Neuroplastic changes in the olfactory bulb associated with nasal inflammation in mice.

BACKGROUND: Rhinitis and rhinosinusitis are olfactory disorders caused by inflammation of the nasal passage and paranasal sinuses. Although patients with chronic rhinosinusitis have smaller olfactory bulbs (OBs), there is limited knowledge regarding the influence of chronic nasal inflammation on OB neurons. OBJECTIVE: Repeated intranasal administration of LPS that induced persistent nasal inflammation in mice caused a loss of olfactory sensory neurons (OSNs) and gliosis and synaptic loss in the OBs within 3 weeks. The present study aimed to clarify the effects of long-term LPS treatment on the OB neurocircuit. METHODS: LPS was repeatedly administered into a mouse nostril for up to 24 weeks. For the recovery analyses, the mice received LPS for 10 weeks and were subsequently maintained without additional treatment for another 10 weeks. The effects of these treatments on the OBs were examined histologically. Three or more mice were analyzed per group. RESULTS: Long-term repeated LPS administration caused OB atrophy, particularly in the layers along which OSN axons travel and in the superficial external plexiform layer, in which tufted cells form synapses with interneurons. Interestingly, the OBs recovered from atrophy after cessation of LPS administration: OB volume and superficial external plexiform layer thickness returned to pretreatment levels after the nontreatment period. In contrast, OSN regeneration was incomplete. CONCLUSION: These results suggest that chronic nasal inflammation induces structural changes in a specific OB circuit related to tufted cells, whereas tufted cells retain a high degree of plasticity that enables recovery from structural damages after inflammation subsides.

Theanine, Antistress Amino Acid in Tea Leaves, Causes Hippocampal Metabolic Changes and Antidepressant Effects in Stress-Loaded Mice.

By comprehensively measuring changes in metabolites in the hippocampus of stress-loaded mice, we investigated the reasons for stress vulnerability and the effect of theanine, i.e., an abundant amino acid in tea leaves, on the metabolism. Stress sensitivity was higher in senescence-accelerated mouse prone 10 (SAMP10) mice than in normal ddY mice when these mice were loaded with stress on the basis of territorial consciousness in males. Group housing was used as the low-stress condition reference. Among the statistically altered metabolites, depression-related kynurenine and excitability-related histamine were significantly higher in SAMP10 mice than in ddY mice. In contrast, carnosine, which has antidepressant-like activity, and ornithine, which has antistress effects, were significantly lower in SAMP10 mice than in ddY mice. The ingestion of theanine, an excellent antistress amino acid, modulated the levels of kynurenine, histamine, and carnosine only in the stress-loaded SAMP10 mice and not in the group-housing mice. Depression-like behavior was suppressed in mice that had ingested theanine only under stress loading. Taken together, changes in these metabolites, such as kynurenine, histamine, carnosine, and ornithine, were suggested to be associated with the stress vulnerability and depression-like behavior of stressed SAMP10 mice. It was also shown that theanine action appears in the metabolism of mice only under stress loading.

Mutation in Sodium-Glucose Cotransporter 2 Results in Down-Regulation of Amyloid Beta (A4) Precursor-Like Protein 1 in Young Age, Which May Lead to Poor Memory Retention in Old Age.

Senescence-accelerated mouse prone 10 (SAMP10) exhibits cerebral atrophy and depression-like behavior. A line of SAMP10 with spontaneous mutation in the Slc5a2 gene encoding the sodium-glucose cotransporter (SGLT) 2 was named SAMP10/TaSlc-Slc5a2slc (SAMP10-ΔSglt2) and was identified as a renal diabetes model. In contrast, a line of SAMP10 with no mutation in SGLT2 (SAMP10/TaIdrSlc, SAMP10(+)) was recently established under a specific pathogen-free condition. Here, we examined the mutation effect in SGLT2 on brain function and longevity. No differences were found in the survival curve, depression-like behavior, and age-related brain atrophy between SAMP10-ΔSglt2 and SAMP10(+). However, memory retention was lower in SAMP10-ΔSglt2 mice than SAMP10(+). Amyloid beta (A4) precursor-like protein 1 (Aplp1) expression was significantly lower in the hippocampus of SAMP10-ΔSGLT2 than in SAMP10(+) at 2 months of age, but was similar at 12 months of age. CaM kinase-like vesicle association (Camkv) expression was remarkably lower in SAMP10(+). These genes have been reported to be involved in dendrite function. Amyloid precursor proteins have been reported to involve in maintaining homeostasis of glucose and insulin. These results suggest that mutation in SGLT2 results in down-regulation of Aplp1 in young age, which can lead to poor memory retention in old age.

Responses of perivascular macrophages to circulating lipopolysaccharides in the subfornical organ with special reference to endotoxin tolerance.

BACKGROUND: Circulating endotoxins including lipopolysaccharides (LPS) cause brain responses such as fever and decrease of food and water intake, while pre-injection of endotoxins attenuates these responses. This phenomenon is called endotoxin tolerance, but the mechanisms underlying it remain unclear. The subfornical organ (SFO) rapidly produces proinflammatory cytokines including interleukin-1ß (IL-1ß) in response to peripherally injected LPS, and repeated LPS injection attenuates IL-1ß production in the SFO, indicating that the SFO is involved in endotoxin tolerance. The purpose of this study is to investigate features of the IL-1ß source cells in the SFO of LPS-non-tolerant and LPS-tolerant mice. METHODS: We first established the endotoxin-tolerant mouse model by injecting LPS into adult male mice (C57BL/6J). Immunohistochemistry was performed to characterize IL-1ß-expressing cells, which were perivascular macrophages in the SFO. We depleted perivascular macrophages using clodronate liposomes to confirm the contribution of IL-1ß production. To assess the effect of LPS pre-injection on perivascular macrophages, we transferred bone marrow-derived cells obtained from male mice (C57BL/6-Tg (CAG-EGFP)) to male recipient mice (C57BL/6N). Finally, we examined the effect of a second LPS injection on IL-1ß expression in the SFO perivascular macrophages. RESULTS: We report that perivascular macrophages but not parenchymal microglia rapidly produced the proinflammatory cytokine IL-1ß in response to LPS. We found that peripherally injected LPS localized in the SFO perivascular space. Depletion of macrophages by injection of clodronate liposomes attenuated LPS-induced IL-1ß expression in the SFO. When tolerance developed to LPS-induced sickness behavior in mice, the SFO perivascular macrophages ceased producing IL-1ß, although bone marrow-derived perivascular macrophages increased in number in the SFO and peripherally injected LPS reached the SFO perivascular space. CONCLUSIONS: The current data indicate that perivascular macrophages enable the SFO to produce IL-1ß in response to circulating LPS and that its hyporesponsiveness may be the cause of endotoxin tolerance.

Novel frame-shift mutation in Slc5a2 encoding SGLT2 in a strain of senescence-accelerated mouse SAMP10.

The senescence-accelerated mouse prone10 (SAMP10) strain, a model of aging, exhibits cognitive impairments and cerebral atrophy. We noticed that SAMP10/TaSlc mice, a SAMP10 substrain, have developed persistent glucosuria over the past few years. In the present study, we characterized SAMP10/TaSlc mice and further identified a spontaneous mutation in the Slc5a2 gene encoding sodium-glucose co-transporter (SGLT) 2. The mean concentration of urine glucose was high in SAMP10/TaSlc mice and increased further with advancing age, whereas other strains of senescence-accelerated mice, including SAMP1/SkuSlc, SAMP6/TaSlc and SAMP8/TaSlc or normal aging control SAMR1/TaSlc mice, exhibited no detectable glucose in urine. SAMP10/TaSlc mice consumed increasing amounts of food and water compared to SAMR1/TaSlc mice, suggesting the compensation of polyuria and the loss of glucose. Oral glucose tolerance tests showed decreased glucose reabsorption in the kidney of SAMP10/TaSlc mice. In addition, blood glucose levels decreased in an age-dependent fashion. The kidney was innately larger than that of control mice with no histological alterations. We examined the expression levels of glucose transporters in the kidney. Among SGLT1, SGLT2, glucose transporter (GLUT) 1 and GLUT2, we found a significant decrease only in the level of SGLT2. DNA sequencing of SGLT2 in SAMP10/TaSlc mice revealed a single nucleotide deletion of guanine at 1236, which resulted in a frameshift mutation that produced a truncated protein. We designate this strain as SAMP10/TaSlc-Slc5a2(slc) (SAMP10-ΔSglt2). Recently, SGLT2 inhibitors have been demonstrated to be effective for the treatment of patients with type 2 diabetes (T2D). SAMP10-ΔSglt2 mice may serve as a unique preclinical model to study the link between aging-related neurodegenerative disorders and T2D.

Niemann-Pick disease type C1 predominantly involving the frontotemporal region, with cortical and brainstem Lewy bodies: an autopsy case.

Niemann-Pick disease type C (NPC) is an autosomal recessive neurovisceral lipid storage disorder. Two disease-causing genes (NPC1 and NPC2) have been identified. NPC is characterized by neuronal and glial lipid storage and NFTs. Here, we report a man with juvenile-onset progressive neurological deficits, including pyramidal signs, ataxia, bulbar palsy, vertical supranuclear ophthalmoplegia, and psychiatric symptoms; death occurred at age 37 before definitive clinical diagnosis. Post mortem gross examination revealed a unique distribution of brain atrophy, predominantly in the frontal and temporal lobes. Microscopically, lipid storage in neurons and widely distributed NFTs were observed. Lipid storage cells appeared in systemic organs and filipin staining indicated intracellular cholesterol accumulation in hepatic macrophages. Electron microscopy revealed accumulation of lipids and characteristic oligolamellar inclusions. These findings suggested an NPC diagnosis. Neuronal loss and gliosis were frequently accompanied by NFTs and occurred in the frontal and temporal cortices, hippocampus, amygdala, basal forebrain, basal ganglia, thalamus, substantia nigra and brain stem nuclei. Lewy bodies (LBs) were observed in most, but not all, regions where NFTs were evident. In contrast, neuronal lipid storage occurred in more widespread areas, including the parietal and occipital cortices where neurodegeneration with either NFTs or LBs was minimal. Molecular genetic analysis demonstrated that the patient had compound heterozygous mutations in the cysteine-rich loop (A1017T and Y1088C) of the NPC1 gene. To our knowledge there has been no previous report of the A1017T mutation. The pathological features of this patient support the notion that NPC has an aspect of α-synucleinopathy, and long-term survivors of NPC may develop a frontotemporal-predominant distribution of brain atrophy.

Anesthetized animal experiments for neuroscience research.

Brain research has progressed with anesthetized animal experiments for a long time. Recent progress in research techniques allows us to measure neuronal activity in awake animals combined with behavioral tasks. The trends became more prominent in the last decade. This new research style triggers the paradigm shift in the research of brain science, and new insights into brain function have been revealed. It is reasonable to consider that awake animal experiments are more ideal for understanding naturalistic brain function than anesthetized ones. However, the anesthetized animal experiment still has advantages in some experiments. To take advantage of the anesthetized animal experiments, it is important to understand the mechanism of anesthesia and carefully handle the obtained data. In this minireview, we will shortly summarize the molecular mechanism of anesthesia in animal experiments, a recent understanding of the neuronal activities in a sensory system in the anesthetized animal brain, and consider the advantages and disadvantages of the anesthetized and awake animal experiments. This discussion will help us to use both research conditions in the proper manner.

Structures and functions of the normal and injured human olfactory epithelium.

The olfactory epithelium (OE) is directly exposed to environmental agents entering the nasal cavity, leaving OSNs prone to injury and degeneration. The causes of olfactory dysfunction are diverse and include head trauma, neurodegenerative diseases, and aging, but the main causes are chronic rhinosinusitis (CRS) and viral infections. In CRS and viral infections, reduced airflow due to local inflammation, inflammatory cytokine production, release of degranulated proteins from eosinophils, and cell injury lead to decreased olfactory function. It is well known that injury-induced loss of mature OSNs in the adult OE causes massive regeneration of new OSNs within a few months through the proliferation and differentiation of progenitor basal cells that are subsequently incorporated into olfactory neural circuits. Although normal olfactory function returns after injury in most cases, prolonged olfactory impairment and lack of improvement in olfactory function in some cases poses a major clinical problem. Persistent inflammation or severe injury in the OE results in morphological changes in the OE and respiratory epithelium and decreases the number of mature OSNs, resulting in irreversible loss of olfactory function. In this review, we discuss the histological structure and distribution of the human OE, and the pathogenesis of olfactory dysfunction associated with CRS and viral infection.

Exome sequencing of senescence-accelerated mice (SAM) reveals deleterious mutations in degenerative disease-causing genes.

BACKGROUND: Senescence-accelerated mice (SAM) are a series of mouse strains originally derived from unexpected crosses between AKR/J and unknown mice, from which phenotypically distinct senescence-prone (SAMP) and -resistant (SAMR) inbred strains were subsequently established. Although SAMP strains have been widely used for aging research focusing on their short life spans and various age-related phenotypes, such as immune dysfunction, osteoporosis, and brain atrophy, the responsible gene mutations have not yet been fully elucidated. RESULTS: To identify mutations specific to SAMP strains, we performed whole exome sequencing of 6 SAMP and 3 SAMR strains. This analysis revealed 32,019 to 38,925 single-nucleotide variants in the coding region of each SAM strain. We detected Ogg1 p.R304W and Mbd4 p.D129N deleterious mutations in all 6 of the SAMP strains but not in the SAMR or AKR/J strains. Moreover, we extracted 31 SAMP-specific novel deleterious mutations. In all SAMP strains except SAMP8, we detected a p.R473W missense mutation in the Ldb3 gene, which has been associated with myofibrillar myopathy. In 3 SAMP strains (SAMP3, SAMP10, and SAMP11), we identified a p.R167C missense mutation in the Prx gene, in which mutations causing hereditary motor and sensory neuropathy (Dejerine-Sottas syndrome) have been identified. In SAMP6 we detected a p.S540fs frame-shift mutation in the Il4ra gene, a mutation potentially causative of ulcerative colitis and osteoporosis. CONCLUSIONS: Our data indicate that different combinations of mutations in disease-causing genes may be responsible for the various phenotypes of SAMP strains.

Selective localization of bone marrow-derived ramified cells in the brain adjacent to the attachments of choroid plexus.

Although the immune system modulates higher functions of the brain under non-inflammatory conditions, how immune cells interact with brain parenchymal cells remains to be determined. Using bone marrow chimeric mice in which the recipients' immune system was reconstituted by marrow cells derived from GFP-transgenic mice by syngeneic intra-bone marrow-bone marrow transplantation (IBM-BMT) and by intravenous (IV)-BMT, we examined the distribution, density and differentiation of donor-derived marrow cells in the brain parenchyma 2 weeks and 1, 4 and 8 months after BMT. Marrow-derived cells started to populate discrete brain regions from 1 to 4 months after BMT, exhibited ramified morphology and expressed Iba-1. The ramified marrow-derived cells were distributed in more brain regions and for a longer time after IBM-BMT than IV-BMT. Most of these discrete regions were adjacent to the attachments of choroid plexus that comprised thinned brain parenchyma consisting of astroglial processes in the narrow channel between the ependyma and pia. These specific portions of astroglial processes expressed fractalkine. In the choroid plexus stroma, not only Iba-1+ myeloid cells but also non-myeloid CXCL12-expressing cells were of bone marrow-origin. Transcripts of fractalkine, CXCL12 and their related molecules such as CX3CR1, ADAM10 and CXCR4 were detected in the tissue consisting of the choroid plexus, the attachments and adjacent brain parenchyma. Thus, bone marrow cells selectively enter the discrete brain regions adjacent to the attachments of choroid plexus and differentiate into ramified myeloid cells. Fractalkine in the attachments of choroid plexus and CXCL12 in the choroid plexus stroma may be involved in these brain-immune interactions.

Infiltration of peripheral immune cells into the olfactory bulb in a mouse model of acute nasal inflammation.

Chronic nasal inflammation induces robust olfactory bulb (OB) atrophy in mice. Here we examined initial events that occur in the OB after bilateral intranasal administration of lipopolysaccharide, focusing on the olfactory nerve fibers and meninges. We analyzed the time course of OB and meninges inflammation using histological and biochemical approaches. Within 12 h, we observed increased chemokine expression and transient infiltration of peripheral immune cells into the OB, resulting in the development of pro-inflammatory status in the OB. Meningeal immunity was activated. Resident microglia produced anti-inflammatory cytokines within 24 h. These could be the initial events that lead to OB atrophy.

Delayed microglial activation associated with the resolution of neuroinflammation in a mouse model of sublethal endotoxemia-induced systemic inflammation.

Systemic inflammation affects brain functions. In our previous study in which lipopolysaccharide (LPS) was injected intraperitoneally into mice at sublethal doses, choroid plexus macrophages produced interleukin-1ß and stimulated neighboring stromal cells. Activated stromal cells stimulate choroid plexus epithelial cells, and then choroid plexus epithelium-derived cytokines enter the brain parenchyma and stimulate astrocytes. Stimulated astrocytes then produce cytokines such as CCL11, CXCL10 and G-CSF and change the brain parenchymal microenvironment. However, the effects of an altered brain microenvironment on other brain cells remain to be determined. In the present study, we hypothesized that microglia are activated in response to astrocyte-induced changes in the brain microenvironment. Using the brains of mice treated with intraperitoneal LPS injection, Luminex multiplex cytokine immunoassays revealed increased hippocampal concentrations of CCL11, CXCL10 and G-CSF at 48 h after systemic LPS challenge. The concentrations of all cytokines examined returned to control levels at 72 h after LPS injection, which indicated a resolution of the neuroinflammation. Immunohistochemistry revealed that microglia were hypertrophied in mice at 48 h after systemic LPS challenge. Following isolation of microglial cells from the brain using magnetic-activated cell sorting, gene expression assays were performed with real-time reverse transcriptase-polymerase chain reaction. Isolated microglial cells exhibited much higher gene expression of the receptors for CCL11, CXCL10 and G-CSF than other brain cells. Microglial cells isolated from the brains of mice at 48 h after systemic LPS challenge exhibited the M2-like phenotype. In conclusion, microglial hypertrophy occurs following astrocytic reactions in a mouse model of sublethal endotoxemia-induced systemic inflammation, and hypertrophic microglia are polarized toward the M2-like phenotype and involved in the resolution of neuroinflammation.

Modification of the immune response by bacteriophages alters methicillin-resistant Staphylococcus aureus infection.

There is an urgent need to develop phage therapies for multidrug-resistant bacterial infections. However, although bacteria have been shown to be susceptible to phage therapy, phage therapy is not sufficient in some cases. PhiMR003 is a methicillin-resistant Staphylococcus aureus phage previously isolated from sewage influent, and it has demonstrated high lytic activity and a broad host range to MRSA clinical isolates in vitro. To investigate the potential of phiMR003 for the treatment of MRSA infection, the effects of phiMR003 on immune responses in vivo were analysed using phiMR003-susceptible MRSA strains in a mouse wound infection model. Additionally, we assessed whether phiMR003 could affect the immune response to infection with a nonsusceptible MRSA strain. Interestingly, wounds infected with both susceptible and nonsusceptible MRSA strains treated with phiMR003 demonstrated decreased bacterial load, reduced inflammation and accelerated wound closure. Moreover, the infiltration of inflammatory cells in infected tissue was altered by phiMR003. While the effects of phiMR003 on inflammation and bacterial load disappeared with heat inactivation of phiMR003. Transcripts of proinflammatory cytokines induced by lipopolysaccharide were reduced in mouse peritoneal macrophages. These results show that the immune modulation occurring as a response to the phage itself improves the clinical outcomes of phage therapy.

Prolonged and extended impacts of SARS-CoV-2 on the olfactory neurocircuit.

The impact of SARS-CoV-2 on the olfactory pathway was studied over several time points using Syrian golden hamsters. We found an incomplete recovery of the olfactory sensory neurons, prolonged activation of glial cells in the olfactory bulb, and a decrease in the density of dendritic spines within the hippocampus. These data may be useful for elucidating the mechanism underlying long-lasting olfactory dysfunction and cognitive impairment as a post-acute COVID-19 syndrome.

Proteomic identification of hippocampal proteins vulnerable to oxidative stress in excitotoxin-induced acute neuronal injury.

Excitotoxicity is involved in seizure-induced acute neuronal death, hypoxic-ischemic encephalopathy, and chronic neurodegenerative conditions such as Alzheimer's disease. Although oxidative stress has been implicated in excitotoxicity, the target proteins of oxidative damage during the course of excitotoxic cell death are still unclear. In the present study, we performed 2D-oxyblot analysis and mass spectrometric amino acid sequencing to identify proteins that were vulnerable to oxidative damage in the rat hippocampus during kainic acid (KA)-induced status epilepticus. We first investigated the time course in which oxidative protein damage occurred using immunohistochemistry. Carbonylated proteins, a manifestation of protein oxidation, were detected in hippocampal neurons as early as 3h after KA administration. Immunoreactivity for 8-hydroxy-2'-deoxyguanosine (8-OHdG) was also elevated at the same time point. The increase in oxidative damage to proteins and DNA occurred concomitantly with the early morphological changes in KA-treated rat hippocampus, i.e., changes in chromatin distribution and swelling of rough endoplasmic reticulum and mitochondria, which preceded the appearance of morphological features of neuronal death such as pyknotic nuclei and hypereosinophilic cytoplasm. Proteomic analysis revealed that several hippocampal proteins were consistently carbonylated at this time point, including heat shock 70kDa protein 4, valosin-containing protein, mitochondrial inner membrane protein (mitofilin), α-internexin, and tyrosine 3-monooxygenase/tryptophan 5-monooxygenase activation protein (14-3-3 protein). We propose that oxidative damage to these proteins may be one of the upstream events in the molecular pathway leading to excitotoxic cell death in KA-treated rat hippocampus, and these proteins may be targets of therapeutic intervention for seizure-induced neuronal death.

Defects in cytokine-mediated neuroprotective glial responses to excitotoxic hippocampal injury in senescence-accelerated mouse.

Aging is a result of damage accumulation, and understanding of the mechanisms of aging requires exploration of the cellular and molecular systems functioning to control damage. Senescence-accelerated mouse prone 10 (SAMP10) has been established as an inbred strain exhibiting accelerated aging with an earlier onset of cognitive impairment due to neurodegeneration than the senescence-resistant control (SAMR1) strain. We hypothesized that tissue-protective responses of glial cells are impaired in SAMP10 mice. We injected kainic acid (KA) to induce hippocampal injury and studied how cytokines were upregulated on Day 3 using 3-month-old SAMP10 and SAMR1 mice. Following microarray-based screening for upregulated genes, we performed real-time RT-PCR and immunohistochemistry. Results indicated well-orchestrated cytokine-mediated glial interactions in the injured hippocampus of SAMR1 mice, in which microglia-derived interferon (IFN)-γ stimulated astrocytes via IFN-γ receptor and thereby induced expression of CXCL10 and macrophage inflammatory protein (MIP)-1α, and activated microglia produced granulocyte-macrophage colony-stimulating factor (GM-CSF) and osteopontin (OPN). OPN was the most strongly upregulated cytokine. CD44, an OPN receptor, was also strongly upregulated in the neuropil, especially on neurons and astrocytes. KA-induced hippocampal upregulation of these cytokines was strikingly reduced in SAMP10 mice compared to SAMR1 mice. On Day 30 after KA injection, SAMP10 but not SAMR1 mice exhibited hippocampal layer atrophy. Since the OPN-CD44 system is essential for neuroprotection and remodeling, these findings highlight the defects of SAMP10 mice in cytokine-mediated neuroprotective glia-neuron interactions, which may be associated with the mechanism underlying the vulnerability of SAMP10 mice to age-related neurodegeneration.

Morphological impairments in microglia precede age-related neuronal degeneration in senescence-accelerated mice.

The ageing brain is characterized by degenerative changes in both neurons and glia. Although neurons are known to lose dendritic complexity with ageing, age-related changes in the morphology of microglia have not been well documented. We investigated potential age-related changes in microglial morphology using mouse models. Senescence-accelerated mouse prone 10 (SAMP10) in which neuronal degeneration begins to appear around 8 months of age and becomes progressively remarkable with advancing age was used as a model of brain ageing. Senescence-accelerated mouse resistant 1 (SAMR1) in which age-related neuronal changes are inconspicuous was used as usual-ageing controls. Hippocampal sections prepared from 3-, 8- and 14-month-old SAMP10 and 3-, 8-, 14- and 24-month-old SAMR1 mice were stained immunohistochemically with anti-Iba-1 antibody to highlight microglia. Stick figures of individual microglia reflecting the length and complexity of cytoplasmic processes were made by camera lucida drawing. Parameters representing morphological features of microglia were quantified using an image analyzer: area of convex closure, cell body area, number of primary processes, maximal branch order, combined projection length, number of segments and number of tips. Pathological changes of processes such as beading and clusters of fragmented twigs were counted. In microglia of 3- and 8-month-old SAMP10 mice, combined projection length was shorter and numbers of segments and tips were smaller than those in age-matched SAMR1 mice. Similar changes were detected in SAMR1 mice at age 14 months and older. Microglia of SAMP10 mice at all ages were characterized by having frequent pathological changes in processes, which were not remarkable in SAMR1 mice at any age. These morphological abnormalities in microglia of SAMP10 mice preceded the onset of neuronal degeneration and may lead to making brain tissue less protective to neurons. We propose that preceding abnormalities in microglia may contribute to the vulnerability to age-related neuronal degeneration in SAMP10 mice.

Increased cytokine expression in the choroid plexus stroma and epithelium in response to endotoxin-induced systemic inflammation in mice.

Sepsis-associated encephalopathy (SAE) is characterized as diffuse brain dysfunction in patients with excessive systemic inflammatory reaction to an infection. In our previous studies using a mouse model of SAE with intraperitoneal injection of lipopolysaccharide (LPS), tissue concentrations of various cytokines were elevated in the entire brain parenchyma 4 and 24 h following LPS administration. Cytokines elevated at 4 h were produced by the choroid plexus, leptomeninges and vascular endothelium, while those at 24 h were produced by astrocytes. Interleukin (IL)-1ß did not increase in the concentration in the brain parenchyma during the period from 1 to 24 h following LPS. In the present study, we hypothesized that the intracranial cells that initially respond to systemic inflammation are situated in the choroid plexus and produce IL-1ß to initiate cytokine-mediated reactions. We quantified the transcript levels of related cytokines within the choroid plexus and specified the choroid plexus cells that are involved in the immediate cytokine-mediated responses. Mice received LPS or saline by intraperitoneal injection. Four hours after treatments, the choroid plexuses were isolated and subjected to cytokine gene expression analyses using real-time reverse transcription-polymerase chain reaction. Another group of mice was fixed at 1, 4 and 24 h after treatments and the expression of cytokines and receptors was studied with double immunohistofluorescence staining. The transcript levels of IL-1ß, CC-motif ligand (CCL)2, CXC-motif ligand (CXCL)1, CXCL2 and IL-6 in the choroid plexus were significantly increased in mice treated with LPS compared to saline control. The IL-1ß expression was remarkable in choroid plexus macrophages at 1 and 4 h but not in the brain parenchyma. Choroid plexus stromal cells expressed IL-1 receptor type 1 (IL-1R1). The IL-1R1-bearing stromal cells produced CCL2, CXCL1, CXCL2 and IL-6 at 4 h. Choroid plexus epithelial cells expressed CXCR2, a common receptor for CXCL1 and CXCL2. Choroid plexus epithelial cells also expressed CCL2, CXCL1 and CXCL2 at 4 h, and IL-1R1-bearing stromal cells expressed CXCR2. Therefore, in response to systemic LPS injection, one of the intracranial reactions was initiated within the choroid plexus using IL-1ß derived from macrophages. The choroid plexus stromal cells subsequently had elevated expression of CCL2, CXCL1, CXCL2 and IL-6. The choroid plexus epithelial cells also had elevated expression of CCL2, CXCL1 and CXCL2. The presence of receptors for these cytokines on both epithelial and stromal cells raised the possibility of reciprocal interactions between these cells. The results suggested that the immediate early responses exerted by the choroid plexus are relevant to understanding how SAE is initiated in clinical settings.

Sex-dependent differences in the gut microbiota following chronic nasal inflammation in adult mice.

A growing body of evidence suggests a relationship between olfactory dysfunction and the pathogenesis of mental disorders. Our previous studies indicated that chronic nasal inflammation caused loss of olfactory sensory neurons and gross atrophy of the olfactory bulb, which may lead to olfactory dysfunction. Simultaneously, increasing numbers of reports have elucidated the importance of gut microbiota to maintain brain function and that dysbiosis may be associated with neuropsychiatric disorders. Here we examined whether chronic nasal inflammation perturbed gut microbiota and whether there were sex differences in this pattern. Eight-week-old C57BL/6 mice repeatedly received bilateral nasal administration of lipopolysaccharide (LPS) 3 times/week to cause chronic nasal inflammation or saline as a control. At 9 weeks, cecal feces were used for 16S metagenomic analysis and whole blood and fresh tissue of spleen were used for ELISA analyses. Microbiome analysis demonstrated a remarkable change of the gut microbiota in male mice with chronic nasal inflammation which was different from that in female mice. In both mice, systemic inflammation did not occur. This has shown for the first time that chronic nasal inflammation correlates with sex-dependent changes in the gut microbiota. The detailed mechanism and potential alteration to brain functions await further studies.

Widespread time-dependent changes in tissue cytokine concentrations in brain regions during the acute phase of endotoxemia in mice.

Sepsis-associated encephalopathy (SAE) is a diffuse brain dysfunction induced by the systemic response to infection in septic patients. In the present study, we modeled SAE by administering lipopolysaccharide (LPS) intraperitoneally to mice at a concentration of 3.0 mg/kg. We investigated regional preferences for cytokine-mediated brain reactions to endotoxemia and at what time point brain inflammation begins, as well as what cytokines are involved in acute brain reactions. Brains were divided into seven parts: cortex (CTX), olfactory system (Olf), hippocampus (Hip), striatum (Str), diencephalon (Die), brain stem (BS), and cerebellum (CBL). In each brain region, we determined the tissue concentrations of 11 cytokines: CCL2, CCL3, CCL11, CXCL1, CXCL2, CXCL9, CXCL10, G-CSF, IL-1ß, IL-6, and TNF-α, in mice injected with LPS or saline, at 1, 4, and 24 h after injection using multiplex cytokine assays. Every brain region responded with the production of multiple cytokines to LPS-induced systemic inflammation during the acute phase (4-24 h) after LPS injection. IL-6, CCL2, CCL3, CXCL1, CXCL2, CXCL9, and TNF-α were "early cytokines" that increased only at 4 h but not at 24 h after LPS injection in most brain regions. CCL11, CXCL10, and G-CSF were "late cytokines" that were elevated up to 24 h after LPS injection in selected brain regions. The regions Olf, Hip, and Die were the most responsive to endotoxemia; these regions produced ten cytokines and continued to produce three "late cytokines" up to 24 h after LPS injection. Str was the least responsive to endotoxemia. The widespread nature of brain cytokine production explains the characteristics of SAE. Further studies on the roles of CCL11, CXCL10, and G-CSF may be especially important in terms of potential prevention of SAE between 4 and 24 h after the onset of sepsis.