Intraventricular murine Aß infusion elicits hippocampal inflammation and disrupts the consolidation, but not retrieval, of conditioned fear in C57BL6/J mice.

Although one of the defining characteristics of Alzheimer's disease is the presence of amyloid-beta (Aß) plaques, the early accumulation of soluble Aß oligomers (AßOs) may disrupt synaptic function and trigger cognitive impairments long before the appearance of plaques. Furthermore, murine models aimed at understanding how AßOs alter formation and retrieval of associative memories are conducted using human Aß species, which are more neurotoxic in the mouse brain than the native murine species. Unfortunately, there is currently a lack of attention in the literature as to what the murine version of the peptide (mAß) does to synaptic function and how it impacts the consolidation and retrieval of associative memories. In the current study, adult mice were infused with mAß 0, 2, 6, or 46 h after contextual-fear conditioning, and were tested 2-48 h later. Interestingly, only mAß infusions within 2 h of training reduced freezing behavior at test, indicating that mAß disrupted the consolidation, but not retrieval of fear memory. This consolidation deficit coincided with increased IL-1ß and reduced synaptophysin mRNA levels, without disrupting other synaptic signaling-related genes here examined. Despite differences between murine and human Aß, the deleterious functional outcomes of early-stage synaptic oligomer presence are similar. Thus, models utilizing or inducing the production of mAß in non-transgenic animals are useful in exploring the role of dysregulated synaptic plasticity and resultant learning deficits induced by Aß oligomers.

Prolonged isolation stress accelerates the onset of Alzheimer's disease-related pathology in 5xFAD mice despite running wheels and environmental enrichment.

Research has demonstrated that stress can exacerbate AD pathology in transgenic mouse models of AD. The purpose of the present studies was to extend this work by determining whether a social stressor, isolation stress, would increase the number of Aß plaques in 5xFAD + transgenic mice in comparison to group-housed controls, and accelerate the onset of cognitive deficits in contextual fear-conditioning. Additionally, we aimed to determine whether the pathological impact of isolation stress could be prevented through exposure to exercise alone or to exercise and an enriched environment throughout the isolation period. Two-month-old 5xFAD + and 5xFAD- animals were isolated or group-housed for two and three months. An additional subset of 5xFAD + mice were housed in isolation, housed in isolation with an exercise wheel, or housed in isolation with an exercise wheel and an enriched environment. Both two and three months of isolation stress significantly increased the number of plaques in the hippocampus of 5xFAD + mice, and three months of isolation increased hippocampal BACE1 expression. Isolated animals also displayed a significant cognitive deficit in contextual fear-conditioning, independent of genotype. Furthermore, neither exercise nor an enriched environment were able to prevent these isolation-induced effects. Understanding how stress impacts the onset and progression of AD is critical, as many individuals endure significant stress over their lifespan, including prolonged social isolation, a societal trend likely to worsen with time.

The α5-GABAAR inverse agonist MRK-016 upregulates hippocampal BDNF expression and prevents cognitive deficits in LPS-treated mice, despite elevations in hippocampal Aß.

Alzheimer's disease is marked by the presence of amyloid-beta (Aß) plaques, elevated central cytokine levels, dysregulation of BDNF-related gene expression, and cognitive decline. Previously, our laboratory has demonstrated that repeated administration of peripheral LPS is sufficient to significantly increase the presence of central Aß in the hippocampus, and that this upregulation corresponds with deficits in learning and memory. We have also previously demonstrated that the inverse benzodiazepine agonist MRK-016 (MRK) can protect against memory acquisition and consolidation errors in mice. To extend these findings, the current study explored the protective effects of MRK in the context of LPS-induced hippocampal Aß accumulation. Hippocampal Aß was significantly elevated, relative to saline-treated animals, following seven days of peripheral LPS injections. Animals were then trained in a contextual fear conditioning paradigm and were immediately treated with MRK or saline once training was complete. Behavioral testing occurred the day after training. Results from this study demonstrate that repeated injections of LPS significantly elevate hippocampal Aß, and inhibit acquisition of contextual fear. Post-training treatment with MRK restored behavioral expression of fear in LPS-treated animals, despite elevated hippocampal Aß, an effect that may be attributed to increased BDNF mRNA expression. Therefore, our data indicate that MRK can prevent LPS- induced cognitive deficits associated with elevated Aß, and restore hippocampal BDNF expression.

Hippocampal Aß expression, but not phosphorylated tau, predicts cognitive deficits following repeated peripheral poly I:C administration.

Alzheimer's disease is marked by the accumulation of the amyloid-beta (Aß) peptide, and increases in phosphorylation of the microtubule associated protein, tau. Changes in these proteins are considered responsible, in part, for the progressive neuronal degeneration and cognitive deficits seen in AD. We examined the effect of repeated consecutive peripheral poly I:C injections on cognitive deficits, central Aß, and phosphorylated tau accumulation, following three treatment durations: 7, 14, and 21 days. Forty-eight hours after the final injection, animals were trained in a contextual fear-conditioning paradigm, and tested 24h later. Immediately after testing, the hippocampus was collected to quantify Aß and phosphorylated tau accumulation. Results showed that, although poly I:C-induced Aß was significantly elevated at all time points examined, poly I:C only disrupted cognition after 14 and 21 days of administration. Moreover, elevations in phosphorylated tau were not seen until the 14-day time point. Interestingly, phosphorylated tau expression then declined at the 21-day time point. Finally, we demonstrated that Aß levels are a stronger predictor of cognitive dysfunction, explaining 37% of the variance, whereas phosphorylated tau levels only accounted for 0.2%. Taken together, these results support the hypothesis that inflammation-induced elevation in Aß disrupts cognition, independently of phosphorylated tau, and suggest that long-term administration of poly I:C may provide a model to investigate the contribution of long-term inflammation toward the development of Alzheimer's-like pathology.

Imatinib methanesulfonate reduces hyperphosphorylation of tau following repeated peripheral exposure to lipopolysaccharide.

For years, the prevailing hypothesis for Alzheimer's Disease (AD) has proposed a mechanism by which deposition of amyloid-beta (Aß) in the brain is independent of tau-pathologies and cognitive decline. However, despite extensive research on the disease, the mechanisms underlying the etiology of tau-pathology remain unknown. Previous research in our lab has shown that imatinib methanesulfonate (IM) blocks the peripheral production of Aß in response to LPS, thereby preventing the buildup of Aß in the hippocampus, and rescuing the cognitive dysfunction that normally follows. The present study aimed to examine the link between Aß and tau following inflammation, and to expand our understanding of how IM affects AD pathology. Specifically, we hypothesized that the IM-mediated inhibition of Aß production following inflammation would successfully protect against the hyperphosphorylation of tau (ptau). Here we show that 7days of LPS treatment in male C57BL/6J mice, which normally produces elevations in peripheral and central Aß, also produces hyperphosphorylation of tau. However, just as pre-treatment and concurrent treatment with IM blocks Aß production, it also blocks the phosphorylation of tau. In addition, 7days of LPS-induced inflammation and Aß production also leads to elevated total tau protein expression. Our results may provide support for the hypothesis that enhanced expression of tau following LPS administration is a protective measure by hippocampal neurons to compensate for the loss of the microtubule-stabilizing protein due to phosphorylation. More importantly, our results support the hypothesis that blocking the production of Aß that follows inflammation also leads to reduced tau phosphorylation, lending credence to a model in which Aß initiates tau phosphorylation.

Pre-treatment of C57BL6/J mice with the TLR4 agonist monophosphoryl lipid A prevents LPS-induced sickness behaviors and elevations in dorsal hippocampus interleukin-1ß, independent of interleukin-4 expression.

Peripheral administration of lipopolysaccharide (LPS) elevates production of pro-inflammatory cytokines, and motivates the expression of sickness behaviors. In this study, we tested the ability of an LPS-derived adjuvant, monophosphoryl lipid A (MPLA), to prevent LPS-induced sickness behaviors in a burrowing paradigm. Testing occurred over a three-day period. Animals received a single injection of either MPLA or saline the first two days of testing. On day three, animals received either LPS or saline. Tissue from the dorsal hippocampus was collected for qRT-PCR to assess expression of IL-1ß and IL-4. Results indicate that, during the pre-treatment phase, administration of MPLA induces an immune response sufficient to trigger sickness behaviors. However, we observed that animals pre-treated with MPLA for two days were resistant to LPS-induced sickness behaviors on day three. Results from the qRT-PCR analysis indicated that LPS-treated animals pre-treated with MPLA expressed significantly less IL-1ß compared to LPS-treated animals pre-treated with saline. However, we did not observe a significant difference in IL-4 expression between groups. Therefore, results indicate that under the given parameters of the study, MPLA pre-treatment protects against LPS-induced sickness behaviors, at least in part, by decreasing expression of the pro-inflammatory cytokine IL-1ß.

Administration of the inverse benzodiazepine agonist MRK-016 rescues acquisition and memory consolidation following peripheral administration of bacterial endotoxin.

Recent evidence suggests that inflammation-induced decrements in cognitive function can be mitigated via manipulation of excitatory or inhibitory transmission. We tested the ability of the inverse benzodiazepine agonist, MRK-016 (MRK) to protect against LPS-induced deficits in memory acquisition and consolidation, using a contextual fear conditioning (CFC) paradigm. In Experiment One, mice received lipopolysaccharide (LPS) and/or MRK injections prior to CFC training, and were then tested 24h after training. In Experiment Two, animals received similar treatment injections immediately after training, and were tested 24h later. Additionally, hippocampal samples were collected 4h after LPS injections and immediately after testing, to evaluate brain-derived neurotrophic factor (BDNF) and insulin-like growth factor 1 (IGF-1) mRNA expression. Results indicate that MRK can protect against LPS-induced learning/memory decrements in both paradigms. We also found, in both paradigms, that animals treated with LPS/Saline expressed significantly less BDNF mRNA when compared to Saline/Saline-treated animals 4h after LPS administration, but that MRK did not restore BDNF expression levels. Further, treatment administrations had no effect on IGF-1 mRNA expression at any collection time-point. In summary, MRK-016 can protect against LPS-induced deficits in memory acquisition and consolidation, in this hippocampus-dependent paradigm, though this protection occurs independently of recovery of BDNF expression.