulating AD-related pathogenic mechanisms including β-amyloid metabolism, Tau protein phosphorylation, and neuroinflammation. Additionally, interventions such as probiotic administration, fecal microbiota transplantation, and antibiotic use have also provided evidence supporting the association between gut microbiota and AD. At the same time, we propose an innovative strategy for treating AD: a healthy lifestyle combined with targeted probiotics and other potential therapeutic interventions, aiming to restore intestinal ecology and microbiota balance.

Conclusion

Despite previous efforts, the molecular mechanisms by which gut microbes act on AD have yet to be fully described. However, intestinal microorganisms may become an essential target for connecting the gut-brain axis and improving the symptoms of AD. At the same time, it requires joint exploration by multiple centers and multiple disciplines.

Dopamine Dilemma Overexcites the Hippocampus in Alzheimer's Disease

Dopamine neuron degeneration in the Ventral Tegmental Area causes hippocampal hyperexcitability in experimental Alzheimer's Disease Spoleti E, La Barbera L, Cauzzi E, De Paolis ML, Saba L, Marino R, Sciamanna G, Di Lazzaro V, Keller F, Nobili A, Krashia P. Mol Psychiatry . 2024;29(5):1265-1280. doi:10.1038/s41380-024-02408-9. Early and progressive dysfunctions of the dopaminergic system from the ventral tegmental area (VTA) have been described in Alzheimer's disease (AD). During the long pre-symptomatic phase, alterations in the function of parvalbumin interneurons (PV-INs) are also observed, resulting in cortical hyperexcitability represented by subclinical epilepsy and aberrant gamma oscillations. However, it is unknown whether the dopaminergic deficits contribute to brain hyperexcitability in AD. Here, using the Tg2576 mouse model of AD, we prove that reduced hippocampal dopaminergic innervation, due to VTA dopamine neuron degeneration, impairs PV-IN firing and gamma waves, weakens the inhibition of pyramidal neurons and induces hippocampal hyperexcitability via lower D2 receptor-mediated activation of the cAMP-response element binding protein (CREB) pathway. These alterations coincide with reduced PV-IN numbers and perineuronal net density. Importantly, L-DOPA and the selective D2 receptor agonist quinpirole rescue p-CREB levels and improve the PV-IN-mediated inhibition, thus reducing hyperexcitability. Moreover, similarly to quinpirole, sumanirole—another D2 receptor agonist and a known anticonvulsant—not only increases p-CREB levels in PV-INs but also restores gamma oscillations in Tg2576 mice. Conversely, blocking the dopaminergic transmission with sulpiride (a D2-like receptor antagonist) in wild-type mice reduces p-CREB levels in PV-INs, mimicking what occurs in Tg2576. Overall, these findings support the hypothesis that the VTA dopaminergic system integrity plays a key role in hippocampal PV-IN function and survival, disclosing a relevant contribution of the reduced dopaminergic tone to aberrant gamma waves, hippocampal hyperexcitability, and epileptiform activity in early AD.

GlyT1 Inhibition by NFPS Promotes Neuroprotection in Amyloid-β-Induced Alzheimer's Disease Animal Model

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid-β, leading to N-methyl-D-aspartate (NMDA) receptor-dependent synaptic depression, spine elimination, and memory deficits. Glycine transporter type 1 (GlyT1) modulates glutamatergic neurotransmission via NMDA receptors (NMDAR), presenting a potential alternative therapeutic approach for AD. This study investigates the neuroprotective potential of GlyT1 inhibition in an amyloid-β-induced AD mouse model. C57BL/6 mice were treated with N-[3-([1,1-Biphenyl]-4-yloxy)-3-(4-fluorophenyl)propyl]-N-methylglycine (NFPS), a GlyT1 inhibitor, 24 h prior to intrahippocampal injection of amyloid-β. NFPS pretreatment prevented amyloid-β-induced cognitive deficits in short-term and long-term memory, evidenced by novel object recognition and spatial memory tasks. Moreover, NFPS pretreatment curbed microglial activation, astrocytic reactivity, and subsequent neuronal damage from amyloid-β injection. An extensive label-free quantitative UPLC-MSE proteomic analysis was performed on the hippocampi of mice treated with NFPS. In proteomics, KEGG enrichment analysis revealed increased in dopaminergic synapse, purine-containing compound biosynthetic process and long-term potentiation, and a reduction in Glucose catabolic process and glycolytic process pathways. The western blot analysis confirmed that NFPS treatment elevated BDNF levels, correlating with enhanced TRKB phosphorylation and mTOR activation. Moreover, NFPS treatment reduced the GluN2B expression after 6 h, which was associated with an increase on CaMKIV and CREB phosphorylation. Collectively, these findings demonstrate that GlyT1 inhibition by NFPS activates diverse neuroprotective pathways, enhancing long-term potentiation signaling and countering amyloid-β-induced hippocampal damage.

Polycatechols inhibit ferroptosis and modulate tau liquid-liquid phase separation to mitigate Alzheimer's disease

Alzheimer's disease (AD) is a complex neurodegenerative disorder that affects learning, memory, and cognition. Current treatments targeting amyloid-β (Aβ) and tau have shown limited effectiveness, necessitating further research on the aggregation and toxicity mechanisms. One of these mechanisms involves the liquid-liquid phase separation (LLPS) of tau, contributing to the formation of pathogenic tau aggregates, although their conformational details remain elusive. Another mechanism is ferroptosis, a type of iron-dependent lipid peroxidation-mediated cell death, which has been implicated in AD. There is a lack of therapeutic strategies that simultaneously target amyloid toxicity and ferroptosis. This study aims to explore the potential of polycatechols, PDP and PLDP, consisting of dopamine and L-Dopa, respectively, as multifunctional agents to modulate the pathological nexus between ferroptosis and AD. Polycatechols were found to sequester the labile iron pool (LIP), inhibit Aβ and tau aggregation, scavenge free radicals, protect mitochondria, and prevent ferroptosis, thereby rescuing neuronal cell death. Interestingly, PLDP promotes tau LLPS, and modulates their intermolecular interactions to inhibit the formation of toxic tau aggregates, offering a conceptually innovative approach to tackle tauopathies. This is a first-of-its-kind polymer-based integrative approach that inhibits ferroptosis, counteracts amyloid toxicity, and modulates tau LLPS to mitigate the multifaceted toxicity of AD.

Transcranial alternating current stimulation (tACS) at gamma frequency: an up-and-coming tool to modify the progression of Alzheimer's Disease

The last decades have witnessed huge efforts devoted to deciphering the pathological mechanisms underlying Alzheimer's Disease (AD) and to testing new drugs, with the recent FDA approval of two anti-amyloid monoclonal antibodies for AD treatment. Beyond these drug-based experimentations, a number of pre-clinical and clinical trials are exploring the benefits of alternative treatments, such as non-invasive stimulation techniques on AD neuropathology and symptoms. Among the different non-invasive brain stimulation approaches, transcranial alternating current stimulation (tACS) is gaining particular attention due to its ability to externally control gamma oscillations. Here, we outline the current knowledge concerning the clinical efficacy, safety, ease-of-use and cost-effectiveness of tACS on early and advanced AD, applied specifically at 40 Hz frequency, and also summarise pre-clinical results on validated models of AD and ongoing patient-centred trials.

Prophylactic treatment with the c-Abl inhibitor, neurotinib, diminishes neuronal damage and the convulsive state in pilocarpine-induced mice

The molecular mechanisms underlying seizure generation remain elusive, yet they are crucial for developing effective treatments for epilepsy. The current study shows that inhibiting c-Abl tyrosine kinase prevents apoptosis, reduces dendritic spine loss, and maintains N-methyl-d-aspartate (NMDA) receptor subunit 2B (NR2B) phosphorylated in in vitro models of excitotoxicity. Pilocarpine-induced status epilepticus (SE) in mice promotes c-Abl phosphorylation, and disrupting c-Abl activity leads to fewer seizures, increases latency toward SE, and improved animal survival. Currently, clinically used c-Abl inhibitors are non-selective and have poor brain penetration. The allosteric c-Abl inhibitor, neurotinib, used here has favorable potency, selectivity, pharmacokinetics, and vastly improved brain penetration. Neurotinib-administered mice have fewer seizures and improved survival following pilocarpine-SE induction. Our findings reveal c-Abl kinase activation as a key factor in ictogenesis and highlight the impact of its inhibition in preventing the insurgence of epileptic-like seizures in rodents and humans.

Perineuronal Net Microscopy: From Brain Pathology to Artificial Intelligence

Perineuronal nets (PNN) are a special highly structured type of extracellular matrix encapsulating synapses on large populations of CNS neurons. PNN undergo structural changes in schizophrenia, epilepsy, Alzheimer's disease, stroke, post-traumatic conditions, and some other brain disorders. The functional role of the PNN microstructure in brain pathologies has remained largely unstudied until recently. Here, we review recent research implicating PNN microstructural changes in schizophrenia and other disorders. We further concentrate on high-resolution studies of the PNN mesh units surrounding synaptic boutons to elucidate fine structural details behind the mutual functional regulation between the ECM and the synaptic terminal. We also review some updates regarding PNN as a potential pharmacological target. Artificial intelligence (AI)-based methods are now arriving as a new tool that may have the potential to grasp the brain's complexity through a wide range of organization levels-from synaptic molecular events to large scale tissue rearrangements and the whole-brain connectome function. This scope matches exactly the complex role of PNN in brain physiology and pathology processes, and the first AI-assisted PNN microscopy studies have been reported. To that end, we report here on a machine learning-assisted tool for PNN mesh contour tracing.

Cognitive performance in aged rats is associated with differences in distinctive neuronal populations in the ventral tegmental area and altered synaptic plasticity in the hippocampus

Introduction

Deterioration of cognitive functions is commonly associated with aging, although there is wide variation in the onset and manifestation. Albeit heterogeneity in age-related cognitive decline has been studied at the cellular and molecular level, there is poor evidence for electrophysiological correlates. The aim of the current study was to address the electrophysiological basis of heterogeneity of cognitive functions in cognitively Inferior and Superior old (19-20 months) rats in the ventral tegmental area (VTA) and the hippocampus, having Young (12 weeks) rats as a control. The midbrain VTA operates as a hub amidst affective and cognitive facets, processing sensory inputs related to motivated behaviours and hippocampal memory. Increasing evidence shows direct dopaminergic and non-dopaminergic input from the VTA to the hippocampus.

Methods

Aged Superior and Inferior male rats were selected from a cohort of 88 animals based on their performance in a spatial learning and memory task. Using in vivo single-cell recording in the VTA, we examined the electrical activity of different neuronal populations (putative dopaminergic, glutamatergic and GABAergic neurons). In the same animals, basal synaptic transmission and synaptic plasticity were examined in hippocampal slices.

Results

Electrophysiological recordings from the VTA and hippocampus showed alterations associated with aging per se, together with differences specifically linked to the cognitive status of aged animals. In particular, the bursting activity of dopamine neurons was lower, while the firing frequency of glutamatergic neurons was higher in VTA of Inferior old rats. The response to high-frequency stimulation in hippocampal slices also discriminated between Superior and Inferior aged animals.

Discussion

This study provides new insight into electrophysiological information underlying compromised cerebral ageing. Further understanding of brain senescence, possibly related to neurocognitive decline, will help develop new strategies towards the preservation of a high quality of life.