Topographical Visualization of the Reciprocal Projection between the Medial Septum and the Hippocampus in the 5XFAD Mouse Model of Alzheimer's Disease

Mapping the bioimaging marker of Alzheimer's disease based on pupillary light response-driven brain-wide fMRI in awake mice

Pupil dynamics has emerged as a critical non-invasive indicator of brain state changes. In particular, pupillary-light-responses (PLR) in Alzheimer's disease (AD) patients may be used as biomarkers of brain degeneration. To characterize AD-specific PLR and its underlying neuromodulatory sources, we combined high-resolution awake mouse fMRI with real-time pupillometry to map brain-wide event-related correlation patterns based on illumination-driven pupil constriction ( P c ) and post-illumination pupil dilation recovery (amplitude, P d , and time, T ). The P c -driven differential analysis revealed altered visual signal processing coupled with reduced thalamocortical activation in AD mice compared with the wild-type normal mice. In contrast, the post-illumination pupil dilation recovery-based fMRI highlighted multiple brain areas related to AD brain degeneration, including the cingulate cortex, hippocampus, septal area of the basal forebrain, medial raphe nucleus, and pontine reticular nuclei (PRN). Also, brain-wide functional connectivity analysis highlighted the most significant changes in PRN of AD mice, which serves as the major subcortical relay nuclei underlying oculomotor function. This work combined non-invasive pupil-fMRI measurements in preclinical models to identify pupillary biomarkers based on neuromodulatory dysfunction coupled with AD brain degeneration.

Hippocampal subfield vulnerability to α-synuclein pathology precedes neurodegeneration and cognitive dysfunction

Cognitive dysfunction is a salient feature of Parkinson's disease (PD) and Dementia with Lewy bodies (DLB). The onset of dementia reflects the spread of Lewy pathology throughout forebrain structures. The mere presence of Lewy pathology, however, provides limited indication of cognitive status. Thus, it remains unclear whether Lewy pathology is the de facto substrate driving cognitive dysfunction in PD and DLB. Through application of α-synuclein fibrils in vivo, we sought to examine the influence of pathologic inclusions on cognition. Following stereotactic injection of α-synuclein fibrils within the mouse forebrain, we measured the burden of α-synuclein pathology at 1-, 3-, and 6-months post-injection within subregions of the hippocampus and cortex. Under this paradigm, the hippocampal CA2/3 subfield was especially susceptible to α-synuclein pathology. Strikingly, we observed a drastic reduction of pathology in the CA2/3 subfield across time-points, consistent with the consolidation of α-synuclein pathology into dense somatic inclusions followed by neurodegeneration. Silver-positive degenerating neurites were observed prior to neuronal loss, suggesting that this might be an early feature of fibril-induced neurotoxicity and a precursor to neurodegeneration. Critically, mice injected with α-synuclein fibrils developed progressive deficits in spatial learning and memory. These findings support that the formation of α-synuclein inclusions in the mouse forebrain precipitate neurodegenerative changes that recapitulate features of Lewy-related cognitive dysfunction.

Interictal Spikes in Alzheimer's Disease: Preclinical Evidence for Dominance of the Dentate Gyrus and Cholinergic Control by Medial Septum

HIGHLIGHTS

Interictal spikes (IIS) occur in 3 mouse lines with Alzheimer's disease featuresIIS in all 3 mouse lines were most frequent during rapid eye movement (REM) sleepThe dentate gyrus showed larger IIS and earlier current sources vs. CA1 or cortexChemogenetic silencing of medial septum (MS) cholinergic neurons reduced IIS during REMMS silencing did not change REM latency, duration, number of bouts or theta power.

Interictal spikes (IIS) are a common type of abnormal electrical activity in Alzheimer's disease (AD) and preclinical models. The brain regions where IIS are largest are not known but are important because such data would suggest sites that contribute to IIS generation. Because hippocampus and cortex exhibit altered excitability in AD models, we asked which areas dominate the activity during IIS along the cortical-CA1-dentate gyrus (DG) dorso-ventral axis. Because medial septal (MS) cholinergic neurons are overactive when IIS typically occur, we also tested the novel hypothesis that silencing the MS cholinergic neurons selectively would reduce IIS.We used mice that simulate aspects of AD: Tg2576 mice, presenilin 2 (PS2) knockout mice and Ts65Dn mice. To selectively silence MS cholinergic neurons, Tg2576 mice were bred with choline-acetyltransferase (ChAT)-Cre mice and offspring were injected in the MS with AAV encoding inhibitory designer receptors exclusively activated by designer drugs (DREADDs). We recorded local field potentials along the cortical-CA1-DG axis using silicon probes during wakefulness, slow-wave sleep (SWS) and rapid eye movement (REM) sleep.We detected IIS in all transgenic or knockout mice but not age-matched controls. IIS were detectable throughout the cortical-CA1-DG axis and occurred primarily during REM sleep. In all 3 mouse lines, IIS amplitudes were significantly greater in the DG granule cell layer vs. CA1 pyramidal layer or overlying cortex. Current source density analysis showed robust and early current sources in the DG, and additional sources in CA1 and the cortex also. Selective chemogenetic silencing of MS cholinergic neurons significantly reduced IIS rate during REM sleep without affecting the overall duration, number of REM bouts, latency to REM sleep, or theta power during REM. Notably, two control interventions showed no effects.Consistent maximal amplitude and strong current sources of IIS in the DG suggest that the DG is remarkably active during IIS. In addition, selectively reducing MS cholinergic tone, at times when MS is hyperactive, could be a new strategy to reduce IIS in AD.

Diosgenin restores memory function via SPARC-driven axonal growth from the hippocampus to the PFC in Alzheimer's disease model mice

Central nervous system axons have minimal capacity to regenerate in adult brains, hindering memory recovery in Alzheimer's disease (AD). Although recent studies have shown that damaged axons sprouted in adult and AD mouse brains, long-distance axonal re-innervation to their targets has not been achieved. We selectively visualized axon-growing neurons in the neural circuit for memory formation, from the hippocampus to the prefrontal cortex, and showed that damaged axons successfully extended to their native projecting area in mouse models of AD (5XFAD) by administration of an axonal regenerative agent, diosgenin. In vivo transcriptome analysis detected the expression profile of axon-growing neurons directly isolated from the hippocampus of 5XFAD mice. Secreted protein acidic and rich in cysteine (SPARC) was the most expressed gene in axon-growing neurons. Neuron-specific overexpression of SPARC via adeno-associated virus serotype 9 delivery in the hippocampus recovered memory deficits and axonal projection to the prefrontal cortex in 5XFAD mice. DREADDs (Designer receptors exclusively activated by designer drugs) analyses revealed that SPARC overexpression-induced axonal growth in the 5XFAD mouse brain directly contributes to memory recovery. Elevated levels of SPARC on axonal membranes interact with extracellular rail-like collagen type I to promote axonal remodeling along their original tracings in primary cultured hippocampal neurons. These findings suggest that SPARC-driven axonal growth in the brain may be a promising therapeutic strategy for AD and other neurodegenerative diseases.

Hippocampal subfield vulnerability to α-synuclein pathology precedes neurodegeneration and cognitive dysfunction

Cognitive dysfunction is a salient feature of Parkinson's disease (PD) and Dementia with Lewy bodies (DLB). The onset of dementia reflects the spread of Lewy pathology throughout forebrain structures. The mere presence of Lewy pathology, however, provides limited indication of cognitive status. Thus, it remains unclear whether Lewy pathology is the de facto substrate driving cognitive dysfunction in PD and DLB. Through application of α-synuclein fibrils in vivo , we sought to examine the influence of pathologic inclusions on cognition. Following stereotactic injection of α-synuclein fibrils within the mouse forebrain, we measured the burden of α-synuclein pathology at 1-, 3-, and 6-months post-injection within subregions of the hippocampus and cortex. Under this paradigm, the hippocampal CA2/3 subfield was especially susceptible to α- synuclein pathology. Strikingly, we observed a drastic reduction of pathology in the CA2/3 subfield across time-points, consistent with the consolidation of α-synuclein pathology into dense somatic inclusions followed by neurodegeneration. Silver-positive degenerating neurites were observed prior to neuronal loss, suggesting that this might be an early feature of fibril-induced neurotoxicity and a precursor to neurodegeneration. Critically, mice injected with α-synuclein fibrils developed progressive deficits in spatial learning and memory. These findings support that the formation of α-synuclein inclusions in the mouse forebrain precipitate neurodegenerative changes that recapitulate features of Lewy-related cognitive dysfunction.

Highlights

Mice injected with α-synuclein fibrils develop hippocampal and cortical α- synuclein pathology with a dynamic regional burden at 1-, 3-, and 6-months post-injection.Silver-positive neuronal processes are an early and enduring degenerative feature of the fibril model, while extensive neurodegeneration of the hippocampal CA2/3 subfield is detected at 6-months post-injection.Mice exhibit progressive hippocampal-dependent spatial learning and memory deficits.Forebrain injection of α-synuclein fibrils may be used to model aspects of Lewy-related cognitive dysfunction.

Protective effects of CCL01 against Aβ-induced neurotoxicity in 5xFAD transgenic mouse model of Alzheimer's disease

Alzheimer's disease (AD) is the most common dementia characterized by the excessive accumulation of amyloid-beta (Aβ) and tau aggregates, as well as neuronal damage and neuroinflammation. Metabolic disruption in AD has been noticed because metabolite alterations closely correlate with Aβ neuropathology and behavioral phenotypes. Accordingly, controlling various neuropathological processes and metabolic disruption is an efficient therapeutic strategy for AD treatment. In this study, we evaluated the effects of a combination of Cuscuta seeds and Lactobacillus paracasei NK112 (CCL01) on AD neuropathology and altered metabolism in five familial AD (5xFAD) transgenic mice and neuronal cell cultures. First, we observed that CCL01 exerted neuroprotective effects in HT22 hippocampal neurons and primary cultured neurons. CCL01 ameliorated memory decline and protected synapses and neuronal survival in 5xFAD mice. These effects were related to the inhibition of tau phosphorylation. CCL01 also inhibited the activation of mitogen-activated protein kinase (MAPK) signaling and neuroinflammatory processes. Moreover, the metabolite profile-particularly characterized by altered phospholipid metabolism-was significantly changed in the 5xFAD group, while CCL01 partly restored the alteration. Lysophosphatidylcholine (lysoPC), the levels of which were higher in the brains of 5xFAD mice, exerted neurotoxicity in vitro, whereas CCL01 protected neurons from lysoPC-induced toxicity by regulating MAPK signaling. Additionally, CCL01 administration reduced gut inflammation in the 5xFAD mice. In summary, we demonstrated that CCL01 improved the memory function of 5xFAD mice by protecting neurons against Aβ- and lysoPC-induced toxicity through the regulation of MAPK signaling, neuroinflammation, tau phosphorylation, and gut inflammation, suggesting the potential of CCL01 as treatment for AD.

The laterodorsal tegmentum and seizure regulation: Revisiting the evidence

Electrical deep brain stimulation (DBS) is now a routine treatment option for patients suffering from medically refractory epilepsy. DBS of the anterior nucleus of the thalamus (ANT) has proven to be effective but, despite its success, few patients experience complete cessation of seizure activity. However, improving the therapy is challenging because the mechanism underlying its action remains largely unknown. One angle on improving the effectiveness of ANT stimulation is to better understand the various anatomic regions that send projections to and through this area. Here, the authors utilized a connectomic atlas of the mouse brain to better understand the regions projecting to the ANT and were particularly interested by the presence of robust cholinergic projections from the laterodorsal tegmentum (LDT). A subsequent review of the literature resulted in limited studies, which presented convincing evidence supporting this region's role in seizure control present in acute rodent models of epilepsy. It is thus the purpose of this paper to encourage further research into the role of the LDT on seizure mitigation, with mechanistic effects likely stemming from its cholinergic projections to the ANT. While previous studies have laid a firm foundation supporting the role of this region in modulation of seizure activity, modern scientific methodology has yet to be applied to further elucidate the mechanisms and potential benefits associated with LDT stimulation in the epileptic population.

Leveraging genetic diversity in mice to inform individual differences in brain microstructure and memory

In human Alzheimer's disease (AD) patients and AD mouse models, both differential pre-disease brain features and differential disease-associated memory decline are observed, suggesting that certain neurological features may protect against AD-related cognitive decline. The combination of these features is known as brain reserve, and understanding the genetic underpinnings of brain reserve may advance AD treatment in genetically diverse human populations. One potential source of brain reserve is brain microstructure, which is genetically influenced and can be measured with diffusion MRI (dMRI). To investigate variation of dMRI metrics in pre-disease-onset, genetically diverse AD mouse models, we utilized a population of genetically distinct AD mice produced by crossing the 5XFAD transgenic mouse model of AD to 3 inbred strains (C57BL/6J, DBA/2J, FVB/NJ) and two wild-derived strains (CAST/EiJ, WSB/EiJ). At 3 months of age, these mice underwent diffusion magnetic resonance imaging (dMRI) to probe neural microanatomy in 83 regions of interest (ROIs). At 5 months of age, these mice underwent contextual fear conditioning (CFC). Strain had a significant effect on dMRI measures in most ROIs tested, while far fewer effects of sex, sex*strain interactions, or strain*sex*5XFAD genotype interactions were observed. A main effect of 5XFAD genotype was observed in only 1 ROI, suggesting that the 5XFAD transgene does not strongly disrupt neural development or microstructure of mice in early adulthood. Strain also explained the most variance in mouse baseline motor activity and long-term fear memory. Additionally, significant effects of sex and strain*sex interaction were observed on baseline motor activity, and significant strain*sex and sex*5XFAD genotype interactions were observed on long-term memory. We are the first to study the genetic influences of brain microanatomy in genetically diverse AD mice. Thus, we demonstrated that strain is the primary factor influencing brain microstructure in young adult AD mice and that neural development and early adult microstructure are not strongly altered by the 5XFAD transgene. We also demonstrated that strain, sex, and 5XFAD genotype interact to influence memory in genetically diverse adult mice. Our results support the usefulness of the 5XFAD mouse model and convey strong relationships between natural genetic variation, brain microstructure, and memory.

Medial and dorsal lateral septum involving social disruption stress-primed escalation in acid-induced writhes

Introduction

Stress may cause prospective escalations in abdominal pain magnitude and accumbal TRPV1 expression, while central neural circuits mediating these stress effects remain unclear.

Methods

Using retrograde tracing methods, we first demonstrated the existence of a medial septal-dorsal lateral septal -accumbal circuit very likely involving social disruption stress-primed escalations in acid-induced writhes and accumbal TRPV1 level. An intersectional viral strategy and virus-carrying hM3Dq and hM4Di DREADDs were, then, employed to selectively modulate GABAergic and cholinergic neuronal activity in medial and dorsal lateral septum.

Results

Exciting medial septal GABAergic neuron was found to prevent social disruption stress-primed escalations in acid-induced writhes and accumbal TRPV1 and PKCε expressions. Likewise, inactivating dorsal lateral septal cholinergic neurons was also effective in abolishing these stress-primed escalations. Inactivating GABAergic neuron in non-stressed animals' medial septum was found to reproduce the stress-primed effects in causing heightened acid-induced writhes and accumbal TRPV1 and PKCε levels.

Discussion

These results, taken together, prompt us to conclude that social disruption stress may produce plastic changes in a newly-identified medial septal-dorsal lateral septal-accumbal circuit. Moreover, medial septal GABAergic hypoactivity and dorsal lateral septal cholinergic hyperactivity are, at least, two likely causes reflecting such stress-produced escalations in abdominal pain magnitude and pain transduction-related protein over-expression in nucleus accumbens.

Mesoscopic Mapping of Visual Pathway in a Female 5XFAD Mouse Model of Alzheimer's Disease

Amyloid-β (Aβ) deposition and Aβ-induced neurodegeneration appear in the retina and retinorecipient areas in the early stages of Alzheimer's disease (AD). Although these Aβ-related changes in the retina cause damage to the visual functions, no studies have yet revealed the alterations in the visual pathways of AD. Therefore, we investigated the alterations of visual circuits in the AD mouse model using anterograde tracer cholera toxin β subunits (CTβ). Moreover, we investigated the Aβ accumulation in the retina and retinorecipient areas and the neuronal loss, and synaptic degeneration in retinorecipient areas by immunofluorescent staining of 4- and 12-month-old female 5XFAD transgenic mice. Our results demonstrated that Aβ accumulation and neurodegeneration occurred in the retina and retinorecipient regions of early and late stages of the 5XFAD mice. Retinal efferents to the suprachiasmatic nucleus and lateral geniculate nucleus were impaired in the early stage of AD. Moreover, retinal connections to the dorsal lateral geniculate nucleus and superior colliculus were degenerated in the late-stage of AD. These findings reveal the Aβ-related pathology induced visual circuit disturbances at the mesoscale level in both the early and late stages of AD and provide anatomical and functional insights into the visual circuitry of AD.

The clinical correlation between Alzheimer's disease and epilepsy

Alzheimer's disease and epilepsy are common nervous system diseases in older adults, and their incidence rates tend to increase with age. Patients with mild cognitive impairment and Alzheimer's disease are more prone to have seizures. In patients older than 65 years, neurodegenerative conditions accounted for ~10% of all late-onset epilepsy cases, most of which are Alzheimer's disease. Epilepsy and seizure can occur in the early and late stages of Alzheimer's disease, leading to functional deterioration and behavioral alterations. Seizures promote amyloid-β and tau deposits, leading to neurodegenerative processes. Thus, there is a bi-directional association between Alzheimer's disease and epilepsy. Epilepsy is a risk factor for Alzheimer's disease and, in turn, Alzheimer's disease is an independent risk factor for developing epilepsy in old age. Many studies have evaluated the shared pathogenesis and clinical relevance of Alzheimer's disease and epilepsy. In this review, we discuss the clinical associations between Alzheimer's disease and epilepsy, including their incidence, clinical features, and electroencephalogram abnormalities. Clinical studies of the two disorders in recent years are summarized, and new antiepileptic drugs used for treating Alzheimer's disease are reviewed.

Alteration of Neural Pathways and Its Implications in Alzheimer’s Disease

Alzheimer’s disease (AD) is a neurodegenerative disease accompanied by cognitive and behavioral symptoms. These AD-related manifestations result from the alteration of neural circuitry by aggregated forms of amyloid-β (Aβ) and hyperphosphorylated tau, which are neurotoxic. From a neuroscience perspective, identifying neural circuits that integrate various inputs and outputs to determine behaviors can provide insight into the principles of behavior. Therefore, it is crucial to understand the alterations in the neural circuits associated with AD-related behavioral and psychological symptoms. Interestingly, it is well known that the alteration of neural circuitry is prominent in the brains of patients with AD. Here, we selected specific regions in the AD brain that are associated with AD-related behavioral and psychological symptoms, and reviewed studies of healthy and altered efferent pathways to the target regions. Moreover, we propose that specific neural circuits that are altered in the AD brain can be potential targets for AD treatment. Furthermore, we provide therapeutic implications for targeting neuronal circuits through various therapeutic approaches and the appropriate timing of treatment for AD.

Glutamatergic Neurotransmission Controls the Functional Lateralization of the mPFC in the Modulation of Anxiety Induced by Social Defeat Stress in Male Mice

The rodent medial prefrontal cortex (mPFC) is anatomically divided into cingulate (Cg1), prelimbic (PrL), and infralimbic (IL) subareas. The left and right mPFC (L and RmPFC) process emotional responses induced by stress-related stimuli, and LmPFC and RmPFC inhibition elicit anxiogenesis and anxiolysis, respectively. Here we sought to investigate (i) the mPFC functional laterality on social avoidance/anxiogenic-like behaviors in male mice subjected to chronic social defeat stress (SDS), (ii) the effects of left prelimbic (PrL) inhibition (with local injection of CoCl₂) on the RmPFC glutamatergic neuronal activation pattern (immunofluorescence assay), and (iii) the effects of the dorsal right mPFC (Cg1 + PrL) NMDA receptor blockade (with local injection of AP7) on the anxiety induced by left dorsal mPFC inhibition in mice exposed to the elevated plus maze (EPM). Results showed that chronic SDS induced anxiogenic-like behaviors followed by the rise of ΔFosB labeling and by ΔFosB + CaMKII double-labeling bilaterally in the Cg1 and IL subareas of the mPFC. Chronic SDS also increased ΔFosB and by ΔFosB + CaMKII labeling only on the right PrL. Also, the left PrL inhibition increased cFos + CaMKII labeling in the contralateral PrL and IL. Moreover, anxiogenesis induced by the left PrL inhibition was blocked by NMDA receptor antagonist AP7 injected into the right PrL. These findings suggest the lateralized control of the glutamatergic neurotransmission in the modulation of emotional-like responses in mice subjected to chronic SDS.

Roles and Mechanisms of Axon-Guidance Molecules in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized by progressive memory decline and cognitive dysfunctions. Although the causes of AD have not yet been established, many mechanisms have been proposed. Axon-guidance molecules play the roles in the occurrence and development of AD by participating in different mechanisms. Therefore, what roles do axon-guidance molecules play in AD? This study aimed at elucidating how axon-guidance molecules Netrins, Slits, Semaphorins, and Ephrins regulate the levels of Aβ, hyperphosphorylation of tau protein, Reelin, and other ways through different signaling pathways, in order to show the roles of axon-guidance molecules in the occurrence and development of AD. And it is hoped that this study can provide a theoretical basis and new perspectives in the search for new therapeutic targets for AD.

An epoxide hydrolase inhibitor reduces neuroinflammation in a mouse model of Alzheimer's disease

Neuroinflammation has been increasingly recognized to play a critical role in Alzheimer's disease (AD). The epoxy fatty acids (EpFAs) are derivatives of the arachidonic acid metabolism pathway and have anti-inflammatory activities. However, their efficacy is limited because of their rapid hydrolysis by the soluble epoxide hydrolase (sEH). We report that sEH is predominantly expressed in astrocytes and is elevated in postmortem brain tissue from patients with AD and in the 5xFAD β amyloid mouse model of AD. The amount of sEH expressed in AD mouse brains correlated with a reduction in brain EpFA concentrations. Using a specific small-molecule sEH inhibitor, 1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea (TPPU), we report that TPPU treatment protected wild-type mice against LPS-induced inflammation in vivo. Long-term administration of TPPU to the 5xFAD mouse model via drinking water reversed microglia and astrocyte reactivity and immune pathway dysregulation. This was associated with reduced β amyloid pathology and improved synaptic integrity and cognitive function on two behavioral tests. TPPU treatment correlated with an increase in EpFA concentrations in the brains of 5xFAD mice, demonstrating brain penetration and target engagement of this small molecule. These findings support further investigation of TPPU as a potential therapeutic agent for the treatment of AD.

Regulation of hippocamposeptal input within the medial septum/diagonal band of Broca

The medial septum/diagonal band of Broca (MS/DBB) receives direct GABAergic input from the hippocampus via hippocamposeptal (HS) projection neurons as part of a reciprocal loop that mediates cognition and is altered in Alzheimer's disease. Cholinergic and GABAergic interactions occur throughout the MS/DBB, but it is not known how HS GABA release is impacted by these circuits. Most HS neurons contain somatostatin (SST), so to evoke HS GABA release we expressed Cre-dependent mCherry/channelrhodopisin-2 (ChR2) in the hippocampi of SST-IRES-Cre mice and then used optogenetics to stimulate HS fibers while performing whole-cell patch clamp recordings from MS/DBB neurons in acute slices. We found that the acetylcholine receptor (AChR) agonist carbachol and the GABA_B receptor (GABA_BR) agonist baclofen significantly decreased HS GABA release in the MS/DBB. Carbachol's effects were blocked by eliminating local GABAergic activity or inhibiting GABA_BRs, indicating that it was indirectly decreasing HS GABA release by increasing GABAergic tone. There was no effect of acute exposure to amyloid-β on HS GABA release. Repetitive stimulation of HS fibers increased spontaneous GABA release in the MS/DBB, revealing that HS projections can modulate local GABAergic tone. These results show that HS GABA release has far-reaching impacts on overall levels of inhibition in the MS/DBB and is under regulatory control by cholinergic and GABAergic activity. This bidirectional modulation of GABA release from local and HS projections in the MS/DBB will likely have profound impact not only on activity within the MS/DBB, but also on output to the hippocampus and hippocampal-dependent learning and memory.

Spatial memory deficiency early in 6xTg Alzheimer's disease mouse model

Alzheimer’s disease (AD) is mainly characterized by the deposition of extracellular amyloid plaques and intracellular accumulation of neurofibrillary tangles (NFTs). While the recent 5xFAD AD mouse model exhibits many AD-related phenotypes and a relatively early and aggressive amyloid β production, it does not show NFTs. Here, we developed and evaluated a novel AD mouse model (6xTg-AD, 6xTg) by crossbreeding 5xFAD mice with mice expressing mutant (P301L) tau protein (MAPT). Through behavioral and histopathological tests, we analyzed cognitive changes and neuropathology in 6xTg mice compared to their respective parental strains according to age. Spatial memory deficits occurred in 6xTg mice at 2 months of age, earlier than they occurred in 5xFAD mice. Histopathological data revealed aggressive Aβ42 and p-tau accumulation in 6xTg mice. Microglial activation occurred in the cortex and hippocampus of 6xTg mice beginning at 2 months. In 6xTg model mice, the synaptic loss was observed in the cortex from 4 months of age and in the hippocampus from 6 months of age, and neuronal loss appeared in the cortex from 4 months of age and in the hippocampus 6 months of age, earlier than it is observed in the 5xFAD and JNPL3 models. These results showed that each pathological symptom appeared much faster than in their parental animal models. In conclusion, these novel 6xTg-AD mice might be an advanced animal model for studying AD, representing a promising approach to developing effective therapy.

Trigonelline recovers memory function in Alzheimer's disease model mice: evidence of brain penetration and target molecule

Trigonelline (TGN; 1-methylpyridin-1-ium-3-carboxylate) is a widely distributed alkaloid derived from plants. Since we previously found a neurite outgrowth effect of TGN, we hypothesised that TGN might help to improve memory deficits. Here, the efficacy of TGN in restoring amyloid β (Aβ)-induced axonal degeneration and in improving memory function was investigated in Alzheimer's disease 5XFAD model mice that overexpress mutated APP and PS1 genes. Exposure of Aβ25-35 for 3 days induced atrophy of axons and dendrites. Post treatment of TGN recovered the lengths of axons and dendrites. Following oral administration of TGN in mice, TGN itself was detected in the plasma and cerebral cortex. Oral administration of TGN to 5XFAD mice for 14 days showed significant improvement in object recognition memory (P < 0.001) and object location memory (P < 0.01). TGN administration also normalised neurofilament light levels in the cerebral cortex (P < 0.05), which is an axonal damage-associated biomarker. Analysis of target proteins of TGN in neurons by a drug affinity responsive target stability (DARTS) method identified that creatine kinase B-type (CKB) is a direct binding protein of TGN. Treatment with a CKB inhibitor cancelled the TGN-induced axonal and dendritic growth. In conclusion, we found for the first time that TGN penetrates the brain and may activate CKB, leading to axonal formation. This study shows the potential of TGN as a new drug candidate, and a new target molecule, CKB, in memory recovery signalling.

Cholinergic Dysfunction Involvement in Chronic Cerebral Hypoperfusion-Induced Impairment of Medial Septum-dCA1 Neurocircuit in Rats

Chronic cerebral hypoperfusion (CCH) is considered a preclinical condition of mild cognitive impairment and thought to precede dementia. However, as the principal cholinergic source of hippocampus, whether the septo-hippocampal neurocircuit was impaired after CCH is still unknown. In this study, we established the CCH rat model by bilateral common carotid artery occlusion (2VO). Under anesthesia, the medial septum (MS) of rats was stimulated to evoke the field excitatory post-synaptic potential (fEPSP) in the pyramidal cell layer of dCA1. Consequently, we observed decreased amplitude of fEPSP and increased paired-pulse ratio (PPR) after 8-week CCH. After tail pinch, we also found decreased peak frequency and shortened duration of hippocampal theta rhythm in 2VO rats, indicating the dysfunction of septo-hippocampal neurocircuit. Besides, by intracerebroventricularly injecting GABAergic inhibitor (bicuculline) and cholinergic inhibitors (scopolamine and mecamylamine), we found that CCH impaired both the pre-synaptic cholinergic release and the post-synaptic nAChR function in MS-dCA1 circuits. These results gave an insight into the role of CCH in the impairment of cholinergic MS-dCA1 neurocircuits. These findings may provide a new idea about the CCH-induced neurodegenerative changes.