Animal models to study cognitive impairment of chronic kidney disease.

Mild cognitive impairment (MCI) is common in people with chronic kidney disease (CKD), and its prevalence increases with progressive loss of kidney function. MCI is characterized by a decline in cognitive performance greater than expected for an individual age and education level but with minimal impairment of instrumental activities of daily living. Deterioration can affect one or several cognitive domains (attention, memory, executive functions, language, and perceptual motor or social cognition). Given the increasing prevalence of kidney disease, more and more people with CKD will also develop MCI causing an enormous disease burden for these individuals, their relatives, and society. However, the underlying pathomechanisms are poorly understood, and current therapies mostly aim at supporting patients in their daily lives. This illustrates the urgent need to elucidate the pathogenesis and potential therapeutic targets and test novel therapies in appropriate preclinical models. Here, we will outline the necessary criteria for experimental modeling of cognitive disorders in CKD. We discuss the use of mice, rats, and zebrafish as model systems and present valuable techniques through which kidney function and cognitive impairment can be assessed in this setting. Our objective is to enable researchers to overcome hurdles and accelerate preclinical research aimed at improving the therapy of people with CKD and MCI.

The SGLT2 inhibitor dapagliflozin improves kidney function in glycogen storage disease XI.

Glycogen storage disease XI, also known as Fanconi-Bickel syndrome (FBS), is a rare autosomal recessive disorder caused by mutations in the SLC2A2 gene that encodes the glucose-facilitated transporter type 2 (GLUT2). Patients develop a life-threatening renal proximal tubule dysfunction for which no treatment is available apart from electrolyte replacement. To investigate the renal pathogenesis of FBS, SLC2A2 expression was ablated in mouse kidney and HK-2 proximal tubule cells. GLUT2Pax8Cre+ mice developed time-dependent glycogen accumulation in proximal tubule cells and recapitulated the renal Fanconi phenotype seen in patients. In vitro suppression of GLUT2 impaired lysosomal autophagy as shown by transcriptomic and biochemical analysis. However, this effect was reversed by exposure to a low glucose concentration, suggesting that GLUT2 facilitates the homeostasis of key cellular pathways in proximal tubule cells by preventing glucose toxicity. To investigate whether targeting proximal tubule glucose influx can limit glycogen accumulation and correct symptoms in vivo, we treated mice with the selective SGLT2 inhibitor dapagliflozin. Dapagliflozin reduced glycogen accumulation and improved metabolic acidosis and phosphaturia in the animals by normalizing the expression of Napi2a and NHE3 transporters. In addition, in a patient with FBS, dapagliflozin was safe, improved serum potassium and phosphate concentrations, and reduced glycogen content in urinary shed cells. Overall, this study provides proof of concept for dapagliflozin as a potentially suitable therapy for FBS.

Deletion of aquaporin-4 improves capillary blood flow distribution in brain edema.

Brain edema is a feared complication to disorders and insults affecting the brain. It can be fatal if the increase in intracranial pressure is sufficiently large to cause brain herniation. Moreover, accruing evidence suggests that even slight elevations of intracranial pressure have adverse effects, for instance on brain perfusion. The water channel aquaporin-4 (AQP4), densely expressed in perivascular astrocytic endfeet, plays a key role in brain edema formation. Using two-photon microscopy, we have studied AQP4-mediated swelling of astrocytes affects capillary blood flow and intracranial pressure (ICP) in unanesthetized mice using a mild brain edema model. We found improved regulation of capillary blood flow in mice devoid of AQP4, independently of the severity of ICP increase. Furthermore, we found brisk AQP4-dependent astrocytic Ca2+ signals in perivascular endfeet during edema that may play a role in the perturbed capillary blood flow dynamics. The study suggests that astrocytic endfoot swelling and pathological signaling disrupts microvascular flow regulation during brain edema formation.

Loss of the Secretin Receptor Impairs Renal Bicarbonate Excretion and Aggravates Metabolic Alkalosis in Mice during Acute Base-Loading.

SIGNIFICANCE STATEMENT: During acute base excess, the renal collecting duct ß -intercalated cells ( ß -ICs) become activated to increase urine base excretion. This process is dependent on pendrin and cystic fibrosis transmembrane regulator (CFTR) expressed in the apical membrane of ß -ICs. The signal that leads to activation of this process was unknown. Plasma secretin levels increase during acute alkalosis, and the secretin receptor (SCTR) is functionally expressed in ß -ICs. We find that mice with global knockout for the SCTR lose their ability to acutely increase renal base excretion. This forces the mice to lower their ventilation to cope with this challenge. Our findings suggest that secretin is a systemic bicarbonate-regulating hormone, likely being released from the small intestine during alkalosis. BACKGROUND: The secretin receptor (SCTR) is functionally expressed in the basolateral membrane of the ß -intercalated cells of the kidney cortical collecting duct and stimulates urine alkalization by activating the ß -intercalated cells. Interestingly, the plasma secretin level increases during acute metabolic alkalosis, but its role in systemic acid-base homeostasis was unclear. We hypothesized that the SCTR system is essential for renal base excretion during acute metabolic alkalosis. METHODS: We conducted bladder catheterization experiments, metabolic cage studies, blood gas analysis, barometric respirometry, perfusion of isolated cortical collecting ducts, immunoblotting, and immunohistochemistry in SCTR wild-type and knockout (KO) mice. We also perfused isolated rat small intestines to study secretin release. RESULTS: In wild-type mice, secretin acutely increased urine pH and pendrin function in isolated perfused cortical collecting ducts. These effects were absent in KO mice, which also did not sufficiently increase renal base excretion during acute base loading. In line with these findings, KO mice developed prolonged metabolic alkalosis when exposed to acute oral or intraperitoneal base loading. Furthermore, KO mice exhibited transient but marked hypoventilation after acute base loading. In rats, increased blood alkalinity of the perfused upper small intestine increased venous secretin release. CONCLUSIONS: Our results suggest that loss of SCTR impairs the appropriate increase of renal base excretion during acute base loading and that SCTR is necessary for acute correction of metabolic alkalosis. In addition, our findings suggest that blood alkalinity increases secretin release from the small intestine and that secretin action is critical for bicarbonate homeostasis.

Serial intravital 2-photon microscopy and analysis of the kidney using upright microscopes.

Serial intravital 2-photon microscopy of the kidney and other abdominal organs is a powerful technique to assess tissue function and structure simultaneously and over time. Thus, serial intravital microscopy can capture dynamic tissue changes during health and disease and holds great potential to characterize (patho-) physiological processes with subcellular resolution. However, successful image acquisition and analysis require significant expertise and impose multiple potential challenges. Abdominal organs are rhythmically displaced by breathing movements which hamper high-resolution imaging. Traditionally, kidney intravital imaging is performed on inverted microscopes where breathing movements are partly compensated by the weight of the animal pressing down. Here, we present a custom and easy-to-implement setup for intravital imaging of the kidney and other abdominal organs on upright microscopes. Furthermore, we provide image processing protocols and a new plugin for the free image analysis software FIJI to process multichannel fluorescence microscopy data. The proposed image processing pipelines cover multiple image denoising algorithms, sample drift correction using 2D registration, and alignment of serial imaging data collected over several weeks using landmark-based 3D registration. The provided tools aim to lower the barrier of entry to intravital microscopy of the kidney and are readily applicable by biomedical practitioners.

Fecal-oral transmission of SARS-CoV-2: A systematic review of evidence from epidemiological and experimental studies.

BACKGROUND: SARS-CoV-2 ribonucleic acid (RNA) has been detected in feces, but RNA is not infectious. This systematic review aims to answer if fecal SARS-CoV-2 is experimentally infectious and if evidence of human fecal-oral SARS-CoV-2 transmission exists. METHODS: On September 19, 2022, we searched PubMed, Embase, Web of Science, medRxiv, and bioRxiv. Biomedical studies inoculating SARS-CoV-2 from feces, rectal, or anal swabs in cells, tissue, organoids, or animals were included. Epidemiological studies of groups differing in exposure to fecal SARS-CoV-2 were included. Risk of bias was assessed using standardized tools. Results were summarized by vote counting, tabulation, and a harvest plot. PROSPERO registration no. CRD42020221719. RESULTS: A total of 4,874 studies were screened; 26 studies were included; and 13 out of 23 biomedical studies (56.5%) succeeded in infection. Two (66.7%) epidemiological studies found limited evidence suggesting fecal-oral transmission. All studies had concerns about the risk of bias. CONCLUSIONS: It is possible to experimentally infect cell cultures, organoids, and animals with fecal SARS-CoV-2. No strong epidemiologic evidence was found to support human fecal-oral transmission. We advise future research to study fecal infectivity at different time points during infection, apply appropriate controls, use in vivo models, and study fecal exposure as a risk factor of transmission in human populations.

Sulfate and acid-base balance.

It has been acknowledged for years that compounds containing sulfur (S) are an important source of endogenous acid production. In the metabolism, S is oxidized to sulfate, and therefore the mEq sulfate excreted in the urine is counted as acid retained in the body. In this study we show that pH in fluids with constant [Na] and [HEPES] declines as sulfate ions are added, and we show that titratable acidity increases exactly with the equivalents of sulfate. Therefore, sulfate excretion in urine is also acid excretion per se. This is in accordance with the down-regulation of proximal sulfate reabsorption under acidosis and the observation that children with distal renal tubular acidosis may be sulfate depleted. These results are well explained using charge-balance modeling, which is based only on the three fundamental principles of electroneutrality, conservation of mass, and rules of dissociation as devised from physical chemistry. In contrast, the findings are in contrast to expectations from conventional narratives. These are unable to understand the decreasing pH as sulfate is added since no conventional acid is present. The results may undermine the traditional notion of endogenous acid production since in the case of sulfur balance, S oxidation and its excretion as sulfate exactly balance each other. Possible clinical correlates with these findings are discussed.

Acid content and buffer-capacity: a charge-balance perspective.

Rational treatment and thorough diagnostic classification of acid-base disorders requires quantitative understanding of the mechanisms that generate and dissipate loads of acid and base. A natural precondition for this tallying is the ability to quantify the acid content in any specified fluid. Physical chemistry defines the pH-dependent charge on any buffer species, and also on strong ions on which, by definition, the charge is pH-invariant. Based, then, on the requirement of electroneutrality and conservation of mass, it was shown in 1914 that pH can be calculated and understood on the basis of the chemical composition of any fluid. Herein we first show that this specification for [H+] of the charge-balance model directly delivers the pH-dependent buffer-capacity as defined in the literature. Next, we show how the notion of acid transport as proposed in experimental physiology can be understood as a change in strong ion difference, ΔSID. Finally, based on Brønsted-Lowry theory we demonstrate that by defining the acid content as titratable acidity, this is equal to SIDref - SID, where SIDref is SID at pH 7.4. Thereby, any chemical situation is represented as a curve in a novel diagram with titratable acidity = SIDref - SID as a function of pH. For any specification of buffer chemistry, therefore, the change in acid content in the fluid is path invariant. Since constituents of SID and titratable acidity are additive, we thereby, based on first principles, have defined a new framework for modeling acid balance across a cell, a whole organ, or the whole-body.

The Probe for Renal Organic Cation Secretion (4-Dimethylaminostyryl)-N-Methylpyridinium (ASP+)) Shows Amplified Fluorescence by Binding to Albumin and Is Accumulated In Vivo.

Accumulation of uremic toxins may lead to the life-threatening condition "uremic syndrome" in patients with advanced chronic kidney disease (CKD) requiring renal replacement therapy. Clinical evaluation of proximal tubular secretion of organic cations (OC), of which some are uremic toxins, is desired, but difficult. The biomedical knowledge on OC secretion and cellular transport partly relies on studies using the fluorescent tracer 4-dimethylaminostyryl)-N-methylpyridinium (ASP+), which has been used in many studies of renal excretion mechanisms of organic ions and which could be a candidate as a PET tracer. This study is aimed at expanding the knowledge of the tracer characteristics of ASP+ by recording the distribution and intensity of ASP+ signals in vivo both by fluorescence and by positron emission tomography (PET) imaging and at investigating if the fluorescence signal of ASP+ is influenced by the presence of albumin. Two-photon in vivo microscopy of male Münich Wistar Frömter rats showed that a bolus injection of ASP+ conferred a fluorescence signal to the blood plasma lasting for about 30 minutes. In the renal proximal tubule, the bolus resulted in a complex pattern of fluorescence including a rapid and strong transient signal at the brush border, a very low signal in the luminal fluid, and a slow transient intracellular signal. PET imaging using 11C-labelled ASP+ showed accumulation in the liver, heart, and kidney. Fluorescence emission spectra recorded in vitro of ASP+ alone and in the presence of albumin using both 1-photon excitation and two-photon excitation showed that albumin strongly enhance the emission from ASP+ and induce a shift of the emission maximum from 600 to 570 nm. Conclusion. The renal pattern of fluorescence observed from ASP+ in vivo is likely affected by the local concentration of albumin, and quantification of ASP+ fluorescent signals in vivo cannot be directly translated to ASP+ concentrations.

Single nephron glomerular filtration rate measured by linescan multiphoton microscopy compared to conventional micropuncture.

Renal micropuncture, which requires the direct access to the renal tubules, has for long time been the technique of choice to measure the single nephron glomerular filtration rate (SNGFR) in animal models. This approach is challenging by virtue of complex animal preparation and numerous technically difficult steps. The introduction of intravital multiphoton microscopy (MPM) offers another approach to the measure of the SNGFR by mean of the high laser-tissue penetration and the optical sectioning capacity. Previous MPM studies measuring SNGFR in vivo relied on fast full-frame acquisition during the filtration process obtainable with high performance resonant scanners. In this study, we describe an innovative linescan-based MPM method. The new method can discriminate SNGFR variations both in conditions of low and high glomerular filtration, and shows results comparable to conventional micropuncture both for rats and mice. Moreover, this novel approach has improved spatial and time resolution and is faster than previous methods, thus enabling the investigation of SNGFR from more tubules and improving options for data-analysis.

SARS-CoV-2 prevalence and transmission in swimming activities: Results from a retrospective cohort study.

There is an urgent need for research on the epidemiology of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causing coronavirus disease 2019 (COVID-19), as the transmissibility differs between settings and populations. Here we report on a questionnaire-based retrospective cohort study of the prevalence and transmission of SARS-CoV-2 among participants in swimming activities in Denmark in the last 5 months of 2020 during the COVID-19 pandemic. Eight of 162 swimming activities with a SARS-CoV-2 positive participant led to transmission to 23 other participants. Overall, the percentage of episodes leading to transmission was 4.9% (competitive swimming 8.9%; recreational swimming 1.3%). Overall, the incidence rate of transmission was 19.5 participants per 100 000 pool activity hours (corresponding values: 43.5 and 4.7 for competitive and recreational swimming, respectively). Compliance with precautionary restrictions was highest regarding hand hygiene (98.1%) and lowest in distancing personal sports bags (69.9%). As a result of low statistical power, the study showed no significant effect of restrictions. Insight into the risk of transmission of SARS-CoV-2 during indoor swimming is needed to estimate the efficiency of restrictive measures on this and other sports and leisure activities. Only when we know how the virus spreads through various settings, optimal strategies to handle the COVID-19 pandemic can be developed.

Quantification of Capillary Perfusion in an Animal Model of Acute Intracranial Hypertension.

Intracranial hypertension (IH) is a common feature of many pathologies, including brain edema. In the brain, the extended network of capillaries ensures blood flow to meet local metabolic demands. Capillary circulation may be severely affected by IH, but no studies have quantified the effect of intracranial pressure (ICP) and cerebral perfusion pressure (CPP) on capillary perfusion during the development of brain edema. We used optical coherence tomography angiography to quantify relative changes of fractional perfused volume (FPV) in cortical capillaries and simultaneously monitored ICP and blood pressure (BP) in anesthetized male C57Bl/6NTac mice during development of brain edema induced by water intoxication (WI) within 30 min. WI induced severe IH and brain herniation. ICP and CPP reached 90.2 mm Hg and 38.4 mm Hg, respectively. FPV was significantly affected already at normal ICP (ICP <15 mm Hg, slope ≈ -1.46, p < 0.001) and, at the onset of IH (ICP = 20-22 mm Hg), FPV was 17.9 ± 13.3% lower than baseline. A decreasing trend was observed until the ICP peak (Δ%FPV = -43.6 ± 19.2%). In the ICP range of 7-42 mm Hg, relative changes in FPV were significantly correlated with ICP, BP, and CPP (p < 0.001), with ICP and CPP being the best predictors. In conclusion, elevated ICP induces a gradual collapse of the cerebral microvasculature, which is initiated before the clinical threshold of IH. In summary, the estimate of capillary perfusion might be essential in patients with IH to assess the state of the brain microcirculation and to improve the availability of oxygen and nutrients to the brain.

Localization and regulation of claudin-14 in experimental models of hypercalcemia.

Variations in the claudin-14 (CLDN14) gene have been linked to increased risk of hypercalciuria and kidney stone formation. However, the exact cellular localization of CLDN14 and its regulation remain to be fully delineated. To this end, we generated a novel antibody that allowed the detection of CLDN14 in paraffin-embedded renal sections. This showed CLDN14 to be detectable in the kidney only after induction of hypercalcemia in rodent models. Protein expression in the kidney is localized exclusively to the thick ascending limbs (TALs), mainly restricted to the cortical and upper medullary portion of the kidney. However, not all cells in the TALs expressed the tight junction protein. In fact, CLDN14 was primarily expressed in cells also expressing CLDN16 but devoid of CLDN10. CLDN14 appeared in very superficial apical cell domains and near cell junctions in a belt-like formation along the apical cell periphery. In transgenic mice, Cldn14 promotor-driven LacZ activity did not show complete colocalization with CLDN14 protein nor was it increased by hypercalcemia, suggesting that LacZ activity cannot be used as a marker for CLDN14 localization and regulation in this model. In conclusion, CLDN14 showed a restricted localization pattern in the apical domain of select cells of the TAL.

Potassium depletion induces cellular conversion in the outer medullary collecting duct altering Notch signaling pathway.

Potassium depletion affects AQP2 expression and the cellular composition of the kidney collecting duct. This, in turn, contributes to the development of a secondary form of nephrogenic diabetes insipidus and hypokalemic nephropathy. Here we show that after 14 days of potassium depletion, the cellular fraction of A-type intercalated cells increases while the fraction of principal cells decreases along the outer medullary collecting duct in rats. The intercalated cells acquired a novel distribution pattern forming rows of cells attached to each other. These morphological changes occur progressively and reverse after 7 days of recovery on normal rat chow diet. The cellular remodeling mainly occurred in the inner stripe of outer medulla similar to the previously seen effect of lithium on the collecting duct cellular profile. The cellular remodeling is associated with the appearance of cells double labelled with both specific markers of principal and type-A intercalated cells. The appearance of this cell type was associated with the downregulation of the Notch signaling via the Hes1 pathways. These results show that the epithelium of the collecting duct has a high degree of plasticity and that Notch signaling likely plays a key role during hypokalemia.

A new experimental mouse model of water intoxication with sustained increased intracranial pressure and mild hyponatremia without side effects of antidiuretics.

The most used experimental mouse model of hyponatremia and elevated intracranial pressure (ICP) is intraperitoneal injection of water in combination with antidiuretics. This model of water intoxication (WI) results in extreme pathological changes and death within 1 h. To improve preclinical studies of the pathophysiology of elevated ICP, we characterized diuresis, cardiovascular parameters, blood ionogram and effects of antidiuretics in this model. We subsequently developed a new mouse model with mild hyponatremia and sustained increased ICP. To investigate the classical protocol (severe WI), C57BL/6mice were anesthetized and received an intraperitoneal injection of 20% body weight of MilliQ water with or without 0.4 µg·kg-1 desmopressin acetate (dDAVP). Corresponding Sham groups were also studied. In the new WI protocol (mild WI), 10% body weight of a solution containing 6.5 mM NaHCO3, 1.125 mM KCl and 29.75 mM NaCl was intraperitoneally injected. By severe WI, ICP and mean arterial pressure increased until brain stem herniation occurred (23 ± 3 min after injection). The cardiovascular effects were accelerated by dDAVP. Severe WI induced a halt to urine production irrespective of the use of dDAVP. Following the new mild WI protocol, ICP also increased but was sustained at a pathologically high level without inducing herniation. Mean arterial pressure and urine production were not affected during mild WI. In conclusion, the new mild WI protocol is a superior experimental model to study the pathophysiological effects of elevated ICP induced by water intoxication.

H+-ATPase B1 subunit localizes to thick ascending limb and distal convoluted tubule of rodent and human kidney.

The vacuolar-type H+-ATPase B1 subunit is heavily expressed in the intercalated cells of the collecting system, where it contributes to H+ transport, but has also been described in other segments of the renal tubule. This study aimed to determine the localization of the B1 subunit of the vacuolar-type H+-ATPase in the early distal nephron, encompassing thick ascending limbs (TAL) and distal convoluted tubules (DCT), in human kidney and determine whether the localization differs between rodents and humans. Antibodies directed against the H+-ATPase B1 subunit were used to determine its localization in paraffin-embedded formalin-fixed mouse, rat, and human kidneys by light microscopy and in sections of Lowicryl-embedded rat kidneys by electron microscopy. Abundant H+-ATPase B1 subunit immunoreactivity was observed in the human kidney. As expected, intercalated cells showed the strongest signal, but significant signal was also observed in apical membrane domains of the distal nephron, including TAL, macula densa, and DCT. In mouse and rat, H+-ATPase B1 subunit expression could also be detected in apical membrane domains of these segments. In rat, electron microscopy revealed that the H+-ATPase B1 subunit was located in the apical membrane. Furthermore, the H+-ATPase B1 subunit colocalized with other H+-ATPase subunits in the TAL and DCT. In conclusion, the B1 subunit is expressed in the early distal nephron. The physiological importance of H+-ATPase expression in these segments remains to be delineated in detail. The phenotype of disease-causing mutations in the B1 subunit may also relate to its presence in the TAL and DCT.

Hemoglobin polymerization via disulfide bond formation in the hypoxia-tolerant turtle Trachemys scripta: implications for antioxidant defense and O2 transport.

The ability of many reptilian hemoglobins (Hbs) to form high-molecular weight polymers, albeit known for decades, has not been investigated in detail. Given that turtle Hbs often contain a high number of cysteine (Cys), potentially contributing to the red blood cell defense against reactive oxygen species, we have examined whether polymerization of Hb could occur via intermolecular disulfide bonds in red blood cells of freshwater turtle Trachemys scripta, a species that is highly tolerant of hypoxia and oxidative stress. We find that one of the two Hb isoforms of the hemolysate HbA is prone to polymerization in vitro into linear flexible chains of different size that are visible by electron microscopy but not the HbD isoform. Polymerization of purified HbA is favored by hydrogen peroxide, a main cellular reactive oxygen species and a thiol oxidant, and inhibited by thiol reduction and alkylation, indicating that HbA polymerization is due to disulfide bonds. By using mass spectrometry, we identify Cys5 of the αA-subunit of HbA as specifically responsible for forming disulfide bonds between adjacent HbA tetramers. Polymerization of HbA does not affect oxygen affinity, cooperativity, and sensitivity to the allosteric cofactor ATP, indicating that HbA is still fully functional. Polymers also form in T. scripta blood after exposure to anoxia but not normoxia, indicating that they are of physiological relevance. Taken together, these results show that HbA polymers may form during oxidative stress and that Cys5αA of HbA is a key element of the antioxidant capacity of turtle red blood cells.

Lithium increases ammonium excretion leading to altered urinary acid-base buffer composition.

Previous reports identify a voltage dependent distal renal tubular acidosis (dRTA) secondary to lithium (Li+) salt administration. This was based on the inability of Li+-treated patients to increase the urine-blood (U-B) pCO2 when challenged with NaHCO3 and, the ability of sodium neutral phosphate or Na2SO4 administration to restore U-B pCO2 in experimental animal models. The underlying mechanisms for the Li+-induced dRTA are still unknown. To address this point, a 7 days time course of the urinary acid-base parameters was investigated in rats challenged with LiCl, LiCitrate, NaCl, or NaCitrate. LiCl induced the largest polyuria and a mild metabolic acidosis. Li+-treatment induced a biphasic response. In the first 2 days, proper urine volume and acidification occurred, while from the 3rd day of treatment, polyuria developed progressively. In this latter phase, the LiCl-treated group progressively excreted more NH4+ and less pCO2, suggesting that NH3/NH4+ became the main urinary buffer. This physiological parameter was corroborated by the upregulation of NBCn1 (a marker of increased ammonium recycling) in the inner stripe of outer medulla of LiCl treated rats. Finally, by investigating NH4+ excretion in ENaC-cKO mice, a model resistant to Li+-induced polyuria, a primary role of the CD was confirmed. By definition, dRTA is characterized by deficient urinary ammonium excretion. Our data question the presence of a voltage-dependent Li+-induced dRTA in rats treated with LiCl for 7 days and the data suggest that the alkaline urine pH induced by NH3/NH4+ as the main buffer has lead to the interpretation dRTA in previous studies.

Disturbances in the control of capillary flow in an aged APPswe/PS1ΔE9 model of Alzheimer's disease.

Vascular changes are thought to contribute to the development of Alzheimer's disease, and both cerebral blood flow and its responses during neural activation are reduced before Alzheimer's disease symptoms onset. One hypothetical explanation is that capillary dysfunction reduces oxygen extraction efficacy. This study compares the morphology and hemodynamics of the microvasculature in the somatosensory cortex of 18-month-old APPSWE/PS1ΔE9 (transgenic [Tg]) mice and wild-type (WT) littermates. In particular, the extent to which their capillary transit times homogenize during functional activation was measured and compared. Capillary length density was similar in both groups but capillary blood flow during rest was lower in the Tg mice, indicating that cortical oxygen availability is reduced. The capillary hemodynamic response to functional activation was larger, and lasted longer in Tg mice than in WT mice. The homogenization of capillary transit times during functional activation, which we previously demonstrated in young mice, was absent in the Tg mice. This study demonstrates that both neurovascular coupling and capillary function are profoundly disturbed in aged Tg and WT mice.