Seasonal fluctuations in BDNF regulate hibernation and torpor in golden-mantled ground squirrels.

Aphagic hibernators such as the golden-mantled ground squirrel (GMGS; Callospermophilus lateralis) can fast for months and exhibit profound seasonal fluctuations in body weight, food intake, and behavior. Brain-derived neurotrophic factor (BDNF) regulates cellular and systemic metabolism via mechanisms that are conserved across mammalian species. In this study, we characterized regional changes in BDNF with hibernation, hypothermia, and seasonal cycle in GMGS. Analysis of BDNF protein concentrations by ELISA revealed overlapping seasonal patterns in the hippocampus and hypothalamus, where BDNF levels were highest in summer and lowest in winter. BDNF is the primary ligand for receptor tyrosine kinase B (TrkB), and BDNF/TrkB signaling in the brain potently regulates energy expenditure. To examine the functional relevance of seasonal variation in BDNF, hibernating animals were injected with the small molecule TrkB agonist 7,8-dihydroxyflavone (DHF) daily for 2 wk. When compared with vehicle, DHF-treated animals exhibited fewer torpor bouts and shorter bout durations. These results suggest that activating BDNF/TrkB disrupts hibernation and raise intriguing questions related to the role of BDNF as a potential regulatory mechanism or downstream response to seasonal changes in body temperature and environment.NEW & NOTEWORTHY Golden-mantled ground squirrels exhibit dramatic seasonal fluctuations in metabolism and can fast for months while hibernating. Brain-derived neurotrophic factor is an essential determinant of cellular and systemic metabolism, and in this study, we characterized seasonal fluctuations in BDNF expression and then administered the small molecule BDNF mimetic 7,8-dihydroxyflavone (DHF) in hibernating squirrels. The results indicate that activating BDNF/TrkB signaling disrupts hibernation, with implications for synaptic homeostasis in prolonged hypometabolic states.

Endothelial Adora2a Activation Promotes Blood-Brain Barrier Breakdown and Cognitive Impairment in Mice with Diet-Induced Insulin Resistance.

Obesity and insulin resistance elicit blood-brain barrier (BBB) breakdown in humans and animal models, but the relative contributions of the two pathologies remain poorly understood. These studies initially addressed the temporal progression of cerebrovascular dysfunction relative to dietary obesity or diet-induced insulin resistance in male mice. Obesity increased BBB permeability to the low molecular weight fluorophore sodium fluorescein (NaFl), whereas diet-induced insulin resistance increased permeability to both NaFl and Evans blue, which forms a high molecular weight complex with serum albumin. Serial section transmission electron microscopy analysis of hippocampal capillaries revealed that diabetes promotes involution of tight junctions, fenestration of endothelial cells, and pericyte regression. Chronic activation of adenosine receptor 2a (Adora2a) erodes tight junctions between endothelial cells of the cerebral vasculature in other models of chronic neuropathology, and we observed that acute Adora2a antagonism normalized BBB permeability in wild-type mice with diet-induced insulin resistance. Experiments in mice with inducible deletion of Adora2a in endothelial cells revealed protection against BBB breakdown with diet-induced insulin resistance, despite comparable metabolic dysfunction relative to nontransgenic littermates. Protection against BBB breakdown was associated with decreased vascular inflammation, recovery of hippocampal synaptic plasticity, and restoration of hippocampus-dependent memory. These findings indicate that Adora2a-mediated signaling in vascular endothelial cells disrupts the BBB in dietary obesity, and implicate cerebrovascular dysfunction as the underlying mechanism for deficits in synaptic plasticity and cognition with obesity and insulin resistance.SIGNIFICANCE STATEMENT The blood-brain barrier (BBB) restricts the entry of circulating factors into the brain, but obesity promotes BBB breakdown in humans and animal models. We used transgenic mice with resistance to BBB breakdown to investigate the role of neurovascular dysfunction in high-fat diet (HFD)-induced cognitive impairment. Transgenic mice with inducible ablation of Adora2a in endothelial cells were protected against BBB breakdown on HFD, despite comparable metabolic impairments relative to normal mice. Transgenic mice were also resistant to HFD-induced cognitive dysfunction and were protected against deficits in hippocampal synaptic plasticity. These findings indicate that Adora2a-mediated signaling in endothelial cells mediates obesity-induced BBB breakdown, and implicate cerebrovascular dysfunction as the mechanism for deficits in synaptic plasticity and cognition with obesity and diabetes.

Neutral Sphingomyelinase-2 Deficiency Ameliorates Alzheimer's Disease Pathology and Improves Cognition in the 5XFAD Mouse.

UNLABELLED: Recent evidence implicates exosomes in the aggregation of Aß and spreading of tau in Alzheimer's disease. In neural cells, exosome formation can be blocked by inhibition or silencing of neutral sphingomyelinase-2 (nSMase2). We generated genetically nSMase2-deficient 5XFAD mice (fro;5XFAD) to assess AD-related pathology in a mouse model with consistently reduced ceramide generation. We conducted in vitro assays to assess Aß42 aggregation and glial clearance with and without exosomes isolated by ultracentrifugation and determined exosome-induced amyloid aggregation by particle counting. We analyzed brain exosome content, amyloid plaque formation, neuronal degeneration, sphingolipid, Aß42 and phospho-tau levels, and memory-related behaviors in 5XFAD versus fro;5XFAD mice using contextual and cued fear conditioning. Astrocyte-derived exosomes accelerated aggregation of Aß42 and blocked glial clearance of Aß42 in vitro Aß42 aggregates were colocalized with extracellular ceramide in vitro using a bifunctional ceramide analog preloaded into exosomes and in vivo using anticeramide IgG, implicating ceramide-enriched exosomes in plaque formation. Compared with 5XFAD mice, the fro;5XFAD mice had reduced brain exosomes, ceramide levels, serum anticeramide IgG, glial activation, total Aß42 and plaque burden, tau phosphorylation, and improved cognition in a fear-conditioned learning task. Ceramide-enriched exosomes appear to exacerbate AD-related brain pathology by promoting the aggregation of Aß. Reduction of exosome secretion by nSMase2 loss of function improves pathology and cognition in the 5XFAD mouse model. SIGNIFICANCE STATEMENT: We present for the first time evidence, using Alzheimer's disease (AD) model mice deficient in neural exosome secretion due to lack of neutral sphingomyelinase-2 function, that ceramide-enriched exosomes exacerbate AD-related pathologies and cognitive deficits. Our results provide rationale to pursue a means of inhibiting exosome secretion as a potential therapy for individuals at risk for developing AD.

TLR2 knockout protects against diabetes-mediated changes in cerebral perfusion and cognitive deficits.

The risk of cognitive decline in diabetes (Type 1 and Type 2) is significantly greater compared with normoglycemic patients, and the risk of developing dementia in diabetic patients is doubled. The etiology for this is likely multifactorial, but one mechanism that has gained increasing attention is decreased cerebral perfusion as a result of cerebrovascular dysfunction. The innate immune system has been shown to play a role in diabetic vascular complications, notably through the Toll-like receptor (TLR)-stimulated release of proinflammatory cytokines and chemokines that lead to vascular damage. TLR2 has been implicated in playing a crucial role in the development of diabetic microvascular complications, such as nephropathy, and thus, we hypothesized that TLR2-mediated cerebrovascular dysfunction leads to decreased cerebral blood flow (CBF) and cognitive impairment in diabetes. Knockout of TLR2 conferred protection from impaired CBF in early-stage diabetes and from hyperperfusion in long-term diabetes, prevented the development of endothelium-dependent vascular dysfunction in diabetes, created a hyperactive and anxiolytic phenotype, and protected against diabetes-induced impairment of long-term hippocampal and prefrontal cortex-mediated fear learning. In conclusion, these findings support the involvement of TLR2 in the pathogenesis of diabetic vascular disease and cognitive impairment.

Tau immunotherapy modulates both pathological tau and upstream amyloid pathology in an Alzheimer's disease mouse model.

In Alzheimer's disease (AD), the pathological accumulation of tau appears to be a downstream effect of amyloid ß protein (Aß). However, the relationship between these two proteins and memory loss is unclear. In this study, we evaluated the specific removal of pathological tau oligomers in aged Tg2576 mice by passive immunotherapy using tau oligomer-specific monoclonal antibody. Removal of tau oligomers reversed memory deficits and accelerated plaque deposition in the brain. Surprisingly, Aß*56 levels decreased, suggesting a link between tau and Aß oligomers in the promotion of cognitive decline. The results suggest that tau oligomerization is not only a consequence of Aß pathology but also a critical mediator of the toxic effects observed afterward in AD. Overall, these findings support the potential of tau oligomers as a therapeutic target for AD.

Diisopropylfluorophosphate Impairs the Transport of Membrane-Bound Organelles in Rat Cortical Axons.

The extensive use of organophosphates (OPs) is an ongoing environmental health concern due to multiple reports of OP-related neurologic abnormalities. The mechanism of the acute toxicity of OPs has been attributed to inhibition of acetylcholinesterase (AChE), but there is growing evidence that this may not account for all the long-term neurotoxic effects of OPs. In previous experiments (using ex vivo and in vitro model systems) we observed that the insecticide OP chlorpyrifos impaired the movements of vesicles and mitochondria in axons. Here, using a time-lapse imaging technique, we evaluated the OP-nerve agent diisopropylfluorophosphate (DFP) across a wide range of concentrations (subnanomolar to micromolar) for effects on fast axonal transport of membrane-bound organelles (MBOs) that contain the amyloid precursor protein (APP) tagged with the fluorescent marker Dendra2 (APPDendra2). Both 1 and 24 hours of exposure to DFP and a positive control compound, colchicine, resulted in a decrease in the velocity of anterograde and retrograde movements of MBOs and an increase in the number of stationary MBOs. These effects occurred at picomolar (100 pM) to low nanomolar (0.1 nM) concentrations that were not associated with compromised cell viability or cytoskeletal damage. Moreover, the effects of DFP on axonal transport occurred at concentrations that did not inhibit AChE activity, and they were not blocked by cholinergic receptor antagonists. Given the fundamental importance of axonal transport to neuronal function, these observations may explain some of the long-term neurologic deficits that have been observed in humans who have been exposed to OPs.

PPARγ recruitment to active ERK during memory consolidation is required for Alzheimer's disease-related cognitive enhancement.

Cognitive impairment is a quintessential feature of Alzheimer's disease (AD) and AD mouse models. The peroxisome proliferator-activated receptor-γ (PPARγ) agonist rosiglitazone improves hippocampus-dependent cognitive deficits in some AD patients and ameliorates deficits in the Tg2576 mouse model for AD amyloidosis. Tg2576 cognitive enhancement occurs through the induction of a gene and protein expression profile reflecting convergence of the PPARγ signaling axis and the extracellular signal-regulated protein kinase (ERK) cascade, a critical mediator of memory consolidation. We therefore tested whether PPARγ and ERK associated in protein complexes that subserve cognitive enhancement through PPARγ agonism. Coimmunoprecipitation of hippocampal extracts revealed that PPARγ and activated, phosphorylated ERK (pERK) associated in Tg2576 in vivo, and that PPARγ agonism facilitated recruitment of PPARγ to pERK during memory consolidation. Furthermore, the amount of PPARγ recruited to pERK correlated with the cognitive reserve in humans with AD and in Tg2576. Our findings implicate a previously unidentified PPARγ-pERK complex that provides a molecular mechanism for the convergence of these pathways during cognitive enhancement, thereby offering new targets for therapeutic development in AD.

Part 3. Assessment of genotoxicity and oxidative damage in rats after chronic exposure to new-technology diesel exhaust in the ACES bioassay.

In 2001, the U.S. Environmental Protection Agency (EPA*) and the California Air Resources Board (CARB) adopted new standards for diesel fuel and emissions from heavy-duty diesel engines. By 2007, diesel engines were required to meet these new standards for particulate matter (PM), with other standards to follow. Through a combination of advanced compression-ignition engine technology, development of exhaust aftertreatment systems, and reformulated fuels, stringent standards were introduced. Before the 2007 standards were put in place by the EPA, human health effects linked to diesel exhaust (DE) exposure had been associated with diesel-fuel solvent and combustion components. In earlier research, diesel engine exhaust components were, in turn, linked to increased mutagenicity in cultures of Salmonella typhimurium and mammalian cells (Tokiwa and Ohnishi 1986). In addition, DE was shown to increase both the incidence of tumors and the induction of 8-hydroxy-deoxyguanosine (8-OHdG) adducts in rodents (Ichinose et al. 1997) and total DNA adducts in rats (Bond et al. 1990). Furthermore, DE is composed of a complex mixture of polycyclic aromatic hydrocarbons (PAHs) and particulates. One such PAH, 3-nitrobenzanthrone (3-NBA), is also found in urban air. 3-NBA has been observed to induce micronucleus formation in the DNA of human hepatoma cells (Lamy et al. 2004). The current study is part of the Advanced Collaborative Emissions Study (ACES), a multidisciplinary program carried out by the Health Effects Institute and the Coordinating Research Council. Its purpose was to determine whether recent improvements in the engineering of heavy-duty diesel engines reduce the toxicity associated with exposure to DE components. To this end, we evaluated potential genotoxicity and induction of oxidative stress in bioassays of serum and tissues from Wistar Han rats chronically exposed--for up to 24 months--to DE from a 2007-compliant diesel engine (new-technology diesel exhaust, or NTDE). Genotoxicity was measured as DNA strand breaks in lung tissue, using an alkaline-modified comet assay. As a correlate of possible DNA damage evaluated in the comet assay, concentrations of the free DNA adduct 8-OHdG were evaluated in serum by a competitive enzyme-linked immunosorbent assay (ELISA). The 8-OHdG fragment found in the serum is a specific biomarker for the repair of oxidative DNA damage. In addition, an assay for thiobarbituric acid reactive substances (TBARS) was used to assess oxidative stress and damage in the form of lipid peroxidation in the hippocampus region of the brains of the DE-exposed animals. These endpoints were evaluated at 1, 3, 12, and 24 months of exposure to DE or to a control atmosphere (filtered air). At the concentrations of DE evaluated, there were no significant effects of exposure in male or female rats after 1, 3, 12, or 24 months in any measure of DNA damage in the comet assay (%DNA in tail, tail length, tail moment, or olive moment). The comparison of exposure groups versus control and the comparison of groups by sex for 1 and 3 months of exposure showed no significant differences in serum 8-OHdG concentrations (P > 0.05). The concentrations of 8-OHdG in all exposure groups at 3 months were higher than those in exposure groups at any other time point (P < 0.05). Looking at the levels of 8-OHdG in serum in the 12-month and 24-month groups, we saw a significant difference from control in the 12-month group at the mid and high levels (P < 0.05), as well as some other scattered changes. Sex differences were noted in the 12-month high-level group (P < 0.05). However, these differences did not follow an exposure-dependent pattern. All other comparisons were not significant (P > 0.05). Hippocampal concentrations of TBARs, measured as malondialdehyde (MDA), showed some small and scattered changes in groups exposed to different levels of DE and at different time points, but we did not consider these to be exposure-related. We concluded that exposure to DE in these rats did not produce any significant increase in oxidative damage to lipids or damage to DNA in the form of strand breaks.

Research tool: Validation of floxed α7 nicotinic acetylcholine receptor conditional knockout mice using in vitro and in vivo approaches.

There is much interest in α7 nicotinic acetylcholine receptors (nAChRs) in CNS function since they are found throughout peripheral tissues as well as being highly expressed in brain regions implicated in attention, learning and memory. As such, the role of these receptors in many aspects of CNS function and disease is being actively investigated. To date, only one null mouse model (A7KO) is available which is non-conditional and constitutive. Since α7 nAChRs are present on neurons and glia (including astrocytes), as well as being developmentally regulated, there is an unmet need for the technical capability to control α7 nAChR gene expression. Therefore we have generated mice in which the fourth exon of the α7 nAChR gene (Chrna7) is flanked by loxP sites (B6-Chrna7(LBDEx4007Ehs)) which we refer to as floxed α7 nAChR conditional knockout or α7nAChR(flox). We validated the chosen approach by mating α7nAChR(flox) with mice expressing Cre recombinase driven by the glial acidic fibrillary protein (GFAP)-Cre promoter (GFAP-A7KO) to test whether α7nAChR(flox), GFAP-A7KO and appropriate littermate controls performed equally in our standard Rodent In Vivo Assessment Core battery to assess general health, locomotion, emotional and cognitive behaviours. Neither α7nAChR(flox) nor GFAP-A7KO exhibited significant differences from littermate controls in any of the baseline behavioural assessments we conducted, similar to the 'first generation' non-conditional A7KO mice. We also determined that α7 nAChR binding sites were absent on GFAP-positive astrocytes in hippocampal slices obtained from GFAP-A7KO offspring from α7nAChR(flox) and GFAP-Cre crosses. Finally, we validated that Cre recombinase (Cre)-mediated excision led to functional, cell- and tissue-specific loss of α7 nAChRs by demonstrating that choline-induced α7 nAChR currents were present in Cre-negative, but not synapsin promoter-driven Cre-positive, CA1 pyramidal neurons. Additionally, electrophysiological characterization of α7 nAChR-mediated current traces was similar in terms of amplitude and time constants of decay (during desensitization) for the α7nAChR(flox) and wild-type (WT) mice. Thus, we have in vivo and in vitro evidence that the Chrna7 exon 4 targeting strategy does not alter behavioural, cognitive, or electrophysiological properties compared to WT and that Cre-mediated excision is an effective approach to delete α7 nAChR expression in a cell-specific manner.

Cognitive enhancement with rosiglitazone links the hippocampal PPARγ and ERK MAPK signaling pathways.

We previously reported that the peroxisome proliferator-activated receptor γ (PPARγ) agonist rosiglitazone (RSG) improved hippocampus-dependent cognition in the Alzheimer's disease (AD) mouse model, Tg2576. RSG had no effect on wild-type littermate cognitive performance. Since extracellular signal-regulated protein kinase mitogen-activated protein kinase (ERK MAPK) is required for many forms of learning and memory that are affected in AD, and since both PPARγ and ERK MAPK are key mediators of insulin signaling, the current study tested the hypothesis that RSG-mediated cognitive improvement induces a hippocampal PPARγ pattern of gene and protein expression that converges with the ERK MAPK signaling axis in Tg2576 AD mice. In the hippocampal PPARγ transcriptome, we found significant overlap between peroxisome proliferator response element-containing PPARγ target genes and ERK-regulated, cAMP response element-containing target genes. Within the Tg2576 dentate gyrus proteome, RSG induced proteins with structural, energy, biosynthesis and plasticity functions. Several of these proteins are known to be important for cognitive function and are also regulated by ERK MAPK. In addition, we found the RSG-mediated augmentation of PPARγ and ERK2 activity during Tg2576 cognitive enhancement was reversed when hippocampal PPARγ was pharmacologically antagonized, revealing a coordinate relationship between PPARγ transcriptional competency and phosphorylated ERK that is reciprocally affected in response to chronic activation, compared with acute inhibition, of PPARγ. We conclude that the hippocampal transcriptome and proteome induced by cognitive enhancement with RSG harnesses a dysregulated ERK MAPK signal transduction pathway to overcome AD-like cognitive deficits in Tg2576 mice. Thus, PPARγ represents a signaling system that is not crucial for normal cognition yet can intercede to restore neural networks compromised by AD.

Sex Differences in Adipose Tissue Distribution Determine Susceptibility to Neuroinflammation in Mice With Dietary Obesity.

Preferential energy storage in subcutaneous adipose tissue (SAT) confers protection against obesity-induced pathophysiology in females. Females also exhibit distinct immunological responses, relative to males. These differences are often attributed to sex hormones, but reciprocal interactions between metabolism, immunity, and gonadal steroids remain poorly understood. We systematically characterized adipose tissue hypertrophy, sex steroids, and inflammation in male and female mice after increasing durations of high-fat diet (HFD)-induced obesity. After observing that sex differences in adipose tissue distribution before HFD were correlated with lasting protection against inflammation in females, we hypothesized that a priori differences in the ratio of subcutaneous to visceral fat might mediate this relationship. To test this, male and female mice underwent SAT lipectomy (LPX) or sham surgery before HFD challenge, followed by analysis of glial reactivity, adipose tissue inflammation, and reproductive steroids. Because LPX eliminated female resistance to the proinflammatory effects of HFD without changing circulating sex hormones, we conclude that sexually dimorphic organization of subcutaneous and visceral fat determines susceptibility to inflammation in obesity.

Loss of alpha7 nicotinic receptors enhances beta-amyloid oligomer accumulation, exacerbating early-stage cognitive decline and septohippocampal pathology in a mouse model of Alzheimer's disease.

Early Alzheimer's disease (AD) is marked by cholinergic hypofunction, neuronal marker loss, and decreased nicotinic acetylcholine receptor (nAChR) density from the cortex and hippocampus. alpha7 nAChRs expressed on cholinergic projection neurons and target regions have been implicated in neuroprotection against beta-amyloid (Abeta) toxicity and maintenance of the septohippocampal phenotype. We tested the role that alpha7 nAChRs perform in the etiology of early AD by genetically deleting the alpha7 nAChR subunit from the Tg2576 mouse model for AD and assessing animals for cognitive function and septohippocampal integrity. Thus, Tg2576 mice transgenic for mutant human amyloid precursor protein (APP) were crossed with alpha7 nAChR knock-out mice (A7KO) to render an animal with elevated Abeta in the absence of alpha7 nAChRs (A7KO-APP). We found that learning and memory deficits seen in 5-month-old APP mice are more severe in the A7KO-APP animals. Analyses of animals in early-stage preplaque cognitive decline revealed signs of neurodegeneration in A7KO-APP hippocampus as well as loss of cholinergic functionality in the basal forebrain and hippocampus. These changes occurred concomitant with the appearance of a dodecameric oligomer of Abeta that was absent from all other genotypic groups, generating the hypothesis that increased soluble oligomeric Abeta may underlie additional impairment of A7KO-APP cognitive function. Thus, alpha7 nAChRs in a mouse model for early-stage AD appear to serve a neuroprotective role through maintenance of the septohippocampal cholinergic phenotype and preservation of hippocampal integrity possibly through influences on Abeta accumulation and oligomerization.

Enhancement of select cognitive domains with rosiglitazone implicates dorsal hippocampus circuitry sensitive to PPARγ agonism in an Alzheimer's mouse model.

INTRODUCTION: Several clinical studies have tested the efficacy of insulin-sensitizing drugs for cognitive enhancement in Alzheimer's disease (AD) patients, as type 2 diabetes (T2D) is a well-recognized risk factor for AD. Pilot studies assessing FDA-approved diabetes drugs in subjects with early-stage disease have found cognitive benefit in subjects comorbid for insulin resistance. In AD mouse models with concomitant insulin resistance, we have shown that 4 weeks of RSG can reverse peripheral and central insulin resistance concomitant with rescue of hippocampus-dependent fear learning and memory and hippocampal circuitry deficits in 9-month-old (9MO) Tg2576 mice with no effect in wild-type (WT) mice. Bioinformatics analysis of genomic and proteomic data reveals an intimate link between PPARγ and MAPK/ERK signaling in the hippocampus. We then demonstrated a direct interaction between PPARγ and phospho-ERK in vitro and in vivo during memory consolidation. The translational value of this discovery is evidenced by the positive correlational relationship between human AD postmortem brain levels of pERK-PPARγ nuclear complexes with cognitive reserve. METHODS: We tested whether insulin sensitizer therapy could rescue spatial navigation, context discrimination, and object recognition learning and memory in aged wild-type and Tg2576 mice in addition to hippocampus-dependent contextual fear learning and memory, as we have previously reported. RESULTS: We found that rosiglitazone treatment improved cognitive domains that predominantly rely upon the dorsal hippocampus rather than those that additionally engage the ventral hippocampus. CONCLUSION: These results suggest that insulin sensitizer therapy with rosiglitazone improved age- and AD-related learning and memory deficits in circuit selective ways.

Beige adipocytes mediate the neuroprotective and anti-inflammatory effects of subcutaneous fat in obese mice.

Visceral obesity increases risk of cognitive decline in humans, but subcutaneous adiposity does not. Here, we report that beige adipocytes are indispensable for the neuroprotective and anti-inflammatory effects of subcutaneous fat. Mice lacking functional beige fat exhibit accelerated cognitive dysfunction and microglial activation with dietary obesity. Subcutaneous fat transplantation also protects against chronic obesity in wildtype mice via beige fat-dependent mechanisms. Beige adipocytes restore hippocampal synaptic plasticity following transplantation, and these effects require the anti-inflammatory cytokine interleukin-4 (IL4). After observing beige fat-mediated induction of IL4 in meningeal T-cells, we investigated the contributions of peripheral lymphocytes in donor fat. There was no sign of donor-derived lymphocyte trafficking between fat and brain, but recipient-derived lymphocytes were required for the effects of transplantation on cognition and microglial morphology. These findings indicate that beige adipocytes oppose obesity-induced cognitive impairment, with a potential role for IL4 in the relationship between beige fat and brain function.

Kinase suppressor of Ras1 compartmentalizes hippocampal signal transduction and subserves synaptic plasticity and memory formation.

The ERK/MAP kinase cascade is important for long-term memory formation and synaptic plasticity, with a myriad of upstream signals converging upon ERK activation. Despite this convergence of signaling, neurons routinely activate appropriate biological responses to different stimuli. Scaffolding proteins represent a mechanism to achieve compartmentalization of signaling and the appropriate targeting of ERK-dependent processes. We report that kinase suppressor of Ras (KSR1) functions biochemically in the hippocampus to scaffold the components of the ERK cascade, specifically regulating the cascade when a membrane fraction of ERK is activated via a PKC-dependent pathway but not via a cAMP/PKA-dependent pathway. Specificity of KSR1-dependent signaling also extends to specific downstream targets of ERK. Behaviorally and physiologically, we found that the absence of KSR1 leads to deficits in associative learning and theta burst stimulation-induced LTP. Our report provides novel insight into the endogenous scaffolding role of KSR1 in controlling kinase activation within the nervous system.

Oral quetiapine treatment results in time-dependent alterations of recognition memory and brain-derived neurotrophic factor-related signaling molecules in the hippocampus of rats.

Antipsychotic drugs (APDs) have a variety of important therapeutic applications for neuropsychiatric disorders. However, they are routinely prescribed off-label across all age categories, a controversial practice given their potential for producing metabolic and extrapyramidal side effects. Evidence also suggests that chronic treatment with some APDs may lead to impairments in cognition and decreases in brain volume, although these findings are controversial. The purpose of the studies described here was to evaluate one of the most commonly prescribed APDs, quetiapine, for chronic effects on recognition memory, brain-derived neurotrophic factor (BDNF), its precursor proBDNF, as well as relevant downstream signaling molecules that are known to influence neuronal plasticity and cognition. Multiple cohorts of adult rats were treated with quetiapine (25.0 mg/kg/day) for 30 or 90 days in their drinking water then evaluated for drug effects on motor function in a catalepsy assessment, recognition memory in a spontaneous novel object recognition (NOR) task, and BDNF-related signaling molecules in the post mortem hippocampus via Western Blot. The results indicated that oral quetiapine at a dose that did not induce catalepsy, led to time-dependent impairments in NOR performance, increases in the proBDNF/BDNF ratio, and decreases in Akt and CREB phosphorylation in the hippocampus. These results indicate that chronic treatment with quetiapine has the potential to adversely affect recognition memory and neurotrophin-related signaling molecules that support synaptic plasticity and cognitive function. Given the widespread use this APD across multiple conditions and patient populations, such long-term effects observed in animals should be considered.

Visceral adipose NLRP3 impairs cognition in obesity via IL-1R1 on CX3CR1+ cells.

Induction of the inflammasome protein cryopyrin (NLRP3) in visceral adipose tissue (VAT) promotes release of the proinflammatory cytokine IL-1ß in obesity. Although this mechanism contributes to peripheral metabolic dysfunction, effects on the brain remain unexplored. We investigated whether visceral adipose NLRP3 impairs cognition by activating microglial IL-1 receptor 1 (IL-1R1). After observing protection against obesity-induced neuroinflammation and cognitive impairment in NLRP3-KO mice, we transplanted VAT from obese WT or NLRP3-KO donors into lean recipient mice. Transplantation of VAT from a WT donor (TRANSWT) increased hippocampal IL-1ß and impaired cognition, but VAT transplants from comparably obese NLRP3-KO donors (TRANSKO) had no effect. Visceral adipose NLRP3 was required for deficits in long-term potentiation (LTP) in transplant recipients, and LTP impairment in TRANSWT mice was IL-1 dependent. Flow cytometric and gene expression analyses revealed that VAT transplantation recapitulated the effects of obesity on microglial activation and IL-1ß gene expression, and visualization of hippocampal microglia revealed similar effects in vivo. Inducible ablation of IL-1R1 in CX3CR1-expressing cells eliminated cognitive impairment in mice with dietary obesity and in transplant recipients and restored immunoquiescence in hippocampal microglia. These results indicate that visceral adipose NLRP3 impairs memory via IL-1-mediated microglial activation and suggest that NLRP3/IL-1ß signaling may underlie correlations between visceral adiposity and cognitive impairment in humans.

Chronic oral treatment with risperidone impairs recognition memory and alters brain-derived neurotrophic factor and related signaling molecules in rats.

Antipsychotic drugs (APDs) are essential for the treatment of schizophrenia and other neuropsychiatric illnesses such as bipolar disease. However, they are also extensively prescribed off-label for many other conditions, a practice that is controversial given their potential for long-term side effects. There is clinical and preclinical evidence that chronic treatment with some APDs may lead to impairments in cognition and decreases in brain volume, although the molecular mechanisms of these effects are unknown. The purpose of the rodent studies described here was to evaluate a commonly prescribed APD, risperidone, for chronic effects on recognition memory, brain-derived neurotrophic factor (BDNF), its precursor proBDNF, as well as relevant downstream signaling molecules that are known to influence neuronal plasticity and cognition. Multiple cohorts of adult rats were treated with risperidone (2.5 mg/kg/day) or vehicle (dilute acetic acid solution) in their drinking water for 30 or 90 days. Subjects were then evaluated for drug effects on recognition memory in a spontaneous novel object recognition task and protein levels of BDNF-related signaling molecules in the hippocampus and prefrontal cortex. The results indicated that depending on the treatment period, a therapeutically relevant daily dose of risperidone impaired recognition memory and increased the proBDNF/BDNF ratio in the hippocampus and prefrontal cortex. Risperidone treatment also led to a decrease in Akt and CREB phosphorylation in the prefrontal cortex. These results indicate that chronic treatment with a commonly prescribed APD, risperidone, has the potential to adversely affect recognition memory and neurotrophin-related signaling molecules that support synaptic plasticity and cognitive function.

c-Rel, an NF-kappaB family transcription factor, is required for hippocampal long-term synaptic plasticity and memory formation.

Transcription is a critical component for consolidation of long-term memory. However, relatively few transcriptional mechanisms have been identified for the regulation of gene expression in memory formation. In the current study, we investigated the activity of one specific member of the NF-kappaB transcription factor family, c-Rel, during memory consolidation. We found that contextual fear conditioning elicited a time-dependent increase in nuclear c-Rel levels in area CA1 and DG of hippocampus. These results suggest that c-rel is active in regulating transcription during memory consolidation. To identify the functional role of c-Rel in memory formation, we characterized c-rel(-/-) mice in several behavioral tasks. c-rel(-/-) mice displayed significant deficits in freezing behavior 24 h after training for contextual fear conditioning but showed normal freezing behavior in cued fear conditioning and in short-term contextual fear conditioning. In a novel object recognition test, wild-type littermate mice exhibited a significant preference for a novel object, but c-rel(-/-) mice did not. These results indicate that c-rel(-/-) mice have impaired hippocampus-dependent memory formation. To investigate the role of c-Rel in long-term synaptic plasticity, baseline synaptic transmission and long-term potentiation (LTP) at Schaffer collateral synapses in c-rel(-/-) mice was assessed. c-rel(-/-) slices had normal baseline synaptic transmission but exhibited significantly less LTP than did wild-type littermate slices. Together, our results demonstrate that c-Rel is necessary for long-term synaptic potentiation in vitro and hippocampus-dependent memory formation in vivo.

Tropisetron enhances recognition memory in rats chronically treated with risperidone or quetiapine.

While impairments of cognition in schizophrenia have the greatest impact on long-term functional outcome, the currently prescribed treatments, antipsychotic drugs (APDs), do not effectively improve cognition. Moreover, while more than 20 years have been devoted to the development of new drugs to treat cognitive deficits in schizophrenia, none have been approved to date. One area that has not been given proper attention at the preclinical or clinical stage of drug development is the chronic medication history of the test subject. Hence, very little is known about how chronic treatment with drugs that affect multiple receptors like APDs influence the response to a potential pro-cognitive agent. Therefore, the purpose of this study was to evaluate the α7 nicotinic acetylcholine receptor (α7 nAChR) partial agonist, tropisetron in rats chronically treated with APDs with distinct pharmacological profiles. Rats were treated orally with either risperidone (2.5 mg/kg/day) or quetiapine (25.0 mg/kg/day) for 30 or 90 days and then an acute injection of vehicle or tropisetron (3.0 mg/kg) was administered before training in a novel object recognition (NOR) task. After a 48 h delay (when recollection of the familiar object was impaired in vehicle-treated animals) neither 30 nor 90 days of risperidone or quetiapine treatment improved NOR performance. In contrast, tropisetron markedly improved NOR performance in rats treated with either APD for 30 or 90 days. These animal data reinforce the argument that two commonly prescribed APDs are not pro-cognitive agents and that α7 nAChR ligands like tropisetron have potential as adjunctive treatments in schizophrenia.