Trade-offs between succulent and non-succulent epiphytes underlie variation in drought tolerance and avoidance.

Epiphyte communities comprise important components of many forest ecosystems in terms of biomass and diversity, but little is known regarding trade-offs that underlie diversity and structure in these communities or the impact that microclimate has on epiphyte trait allocation. We measured 22 functional traits in vascular epiphyte communities across six sites that span a microclimatic gradient in a tropical montane cloud forest region in Costa Rica. We quantified traits that relate to carbon and nitrogen allocation, gas exchange, water storage, and drought tolerance. Functional diversity was high in all but the lowest elevation site where drought likely limits the success of certain species with particular trait combinations. For most traits, variation was explained by relationships with other traits, rather than differences in microclimate across sites. Although there were significant differences in microclimate, epiphyte abundance, and diversity, we found substantial overlap in multivariate trait space across five of the sites. We found significant correlations between functional traits, many of which related to water storage (leaf water content, leaf thickness, hydrenchymal thickness), drought tolerance (turgor loss point), and carbon allocation (specific leaf area, leaf dry matter content). This suite of trait correlations suggests that the epiphyte community has evolved functional strategies along with a drought avoidance versus drought tolerance continuum where leaf succulence emerged as a pivotal overall trait.

Safety and Efficiency of Intravenous Push Lacosamide Administration.

BACKGROUND/OBJECTIVE: Intravenous (IV) lacosamide use for status epilepticus has increased in recent years and is recommended for refractory status epilepticus by current guidelines. Per the lacosamide package labeling, the preferred route of administration is diluted and infused over 30-60 min; however, administration undiluted is also acceptable and recent literature demonstrated safety at a maximum rate of 80 mg per minute (Kellinghaus et al. in Acta Neurol Scand 123:137-141, 2011). Undiluted administration as an IV push has potential to increase efficiency of administration to patients needing urgent seizure control since it may be dispensed from automatic dispensing cabinets in patient care areas. This study aims to compare safety outcomes and efficiency of administration in patients receiving lacosamide IV push compared to IV piggyback. METHODS: We present a single-center, retrospective cohort study of patients receiving lacosamide via IV piggyback or IV push from June 2016 to July 2017. Baseline characteristics, data related to potential safety concerns and timing of ordering, verification, and administration were collected. The primary safety outcomes were incidence of infusion site reactions, hypotension (systolic blood pressure [SBP] < 90 mm Hg), and bradycardia (heart rate [HR] < 50 beats per minute) documented within 2 h of each lacosamide dose. Secondary safety outcomes included the incidence of PR interval prolongation in patients with at least one electrocardiogram measured. The primary efficiency outcome was the time between order verification and administration. RESULTS: Patients in the IV piggyback (n = 88) and IV push (n = 78) groups had similar baseline characteristics, initial dose, SBP, and HR. Hypotension (8 vs. 10.3%) and bradycardia (2.3 vs. 2.6%) rates were similar among both groups (p > 0.05). Only one patient in each group had documented PR prolongation, and no documented infusion reactions occurred. Median time from order verification to administration was significantly reduced in the IV push group (35 min vs. 1 h 49 min; p < 0.001). CONCLUSIONS: Administration of lacosamide via IV push results in similar adverse effect rates to IV piggyback preparations with more efficient time to administration.

Impact of Moderate Hyperchloremia on Clinical Outcomes in Intracerebral Hemorrhage Patients Treated With Continuous Infusion Hypertonic Saline: A Pilot Study.

OBJECTIVES: Hyperchloremia has been associated with increased morbidity and mortality in critically ill patients. While previous research has demonstrated an association between hypertonic saline and hyperchloremia, limited data exist in neurocritical care patients. The objective of this study is to determine the impact of moderate hyperchloremia (chloride ≥ 115 mmol/L) on clinical outcomes in intracerebral hemorrhage patients treated with continuous IV infusion 3% hypertonic saline. DESIGN: Multicenter, retrospective, propensity-matched cohort study. SETTING: Neurocritical care units at two academic medical centers with dedicated neurocritical care teams and comprehensive stroke center designation. PATIENTS: Intracerebral hemorrhage patients discharged between September 2011 and September 2015 were evaluated and matched 1:1 based on propensity scoring. INTERVENTIONS: Continuous IV infusion 3% hypertonic saline. MEASUREMENTS AND MAIN RESULTS: A total of 219 patients were included in the unmatched cohort (143 moderate hyperchloremia and 76 nonhyperchloremia) and 100 patients in the propensity-matched cohort. In-hospital mortality was significantly higher in those who developed moderate hyperchloremia in a propensity-matched cohort (34% vs 14%; p = 0.02). Moderate hyperchloremia independently predicted in-hospital mortality in multivariable logistic regression analysis (odds ratio, 4.4 [95% CI, 1.4-13.5]; p = 0.01). CONCLUSIONS: We observed higher rates of in-hospital mortality in patients who developed moderate hyperchloremia during treatment with continuous IV infusion 3% hypertonic saline, with moderate hyperchloremia independently predicting in-hospital mortality. These results suggest that chloride values should be monitored closely during hypertonic saline treatment as moderate elevations may impact outcomes in intracerebral hemorrhage patients.

Use of direct oral anticoagulants in patients on immunomodulatory agents.

Immunomodulatory agents (IMiDs) are used to treat multiple hematologic malignancies. Their use is also associated with increased risk of venous thromboembolism (VTE). Direct oral anticoagulants (DOACs) have been increasingly utilized but due to their relative novelty, their role in malignancy has only been recently investigated. The objective of this study was to assess the safety and efficacy of DOACs in patients receiving IMiDs. This was a retrospective study of patients at our institution treated with an IMiD and concomitant warfarin or DOAC between January 1, 2010 and December 31, 2015. Information on demographic and clinical characteristics was collected. Separate encounters were collected for each specific combination of IMiD and anticoagulant. Bleeding and thrombotic events were recorded. There were four bleeding events in the DOAC group; all were non-major. There were six bleeding events in the warfarin group, two of which were major (gastrointestinal bleeding (GIB) and subarachnoid hemorrhage (SAH)) and four of which were non-major. Of the two major bleeds in this group, neither event occurred with concomitant antiplatelet therapy. There was one thrombotic event in the DOAC group, which was a myocardial infarction, suspected to be related to carfilzomib. There were no thrombotic events in the warfarin group. This was a retrospective, single-institution study assessing the safety and efficacy of DOACs as compared to warfarin in patients on IMiDs. DOACs may represent an attractive alternative to warfarin for VTE prophylaxis in patients on IMiDs but prospective studies in this population are warranted.

Bias in beliefs about the self is associated with depressive but not anxious mood.

BACKGROUND: Biases in beliefs about the self are associated with psychopathology and depressive and anxious mood, but it is not clear if both negative and positive beliefs are associated with depression or anxiety. We examined these relationships in people who present with a wide range of depressive and anxious mood across diagnostic categories. METHODS: We probed positive and negative beliefs about the self with a task in which 74 female participants with either affective disorder (depression and/or anxiety), borderline personality disorder or no psychiatric history indicated the degree to which 60 self-related words was "like them" or "not like them". Depressive and anxious mood were assessed with the Beck Depression Inventory-II and the Beck Anxiety Inventory. RESULTS: The participants with no psychiatric history (n=25) reported a positive bias in their beliefs about the self, the participants with affective disorder (n=23) reported no bias, and the participants with BPD (n=26) reported a negative bias. Two hierarchical multiple regressions demonstrated that the positive and negative beliefs contributed additively to the ratings of depression (corrected for anxiety), but did not contribute to the ratings of anxiety (corrected for depression). LIMITATIONS: Despite the apparent small sample size, the regression analyses indicated adequate sampling. Anxiety is a much more heterogeneous condition than is depression, so it may be difficult to find relevant self-descriptors. Only measures of endorsement were used. CONCLUSIONS: Biases in beliefs about the self are associated with depressed, but not anxious mood, across diagnostic categories.

Different pathways of molecular pathophysiology underlie cognitive and motor tauopathy phenotypes in transgenic models for Alzheimer's disease and frontotemporal lobar degeneration.

A poorly understood feature of the tauopathies is their very different clinical presentations. The frontotemporal lobar degeneration (FTLD) spectrum is dominated by motor and emotional/psychiatric abnormalities, whereas cognitive and memory deficits are prominent in the early stages of Alzheimer's disease (AD). We report two novel mouse models overexpressing different human tau protein constructs. One is a full-length tau carrying a double mutation [P301S/G335D; line 66 (L66)] and the second is a truncated 3-repeat tau fragment which constitutes the bulk of the PHF core in AD corresponding to residues 296-390 fused with a signal sequence targeting it to the endoplasmic reticulum membrane (line 1; L1). L66 has abundant tau pathology widely distributed throughout the brain, with particularly high counts of affected neurons in hippocampus and entorhinal cortex. The pathology is neuroanatomically static and declines with age. Behaviourally, the model is devoid of a higher cognitive phenotype but presents with sensorimotor impairments and motor learning phenotypes. L1 displays a much weaker histopathological phenotype, but shows evidence of neuroanatomical spread and amplification with age that resembles the Braak staging of AD. Behaviourally, the model has minimal motor deficits but shows severe cognitive impairments affecting particularly the rodent equivalent of episodic memory which progresses with advancing age. In both models, tau aggregation can be dissociated from abnormal phosphorylation. The two models make possible the demonstration of two distinct but nevertheless convergent pathways of tau molecular pathogenesis. L1 appears to be useful for modelling the cognitive impairment of AD, whereas L66 appears to be more useful for modelling the motor features of the FTLD spectrum. Differences in clinical presentation of AD-like and FTLD syndromes are therefore likely to be inherent to the respective underlying tauopathy, and are not dependent on presence or absence of concomitant APP pathology.

Mathematics interventions for children and adolescents with Down syndrome: a research synthesis.

BACKGROUND: Many children and adolescents with Down syndrome fail to achieve proficiency in mathematics. Researchers have suggested that tailoring interventions based on the behavioural phenotype may enhance efficacy. METHOD: The research questions that guided this review were (1) what types of mathematics interventions have been empirically evaluated with children and adolescents with Down syndrome?; (2) do the studies demonstrate sufficient methodological rigor?; (3) is there evidence of efficacy for the evaluated mathematics interventions?; and (4) to what extent have researchers considered aspects of the behavioural phenotype in selecting, designing and/or implementing mathematics interventions for children and adolescents with Down syndrome? Nine studies published between 1989 and 2012 were identified for inclusion. RESULTS: Interventions predominantly focused on early mathematics skills and reported positive outcomes. However, no study met criteria for methodological rigor. Further, no authors explicitly considered the behavioural phenotype. CONCLUSIONS: Additional research using rigorous experimental designs is needed to evaluate the efficacy of mathematics interventions for children and adolescents with Down syndrome. Suggestions for considering the behavioural phenotype in future research are provided.

Molecular testing of 163 patients with Morquio A (Mucopolysaccharidosis IVA) identifies 39 novel GALNS mutations.

Morquio A (Mucopolysaccharidosis IVA; MPS IVA) is an autosomal recessive lysosomal storage disorder caused by partial or total deficiency of the enzyme galactosamine-6-sulfate sulfatase (GALNS; also known as N-acetylgalactosamine-6-sulfate sulfatase) encoded by the GALNS gene. Patients who inherit two mutated GALNS gene alleles have a decreased ability to degrade the glycosaminoglycans (GAGs) keratan sulfate and chondroitin 6-sulfate, thereby causing GAG accumulation within lysosomes and consequently pleiotropic disease. GALNS mutations occur throughout the gene and many mutations are identified only in single patients or families, causing difficulties both in mutation detection and interpretation. In this study, molecular analysis of 163 patients with Morquio A identified 99 unique mutations in the GALNS gene believed to negatively impact GALNS protein function, of which 39 are previously unpublished, together with 26 single-nucleotide polymorphisms. Recommendations for the molecular testing of patients, clear reporting of sequence findings, and interpretation of sequencing data are provided.

Insight, duration of untreated psychosis and attachment in first-episode psychosis: prospective study of psychiatric recovery over 12-month follow-up.

BACKGROUND: Increasing evidence shows attachment security influences symptom expression and adaptation in people diagnosed with schizophrenia and other psychoses. AIMS: To describe the distribution of secure and insecure attachment in a cohort of individuals with first-episode psychosis, and to explore the relationship between attachment security and recovery from positive and negative symptoms in the first 12 months. METHOD: The study was a prospective 12-month cohort study. The role of attachment, duration of untreated psychosis (DUP), baseline symptoms and insight in predicting and mediating recovery from symptoms was investigated using multiple regression analysis and path analysis. RESULTS: Of the 79 participants, 54 completed the Adult Attachment Interview (AAI): 37 (68.5%) were classified as insecure, of which 26 (48.1%) were insecure/dismissing and 11 (20.4%) insecure preoccupied. Both DUP and insight predicted recovery from positive symptoms at 12 months. Attachment security, DUP and insight predicted recovery from negative symptoms at 12 months. CONCLUSIONS: Attachment is an important construct contributing to understanding and development of interventions promoting recovery following first-episode psychosis.

Guidance for the gastrointestinal evaluation and management of iron deficiency in Sub-Saharan Africa.

BACKGROUND: Over 30% of the world's population is anaemic, with a significant proportion of these being iron deficient. As iron deficiency (ID) anaemia in men and post-menopausal women is mostly caused by gastrointestinal blood loss or malabsorption, the initial evaluation of a patient with ID anaemia involves referral to a gastroenterologist. The current drive towards patient blood management in sub-Saharan Africa (SSA)prescribes that we regulate not only the use of blood transfusion but also the management of patients in whom the cause of iron loss or inadequate iron absorption is sought. Recommendations have been developed to: (i) aid clinicians in the evaluation of suspected gastrointestinal iron loss and iron malabsorption, and often a combination of these; (ii) improve clinical outcomes for patients with gastrointestinal causes of ID; (iii) provide current, evidence-based, context-specific recommendations for use in the management of ID; and (iv) conserve resources by ensuring rational utilisation of blood and blood products. METHOD: Development of the guidance document was facilitated by the Gastroenterology Foundation of Sub-Saharan Africa and the South African Gastroenterology Society. The consensus recommendations are based on a rigorous process involving 21 experts in gastroenterology and haematology in SSA. Following discussion of the scope and purpose of the guidance document among the experts, an initial review of the literature and existing guidelines was undertaken. Thereafter, draft recommendation statements were produced to fulfil the outlined purpose of the guidance document. These were reviewed in a round-table discussion and were subjected to two rounds of anonymised consensus voting by the full committee in an electronic Delphi exercise during 2022 using the online platform, Research Electronic Data Capture. Recommendations were modified by considering feedback from the previous round, and those reaching a consensus of over 80% were incorporated into the final document. Finally, 44 statements in the document were read and approved by all members of the working group. CONCLUSION: The recommendations incorporate six areas, namely: general recommendations and practice, Helicobacter pylori, coeliac disease, suspected small bowel bleeding, inflammatory bowel disease, and preoperative care. Implementation of the recommendations is aimed at various levels from individual practitioners to healthcare institutions, departments and regional, district, provincial and national platforms. It is intended that the recommendations spur the development of centre-specific guidelines and that they are integrated with the relevant patient blood management protocols. Integration of the recommendations is intended to promote optimal evaluation and management of patients with ID, regardless of the presence of anaemia.

Wnt/ß-catenin pathway regulates bone morphogenetic protein (BMP2)-mediated differentiation of dental follicle cells.

BACKGROUND AND OBJECTIVE: Bone morphogenetic protein 2 (BMP2)-induced osteogenic differentiation has been shown to occur through the canonical Wnt/ßcatenin pathway, whereas factors promoting canonical Wnt signaling in cementoblasts inhibit cell differentiation and promote cell proliferation in vitro. The aim of this study was to investigate whether putative precursor cells of cementoblasts, dental follicle cells (murine SVF4 cells), when stimulated with BMP2, would exhibit changes in genes/proteins associated with the Wnt/ß-catenin pathway. MATERIAL AND METHODS: SVF4 cells were stimulated with BMP2, and the following assays were carried out: (i) Wnt/ß-catenin pathway activation assessed by western blotting, ß-catenin/transcription factor (TCF) reporter assays and expression of the lymphoid enhancer-binding factor-1 (Lef1), transcription factor 7 (Tcf7), Wnt inhibitor factor 1 (Wif1) and Axin2 (Axin2) genes; and (ii) cementoblast/osteoblast differentiation assessed by mineralization in vitro, and by the mRNA levels of runt-related transcription factor 2 (Runx2), osterix (Osx), alkaline phosphatase (Alp), osteocalcin (Ocn) and bone sialoprotein (Bsp), determined by quantitative PCR after treatment with wingless-type MMTV integration site family, member 3A (WNT3A) and knockdown of ß-catenin. RESULTS: WNT3A induced ß-catenin nuclear translocation and up-regulated the transcriptional activity of a canonical Wnt-responsive reporter, suggesting that the Wnt/ß-catenin pathway functions in SVF4 cells. Activation of Wnt signaling with WNT3A suppressed BMP2-mediated induction of cementoblast/osteoblast maturation of SVF4 cells. However, ß-catenin knockdown showed that the BMP2-induced expression of cementoblast/osteoblast differentiation markers requires endogenous ß-catenin. WNT3A down-regulated transcripts for Runx2, Alp and Ocn in SVF4 cells compared with untreated cells. In contrast, BMP2 induction of Bsp transcripts occurred independently of Wnt/ß-catenin signaling. CONCLUSION: These data suggest that stabilization of ß-catenin by WNT3A inhibits BMP2-mediated induction of cementoblast/osteoblast differentiation in SVF4 cells, although BMP2 requires endogenous Wnt/ß-catenin signaling to promote cell maturation.

Effects of Presbyphagia on Oropharyngeal Swallowing Observed during Modified Barium Swallow Studies.

OBJECTIVES: Understanding how aging impacts swallowing can help differentiate typical from atypical behaviors. This study aimed to quantify age-related swallowing alterations observed during a modified barium swallow study. DESIGN: Cross-sectional study. SETTING: Adult fluoroscopy suite in a metropolitan hospital at an academic center. PARTICIPANTS: 195 healthy adults distributed across 3 age categories: 21-39; 40-59; 60+ years. MEASUREMENTS: 17 physiologic components of swallowing across three functional domains (oral, pharyngeal, esophageal), including summed composite scores (Oral Total [OT] and Pharyngeal Total [PT]), from the validated and standardized Modified Barium Swallow Impairment Profile. RESULTS: Most components (65%) demonstrated no impairment (scores of "0"). The odds of a worse (higher) score increased significantly with age for: Tongue Control during Bolus Hold, Hyolaryngeal Movement, Laryngeal Closure, Pharyngeal Contraction, and Pharyngoesophageal Segment Opening. OT and PT scores for 40-59-year-olds were worse than the youngest group (p=.01 and p <.001, respectively). Adults 60+ years had significantly worse PT scores among all groups (p-values <.01). CONCLUSION: Oropharyngeal swallowing physiology evolves as healthy adults age and should be considered during clinical decision-making.

PtdIns(3)P regulates the neutrophil oxidase complex by binding to the PX domain of p40(phox).

The production of reactive oxygen species (ROS) by neutrophils has a vital role in defence against a range of infectious agents, and is driven by the assembly of a multi-protein complex containing a minimal core of five proteins: the two membrane-bound subunits of cytochrome b(558) (gp91(phox) and p22(phox)) and three soluble factors (GTP-Rac, p47(phox) and p67(phox) (refs 1, 2). This minimal complex can reconstitute ROS formation in vitro in the presence of non-physiological amphiphiles such as SDS. p40(phox) has subsequently been discovered as a binding partner for p67(phox) (ref. 3), but its role in ROS formation is unclear. Phosphoinositide-3-OH kinases (PI(3)Ks) have been implicated in the intracellular signalling pathways coordinating ROS formation but through an unknown mechanism. We show that the addition of p40(phox) to the minimal core complex allows a lipid product of PI(3)Ks, phosphatidylinositol 3-phosphate (PtdIns(3)P), to stimulate specifically the formation of ROS. This effect was mediated by binding of PtdIns(3)P to the PX domain of p40(phox). These results offer new insights into the roles for PI(3)Ks and p40(phox) in ROS formation and define a cellular ligand for the orphan PX domain.

Examining the ultraviolet optical screening tool as a viable means for delineating a contaminated organic sediment.

Rapid and accurate delineation of contaminated sediments in marine environments is critical for the effective assessment of site risks and the development of appropriate remedial action plans. In this study, a new application of the ultraviolet optical screening tool (UVOST) equipped with electrical conductivity measurement (UVOST-EC) is proposed to delineate a water-covered sediment contaminated with dioxins and furans in a decommissioned pulp and paper wastewater stabilization basin. Bench scale experiments are presented that were used to develop a UVOST-EC interpretation method for delineating between two different sediment types present in the basin: an anthropogenically derived organic rich contaminated sediment ("black sediment") and a naturally occurring grey organic silt sediment with marine provenance ("grey sediment"). The method involves comparative analysis of fluorescence and electrical conductivity signatures between the two sediments. Results indicate that each sediment type presents unique "signatures" related to fluorescence and electrical signals which corresponds to variability in their physio-chemical structure. Almost 100 UVOST-EC tests performed at the study site were paired with ex situ physical gravity core measurements of the black sediment to test the accuracy of the UVOST-EC-based method. A statistical analysis at seven sample "cluster" sites (i.e. multiple sub-samples within a defined area) indicated that the mean of sediment thickness obtained by the UVOST-EC measurement technique at a given site were not significantly different (p = 0.05) from measurements derived from sediment gravity core measurements. The UVOST-EC-based sediment thickness delineation method reliably determined the thickness of the dioxin and furan contaminated sediments as compared to gravity core determination for the sediment in this study. Application of this approach to other studies should be assessed in a similar manner. The UVOST-EC method offers health and safety, cost, logistics, and data interpretation benefits.

Effect of Alteplase Administration on International Normalized Ratio in Patients With Acute Ischemic Stroke.

BACKGROUND/OBJECTIVE: Alteplase may elevate international normalized ratio (INR) results, although the exact rate of elevation occurrence is not firmly established in the literature. The purpose of this study is to determine the occurrence rate of INR elevation following alteplase administration. We also aimed to determine what factors are independently associated with the development of elevated INR following alteplase administration for ischemic stroke. METHODS: We conducted a multicenter, retrospective, cohort study of patients who received alteplase for acute ischemic stroke. Patients were screened for baseline INR measurement and a repeat value within 24 hours of alteplase administration. The primary outcome was the percent of patients who experienced ≥0.4-point increase in INR. Secondary outcomes included the rate of adverse bleeding events and identification of factors independently associated with elevated INR following alteplase administration. RESULTS AND CONCLUSIONS: Two hundred and sixty-one patients were included, with 44 (16.9%) patients having an INR increase of 0.4 or more. Patients with an INR increase ≥0.4 experienced a nonstatistically significant increase in bleeding episodes (8.8% vs 18.2%; P = .10). We identified African American race (odds ratio, 3.48, 95% confidence interval, 1.5-7.6; P = .002) as an independent predictor of INR increase ≥0.04. An INR elevation is common following receipt of alteplase for ischemic stroke. Those of African American race were at increased risk of INR elevation; however, more studies are needed to determine whether these patients are at a higher bleeding risk as a result of INR elevation.

The most luminous stars.

Stars with individual luminosities more than a million times that of the sun are now being studied in a variety of contexts. Observational and theoretical ideas about the most luminous stars have changed greatly in the past few years. They can be observed spectroscopically even in nearby galaxies. They are not very stable; some have had violent outbursts in which large amounts of mass were lost. Because of their instabilities, these stars do not evolve to become red superglants as less luminous stars do. Theoretical scenarios for the evolution of these most massive stars depend on the effects of turbulence and mixing combined with high radition densities.

Isolated nephron segments from rabbit models of obstructive nephropathy.

Micropuncture and microcatheterization studies have been used extensively to investigate the pathophysiologic alterations in renal function induced by urinary tract obstruction. The present isolated tubule microperfusion studies were designed to examine the intrinsic alterations in segmental nephron function induced by 24 h of bilateral (BUO) and unilateral (UUO) urinary tract obstruction. Following UUO superficial proximal convoluted tubule reabsorption rate (J(v)) was not different from contralateral control (0.75+/-0.08 vs. 0.73+/-0.11 nl/mm per min, NS). Following UUO J(v) in juxtamedullary proximal convoluted tubules (JMPCT) was reduced 32% (0.69+/-0.06 vs. 0.47+/-0.04 nl/mm per min, P < 0.02). Following UUO J(v) in proximal straight tubules (PST) was reduced 52% (0.25+/-0.02 vs. 0.12+/-0.03, P < 0.01). Thick ascending limb (T-ALH) function was assessed by measurement of ability to lower perfusate chloride ion concentration (DeltaCl). Following UUO DeltaCl was reduced 76% (-39+/-9 vs. -9+/-1 meq/liter, P < 0.001). Cortical collecting tubule (CCT) function was assessed by measurement of antiduiretic hormone (ADH)-dependent osmotic water flow. Following UUO osmotic water flow was reduced 76% (0.90+/-0.08 vs. 0.22+/-0.04 nl/mm per min, P < 0.01) and this ADH resistance could not be overcome by cAMP. Nephron segments were then examined following relief of BUO. There were no differences in intrinsic function following relief of BUO when compared with UUO. We conclude that in UUO and BUO (a) the intrinsic tubular defects are identical, (b) the natriuresis noted is due, in part, to disordered JMPCT, PST, and T-ALH NaCl reabsorption, (c) the impaired concentrating ability is due, in part, to depressed function in T-ALH and ADH resistance of the CCT, and (d) the ADH resistance occurs at a site distal to the intracellular generation of cAMP.

In vivo and in vitro studies of urinary concentrating ability in potassium-depleted rabbits.

The factors responsible for the urinary concentrating defect associated with the potassium-depleted (KD) state are uncertain. The present studies were designed to, first, determine whether a urinary concentrating defect exists in potassium-depleted rabbits and, second, to use the technique of in vitro perfusion to evaluate directly the antidiuretic hormone (ADH) responsiveness of cortical collecting tubules (CCT) in this setting. Feeding female New Zealand White rabbits a potassium-deficient diet for 2 wk caused a significant fall in plasma potassium levels in both the ad-libitum and controlled water intake groups (P less than 0.001). Muscle potassium content after 2 wk of potassium restriction fell from 45.6 +/- 0.9 to 29.0 +/- 1.2 meq/100 g fat-free dry solids (P less than 0.001). Renal papillary sodium content fell significantly from a control value of 234.6 +/- 8.0 to 182.46 +/- 10.0 meq/kg H2O after 2 wk of potassium restriction. Maximal urinary osmolality measured after 12 h of dehydration and 1.25 U pitressin IM was significantly decreased in rabbits after 2 wk of potassium restriction in both the ad-libitum and controlled water intake groups (P less than 0.001). The relationship between plasma potassium concentration and maximum urinary osmolality was significantly correlated in both the ad-libitum and controlled water intake groups, r = 0.73 and 0.68 (P less than 0.001), respectively. In addition, refeeding KD rabbits with normal chow for 1 wk resulted in normalization of both plasma potassium levels and urinary concentrating ability. CCT from control and KD rabbits were perfused in vitro at 25 degrees C. The hydraulic conductivity coefficient, Lp, was significantly reduced at all doses of ADH tested in tubules from KD rabbits when compared with control tubules. In addition, the maximal hydraulic conductivity in tubules from KD rabbits when tested with 200 microU/ml ADH at 37.5 degrees C was only 23% of control values (P less than 0.05). Furthermore, this reduced ADH responsiveness persisted when the bath potassium was elevated from 5 to 20 mM. The reflection coefficient for NaCl when compared with raffinose was 0.91 in tubules from KD animals. Thus, these data suggest that the ADH-resistant urinary concentrating defect associated with potassium depletion is due, at least in part, to a diminished responsiveness of the CCT to ADH. Therefore, further studies were designed to investigate the cellular steps involved in this abnormal response. There was no difference in the 8-para-chlorophenylthio cyclic AMP induced hydroosmotic response between CCT from KD and control rabbits. Since the cAMP-induced hydroosmotic response was similar between KD and control CCT, experiments were performed to evaluate the contribution of phosphodiesterase (PDIE) activity by using the potent PDIE inhibitor isobutylmethylxanthine (10(-4) and 10(-3)M) in the presence of ADH (200 U/ml). Although Lp was increased by PDIE inhibition in CCT from both control and KD animals, the overall hydroosmotic response in CCT from KD rabbits was still significantly reduced when compared with controls. The final experiments used forskolin to evaluate further the adenylate cyclase complex. The resulting hydroosmotic response in CCT from KD rabbits was almost identical to that obtained in controls. In conclusion, these data suggest that the decreased responsiveness of CCT from KD rabbits to ADH involves a step at or proximal to the stimulation of the catalytic subunit of adenylate cyclase, and that PDIE activity makes no contribution to this abnormal hydroosmotic response.

Identification of connexin36 in gap junctions between neurons in rodent locus coeruleus.

Locus coeruleus neurons are strongly coupled during early postnatal development, and it has been proposed that these neurons are linked by extraordinarily abundant gap junctions consisting of connexin32 (Cx32) and connexin26 (Cx26), and that those same connexins abundantly link neurons to astrocytes. Based on the controversial nature of those claims, immunofluorescence imaging and freeze-fracture replica immunogold labeling were used to re-investigate the abundance and connexin composition of neuronal and glial gap junctions in developing and adult rat and mouse locus coeruleus. In early postnatal development, connexin36 (Cx36) and connexin43 (Cx43) immunofluorescent puncta were densely distributed in the locus coeruleus, whereas Cx32 and Cx26 were not detected. By freeze-fracture replica immunogold labeling, Cx36 was found in ultrastructurally-defined neuronal gap junctions, whereas Cx32 and Cx26 were not detected in neurons and only rarely detected in glia. In 28-day postnatal (adult) rat locus coeruleus, immunofluorescence labeling for Cx26 was always co-localized with the glial gap junction marker Cx43; Cx32 was associated with the oligodendrocyte marker 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase); and Cx36 was never co-localized with Cx26, Cx32 or Cx43. Ultrastructurally, Cx36 was localized to gap junctions between neurons, whereas Cx32 was detected only in oligodendrocyte gap junctions; and Cx26 was found only rarely in astrocyte junctions but abundantly in pia mater. Thus, in developing and adult locus coeruleus, neuronal gap junctions contain Cx36 but do not contain detectable Cx32 or Cx26, suggesting that the locus coeruleus has the same cell-type specificity of connexin expression as observed ultrastructurally in other regions of the CNS. Moreover, in both developing and adult locus coeruleus, no evidence was found for gap junctions or connexins linking neurons with astrocytes or oligodendrocytes, indicating that neurons in this nucleus are not linked to the pan-glial syncytium by Cx32- or Cx26-containing gap junctions or by abundant free connexons composed of those connexins.