Tonic extracellular glutamate and ischaemia: glutamate antiporter system xc - regulates anoxic depolarization in hippocampus

In stroke, the sudden deprivation of oxygen to neurons triggers a profuse release of glutamate that induces anoxic depolarization (AD) and leads to rapid cell death. Importantly, the latency of the glutamate-driven AD event largely dictates subsequent tissue damage. Although the contribution of synaptic glutamate during ischaemia is well-studied, the role of tonic (ambient) glutamate has received far less scrutiny. The majority of tonic, non-synaptic glutamate in the brain is governed by the cystine/glutamate antiporter, system x_c ^- . Employing hippocampal slice electrophysiology, we showed that transgenic mice lacking a functional system x_c ^- display longer latencies to AD and altered depolarizing waves compared to wild-type mice after total oxygen deprivation. Experiments which pharmacologically inhibited system x_c ^- , as well as those manipulating tonic glutamate levels and those antagonizing glutamate receptors, revealed that the antiporter's putative effect on ambient glutamate precipitates the ischaemic cascade. As such, the current study yields novel insight into the pathogenesis of acute stroke and may direct future therapeutic interventions. KEY POINTS: Ischaemic stroke remains the leading cause of adult disability in the world, but efforts to reduce stroke severity have been plagued by failed translational attempts to mitigate glutamate excitotoxicity. Elucidating the ischaemic cascade, which within minutes leads to irreversible tissue damage induced by anoxic depolarization, must be a principal focus. Data presented here show that tonic, extrasynaptic glutamate supplied by system x_c ^- synergizes with ischaemia-induced synaptic glutamate release to propagate AD and exacerbate depolarizing waves. Exploiting the role of system x_c ^- and its obligate release of ambient glutamate could, therefore, be a novel therapeutic direction to attenuate the deleterious effects of acute stroke.

Health of the Food Environment Is Associated With Heart Failure Mortality in the United States

BACKGROUND

Food environment factors contribute to cardiovascular disease, but their effect on population-level heart failure (HF) mortality is unclear.

METHODS

We utilized the National Vital Statistics System and USDA Food Environment Atlas to collect HF mortality rates (MR) and 2 county food environment indices: (1) food insecurity percentage (FI%) and (2) food environment index (FEI), a scaled index (0-10, 10 best) incorporating FI% and access to healthy food. We used linear regression to estimate the association between food environment and HF MR Results: Mean county FI% and FEI were 13% and 7.8 in 2956 included counties. Counties with FI% above the national median had significantly higher HF MR (30.7 versus 26.7 per 100 000; P<0.001) compared with FI% below the national median. Counties with HF MR above the national median had higher FI%, lower FEI, lower density of grocery stores, poorer access to stores among older adults, and lower Supplemental Nutrition Assistance Program participation rate (P<0.001 for all). Lower county FI% (β=-1.3% per 1% decrease) and higher county FEI (β=-3.6% per 1-unit increase in FEI) were significantly associated with lower HF MR after adjustment for county demographic, socioeconomic, and health factors. This association was stronger for HF MR compared with non-HF cardiovascular disease MR and all-cause MR The relationship between food environment and HF MR was stronger in counties with the highest income inequity and poverty rate.

CONCLUSIONS

Healthier food environment is significantly associated with lower HF mortality at the county level. This reinforces the role of food security on cardiovascular outcomes.

Association Between Biventricular Pacing and Incidence of Ventricular Arrhythmias in the Early Post-Operative Period after Left Ventricular Assist Device Implantation

INTRODUCTION

Cardiac resynchronization therapy (CRT) and left ventricular assist devices (LVAD) improve outcomes in heart failure patients. Early ventricular arrhythmias (VA) are common after LVAD and are associated with increased mortality. The association between left ventricular pacing (LVP) with CRT and VAs in the early post-LVAD period remains unclear.

METHODS

This was a retrospective study of all patients undergoing LVAD implantation from 1/2016 - 12/2019. Patients were divided into those with CRT and active LVP (CRT-LVP) immediately post-LVAD implant versus those without CRT-LVP. ICD electrograms were reviewed and early VAs were defined as sustained VT/VF occurring within 30 days of LVAD implantation.

RESULTS

Of 186 included patients (mean age 53 years, 75% male, mean BMI 28), 72 had CRT devices, 63 of whom had LV pacing enabled after LVAD implant (CRT-LVP group). Patients with CRT-LVP were more likely to have VA in the early post-operative period (21% vs 4%; p=0.0001). All 9 patients with CRT in whom LVP was disabled had no early VA. Among those with early VA, patients with CRT-LVP were more likely to have monomorphic VT (77% vs 40%; p=0.07). In multiple logistic regression, CRT-LVP pacing remained an independent predictor of early VA after adjustment for history of VA and AF.

CONCLUSIONS

Patients with CRT-LVP after LVAD implant had a higher incidence of early VA (specifically monomorphic VT). Epicardial LV pacing may be proarrhythmic in the early post-operative period after LVAD. This article is protected by copyright. All rights reserved.

The naked truth: a comprehensive clarification and classification of current 'myths' in naked mole-rat biology

The naked mole-rat (Heterocephalus glaber) has fascinated zoologists for at least half a century. It has also generated considerable biomedical interest not only because of its extraordinary longevity, but also because of unusual protective features (e.g. its tolerance of variable oxygen availability), which may be pertinent to several human disease states, including ischemia/reperfusion injury and neurodegeneration. A recent article entitled 'Surprisingly long survival of premature conclusions about naked mole-rat biology' described 28 'myths' which, those authors claimed, are a 'perpetuation of beautiful, but falsified, hypotheses' and impede our understanding of this enigmatic mammal. Here, we re-examine each of these 'myths' based on evidence published in the scientific literature. Following Braude et al., we argue that these 'myths' fall into four main categories: (i) 'myths' that would be better described as oversimplifications, some of which persist solely in the popular press; (ii) 'myths' that are based on incomplete understanding, where more evidence is clearly needed; (iii) 'myths' where the accumulation of evidence over the years has led to a revision in interpretation, but where there is no significant disagreement among scientists currently working in the field; (iv) 'myths' where there is a genuine difference in opinion among active researchers, based on alternative interpretations of the available evidence. The term 'myth' is particularly inappropriate when applied to competing, evidence-based hypotheses, which form part of the normal evolution of scientific knowledge. Here, we provide a comprehensive critical review of naked mole-rat biology and attempt to clarify some of these misconceptions.

Efficacy and tolerability of quinidine as salvage therapy for monomorphic ventricular tachycardia in patients with structural heart disease

INTRODUCTION

Quinidine is an effective therapy for a subset of polymorphic ventricular tachycardia and ventricular fibrillation (VF) syndromes; however, the efficacy of quinidine in scar-related monomorphic ventricular tachycardia (MMVT) is unclear.

METHODS AND RESULTS

Between 2009 and 2020 a single VT referral center, a total of 23 patients with MMVT and structural heart disease (age 66.7 ± 10.9, 20 males, 15 with ischemic cardiomyopathy, mean LVEF 22.2 ± 12.3%, 9 with left ventricular assist device [LVAD]) were treated with quinidine (14 quinidine gluconate; 996 ± 321 mg, 8 quinidine sulfate; 1062 ± 588 mg). Quinidine was used in combination with other antiarrhythmics (AAD) in 19 (13 also on amiodarone). All patients previously failed >1 AAD (amiodarone 100%, mexiletine 73%, sotalol 32%, other 32%) and eight had prior ablations (median of 1.5). Quinidine was initiated in the setting of VT storm despite AADs (6), inability to tolerate other AADs (4), or recurrent VT(12). Ventricular arrhythmias recurred despite quinidine in 13 (59%) patients at a median of 26 (4-240) days after quinidine initiation. In patients with recurrent MMVT, VT cycle length increased from 359 to 434 ms (p = .02). Six (27.3%) patients remained on quinidine at 1 year with recurrence of ventricular arrhythmias in all. The following adverse effects were seen: gastrointestinal side effects (6), QT prolongation (2), rash (1), thrombocytopenia (1), neurologic side effects (1). One patient discontinued due to cost.

CONCLUSION

Quinidine therapy has limited tolerability and long-term efficacy when used in the management of amiodarone-refractory scar-related MMVT.

Prospective evaluation of health status, quality of life and clinical outcomes following implantable defibrillator generator exchange

BACKGROUND

Little is known about health status and quality of life (QoL) after implantable cardioverter-defibrillator (ICD) generator exchange (GE).

METHODS

We prospectively followed patients undergoing first-time ICD GE. Serial assessments of health status were performed by administering the 36-Item Short Form Survey (SF-36).

RESULTS

Mean age was 67.5 ± 14.3 years, left ventricle ejection fraction (LVEF) was 36.5% ± 15.0% and over 40% of the cohort had improved LVEF to > 35% at the time of GE. SF-36 scores were significantly worse in physical/general health domains compared to domains of emotional/social well-being ( P < 0.001 for each comparison). Physical health scores were significantly worse among those with medical comorbidities including diabetes, chronic obstructive pulmonary disease and atrial fibrillation. Mean follow-up was 1.6 ± 0.5 years after GE. Overall SF-36 scores remained stable across all domains during follow-up. Survival at 3 years post-GE was estimated at 80%. Five patients died during follow-up and most deaths were adjudicated as non-arrhythmic in origin. Four patients experienced appropriate ICD shocks after GE, three of whom had LVEF which remains impaired LVEF (i.e., < 35%) at the time of GE.

CONCLUSION

Patients undergoing ICD GE have significantly worse physical health compared to emotional/social well-being, which is associated with the presence of medical comorbidities. In terms of clinical outcomes, the incidence of appropriate shocks after GE among those with improvement in LVEF is very low, and most deaths post-procedure appear to be non-arrhythmic in origin. These data represent an attempt to more fully characterize the spectrum of QoL and clinical outcomes after GE.

A multi-method approach to modeling COVID-19 disease dynamics in the United States

In this paper, we proposed a multi-method modeling approach to community-level spreading of COVID-19 disease. Our methodology was composed of interconnected age-stratified system dynamics models in an agent-based modeling framework that allowed for a granular examination of the scale and severity of disease spread, including metrics such as infection cases, deaths, hospitalizations, and ICU usage. Model parameters were calibrated using an optimization technique with an objective function to minimize error associated with the cumulative cases of COVID-19 during a training period between March 15 and October 31, 2020. We outlined several case studies to demonstrate the model's state- and local-level projection capabilities. We further demonstrated how model outcomes could be used to evaluate perceived levels of COVID-19 risk across different localities using a multi-criteria decision analysis framework. The model's two, three, and four week out-of-sample projection errors varied on a state-by-state basis, and generally increased as the out-of-sample projection period was extended. Additionally, the prediction error in the state-level projections was generally due to an underestimation of cases and an overestimation of deaths. The proposed modeling approach can be used as a virtual laboratory to investigate a wide range of what-if scenarios and easily adapted to future high-consequence public health threats.

Extracellular ATP-Induced Alterations in Extracellular H+ Fluxes From Cultured Cortical and Hippocampal Astrocytes

Small alterations in the level of extracellular H⁺ can profoundly alter neuronal activity throughout the nervous system. In this study, self-referencing H⁺-selective microelectrodes were used to examine extracellular H⁺ fluxes from individual astrocytes. Activation of astrocytes cultured from mouse hippocampus and rat cortex with extracellular ATP produced a pronounced increase in extracellular H⁺ flux. The ATP-elicited increase in H⁺ flux appeared to be independent of bicarbonate transport, as ATP increased H⁺ flux regardless of whether the primary extracellular pH buffer was 26 mM bicarbonate or 1 mM HEPES, and persisted when atmospheric levels of CO₂ were replaced by oxygen. Adenosine failed to elicit any change in extracellular H⁺ fluxes, and ATP-mediated increases in H⁺ flux were inhibited by the P2 inhibitors suramin and PPADS suggesting direct activation of ATP receptors. Extracellular ATP also induced an intracellular rise in calcium in cultured astrocytes, and ATP-induced rises in both calcium and H⁺ efflux were significantly attenuated when calcium re-loading into the endoplasmic reticulum was inhibited by thapsigargin. Replacement of extracellular sodium with choline did not significantly reduce the size of the ATP-induced increases in H⁺ flux, and the increases in H⁺ flux were not significantly affected by addition of EIPA, suggesting little involvement of Na⁺/H⁺ exchangers in ATP-elicited increases in H⁺ flux. Given the high sensitivity of voltage-sensitive calcium channels on neurons to small changes in levels of free H⁺, we hypothesize that the ATP-mediated extrusion of H⁺ from astrocytes may play a key role in regulating signaling at synapses within the nervous system.

Synaptic and Network Contributions to Anoxic Depolarization in Mouse Hippocampal Slices

Ischemic stroke remains the third leading cause of death and leading cause of adult disability worldwide. A key event in the pathophysiology of stroke is the anoxic depolarization (AD) of neurons in the ischemic core. Previous studies have established that both the latency to AD and the time spent in AD prior to re-oxygenation are predictors of neuronal death. The present studies used hippocampal slices from male and female mice to investigate the electrophysiological events that affect latency to AD after oxygen deprivation. The results confirm that the epoch between AD and re-oxygenation largely determines the magnitude of synaptic recovery after anoxic challenge. Using a selective antagonist of adenosine A₁ receptors, we also confirmed that adenosine released during anoxia (ANOX) suppresses synaptic glutamate release; however, this action has no effect on AD latency or the potential for post-anoxic recovery of synaptic transmission. In contrast, antagonism of AMPA- and NMDA-type glutamate receptors significantly prolongs the latency to AD and alters the speed and synchrony of associated depolarizing waves. Experiments using slices with fields Cornu ammonis 3 (CA3) and Cornu ammonis 1 (CA1) disconnected showed that AD latency is longer in CA1 than in CA3; however, the early AD in CA3 is propagated to CA1 in intact slices. Finally, AD latency in CA1 was found to be longer in slices from female mice than in those from age-matched male mice. The results have implications for stroke prevention and for understanding brain adaptations in hypoxia-tolerant animals.

African Naked Mole-Rats Demonstrate Extreme Tolerance to Hypoxia and Hypercapnia

Naked mole-rats are extremely tolerant to low concentrations of oxygen (hypoxia) and high concentrations of carbon dioxide (hypercapnia), which is consistent with the environment that they inhabit. Naked mole-rats combine subterranean living with living in very densely populated colonies where oxygen becomes depleted and carbon dioxide accumulates. In the laboratory, naked mole-rats fully recover from 5 h exposure to 5% O₂ and 5 h exposure to 80% CO₂, whereas both conditions are rapidly lethal to similarly sized laboratory mice. During anoxia (0% O₂) naked mole-rats enter a suspended animation-like state and switch from aerobic metabolism of glucose to anaerobic metabolism of fructose. Additional fascinating characteristics include that naked mole-rats show intrinsic brain tolerance to anoxia; a complete lack of hypoxia-induced and CO₂-induced pulmonary edema; and reduced aversion to high concentrations of CO₂ and acidic fumes. Here we outline a constellation of physiological and molecular adaptations that correlate with the naked mole-rat's hypoxic/hypercapnic tolerance and which offer potential targets for ameliorating pathological conditions in humans, such as the damage caused during cerebral ischemia.

Sex-based differences in procedural complications associated with atrial fibrillation catheter ablation: A systematic review and meta-analysis

BACKGROUND

Women undergoing atrial fibrillation catheter ablation (AFCA) have higher rates of vascular complications and major bleeding. However, most studies have been underpowered to detect differences in rarer complications such as stroke/transient ischemic attack (TIA) and procedural mortality.

METHODS

We performed a systematic review of databases (PubMed, World of Science, and Embase) to identify studies published since 2010 reporting AFCA complications by sex. Six complications of interest were (1) vascular/groin complications; (2) pericardial effusion/tamponade; (3) stroke/TIA; (4) permanent phrenic nerve injury; (5) major bleeding; and (6) procedural mortality. For meta-analysis, random effects models were used when heterogeneity between studies was ≥50% (vascular complications and major bleeding) and fixed effects models for other endpoints.

RESULTS

Of 5716 citations, 19 studies met inclusion criteria, comprising 244,353 patients undergoing AFCA, of whom 33% were women. Women were older (65.3 ± 11.2 vs. 60.4 ± 13.2 years), more likely hypertensive (60.6% vs. 55.5%) and diabetic (18.3% vs. 16.5%), and had higher CHA₂ DS₂ -VASc scores (3.0 ± 1.8 vs. 1.4 ± 1.4) (p < .0001 for all comparisons). The rates of all six complications were significantly higher in women. However, despite statistically significant differences, the overall incidences of major complications were very low in both sexes: stroke/TIA (women 0.51% vs. men 0.39%) and procedural mortality (women 0.25% vs. men 0.19%).

CONCLUSION

Women experience significantly higher rates of AFCA complications. However, the incidence of major procedural complications is very low in both sexes. The higher rate of complications in women may be partially attributable to older age and a higher prevalence of comorbidities at the time of ablation. More detailed studies are needed to better define the mechanisms of increased risk in women and to identify strategies for closing the sex gap.

Impact of insufficient admission vitamin D serum concentrations on sepsis incidence and clinical outcomes in patients with thermal injury

INTRODUCTION

In burn patients, vitamin D has been studied primarily in the pediatric population and focused mainly on the correlation with bone marker measurements and incidence of fractures. There is an association between vitamin D deficiency and the development of sepsis in non-burn critically-ill patients. However, there is limited data on vitamin D concentrations and clinical outcomes in burn patients, such as sepsis. The objective of this study is to evaluate the impact of vitamin D concentrations on the incidence of sepsis in adult burn patients.

METHODS

This was a retrospective cohort of patients 18 years of age and older admitted between February 1, 2016 and February 28, 2018 to an American Burn Association (ABA) verified burn center with diagnosis of burn injury. The primary endpoint was incidence of sepsis using the ABA 2007 Sepsis Consensus Criteria between patients with adequate vitamin D concentrations (25[OH]D > 20 ng/mL) and insufficient vitamin D (25[OH]D < 20 ng/mL) concentrations measured on admission. Descriptive statistics were used for baseline demographics. Univariate analysis was conducted using Chi-square, Fisher's exact test or Mann-Whitney U test, as appropriate.

RESULTS

A total of 115 patients were screened and 107 patients were included in this study. Sixty three patients (58.9%) had insufficient vitamin D concentrations. Patient demographics were overall similar between groups. The median total body surface area burned was 14.6% in the insufficient vitamin D group, and 12.1% in the adequate vitamin D group (p = 0.2). There was a trend towards greater incidence of sepsis in the insufficient vitamin D group in the univariate analysis (15.9% vs. 4.5%, p = 0.07). The multivariable logistic regression analysis found that adequate vitamin D concentrations was associated with a reduction in the incidence of sepsis (OR 0.10, 95% CI 0.01-0.88). The insufficient vitamin D group had a longer median hospital LOS (19 [IQR 11-37] vs 11.5 [IQR 7-20] days, p < 0.05), longer intensive care unit LOS (17 [IQR 10-37] vs 5 [IQR 2-19.5] days, p < 0.05) and fewer ventilator free days (26 [IQR 18-28] vs 28 [IQR 27-28] days, p < 0.05). There was no difference in mortality between groups (p = 0.69).

CONCLUSIONS

Patients with adequate vitamin D concentrations on admission had a reduction in the incidence of sepsis as compared to patients with insufficient vitamin D concentrations. Insufficient vitamin D concentrations may contribute to other worsened clinical outcomes in burn patients. Our findings set the stage for future, multicenter studies to determine the role of vitamin D supplementation in burn patients.

Improving the detection of environmental enteric dysfunction: a lactulose, rhamnose assay of intestinal permeability in children aged under 5 years exposed to poor sanitation and hygiene

Background

Environmental enteric dysfunction (EED) is an asymptomatic intestinal disorder affecting populations living in conditions of poor sanitation and hygiene. The study tested intestinal barrier function in infants with EED.

Methods

We prospectively studied an advanced high-performance liquid chromatography mass spectrometry assay of urine collected after oral intake of the monosaccharide, L-rhamnose and the disaccharide, lactulose, in 112 children from three continents.

Findings

Compared to the US cohort (n=27), the cohorts of children from Peru (n=19) and Zambia (n=85) were older with evidence of growth impairment. The median (range) of age (months) was 8.0 (2.0 to 13.0), 27.0 (15.0 to 29.0) and 21.0 (12.0 to 36.0), respectively. The median (range) of height for age Z score was −0.1 (−1.8 to 2.4), −1.8 (−3.3 to −0.2) and −2.3 (−8.5 to 1.2), respectively. Among children with valid sugar data (n=22 USA, n=19 Peru, n=73 Zambia), there were no significant differences in the median rhamnose urine concentrations between the three groups. The median (range) lactulose concentration (µg/mL) was 6.78 (0.29 to 31.90), 47.60 (4.23 to 379.00) and 75.40 (0.67 to 873.00) in the US, Peruvian and Zambian cohorts, respectively (p<0.001). The lactulose/rhamnose ratio (LRR) was higher in cohorts from Peru (0.75, 0.15, 5.02) and Zambia (2.26, 0.08, 14.48) compared to the US (0.14, 0.06, 1.00) cohort (p<0.001). In a multivariate effect modification model, higher weight-for-age z scores were associated with lower post-dose lactulose when rhamnose excretion was constant (p=0.003).

Conclusions

This non-invasive two saccharide permeability protocol measures changes in intestinal permeability in children with EED and permits the identification of individuals for interventional trials.

A multifunctional therapeutic approach to disease modification in multiple familial mouse models and a novel sporadic model of Alzheimer's disease

Background

Clinical failures singularly targeting amyloid-β pathology indicate a critical need for alternative Alzheimer’s disease (AD) therapeutic strategies. The mixed pathology reported in a large population of AD patients demands a multifunctional drug approach. Since activation of cAMP response element binding protein (CREB) plays a crucial role in synaptic strengthening and memory formation, we retooled a clinical drug with known neuroprotective and anti-inflammatory activity to activate CREB, and validated this novel multifunctional drug, NMZ, in 4 different mouse models of AD.

Results

NMZ was tested in three mouse models of familial AD and one model of sporadic AD. In 3 × Tg hippocampal slices, NMZ restored LTP. In vivo, memory was improved with NMZ in all animal models with robust cognitive deficits. NMZ treatment lowered neurotoxic forms of Aβ in both APP/PS1 and 3 × Tg transgenic mice while also restoring neuronal plasticity biomarkers in the 3 × Tg mice. In EFAD mice, incorporation of the major genetic AD risk factor, hAPOE4, did not mute the beneficial drug effects. In a novel sporadic mouse model that manifests AD-like pathology caused by accelerated oxidative stress in the absence of any familial AD mutation, oral administration of NMZ attenuated hallmark AD pathology and restored biomarkers of synaptic and neuronal function.

Conclusions

The multifunctional approach, embodied by NMZ, was successful in mouse models of AD incorporating Aβ pathology (APP/PS1), tau pathology (3xTg), and APOE4, the major human genetic risk factor for AD (EFAD). The efficacy observed in a novel model of sporadic AD (Aldh2^−/−) demonstrates that the therapeutic approach is not limited to rare, familial AD genetic mutations. The multifunctional drug, NMZ, was not designed directly to target Aβ and tau pathology; however, the attenuation of this hallmark pathology suggests the approach to be a highly promising, disease-modifying strategy for AD and mixed pathology dementia.

A new solid state extractor pulser for the FNAL magnetron ion source

A new solid state extractor pulser has been installed on the Fermi National Accelerator Laboratory (FNAL) magnetron ion source, replacing a vacuum tube style pulser that was used for over 40 years. The required ion source extraction voltage is 35 kV for injection into the radio frequency quadrupole. At this voltage, the old pulser had a rise time of over 150 μs due to the current limit of the vacuum tube. The new solid state pulsers are capable of 50 kV, 100 A peak current pulses and have a rise time of 9 μs when installed in the operational system. This paper will discuss the pulser design and operational experience to date.

Hydrogel-Based Engineering of Beige Adipose Tissue

Brown and beige adipose tissues have a significant capacity for energy expenditure that may be exploited as a treatment for obesity and metabolic disease. However, the limited volumes of these tissues in adults hinders realization of this potential. Engineering beige adipose tissue may provide an alternative source of this tissue. In this paper we describe the preparation of poly(ethylene glycol) (PEGDA) hydrogels with mechanical properties similar to native adipose tissue. Adipose derived stem cells (ASC) were cultured in hydrogels without adhesive sequences or degradable monomers. Cells were able to differentiate, independent of scaffold properties and were maintained as a viable and functioning adipose tissue mass. The cells expressed their own basement membrane proteins consistent with the composition of adipose tissue. The ASCs could be induced to express uncoupling protein-1 (UCP-1) and cIDEA, makers of beige adipocytes with expression level varying with hydrogel stiffness. This hydrogel-based culture system serves as a first step in engineering beige adipose tissue.

Theta-burst LTP

This review covers the spatial and temporal rules governing induction of hippocampal long-term potentiation (LTP) by theta-burst stimulation. Induction of LTP in field CA1 by high frequency stimulation bursts that resemble the burst discharges (complex-spikes) of hippocampal pyramidal neurons involves a multiple-step mechanism. A single burst is insufficient for LTP induction because it evokes both excitatory and inhibitory currents that partially cancel and limit postsynaptic depolarization. Bursts repeated at the frequency (~5 Hz) of the endogenous theta rhythm induce maximal LTP, primarily because this frequency disables feed-forward inhibition and allows sufficient postsynaptic depolarization to activate voltage-sensitive NMDA receptors. The disinhibitory process, referred to as "priming", involves presynaptic GABA autoreceptors that inhibit GABA release. Activation of NMDA receptors allows a calcium flux into dendritic spines that serves as the proximal trigger for LTP. We include new data showing that theta-burst stimulation is more efficient than other forms of stimulation for LTP induction. In addition, we demonstrate that associative interactions between synapses activated during theta-bursts are limited to major dendritic domains since such interactions occur within apical or basal dendritic trees but not between them. We review evidence that recordings of electrophysiological responses during theta burst stimulation can help to determine if experimental manipulations that affect LTP do so by affecting events antecedent to the induction process, such as NMDA receptor activation, or downstream signaling cascades that result from postsynaptic calcium fluxes. Finally, we argue that theta-burst LTP represents a minimal model for stable, non-decremental LTP that is more sensitive to a variety of experimental manipulations than is LTP induced by other stimulation paradigms. This article is part of a Special Issue entitled SI: Brain and Memory.

No oxygen? No problem! Intrinsic brain tolerance to hypoxia in vertebrates

Many vertebrates are challenged by either chronic or acute episodes of low oxygen availability in their natural environments. Brain function is especially vulnerable to the effects of hypoxia and can be irreversibly impaired by even brief periods of low oxygen supply. This review describes recent research on physiological mechanisms that have evolved in certain vertebrate species to cope with brain hypoxia. Four model systems are considered: freshwater turtles that can survive for months trapped in frozen-over lakes, arctic ground squirrels that respire at extremely low rates during winter hibernation, seals and whales that undertake breath-hold dives lasting minutes to hours, and naked mole-rats that live in crowded burrows completely underground for their entire lives. These species exhibit remarkable specializations of brain physiology that adapt them for acute or chronic episodes of hypoxia. These specializations may be reactive in nature, involving modifications to the catastrophic sequelae of oxygen deprivation that occur in non-tolerant species, or preparatory in nature, preventing the activation of those sequelae altogether. Better understanding of the mechanisms used by these hypoxia-tolerant vertebrates will increase appreciation of how nervous systems are adapted for life in specific ecological niches as well as inform advances in therapy for neurological conditions such as stroke and epilepsy.

A case-control study of childhood trauma in the development of irritable bowel syndrome

BACKGROUND

The etiology of irritable bowel syndrome (IBS) is not been fully elucidated, but childhood trauma may disturb the brain-gut axis and therefore be important. Thus, we conducted a family based case-control study of IBS cases and their relatives with the aims to (i) determine the frequency of childhood trauma among IBS cases and controls as well as their relatives, and (ii) assess childhood trauma among IBS cases with affected relatives (familial IBS).

METHODS

Outpatients with IBS, matched controls, and their first-degree relatives completed a self-report version of Bremner' Early Trauma Inventory. Percent of cases and controls with a family history were compared and odds ratios were computed using chi-squared test; recurrence risks to relatives were computed using logistic regression and generalized estimating equations.

KEY RESULTS

Data were collected from 409 cases, 415 controls, 825 case relatives, and 921 control relatives. IBS cases had a median age of 50 and 83% were women. Of IBS cases, 74% had experienced any general trauma compared to 59% among controls, yielding an odds ratio of 1.56 (95% CI: 1.13-2.15, p < 0.008). There were no statistical differences between IBS relatives and control relatives with regards to lifetime trauma.

CONCLUSIONS & INFERENCES

IBS is associated with childhood trauma, and these traumas often occur prior to onset of IBS symptoms. This provides further insight into how traumatic childhood events are associated with development of adult IBS.

Short-latency single unit processing in olfactory cortex

Abstract Single-unit recording of layer II-III cells in olfactory (piriform) cortex was performed on awake, unrestrained rats actively engaged in learning novel odors in an olfactory discrimination task. Five of the 67 cells tested had very brief monophasic action potentials and high spontaneous firing rates (30-80 Hz); it is suggested that these units were interneurons. The remainder of the neurons had broader spikes and did not discharge for prolonged periods. Thirty-nine percent of the broad spike cells responded to at least one and usually more of the odors presented to the rats during either of the first two trials on which that odor was present, but, in most cases, these responses occurred only very infrequently over the course of subsequent trials. Six percent of the broad-spike group, how ever, continued firing robustly to a single odor but not to others. From these results it appears that most cells in piriform cortex do not respond to most odors, i.e., coding is exceedingly sparse. A subgroup of the predominant broad-spike cell type does react to several odors but this response drops out with repeated exposure, perhaps because of training. However, a few members of this class (a small fraction of the total cell population) do go on responding to a particular odor, thus exhibiting a form of odor specificity. The results are discussed with regard to predictions from recently developed models of the olfactory cortex.

An NO donor approach to neuroprotective and procognitive estrogen therapy overcomes loss of NO synthase function and potentially thrombotic risk

Selective estrogen receptor modulators (SERMs) are effective therapeutics that preserve favorable actions of estrogens on bone and act as antiestrogens in breast tissue, decreasing the risk of vertebral fractures and breast cancer, but their potential in neuroprotective and procognitive therapy is limited by: 1) an increased lifetime risk of thrombotic events; and 2) an attenuated response to estrogens with age, sometimes linked to endothelial nitric oxide synthase (eNOS) dysfunction. Herein, three 3(rd) generation SERMs with similar high affinity for estrogen receptors (ERα, ERβ) were studied: desmethylarzoxifene (DMA), FDMA, and a novel NO-donating SERM (NO-DMA). Neuroprotection was studied in primary rat neurons exposed to oxygen glucose deprivation; reversal of cholinergic cognitive deficit was studied in mice in a behavioral model of memory; long term potentiation (LTP), underlying cognition, was measured in hippocampal slices from older 3×Tg Alzheimer's transgenic mice; vasodilation was measured in rat aortic strips; and anticoagulant activity was compared. Pharmacologic blockade of GPR30 and NOS; denudation of endothelium; measurement of NO; and genetic knockout of eNOS were used to probe mechanism. Comparison of the three chemical probes indicates key roles for GPR30 and eNOS in mediating therapeutic activity. Procognitive, vasodilator and anticoagulant activities of DMA were found to be eNOS dependent, while neuroprotection and restoration of LTP were both shown to be dependent upon GPR30, a G-protein coupled receptor mediating estrogenic function. Finally, the observation that an NO-SERM shows enhanced vasodilation and anticoagulant activity, while retaining the positive attributes of SERMs even in the presence of NOS dysfunction, indicates a potential therapeutic approach without the increased risk of thrombotic events.

Evidence for loss of synaptic AMPA receptors in anterior piriform cortex of aged mice

It has been suggested that age-related impairments in learning and memory may be due to age-related deficits in long-term potentiation of glutamatergic synaptic transmission. For example, olfactory discrimination learning is significantly affected by aging in mice and this may be due, in part, to diminished synaptic plasticity in piriform cortex. In the present study, we tested for alterations in electrophysiological properties and synaptic transmission in this simple cortical network. Whole-cell recordings were made from principal neurons in slices of anterior piriform cortex from young (3–6 months old) and old (24–28 months) C57Bl/6 mice. Miniature excitatory postsynaptic currents (mEPSCs) mediated by AMPA receptors were collected from cells in presence of tetrodotoxin (TTX) and held at -80 mV in voltage-clamp. Amplitudes of mEPSCs were significantly reduced in aged mice, suggesting that synaptic AMPA receptor expression is decreased during aging. In a second set of experiments, spontaneous excitatory postsynaptic currents (s/mEPSCs) were recorded in slices from different cohorts of young and old mice, in the absence of TTX. These currents resembled mEPSCs and were similarly reduced in amplitude in old mice. The results represent the first electrophysiological evidence for age-related declines in glutamatergic synaptic function in the mammalian olfactory system.

Immunocytochemical localization of reelin in the olfactory bulb of the heterozygous reeler mouse: An animal model for schizophrenia

Because heterozygous reeler (HR) mice share some abnormal traits with schizophrenic patients, and schizophrenia is often accompanied by impairment of olfactory function, this study examines reelin in the olfactory bulb of the HR mouse. In the WT mouse, reelin immunoreactivity is found in the extracellular matrix, and in the cytoplasm of olfactory nerve fibers, GABAergic interneurons, and glutamatergic mitral cells. Western blot analysis reveals that reelin immunoreactivity in the HR mouse is reduced by 45% compared to WT mouse. This is especially evident in the glomerular GABAergic interneurons. In WT mitral cells, reelin is found in discrete clumps near the axon hillock and within the axon. In the HR mouse, reelin axonal staining is diffuse and densely packed. In the rostral migratory stream of the HR mouse, immunolabeling shows an accumulation of reelin-containing neuronal precursors, apparently unable to shift from tangential to radial migration. These observations indicate that there is a downregulation of reelin in the HR mouse and suggest that secretion of reelin may be compromised. Further studies of the HR mouse may provide a new basis for understanding the role of reelin in the adult CNS, especially as it may relate to schizophrenia.

Primary microRNA precursor transcripts are localized at post-synaptic densities in adult mouse forebrain

In a previous study, we reported that microRNA (miRNA) precursors are expressed in synaptic fractions within adult mouse forebrain, where they are enriched at post-synaptic densities (PSDs). However, because that study employed qRT-PCR primers that recognize the hairpin region, it was not able to distinguish between primary microRNA gene transcripts (pri-miRs) and small hairpin precursors (pre-miRs). Here, using primer sets that selectively measure regions upstream, downstream and flanking the hairpin, we demonstrate that pri-miRs are present in synaptic fractions (enriched several-fold relative to total tissue homogenate) and are especially enriched in isolated PSDs. Drosha and DGCR8 proteins are also expressed in synaptic fractions and PSDs, and are tightly associated with pri-miRs as assessed by coimmunoprecipitation under stringent conditions. Pri-miRs, drosha, and DGCR8 are highly enriched in fractions that contain mRNA transport particles, and cytosolic drosha is associated with kinesin heavy chain; these findings suggest that pri-miRs are transported to synaptic regions in a manner similar to mRNAs. This study supports the notion that miRNA biogenesis occurs locally near synapses in a regulated fashion.

Synaptic NMDA receptor-mediated currents in anterior piriform cortex are reduced in the adult fragile X mouse

Fragile X syndrome is a neurodevelopmental condition caused by the transcriptional silencing of the fragile X mental retardation 1 (FMR1) gene. The Fmr1 knockout (KO) mouse exhibits age-dependent deficits in long term potentiation (LTP) at association (ASSN) synapses in anterior piriform cortex (APC). To investigate the mechanisms for this, whole-cell voltage-clamp recordings of ASSN stimulation-evoked synaptic currents were made in APC of slices from adult Fmr1-KO and wild-type (WT) mice, using the competitive N-methyl-D-aspartate (NMDA) receptor antagonist, CPP, to distinguish currents mediated by NMDA and AMPA receptors. NMDA/AMPA current ratios were lower in Fmr1-KO mice than in WT mice, at ages ranging from 3-18months. Since amplitude and frequency of miniature excitatory postsynaptic currents (mEPSCs) mediated by AMPA receptors were no different in Fmr1-KO and WT mice at these ages, the results suggest that NMDA receptor-mediated currents are selectively reduced in Fmr1-KO mice. Analyses of voltage-dependence and decay kinetics of NMDA receptor-mediated currents did not reveal differences between Fmr1-KO and WT mice, suggesting that reduced NMDA currents in Fmr1-KO mice are due to fewer synaptic receptors rather than differences in receptor subunit composition. Reduced NMDA receptor signaling may help to explain the LTP deficit seen at APC ASSN synapses in Fmr1-KO mice at 6-18months of age, but does not explain normal LTP at these synapses in mice 3-6months old. Evoked currents and mEPSCs were also examined in senescent Fmr1-KO and WT mice at 24-28months of age. NMDA/AMPA ratios were similar in senescent WT and Fmr1-KO mice, due to a decrease in the ratio in the WT mice, without significant change in AMPA receptor-mediated mEPSCs.

Barriers and motivators affecting tuberculosis infection control practices of Russian health care workers

SETTING

Five in-patient and out-patient tuberculosis (TB) care facilities in two regions of Russia.

OBJECTIVE

To identify barriers and motivators to the use of infection control measures among Russian TB health care workers.

DESIGN

In this qualitative study, a convenience sample of 96 health care workers (HCWs) was used to generate 15 homogeneous focus groups, consisting of physicians, nurses, and laboratory or support staff.

RESULTS

Barriers and motivators related to knowledge, attitudes and beliefs, and practices were identified. The three main barriers were 1) knowledge deficits, including the belief that TB was transmitted by dust, linens and eating utensils; 2) negative attitudes related to the discomfort of respirators; and 3) practices with respect to quality and care of respirators. Education and training, fear of infecting loved ones, and fear of punishment were the main motivators.

CONCLUSIONS

Our results point to the need for evaluation of current educational programs. Positive health promotion messages that appeal to fear might also be successful in promoting TB infection control. Individualized rewards based on personal motivators or group rewards that build on collectivist theory could be explored.

Blunted neuronal calcium response to hypoxia in naked mole-rat hippocampus

Naked mole-rats are highly social and strictly subterranean rodents that live in large communal colonies in sealed and chronically oxygen-depleted burrows. Brain slices from naked mole-rats show extreme tolerance to hypoxia compared to slices from other mammals, as indicated by maintenance of synaptic transmission under more hypoxic conditions and three fold longer latency to anoxic depolarization. A key factor in determining whether or not the cellular response to hypoxia is reversible or leads to cell death may be the elevation of intracellular calcium concentration. In the present study, we used fluorescent imaging techniques to measure relative intracellular calcium changes in CA1 pyramidal cells of hippocampal slices during hypoxia. We found that calcium accumulation during hypoxia was significantly and substantially attenuated in slices from naked mole-rats compared to slices from laboratory mice. This was the case for both neonatal (postnatal day 6) and older (postnatal day 20) age groups. Furthermore, while both species demonstrated more calcium accumulation at older ages, the older naked mole-rats showed a smaller calcium accumulation response than even the younger mice. A blunted intracellular calcium response to hypoxia may contribute to the extreme hypoxia tolerance of naked mole-rat neurons. The results are discussed in terms of a general hypothesis that a very prolonged or arrested developmental process may allow adult naked mole-rat brain to retain the hypoxia tolerance normally only seen in neonatal mammals.

Impaired survival of neural progenitor cells in dentate gyrus of adult mice lacking fMRP

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability in humans. Individuals affected with the disorder exhibit a deficiency of the fragile X mental retardation protein (FMRP), due to transcriptional silencing of the Fmr1 gene. It is widely accepted that learning deficits in FXS result from impaired synaptic function and/or plasticity in the brain. Interestingly, recent evidence suggests that conditional knockout of Fmr1 in neural progenitor cells in mice impairs hippocampal neurogenesis, which in turn contributes to learning impairments. To examine the nature of the neurogenic impairments and determine whether they impact the morphology of the dentate gyrus, we assessed the extent of neural progenitor cell proliferation, survival, and differentiation in older adult Fmr1 knockout mice. Here, we show that the number of fast-proliferating cells in the subgranular layer of the dentate gyrus, as well as the subsequent survival of these cells, are dramatically reduced in Fmr1 knockout mice. In addition, the number of mature neurons in the granule layer of the dentate gyrus of these mice is significantly smaller than in wild type littermate controls, suggesting that impaired proliferation and survival of neural progenitor cells compromises the structure of the dentate gyrus. Impaired adult neurogenesis may underlie, at least in part, the learning deficits that characterize fragile X syndrome.

Absence of tolerance to the anticonvulsant and neuroprotective effects of imidazenil against DFP-induced seizure and neuronal damage

The clinical use of diazepam or midazolam to control organophosphate (OP) nerve agent-induced seizure activity is limited by their unwanted effects including sedation, amnesia, withdrawal, and anticonvulsant tolerance. Imidazenil is an imidazo-benzodiazepine derivative with high intrinsic efficacy and selectivity for α2-, α3-, and α5- but low intrinsic efficacy for α1-containing GABA(A) receptors. We have previously shown that imidazenil is more efficacious than diazepam at protecting rats and mice from diisopropyl fluorophosphate (DFP)-induced seizures and neuronal damage without producing sedation. In the present study, we compared the tolerance liability of imidazenil and diazepam to attenuate the seizure activity and neurotoxic effects of DFP. Rats received protracted (14 days) oral treatment with increasing doses of imidazenil (1-4 mg/kg), diazepam (5-20 mg/kg), or vehicle. Eighteen hours after the last dose of the protracted treatment schedule, rats were tested for anticonvulsant tolerance after a 30 min pretreatment with a single test dose of imidazenil (0.5 mg/kg) or diazepam (5 mg/kg) prior to a DFP challenge (1.5 mg/kg). The anticonvulsant (modified Racine score scale) and neuroprotective (fluoro-jade B staining) effects of diazepam were significantly reduced in protracted diazepam-treated animals whereas the effects of imidazenil were not altered in protracted imidazenil-treated animals. The present findings indicate that protracted imidazenil treatment does not produce tolerance to its protective action against the neurotoxic effects of OP exposure.

Nested case-control study of feline calicivirus viruria, oral carriage, and serum neutralizing antibodies in cats with idiopathic cystitis

BACKGROUND

The epidemiology of feline calicivirus (FCV) infection in cats with idiopathic cystitis (FIC) has not been investigated by contemporary molecular biologic methods.

OBJECTIVES

To determine the prevalence of and evaluate risk factors for FCV viruria, oral carriage, and virus neutralizing (VN) antibodies in cats with and without FIC.

ANIMALS

Cats with nonobstructive FIC (n = 47), obstructive FIC (n = 22), and FCV upper respiratory tract infection (URI; n = 25), and healthy client-owned (n = 18) and colony-housed (n = 24) cats.

METHODS

Oropharyngeal secretions and urine were evaluated with a FCV p30 gene-based real-time reverse-transcriptase polymerase chain reaction (RT-PCR) assay. Serum VN antibody titers were determined by a modified microtiter assay. Associations of risk factors with log-transformed antibody titers were determined by multivariable generalized linear regression.

RESULTS

FCV viruria was detected in 4 (6%) and 3 (12%) cats with FIC and URI, respectively. In 3 FIC cats, viruria was unassociated with detectable oral virus carriage. Oral FCV carriage was detected in 7 (10%) FIC cats. Median antibody titers were significantly higher in cats with obstructive FIC (1 :256), nonobstructive FIC (1:128), and URI (1:512) compared with healthy client-owned (1:16) and colony-housed (1:4) cats (P < .001). Other than disease, multivariate analysis did not identify any other explanatory variables for increased titers in cats with FIC or URI.

CONCLUSIONS AND CLINICAL IMPORTANCE

FCV viruria was detected in cats with FIC and URI, however, its etiologic significance is uncertain. Serologic results suggest increased FCV exposure in FIC cats compared with controls. Further investigations are needed to clarify the potential role of FCV in FIC.

Endogenous siRNAs and noncoding RNA-derived small RNAs are expressed in adult mouse hippocampus and are up-regulated in olfactory discrimination training

We previously proposed that endogenous siRNAs may regulate synaptic plasticity and long-term gene expression in the mammalian brain. Here, a hippocampal-dependent task was employed in which adult mice were trained to execute a nose-poke in a port containing one of two simultaneously present odors in order to obtain a reward. Mice demonstrating olfactory discrimination training were compared to pseudo-training and nose-poke control groups; size-selected hippocampal RNA was subjected to Illumina deep sequencing. Sequences that aligned uniquely and exactly to the genome without uncertain nucleotide assignments, within exons or introns of MGI annotated genes, were examined further. The data confirm that small RNAs having features of endogenous siRNAs are expressed in brain; that many of them derive from genes that regulate synaptic plasticity (and have been implicated in neuropsychiatric diseases); and that hairpin-derived endo-siRNAs and the 20- to 23-nt size class of small RNAs show a significant increase during an early stage of training. The most abundant putative siRNAs arose from an intronic inverted repeat within the SynGAP1 locus; this inverted repeat was a substrate for dicer in vitro, and SynGAP1 siRNA was specifically associated with Argonaute proteins in vivo. Unexpectedly, a dramatic increase with training (more than 100-fold) was observed for a class of 25- to 30-nt small RNAs derived from specific sites within snoRNAs and abundant noncoding RNAs (Y1 RNA, RNA component of mitochondrial RNAse P, 28S rRNA, and 18S rRNA). Further studies are warranted to characterize the role(s) played by endogenous siRNAs and noncoding RNA-derived small RNAs in learning and memory.

Complex environment experience rescues impaired neurogenesis, enhances synaptic plasticity, and attenuates neuropathology in familial Alzheimer's disease-linked APPswe/PS1DeltaE9 mice

Experience in complex environments induces numerous forms of brain plasticity, improving structure and function. It has been long debated whether brain plasticity can be induced under neuropathological conditions, such as Alzheimer's disease (AD), to an extent that would reduce neuropathology, rescue brain structure, and restore its function. Here we show that experience in a complex environment rescues a significant impairment of hippocampal neurogenesis in transgenic mice harboring familial AD-linked mutant APPswe/PS1DeltaE9. Proliferation of hippocampal cells is enhanced significantly after enrichment, and these proliferating cells mature to become new neurons and glia. Enhanced neurogenesis was accompanied by a significant reduction in levels of hyperphosphorylated tau and oligomeric Abeta, the precursors of AD hallmarks, in the hippocampus and cortex of enriched mice. Interestingly, enhanced expression of the neuronal anterograde motor kinesin-1 was observed, suggesting enhanced axonal transport in hippocampal and cortical neurons after enrichment. Examination of synaptic physiology revealed that environmental experience significantly enhanced hippocampal long-term potentiation, without notable alterations in basal synaptic transmission. This study suggests that environmental modulation can rescue the impaired phenotype of the Alzheimer's brain and that induction of brain plasticity may represent therapeutic and preventive avenues in AD.