Atrial Arrhythmia in Ageing Spontaneously Hypertensive Rats: Unraveling the Substrate in Hypertension and Ageing

Background

Both ageing and hypertension are known risk factors for atrial fibrillation (AF) although the pathophysiological contribution or interaction of the individual factors remains poorly understood. Here we aim to delineate the arrhythmogenic atrial substrate in mature spontaneously hypertensive rats (SHR).

Methods

SHR were studied at 12 and 15 months of age (n = 8 per group) together with equal numbers of age-matched normotensive Wistar-Kyoto control rats (WKY). Electrophysiologic study was performed on superfused isolated right and left atrial preparations using a custom built high-density multiple-electrode array to determine effective refractory periods (ERP), atrial conduction and atrial arrhythmia inducibility. Tissue specimens were harvested for structural analysis.

Results

Compared to WKY controls, the SHR demonstrated: Higher systolic blood pressure (p<0.0001), bi-atrial enlargement (p<0.05), bi-ventricular hypertrophy (p<0.05), lower atrial ERP (p = 0.008), increased atrial conduction heterogeneity (p = 0.001) and increased atrial interstitial fibrosis (p = 0.006) & CD68-positive macrophages infiltration (p<0.0001). These changes resulted in higher atrial arrhythmia inducibility (p = 0.01) and longer induced AF episodes (p = 0.02) in 15-month old SHR. Ageing contributed to incremental bi-atrial hypertrophy (p<0.01) and atrial conduction heterogeneity (p<0.01) without affecting atrial ERP, fibrosis and arrhythmia inducibility. The limited effect of ageing on the atrial substrate may be secondary to the reduction in CD68-positive macrophages.

Conclusions

Significant atrial electrical and structural remodeling is evident in the ageing spontaneously hypertensive rat atria. Concomitant hypertension appears to play a greater pathophysiological role than ageing despite their compounding effect on the atrial substrate. Inflammation is pathophysiologically linked to the pro-fibrotic changes in the hypertensive atria.     

Characterization of Dinophysis spp. (Dinophyceae,Dinophysiales) from the mid-Atlantic region of the United States1

Due to the increasing prevalence of Dinophysis spp. and their toxins on every US coast in recent years, the need to identify and monitor for problematic Dinophysis populations has become apparent. Here, we present morphological analyses, using light and scanning electron microscopy, and rDNA sequence analysis, using a ~2-kb sequence of ribosomal ITS1, 5.8S, ITS2, and LSU DNA, of Dinophysis collected in mid-Atlantic estuarine and coastal waters from Virginia to New Jersey to better characterize local populations. In addition, we analyzed for diarrhetic shellfish poisoning (DSP) toxins in water and shellfish samples collected during blooms using liquid-chromatography tandem mass spectrometry and an in vitro protein phosphatase inhibition assay and compared this data to a toxin profile generated from a mid-Atlantic Dinophysis culture. Three distinct morphospecies were documented in mid-Atlantic surface waters: D. acuminata, D. norvegica, and a “small Dinophysis sp.” that was morphologically distinct based on multivariate analysis of morphometric data but was genetically consistent with D. acuminata. While mid-Atlantic D. acuminata could not be distinguished from the other species in the D. acuminata-complex (D. ovum from the Gulf of Mexico and D. sacculus from the western Mediterranean Sea) using the molecular markers chosen, it could be distinguished based on morphometrics. Okadaic acid, dinophysistoxin 1, and pectenotoxin 2 were found in filtered water and shellfish samples during Dinophysis blooms in the mid-Atlantic region, as well as in a locally isolated D. acuminata culture. However, DSP toxins exceeded regulatory guidance concentrations only a few times during the study period and only in noncommercial shellfish samples.     

Diet of six deep-sea grenadiers (Macrouridae)

Feeding habits of six deep-sea demersal trawl-caught macrourids on Chatham Rise, New Zealand, were examined from stomach contents during the austral summer. Three species were predominantly benthic foragers: smallbanded rattail Coelorinchus parvifasciatus on small epifaunal crustaceans, twosaddle rattail Coelorinchus biclinozonalis on epifaunal decapods and humpback rattail Coryphaenoides dossenus on benthic fishes and epifaunal decapods. Three species were predominantly benthopelagic foragers: banded rattail Coelorinchus fasciatus on hyperiid and gammarid amphipods and calanoid copepods, blackspot rattail Lucigadus nigromaculatus on small epifaunal crustaceans and suprabenthic mysids and Mahia rattail Coelorinchus matamua on epifaunal decapods and calanoid copepods. The most important predictors of diet variability were identified using distance-based linear models and included areal predictors in C. parvifasciatus, L. nigromaculatus and C. dossenus, fish size in C. dossenus, C. biclinozonalis and C. matamua, sample year in C. biclinozonalis and C. fasciatus and depth in C. matamua. Results are compared with previously published data for four other macrourid species from the same study area. The 10 grenadier species comprise benthic, benthopelagic and mesopelagic foraging guilds. This study brings the number of grenadier species for which diet on Chatham Rise has been described in detail to 12.     

Variation in abundance and harvest of sooty shearwaters (Puffinus griseus) by Rakiura Maori on Putauhinu Island,New Zealand

Abstract

Sooty shearwater (Puffinus griesus, titi) abundance, harvest levels and chick mass were monitored repeatedly on Putauhinu Island, south‐west of Rakiura (Stewart Island) between 1997 and 2005. Putauhinu is the second largest of the Titi Islands and has a relatively high density of chicks distributed over most of the island, so it supports what is likely the second‐largest population of sooty shearwaters in the Rakiura region (after Taukihepa, Big South Cape Island). Rakiura Maori harvested chicks from five “manu” (family birding areas) that covered 56% of the 128.4 ha of breeding colony of the island. Chick density was lower on the unharvested area in the interior of the island than on harvested areas. Burrow entrance density was higher where there was more ground cover (mainly fern) vegetation, but these areas had lower burrow occupancy, so overall chick density was similar at different levels of ground cover. Twenty‐six harvesters present on Putauhinu in 2005 took 31 280 chicks in total, equivalent to 8.4% (95% CI = 6.6–12%) of the available chicks on the entire island. Seasonal variation in total chicks harvested (CV 15–22%) was not related to chick abundance or mass. Refuges, including impenetrable patches of vegetated ground within manu, the unharvested centre of the island, and even nearby unharvested islands, will ameliorate localised impacts of harvest if density‐dependent immigration is operating.     

Prevalence estimates of chronic kidney disease in Canada: results of a nationally representative survey

Background:

Chronic kidney disease is an important risk factor for death and cardiovascular-related morbidity, but estimates to date of its prevalence in Canada have generally been extrapolated from the prevalence of end-stage renal disease. We used direct measures of kidney function collected from a nationally representative survey population to estimate the prevalence of chronic kidney disease among Canadian adults.

Methods:

We examined data for 3689 adult participants of cycle 1 of the Canadian Health Measures Survey (2007–2009) for the presence of chronic kidney disease. We also calculated the age-standardized prevalence of cardiovascular risk factors by chronic kidney disease group. We cross-tabulated the estimated glomerular filtration rate (eGFR) with albuminuria status.

Results:

The prevalence of chronic kidney disease during the period 2007–2009 was 12.5%, representing about 3 million Canadian adults. The estimated prevalence of stage 3–5 disease was 3.1% (0.73 million adults) and albuminuria 10.3% (2.4 million adults). The prevalence of diabetes, hypertension and hypertriglyceridemia were all significantly higher among adults with chronic kidney disease than among those without it. The prevalence of albuminuria was high, even among those whose eGFR was 90 mL/min per 1.73 m² or greater (10.1%) and those without diabetes or hypertension (9.3%). Awareness of kidney dysfunction among adults with stage 3–5 chronic kidney disease was low (12.0%).

Interpretation:

The prevalence of kidney dysfunction was substantial in the survey population, including individuals without hypertension or diabetes, conditions most likely to prompt screening for kidney dysfunction. These findings highlight the potential for missed opportunities for early intervention and secondary prevention of chronic kidney disease.Chronic kidney disease is defined as the presence of kidney damage or reduced kidney function for more than 3 months and requires either a measured or estimated glomerular filtration rate (eGFR) of less than 60 mL/min per 1.73 m², or the presence of abnormalities in urine sediment, renal imaging or biopsy results.¹ Between 1.3 million and 2.9 million Canadians are estimated to have chronic kidney disease, based on an extrapolation of the prevalence of end-stage renal disease.² In the United States, the 1999–2004 National Health and Nutrition Examination Survey reported a prevalence of 5.0% for stage 1 and 2 disease and 8.1% for stage 3 and 4 disease.^3,4Chronic kidney disease has been identified as a risk factor for death and cardiovascular-related morbidity and is a substantial burden on the health care system.^1,5 Hemodialysis costs the Canadian health care system about $60 000 per patient per year of treatment.¹ The increasing prevalence of chronic kidney disease can be attributed in part to the growing elderly population and to increasing rates of diabetes and hypertension.^1,6,7Albuminuria, which can result from abnormal vascular permeability, atherosclerosis or renal disease, has gained recognition as an independent risk factor for progressive renal dysfunction and adverse cardiovascular outcomes.^8–10 In earlier stages of chronic kidney disease, albuminuria has been shown to be more predictive of renal and cardiovascular events than eGFR.^4,9 This has prompted the call for a new risk stratification for cardiovascular outcomes based on both eGFR and albuminuria.¹¹A recent review advocated screening people for chronic kidney disease if they have hypertension, diabetes, clinically evident cardiovascular disease or a family history of kidney failure or are more than 60 years old.⁴ The Canadian Society of Nephrology published guidelines on the management of chronic kidney disease but did not offer guidance on screening.¹ The Canadian Diabetes Association recommends annual screening with the use of an albumin:creatinine ratio,¹² and the Canadian Hypertension Education Program guideline recommends urinalysis as part of the initial assessment of hypertension.¹³ Screening for chronic kidney disease on the basis of eGFR and albuminuria is not considered to be cost-effective in the general population, among older people or among people with hypertension.¹⁴The objective of our study was to use direct measures (biomarkers) of kidney function to generate nationally representative, population-based prevalence estimates of chronic kidney disease among Canadian adults overall and in clinically relevant groups.     

Effect of contact location on vibrotactile thresholds at the fingertip

Vibrotactile thresholds depend on the characteristics of the vibration, the location of contact with the skin, and the geometry of the contact with the skin. This experimental study investigated vibrotactile thresholds (from 8 to 250?Hz) at five locations on the distal phalanx of the finger with two contactors: (i) a 1-mm diameter circular probe (0.78-mm² area) with a 1-mm gap to a fixed circular surround (i.e., 7.1-mm² excitation area), and (ii) a 6-mm diameter circular probe (28-mm² area) with a 2-mm gap to a fixed circular surround (i.e., 79-mm² excitation area). With both contactors, especially the smaller contactor at low frequencies (i.e., 8, 16, and 31.5?Hz), thresholds decreased towards the tip of the finger, although there was little variation around the whorl. With low frequencies of vibration, and at all five locations on the finger, similar thresholds were obtained with both contactors, consistent with the NPI channel not changing in sensitivity with a change in the area of stimulation. At high frequencies (i.e., 63, 125, and 250?Hz), thresholds were lower with the larger area of stimulation at all locations, except at the extreme tip of the finger, consistent with spatial summation in the Pacinian channel. It is concluded that with a 6-mm diameter contactor, moderate variations in location around the whorl have little influence on the measured thresholds. With the 1-mm diameter contactor there were greater variations in thresholds and extreme locations, near the nail and the distal interphalangeal joint, may be unsuitable for investigating sensorineural disorders.     

Postembryonic lineages of the Drosophila brain: I. Development of the lineage-associated fiber tracts

Neurons of the Drosophila central brain fall into approximately 100 paired groups, termed lineages. Each lineage is derived from a single asymmetrically-dividing neuroblast. Embryonic neuroblasts produce 1,500 primary neurons (per hemisphere) that make up the larval CNS followed by a second mitotic period in the larva that generates approximately 10,000 secondary, adult-specific neurons. Clonal analyses based on previous works using lineage-specific Gal4 drivers have established that such lineages form highly invariant morphological units. All neurons of a lineage project as one or a few axon tracts (secondary axon tracts, SATs) with characteristic trajectories, thereby representing unique hallmarks. In the neuropil, SATs assemble into larger fiber bundles (fascicles) which interconnect different neuropil compartments. We have analyzed the SATs and fascicles formed by lineages during larval, pupal, and adult stages using antibodies against membrane molecules (Neurotactin/Neuroglian) and synaptic proteins (Bruchpilot/N-Cadherin). The use of these markers allows one to identify fiber bundles of the adult brain and associate them with SATs and fascicles of the larval brain. This work lays the foundation for assigning the lineage identity of GFP-labeled MARCM clones on the basis of their close association with specific SATs and neuropil fascicles, as described in the accompanying paper (Wong et al., 2013. Postembryonic lineages of the Drosophila brain: II. Identification of lineage projection patterns based on MARCM clones. Submitted.).     

Effects of wood removal on stream habitat and nitrate uptake in two northeastern US headwater streams

Forested headwater streams play an important role in watershed nutrient dynamics, and wood is thought to be a key factor influencing habitat structure and nitrate-nitrogen dynamics in many forested streams. Because wood in streams can promote nitrogen uptake through denitrification, we hypothesized that nitrate uptake velocities would decrease following wood removal. We measured stream characteristics and nitrate uptake velocities before and after wood manipulation experiments conducted at Hubbard Brook Experimental Forest, NH, and the Sleepers River watershed, VT. The mean size of stream substrates and the amount of riffle habitat increased following wood removal. In contrast to our expectations, summer nitrate uptake velocities increased in the wood removal treatments relative to the reference treatments, possibly because wood removal increased the availability of stable substrates for periphyton growth, therefore increasing nitrate demand in these streams. Our results highlight that effects of wood on stream ecosystems occur through multiple pathways and suggest that the relative importance of these pathways may vary seasonally.