Fentanyl self-administration impacts brain immune responses in male Sprague-Dawley rats.

Opioid use disorder (OUD) affects over two million in the United States and is an increasing public health crisis. The abuse of fentanyl and the emergence of potent fentanyl derivatives increases the risk for the user to succumb to overdose, but also to develop OUD. While intense attention is currently focused on understanding the complexity of behaviors and neural functions that contribute to OUD, much remains to be discovered concerning the interactions of opioid intake with the immune response in the central nervous system (CNS). In the present studies, we tested the hypothesis that short-term abstinence from fentanyl self-administration associates with altered expression of innate immune markers. Male Sprague-Dawley rats were trained to self-administer fentanyl (0.0032 mg/kg/infusion) to stability followed by 24 h of abstinence. Several innate immune markers, as well as opioid receptors (ORs) and intracellular pattern recognition receptors (PRRs), were interrogated within nodes of the neurocircuitry involved in OUD processes, including the prefrontal cortex (PFC), nucleus accumbens (NAc), caudate putamen (CPu), hippocampus (HIP) and midbrain (MB). In the present study, few immune targets were impacted in the PFC and MB during short-term abstinence from fentanyl (relative to saline) self-administration. However, increased expression of cytokines [e.g., interleukin (IL)1ß, IL5], chemokines [e.g., C-C motif chemokine 20 (MIP3α)], tumor necrosis factor α (TNFα) and interferon (IFN) proteins (e.g., IFNß and IFNγ)] was seen in the NAc, while decreased expression of cytokines (e.g., several ILs), chemokines [e.g., granulocyte-macrophage colony-stimulating factor (GMCSF), monocyte chemoattractant protein (MCP) MCP1, MIP3α], the chemokine ligand 5 (RANTES) and interferons (e.g., IFNß and IFNγ) in the HIP. Positive correlations were observed between cumulative fentanyl intake and expression of IL1ß and IL6 in the NAc, and significant negative correlations with fentanyl intake and IFN ß, IL2, IL5, IL12p70 and IL17 in the HIP. Few changes in OR expression was observed during early abstinence from fentanyl self-administration. Excitingly, the expression of the PRR, stimulator of interferon genes (STING) negatively correlated with cumulative fentanyl intake and significantly correlated to specific cytokines, chemokines and interferon proteins in the HIP. Although the CPu appears relatively invulnerable to changes in innate immune markers, the highest correlations between cumulative fentanyl intake with MAVS and/or STING was measured in the CPu. Our findings provide the first evidence of CNS innate immune responses and implicate STING as novel mechanistic targets of immunomodulation during short-term abstinence from fentanyl self-administration.

Elevated Neuroglobin Lessens Neuroinflammation and Alleviates Neurobehavioral Deficits Induced by Acute Inhalation of Combustion Smoke in the Mouse.

Acute inhalation of combustion smoke produces long-term neurologic deficits in survivors. To study the mechanisms that contribute to the development of neurologic deficits and identify targets for prevention, we developed a mouse model of acute inhalation of combustion smoke, which supports longitudinal investigation of mechanisms that underlie the smoke induced inimical sequelae in the brain. Using a transgenic mouse engineered to overexpress neuroglobin, a neuroprotective oxygen-binding globin protein, we previously demonstrated that elevated neuroglobin preserves mitochondrial respiration and attenuates formation of oxidative DNA damage in the mouse brain after smoke exposure. In the current study, we show that elevated neuronal neuroglobin attenuates the persistent inflammatory changes induced by smoke exposure in the mouse brain and mitigates concordant smoke-induced long-term neurobehavioral deficits. Specifically, we found that increases in hippocampal density of GFAP and Iba-1 positive cells that are detected post-smoke in wild-type mice are absent in the neuroglobin overexpressing transgenic (Ngb-tg) mice. Similarly, the smoke induced hippocampal myelin depletion is not observed in the Ngb-tg mice. Importantly, elevated neuroglobin alleviates behavioral and memory deficits that develop after acute smoke inhalation in the wild-type mice. Taken together, our findings suggest that the protective effects exerted by neuroglobin in the brains of smoke exposed mice afford protection from long-term neurologic sequelae of acute inhalation of combustion smoke. Our transgenic mouse provides a tool for assessing the potential of elevated neuroglobin as possible strategy for management of smoke inhalation injury.

PPARγ agonism attenuates cocaine cue reactivity.

Cocaine use disorder is a chronic relapsing condition characterized by compulsive drug seeking and taking even after prolonged abstinence periods. Subsequent exposure to drug-associated cues can promote intense craving and lead to relapse in abstinent humans and rodent models. The responsiveness to these cocaine-related cues, or 'cue reactivity', can trigger relapse and cocaine-seeking behaviors; cue reactivity is measurable in cocaine-dependent humans as well as rodent models. Cue reactivity is thought to be predictive of cocaine craving and relapse. Here we report that PPARγ agonism during abstinence from cocaine self-administration reduced previously active lever pressing in Sprague Dawley rats during cue-reactivity tests, while administration of the PPARγ antagonist, GW9662, reversed this effect. PPARγ agonism also normalized nuclear ERK activity in the medial prefrontal cortex and hippocampus which was reversed with GW9662. Our results support the utility of PPARγ agonism as a relapse prevention strategy to maintain abstinence in the presence of cocaine-associated cues.

Acute inhalation of combustion smoke triggers neuroinflammation and persistent anxiety-like behavior in the mouse.

CONTEXT: Acute inhalation of combustion smoke triggers neurologic sequelae in survivors. Due to the challenges posed by heterogeneity of smoke exposures in humans, mechanistic links between acute smoke inhalation and neuropathologic sequelae have not been systematically investigated. METHODS: Here, using mouse model of acute inhalation of combustion smoke, we studied longitudinal neurobehavioral manifestations of smoke exposures and molecular/cellular changes in the mouse brain. RESULTS: Immunohistochemical analyses at eight months post-smoke, revealed hippocampal astrogliosis and microgliosis accompanied by reduced myelination. Elevated expression of proinflammatory cytokines was also detected. Longitudinal testing in different neurobehavioral paradigms in the course of post-smoke recovery, revealed lasting anxiety-like behavior. The examined paradigms included the open field exploration/anxiety testing at two, four and six months post-smoke, which detected decreases in total distance traveled and time spent in the central arena in the smoke-exposed compared to sham-control mice, suggestive of dampened exploratory activity and increased anxiety-like behavior. In agreement with reduced open field activity, cued fear conditioning test revealed increased freezing in response to conditioned auditory stimulus in mice after acute smoke inhalation. Similarly, elevated plus maze testing demonstrated lesser presence in open arms of the maze, consistent with anxiety-like behavior, for the post-smoke exposure mice. CONCLUSIONS: Taken together, our data demonstrate for the first time persistent neurobehavioral manifestations of acute inhalation of combustion smoke and provide new insights into long-term progression of events initiated by disrupted brain oxygenation that might contribute to lasting adverse sequelae in survivors of smoke inhalation injuries.

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.

Animal Model of Sensorineural Hearing Loss Associated with Lassa Virus Infection.

UNLABELLED: Approximately one-third of Lassa virus (LASV)-infected patients develop sensorineural hearing loss (SNHL) in the late stages of acute disease or in early convalescence. With 500,000 annual cases of Lassa fever (LF), LASV is a major cause of hearing loss in regions of West Africa where LF is endemic. To date, no animal models exist that depict the human pathology of LF with associated hearing loss. Here, we aimed to develop an animal model to study LASV-induced hearing loss using human isolates from a 2012 Sierra Leone outbreak. We have recently established a murine model for LF that closely mimics many features of human disease. In this model, LASV isolated from a lethal human case was highly virulent, while the virus isolated from a nonlethal case elicited mostly mild disease with moderate mortality. More importantly, both viruses were able to induce SNHL in surviving animals. However, utilization of the nonlethal, human LASV isolate allowed us to consistently produce large numbers of survivors with hearing loss. Surviving mice developed permanent hearing loss associated with mild damage to the cochlear hair cells and, strikingly, significant degeneration of the spiral ganglion cells of the auditory nerve. Therefore, the pathological changes in the inner ear of the mice with SNHL supported the phenotypic loss of hearing and provided further insights into the mechanistic cause of LF-associated hearing loss. IMPORTANCE: Sensorineural hearing loss is a major complication for LF survivors. The development of a small-animal model of LASV infection that replicates hearing loss and the clinical and pathological features of LF will significantly increase knowledge of pathogenesis and vaccine studies. In addition, such a model will permit detailed characterization of the hearing loss mechanism and allow for the development of appropriate diagnostic approaches and medical care for LF patients with hearing impairment.

Behavioural and neurological symptoms accompanied by cellular neuroinflammation in IL-10-deficient mice infected with Plasmodium chabaudi.

BACKGROUND: Cerebral malaria is one of the most severe complications of Plasmodium falciparum infection and occurs mostly in young African children. This syndrome results from a combination of high levels of parasitaemia and inflammation. Although parasite sequestration in the brain is a feature of the human syndrome, sequestering strains do not uniformly cause severe malaria, suggesting interplay with other factors. Host genetic factors such as mutations in the promoters of the cytokines IL-10 and TNF are also clearly linked to severe disease. Plasmodium chabaudi, a rodent malaria parasite, leads to mild illness in wildtype animals. However, IL-10(-/-) mice respond to parasite with increased levels of pro-inflammatory cytokines IFN-γ and TNF, leading to lethal disease in the absence of sequestration in the brain. These mice also exhibit cerebral symptoms including gross cerebral oedema and haemorrhage, allowing study of these critical features of disease without the influence of sequestration. METHODS: The neurological consequences of P. chabaudi infection were investigated by performing a general behavioural screen (SHIRPA). The immune cell populations found in the brain during infection were also analysed using flow cytometry and confocal microscopy. RESULTS: IL-10(-/-) mice suffer significant declines in behavioural and physical capacities during infection compared to wildtype. In addition, grip strength and pain sensitivity were affected, suggestive of neurological involvement. Several immune cell populations were identified in the perfused brain on day 7 post-infection, suggesting that they are tightly adherent to the vascular endothelium, or potentially located within the brain parenchyma. There was an increase in both inflammatory monocyte and resident macrophage (CD11b(hi), CD45(+), MHCII(+), Ly6C(+/-)) numbers in IL-10(-/-) compared to wildtype animals. In addition, the activation state of all monocytes and microglia (CD11b(int), CD45(-), MHC-II(+)) were increased. T cells making IFN-γ were also identified in the brain, but were localized within the vasculature, and not the parenchyma. CONCLUSIONS: These studies demonstrate exacerbated neuroinflammation concurrent with development of behavioural symptoms in P. chabaudi infection of IL-10(-/-) animals.

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.

Cognitive enhancing treatment with a PPARγ agonist normalizes dentate granule cell presynaptic function in Tg2576 APP mice.

Hippocampal network hyperexcitability is considered an early indicator of Alzheimer's disease (AD) memory impairment. Some AD mouse models exhibit similar network phenotypes. In this study we focused on dentate gyrus (DG) granule cell spontaneous and evoked properties in 9-month-old Tg2576 mice that model AD amyloidosis and cognitive deficits. Using whole-cell patch-clamp recordings, we found that Tg2576 DG granule cells exhibited spontaneous EPSCs that were higher in frequency but not amplitude compared with wild-type mice, suggesting hyperactivity of DG granule cells via a presynaptic mechanism. Further support of a presynaptic mechanism was revealed by increased I-O relationships and probability of release in Tg2576 DG granule cells. Since we and others have shown that activation of the peroxisome proliferator-activated receptor gamma (PPARγ) axis improves hippocampal cognition in mouse models for AD as well as benefitting memory performance in some humans with early AD, we investigated how PPARγ agonism affected synaptic activity in Tg2576 DG. We found that PPARγ agonism normalized the I-O relationship of evoked EPSCs, frequency of spontaneous EPSCs, and probability of release that, in turn, correlated with selective expression of DG proteins essential for presynaptic SNARE function that are altered in patients with AD. These findings provide evidence that DG principal cells may contribute to early AD hippocampal network hyperexcitability via a presynaptic mechanism, and that hippocampal cognitive enhancement via PPARγ activation occurs through regulation of presynaptic vesicular proteins critical for proper glutamatergic neurotransmitter release, synaptic transmission, and short-term plasticity.

Passive immunization with Tau oligomer monoclonal antibody reverses tauopathy phenotypes without affecting hyperphosphorylated neurofibrillary tangles.

Recent findings suggest that tau oligomers, which form before neurofibrillary tangles (NFTs), are the true neurotoxic tau entities in neurodegenerative tauopathies, including Alzheimer's disease (AD). Studies in animal models of tauopathy suggest that tau oligomers play a key role in eliciting behavioral and cognitive impairments. Here, we used a novel tau oligomer-specific monoclonal antibody (TOMA) for passive immunization in mice expressing mutant human tau. A single dose of TOMA administered either intravenously or intracerebroventricularly was sufficient to reverse both locomotor and memory deficits in a mouse model of tauopathy for 60 d, coincident with rapid reduction of tau oligomers but not phosphorylated NFTs or monomeric tau. Our data demonstrate that antibody protection is mediated by extracellular and rapid peripheral clearance. These findings provide the first direct evidence in support of a critical role for tau oligomers in disease progression and validate tau oligomers as a target for the treatment of AD and other neurodegenerative tauopathies.

Impaired firing properties of dentate granule neurons in an Alzheimer's disease animal model are rescued by PPARγ agonism.

Early cognitive impairment in Alzheimer's disease (AD) correlates with medial temporal lobe dysfunction, including two areas essential for memory formation: the entorhinal cortex and dentate gyrus (DG). In the Tg2576 animal model for AD amyloidosis, activation of the peroxisome proliferator-activated receptor-gamma (PPARγ) with rosiglitazone (RSG) ameliorates hippocampus-dependent cognitive impairment and restores aberrant synaptic activity at the entorhinal cortex to DG granule neuron inputs. It is unknown, however, whether intrinsic firing properties of DG granule neurons in these animals are affected by amyloid-ß pathology and if they are sensitive to RSG treatment. Here, we report that granule neurons from 9-mo-old wild-type and Tg2576 animals can be segregated into two cell types with distinct firing properties and input resistance that correlate with less mature type I and more mature type II neurons. The DG type I cell population was greater than type II in wild-type littermates. In the Tg2576 animals, the type I and type II cell populations were nearly equal but could be restored to wild-type levels through cognitive enhancement with RSG. Furthermore, Tg2576 cell firing frequency and spike after depolarization were decreased in type I and increased in type II cells, both of which could also be restored to wild-type levels upon RSG treatment. That these parameters were restored by PPARγ activation emphasizes the therapeutic value of RSG against early AD cognitive impairment.

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.

Insulin resistance in Alzheimer's disease.

Insulin is a key hormone regulating metabolism. Insulin binding to cell surface insulin receptors engages many signaling intermediates operating in parallel and in series to control glucose, energy, and lipids while also regulating mitogenesis and development. Perturbations in the function of any of these intermediates, which occur in a variety of diseases, cause reduced sensitivity to insulin and insulin resistance with consequent metabolic dysfunction. Chronic inflammation ensues which exacerbates compromised metabolic homeostasis. Since insulin has a key role in learning and memory as well as directly regulating ERK, a kinase required for the type of learning and memory compromised in early Alzheimer's disease (AD), insulin resistance has been identified as a major risk factor for the onset of AD. Animal models of AD or insulin resistance or both demonstrate that AD pathology and impaired insulin signaling form a reciprocal relationship. Of note are human and animal model studies geared toward improving insulin resistance that have led to the identification of the nuclear receptor and transcription factor, peroxisome proliferator-activated receptor gamma (PPARγ) as an intervention tool for early AD. Strategic targeting of alternate nodes within the insulin signaling network has revealed disease-stage therapeutic windows in animal models that coalesce with previous and ongoing clinical trial approaches. Thus, exploiting the connection between insulin resistance and AD provides powerful opportunities to delineate therapeutic interventions that slow or block the pathogenesis of AD.

VEEV TC-83 Triggers Dysregulation of the Tryptophan-Kynurenine Pathway in the Central Nervous System That Correlates with Cognitive Impairment in Tg2576 Mice.

Neurodegenerative diseases are chronic conditions affecting the central nervous system (CNS). Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the accumulation of amyloid beta in the limbic and cortical brain regions. AD is presumed to result from genetic abnormalities or environmental factors, including viral infections, which may have deleterious, long-term effects. In this study, we demonstrate that the Venezuelan equine encephalitis virus (VEEV) commonly induces neurodegeneration and long-term neurological or cognitive sequelae. Notably, the effects of VEEV infection can persistently influence gene expression in the mouse brain, suggesting a potential link between the observed neurodegenerative outcomes and long-term alterations in gene expression. Additionally, we show that alphavirus encephalitis exacerbates the neuropathological profile of AD through crosstalk between inflammatory and kynurenine pathways, generating a range of metabolites with potent effects. Using a mouse model for ß-amyloidosis, Tg2576 mice, we found that cognitive deficits and brain pathology were more severe in Tg2576 mice infected with VEEV TC-83 compared to mock-infected controls. Thus, during immune activation, the kynurenine pathway plays a more active role in the VEEV TC-83-infected cells, leading to increases in the abundance of transcripts related to the kynurenine pathway of tryptophan metabolism. This pathway generates several metabolites with potent effects on neurotransmitter systems as well as on inflammation, as observed in VEEV TC-83-infected animals.

Arbovirus infection increases the risk for the development of neurodegenerative disease pathology in the murine model.

Alzheimer's disease is classified as a progressive disorder resulting from protein misfolding, also known as proteinopathies. Proteinopathies include synucleinopathies triggered by misfolded amyloid α-synuclein, tauopathies triggered by misfolded tau, and amyloidopathies triggered by misfolded amyloid of which Alzheimer's disease (ß-amyloid) is most prevalent. Most neurodegenerative diseases (>90%) are not due to dominantly inherited genetic causes. Instead, it is thought that the risk for disease is a complicated interaction between inherited and environmental risk factors that, with age, drive pathology that ultimately results in neurodegeneration and disease onset. Since it is increasingly appreciated that encephalitic viral infections can have profoundly detrimental neurological consequences long after the acute infection has resolved, we tested the hypothesis that viral encephalitis exacerbates the pathological profile of protein-misfolding diseases. Using a robust, reproducible, and well-characterized mouse model for ß-amyloidosis, Tg2576, we studied the contribution of alphavirus-induced encephalitis (TC-83 strain of VEEV to model alphavirus encephalitis viruses) on the progression of neurodegenerative pathology. We longitudinally evaluated neurological, neurobehavioral, and cognitive levels, followed by a post-mortem analysis of brain pathology focusing on neuroinflammation. We found more severe cognitive deficits and brain pathology in Tg2576 mice inoculated with TC-83 than in their mock controls. These data set the groundwork to investigate sporadic Alzheimer's disease and treatment interventions for this infectious disease risk factor.

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.

Soluble pathogenic tau enters brain vascular endothelial cells and drives cellular senescence and brain microvascular dysfunction in a mouse model of tauopathy.

Vascular mechanisms of Alzheimer's disease (AD) may constitute a therapeutically addressable biological pathway underlying dementia. We previously demonstrated that soluble pathogenic forms of tau (tau oligomers) accumulate in brain microvasculature of AD and other tauopathies, including prominently in microvascular endothelial cells. Here we show that soluble pathogenic tau accumulates in brain microvascular endothelial cells of P301S(PS19) mice modeling tauopathy and drives AD-like brain microvascular deficits. Microvascular impairments in P301S(PS19) mice were partially negated by selective removal of pathogenic soluble tau aggregates from brain. We found that similar to trans-neuronal transmission of pathogenic forms of tau, soluble tau aggregates are internalized by brain microvascular endothelial cells in a heparin-sensitive manner and induce microtubule destabilization, block endothelial nitric oxide synthase (eNOS) activation, and potently induce endothelial cell senescence that was recapitulated in vivo in microvasculature of P301S(PS19) mice. Our studies suggest that soluble pathogenic tau aggregates mediate AD-like brain microvascular deficits in a mouse model of tauopathy, which may arise from endothelial cell senescence and eNOS dysfunction triggered by internalization of soluble tau aggregates.

α-Synuclein oligomers oppose long-term potentiation and impair memory through a calcineurin-dependent mechanism: relevance to human synucleopathic diseases.

Intracellular deposition of fibrillar aggregates of α-synuclein (αSyn) characterizes neurodegenerative diseases such as Parkinson's disease (PD) and dementia with Lewy bodies. However, recent evidence indicates that small αSyn oligomeric aggregates that precede fibril formation may be the most neurotoxic species and can be found extracellularly. This new evidence has changed the view of pathological αSyn aggregation from a self-contained cellular phenomenon to an extracellular event and prompted investigation of the putative effects of extracellular αSyn oligomers. In this study, we report that extracellular application of αSyn oligomers detrimentally impacts neuronal welfare and memory function. We found that oligomeric αSyn increased intracellular Ca(2+) levels, induced calcineurin (CaN) activity, decreased cAMP response element-binding protein (CREB) transcriptional activity and resulted in calcineurin-dependent death of human neuroblastoma cells. Similarly, CaN induction and CREB inhibition were observed when αSyn oligomers were applied to organotypic brain slices, which opposed hippocampal long-term potentiation. Furthermore, αSyn oligomers induced CaN, inhibited CREB and evoked memory impairments in mice that received acute intracerebroventricular injections. Notably, all these events were reversed by pharmacological inhibition of CaN. Moreover, we found decreased active CaN and reduced levels of phosphorylated CREB in autopsy brain tissue from patients affected by dementia with Lewy bodies, which is characterized by deposition of αSyn aggregates and progressive cognitive decline. These results indicate that exogenously applied αSyn oligomers impact neuronal function and produce memory deficits through mechanisms that involve CaN activation.

Heightened cocaine-seeking in male rats associates with a distinct transcriptomic profile in the medial prefrontal cortex.

Drug overdose deaths involving cocaine have skyrocketed, an outcome attributable in part to the lack of FDA-approved medications for the treatment of cocaine use disorder (CUD), highlighting the need to identify new pharmacotherapeutic targets. Vulnerability to cocaine-associated environmental contexts and stimuli serves as a risk factor for relapse in CUD recovery, with individual differences evident in the motivational aspects of these cues. The medial prefrontal cortex (mPFC) provides top-down control of striatal circuitry to regulate the incentive-motivational properties of cocaine-associated stimuli. Clinical and preclinical studies have identified genetic variations that impact the degree of executive restraint over drug-motivated behaviors, and we designed the present study to employ next-generation sequencing to identify specific genes associated with heightened cue-evoked cocaine-seeking in the mPFC of male, outbred rats. Rats were trained to stably self-administer cocaine, and baseline cue-reinforced cocaine-seeking was established. Rats were phenotyped as either high cue (HC) or low cue (LC) responders based upon lever pressing for previously associated cocaine cues and allowed 10 days of abstinence in their home cages prior to mPFC collection for RNA-sequencing. The expression of 309 genes in the mPFC was significantly different in HC vs. LC rats. Functional gene enrichment analyses identified ten biological processes that were overrepresented in the mPFC of HC vs. LC rats. The present study identifies distinctions in mPFC mRNA transcripts that characterizes individual differences in relapse-like behavior and provides prioritized candidates for future pharmacotherapeutics aimed to help maintain abstinence in CUD. In particular the Htr2c gene, which encodes the serotonin 5-HT2C receptor (5-HT2CR), is expressed to a lower extent in HC rats, relative to LC rats. These findings build on a plethora of previous studies that also point to the 5-HT2CR as an attractive target for the treatment of CUD.

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.