Oxalate balance in fat sand rats feeding on high and low calcium diets

Oxalate reduces calcium availability of food because it chelates calcium, forming the sparingly soluble salt calcium-oxalate. Nevertheless, fat sand rats (Psammomys obesus; Gerbillinae) feed exclusively on plants containing much oxalate. We measured the effects of calcium intake on oxalate balance by comparing oxalate intake and excretion in wild fat sand rats feeding on their natural, oxalate-rich, calcium-poor diet with commercially-bred fat sand rats feeding on an artificial, calcium-rich, oxalate-poor diet of rodent pellets. We also tested for the presence of the oxalate degrading bacterium Oxalobacter sp. in the faeces of both groups. Fat sand rats feeding on saltbush ingested significantly more oxalate than fat sand rats feeding on pellets (P < 0.001) and excreted significantly more oxalate in urine and faeces (P < 0.01 for both). However the fraction of oxalate recovered in excreta [(oxalate excreted in urine + oxalate excreted in faeces)/oxalate ingested] was significantly higher in pellet-fed fat sand rats (61%) than saltbush-fed fat sand rats (27%). We found O. sp. in the faeces of both groups indicating that fat sand rats harbor oxalate degrading bacteria, and these are able, to some extent, to degrade oxalate in its insoluble form.     

The problem of diabetic angiolopathy in sand rats (Psammomys obesus)

No diabetic angiolopathy was found in the retinas, kidneys and skeletal muscles of protodiabetic and overtly diabetic sand rats. The terminal blood vessels were investigated using histological, enzyme histochemical, immunofluorescence microscopic, autoradiographic and electron microscopic methods. There seems to be little or no connection in sand rats between the diabetic metabolism syndrome and the metabolic process leading to angiolopathy.     

Impaired hormonal regulation of lipolysis and the interference with adenosine in adipose tissue from hyperglycemic sand rats in vitro

Sand rats (Psammomys obesus) developed in response to different food intake various states of hyperglycemia and hyperinsulinism. 12 normo- and 10 hyperglycemic animals were selected by means of a weekly control of plasma glucose and plasma insulin over a period of 12 weeks after separation from the mother. During this time also the development of body weight gain was checked. In both groups of rats the hormonal regulation of glycerol release by incubated adipose tissue was investigated. In any case, the fat tissue from hyperglycemic sand rats showed a lower lipolytic responsiveness to noradrenaline stimulation than that of their normoglycemic controls. This correlates well with previous results in hyperglycemic sand rats in which the catecholamine-stimulated cAMP production was disturbed (Knospe and K?hler 1981). Degradation of released adenosine by addition of adenosine deaminase significantly enhanced the noradrenaline action on glycerol release in both groups of sand rats. Even though the noradrenaline-stimulated lipolytic activity of adipose tissue from normo- and hyperglycemic animals was enhanced in the presence of adenosine deaminase, the hormone resistance of adipose tissue from hyperglycemic sand rats was nevertheless not abolished. The theophylline-mediated adenosine receptor blockade gave further evidence that particularly endogenous adenosine released during incubation of adipose tissue from sand rats inhibited the noradrenaline action on lipolysis. The antilipolytic action of insulin on glycerol release is negligibly low in normoglycemic as well as hyperglycemic sand rats. The degradation of adenosine by adenosine deaminase failed to improve the insulin action. Adenosine addition completely blocked the stimulating effects of noradrenaline on glycerol release.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breakdown of exogenous insulin by langerhans islets of the pancreas in vitro

Pancreatic islets were isolated from Wistar rats, albino mice, spiny mice and sand rats (Psammomys obesus). Evidence is presented that pancreatic islets contain an enzyme system degrading insulin in the presence of glutathione or other sulfhydryl-containing compounds. Apparent K_m values for insulin and glutathione (in the presence of EDTA) are 14.0 μM (mol. wt 5700) and 1.28 mM, respectively. Maximum breakdown of ¹²⁵I-labeled insulin was found at about pH 7.2. After ultracentrifugation of islet homogenates the microsomal fraction contained the greatest relative specific insulin-degrading activity. The specific insulin-degrading actvitity was found to be higher in Wistar rats and albino mice than in spiny mice and sand rats. Starvation of Wistar rats for 72 h caused a decrease inthe enzymatic activity.     

Establishment of an albino sand rat (Psammomys obesus colony and comparison with the natural coloured animal

The lifespan and fertility of albino sand rats were found to be severely reduced in comparison with a laboratory colony of brown sand rats. The albinos were also much more susceptible to diabetes, as judged by their glucose tolerance. In fact, untreated albinos had a higher incidence of diabetic response than coloured sand rats fed a diabetogenic diet. The albino sand rats reproduced poorly because of a reduction in male fertility. Circulating testosterone levels and seminal vesicle weights were reduced in the albinos. It is speculated that the reduction in reproductive capacity is related to diabetes.     

Energy requirements of fat sand rats (Psammomys obesus) and their efficiency of utilization of the saltbush Atriplex halimus for maintenance

The fat sand rat (Psammomys obesus; Gerbillinae), a diurnal gerbillid rodent, is herbivorous and able to thrive while consuming only the saltbush Atriplex halimus (Chenopodiaceae), a plant relatively low in energy content and high in ash and water. We measured the basal metabolic rate offat sand rats, their energy requirements in captivity when they were offered only A. halimus, and their efficiency of utilization of this diet for maintenance.
Before consuming A. halimus leaves, the fat sand rats scraped off the surface layers with their teeth. This behavioural activity removed 6.4% to 8.5% of the dry matter of the leaf, but increased the gross energy and organic matter content of the leaf by only approximately 3.1%. Basal metabolic rate of the fat sand rats was 167.9 kJ.kg-O 7s d-', approximately 57% of that expected for an eutherian mammal of its body mass, and energy requirements for maintenance, or average daily metabolic rate, were 498.7 kJ.kg-0'7s d-', approximately 90% of that expected for a rodent of its body mass. Dry matter digestibility of the consumed A. halimus averaged 67% and apparent digestible energy and apparent metabolizable energy averaged 65.3% and 63.4% of the gross energy, respectively. The efficiency of utilization of A . halimus for maintenance energy (k,) by the fat sand rats was 0.32 and the heat increment of feeding (HIF) was 0.68. The k, of A. halimus appeared to be low compared to other feeds, and this characteristic plus its low energy value and high water content forced the fat sand rats to consume large quantities of forage for maintenance.
It was concluded that although A. halimus has a low energy and high ash content, there are several advantages for fat sand rats consuming mainly this diet. Among them are: (1) it provides a more stable diet throughout the year than do seeds; (2) fat sand rats have no competition for this food resource from other rodents; and (3) their burrows are at the base of the     

Oxalate, calcium and ash intake and excretion balances in fat sand rats (Psammomys obesus) feeding on two different diets

Fat sand rats Psammomys obesus feed exclusively on plants of the family Chenopodiaceae, which contain high concentrations of chloride salts (NaCl, KCl) and oxalate salts. Ingestion of large quantities of oxalate is challenging for mammals because oxalate chelates Ca(2+) cations, reducing Ca(2+) availability. Oxalate is a metabolic end-point in mammalian metabolism, however it can be broken-down by intestinal bacteria. We predicted that in fat sand rats microbial breakdown of oxalate will be substantial due to the high dietary load. In addition, since a high concentration of soluble chloride salts increases the solubility of calcium oxalate in solution, we examined whether a change in the intake of chloride salts affects microbial oxalate breakdown and calcium excretion in fat sand rats. We measured oxalate, calcium and other inorganic matter (ash) intake and excretion in fat sand rats feeding on two different diets: saltbush (Atriplex halimus), their natural diet, and goose-foot (Chenopodium album), a non-native chenopod on which fat sand rats will readily feed and that has a similar oxalate content to saltbush but only 2/3 of the ash content. In animals feeding on both diets, 65-80% of the oxalate ingested did not appear in urine or faeces. In animals consuming the more saline saltbush, significantly more oxalate was apparently degraded (p<0.001), while significantly less oxalate was excreted in urine (p<0.01) and in faeces (p<0.05). We propose, therefore, that fat sand rats rely on symbiotic bacteria to remove a large portion of the oxalates ingested with their diet, and that the high dietary salt intake may play a beneficial role in their oxalate and calcium metabolism.     

Obesity, insulin resistance and diabetes in the sand rat exposed to a hypercaloric diet; possible protective effect for IL1-β

It is well established that, upon changing their natural desert low caloric (succulent halophilic plants) to a regular laboratory high caloric diet, sand rats undergo various phenotypic changes depending on their genetic background and including obesity and various degrees of insulin resistance. Our aim was to investigate the acute effects of Interleukin-1β (IL-1β) and Interferon-γ (IFN-γ) on glucose-induced insulin secretion in normal lean sand rats maintained on their natural diet and in obese insulin resistant normoglycemic or type 2 diabetic animals after a 9-month high caloric diet. Animals were fed either a low or a high caloric diet; after 9 months, pancreatic islets were isolated and incubated in the presence of increasing cytokine concentrations. At the end of the high-energy diet, animals were all over-weight, and probably due to a different genetic background, they displayed either insulin resistance, hyperinsulinemia and normoglycemia or a marked type-2 diabetic state. Pancreatic islets from obese insulin resistant normoglycemic animals were much more sensitive and responsive to IL-1β when compared to lean controls. The cytokine was inefficient in diabetic islets. In conclusion, the markedly increased insulinotropic effect of IL-1β in obese diabetes-resistant sand rat could participate and be involved in pancreatic β-cell hyperactivity that compensates for insulin resistance and thereby prevent the development of type 2 diabetes in these animals.     

Water, electrolyte and nitrogen balances of fat sand rats (Psammomys obesus) when consuming the saltbush Atriplex halimus

The fat sand rat (Psammomys obesus), a diurnal gerbillid rodent, is able to thrive while consuming only the saltbush Atriplex halimus. This plant has a high ash, nitrogen and water content but low energy yield. We measured the electrolyte, nitrogen (N) and water balances of fat sand rats in captivity when they were offered only A. halimus.
The fat sand rats scraped the outer layers of A. halimus leaves before consuming them. This removed 14.3% to 19.6% of the ash content of the leaves, and thus substantially reduced the electrolyte intake of the fat sand rats. Total urine osmolality ranged between 2739 and 3098 mOsm/kg, with Na+, K+ and CI - comprising 74.3% to 82.5% of the total osmolytes, percentages much higher than those usually found in desert rodents. Water intake was relatively high compared to other rodents because of the high water content of A. halimus. Evaporative water loss averaged approximately 50% of the total water output. Nitrogen requirements were easily fulfilled, even when the fat sand rats did not meet their energy requirements because of the high N content of the plant. Metabolic faecal nitrogen was 70.5 mg-kg-' 75.d-', endogenous urinary nitrogen was 171.9 mg. kg-0'75 d-' and minimal N requirements were 242.3 mg.k g-75d -1 . Minimal N requirements for the fat sand rats were approximately 98% of that expected for a eutherian mammal of its body mass.
It was concluded that fat sand rats can maintain water, electrolyte and nitrogen balances when consuming only A. halimus without producing highly concentrated urine. This is due, in part, to their ability to remove much of the electrolytes before consuming the plant and by producing urine of which Na+, K+ and C1- comprise a large percentage of the total osmolytes.     

A summary of the evidence for the change in European distribution of phlebotomine sand flies (Diptera: Psychodidae) of public health importance

The phlebotomine sand flies (Diptera: Psychodidae, Phlebotominae) are vectors of several infectious pathogens. The presence of a sand fly vector is considered to be a risk factor for the emergence of leishmaniasis in temperate Europe. Hence, the occurrence of phlebotomine sand flies and any changes in their distribution is important in determining the potential change in distribution of leishmaniasis in Europe. Therefore, published evidence for a changing distribution of the important phlebotomine sand fly vectors of leishmaniasis and phlebovirus infection in Europe is reviewed. This paper presents evidence of an increasing risk of establishment by sand fly species, especially for the Atlantic Coast and inland parts of Germany, Switzerland, and Austria. In addition to detection in potentially appropriate areas, the findings show areas of potential future establishment of the species. The most important and urgent necessity within the community of entomologists working on phlebotomines is the need to record the extremes of distribution of each species and obtain data on their regional presence/absence along with increased sharing of the data throughout European projects.     

Insulin and glucagon binding to isolated hepatocytes of Egyptian sand rats (Psammomys obesus): evidence for an insulin receptor defect

To determine whether a defect in insulin binding could contribute to insulin resistance in Egyptian sand rats (Psammomys obesus), insulin binding to isolated hepatocytes from euglycemic sand rats was compared to that of normal Sprague-Dawley rats (Rattus norvegicus). Because of its potential importance in glucoregulation, glucagon binding to hepatocytes from these species was also measured. Hepatocytes of sand rats exhibit an almost complete lack of insulin receptors compared to hepatocytes from Sprague-Dawley rats, whereas there are numerous high affinity glucagon binding sites on sand rat hepatocytes. The lack of insulin binding to sand rat tissues is sufficient to entirely explain the insulin resistance seen in this species. Glucagon may be primarily responsible for glucose homeostasis in Psammomys obesus.     

Density of sand flies (Diptera: psychodidae) in domestic and wild animal shelters in an area of visceral Leishmaniasis in the state of Rio Grande do Norte, Brazil.

The objective of the present study was to determine the association of sand flies with the presence of domestic and wild animals in the peridomiciliary area. The sand flies were collected using direct aspiration and CDC light traps placed in animal shelters. The results suggest that different sand flies species have different behavioral characteristics in an apparent preference for animal baits and that Lutzomyia longipalpis and Lu. evandroi were the most eclectic species regarding their biotope choice. Lu. longipalpis showed a distinct preference for horses and Lu. evandroi for armadillos.     

The effect of vegetation cover on vigilance and foraging tactics in the fat sand rat Psammomys obesus

The combination of the visual obstruction and protection properties of vegetation is considered to be one of the most important factors determining the trade-off between vigilance and foraging in a prey species. In the Negev desert, diurnal fat sand rats construct their burrows in the ephemeral river beds ("wadis"), under dense and tall shrubs of Atriplex halimus, or on the open first fluvial terrace, covered with scattered low shrubs of Anabasis articulata. We tested the hypothesis that properties of the vegetation would affect the time budget of female sand rats. Sand rats spent more time aboveground, rested more, were less vigilant, and moved more slowly under the dense cover in the wadi than at the open terrace. No differences in the total foraging time were revealed, but foraging tactics varied between habitats: individuals in the wadi mainly fed aboveground, whereas those at the terrace mainly hoarded. Our results indicate that sand rats perceive the dense vegetation cover as good protection despite its visual obstructive nature, and that vigilance in Psammomys obesus is performed at the cost of resting rather than at the cost of foraging. Received: January 15, 2001 / Accepted: April 17, 2001     

The adhesive properties of a nonenteropathogenic strain of Escherichia coli in systems in vitro on isolated rat enterocytes and in vivo

The adhesive properties and colonizing capacity of E. coli strain O83, isolated from feces of healthy humans and marked according to its resistance to rifampicin and nalidixic acid, were studied. In vivo experiments on germ-free rats revealed that these bacteria were capable of colonizing intestinal mucosa; colonization increased from the small to large intestine and E. coli cells were mainly concentrated in the intestinal lumen and in mucin. In vitro studies showed that this nonenteropathogenic E. coli strain possessed pronounced adhesive properties with respect to the colonic cells of germ-free rats; these properties were considerably less pronounced with respect to the enteric cells of the small intestine. The electron microscopic study of E. coli cells revealed the presence of fimbriae and fibrillae on their surface.     

Glucose disappearance rates into peripheral tissues of adult rabbits (Silvilagus floridans), Wistar rats (Rattus rattus) and sand rats (Psammomys obesus) in relation to body weight and blood glucose concentration

1. Glucose disappearance rates into peripheral tissues (RD) were measured in vivo in adult eviscerated, nephrectomized and adrenalectomized rabbits, Wistar rats and nondiabetic sand rats with physiological insulin concentrations in the blood. 2. The RD of Wistar rats was high (7.50 mg/kg/min) in comparison with that of rabbits (2.67 mg/kg/min). In the particular case of sand rats the RD was only 44% of that in Wistar rats having about the same body weight. 3. A 2.4-fold elevation of blood glucose above the basal level produces different increases of the RD: in rabbits 1.06-fold, in Wistar rats 1.5-fold and in sand rats 2.0-fold.     

Life in Darwin's dust: intercontinental transport and survival of microbes in the nineteenth century

Charles Darwin, like others before him, collected aeolian dust over the Atlantic Ocean and sent it to Christian Gottfried Ehrenberg in Berlin. Ehrenberg's collection is now housed in the Museum of Natural History and contains specimens that were gathered at the onset of the Industrial Revolution. Geochemical analyses of this resource indicated that dust collected over the Atlantic in 1838 originated from the Western Sahara, while molecular-microbiological methods demonstrated the presence of many viable microbes. Older samples sent to Ehrenberg from Barbados almost two centuries ago also contained numbers of cultivable bacteria and fungi. Many diverse ascomycetes, and eubacteria were found. Scanning electron microscopy and cultivation suggested that Bacillus megaterium , a common soil bacterium, was attached to historic sand grains, and it was inoculated onto dry sand along with a non-spore-forming control, the Gram-negative soil bacterium Rhizobium sp. NGR234. On sand B. megaterium quickly developed spores, which survived for extended periods and even though the numbers of NGR234 steadily declined, they were still considerable after months of incubation. Thus, microbes that adhere to Saharan dust can live for centuries and easily survive transport across the Atlantic.     

Fibronectin content of the annulus fibrosus in diabetic and non-diabetic sand rats

Annulus fibrosus of intervertebral discs from diabetic and non-diabetic sand rats were examined by microspectrophotometry for fibronectin content. This was higher in the diabetic animals both in the dorsal and ventral parts and in the outer and inner lamellae of the annulus. It is suggested that diabetes-related changes in fibronectin are similar to changes in annular collagen observed in species other than sand rats.     

Environmental transmission of a sulfur-oxidizing bacterial gill endosymbiont in the tropical lucinid bivalve Codakia orbicularis.

Codakia orbicularis is a large tropical member of the bivalve mollusk family Lucinidae which inhabits shallow-water sea-grass beds (Thalassia testudinum environment) and harbors sulfur-oxidixing endosymbiotic bacteria within bacteriocytes of its gill filaments. When a C. orbicularis-specific 16S rDNA (DNA encoding rRNA) primer is used with a bacterium-specific 16S rDNA reverse primer in amplifications by PCR, the primer set was unsuccessful in amplifying symbiont DNA targets from ovaries, eggs, veligers, and metamorphosed juveniles (600 microns to 1 mm in shell length) cultivated in sterile sand, whereas successful amplifications were obtained from gill tissue of adult specimens and from metamorphosed juveniles (600 microns to 1 mm in shell length) cultivated in unsterilized sea-grass bed sand. To ascertain the presence of the symbiont target in juveniles, restriction fragment length polymorphism analysis, Southern blotting, and transmission electron microscopy were used. Specific hybridizations and observation of endosymbiotic bacteria in the gills of numerous juveniles cultivated in unsterilized sea-grass bed sand showed that the sulfur-oxidizing endosymbionts of C. orbicularis are environmentally transmitted to the new generation after larval metamorphosis.     

大鼠海马神经元突触超微结构的增龄变化

目的为研究脑老化过程中学习、记忆功能减退的神经结构基础提供实验依据。方法应用透射电子显微镜,观察比较从出生1 d至24月龄（1 d、1月龄、3月龄、6月龄、18月龄、24月龄）的Sprague Dawley大鼠海马神经元突触超微结构的随增龄变化,同时观察与脑老化密切相关的指标脂褐素沉积。结果在大鼠6月龄之前,随着月龄的增加,海马神经元突触超微结构的发育逐渐完善,至6月龄大鼠突触数量明显增多;此后突触数量逐渐减少,至24月龄大鼠神经元突触数量最少。从1月龄开始海马神经元内即可见少量脂褐素颗粒沉积,随着月龄的逐渐增加,至24月龄时脂褐素颗粒沉积显著。结论青年期大鼠的海马神经元突触发育最好,进入老年期后,突触结构受损,老年期损伤最为严重,同时伴有大量的脂褐素颗粒沉积。     

The involvement of sand disturbance, cannibalism and intra-guild predation in competitive interactions among pit-building antlion larvae

Competition in trap-building predators such as antlion larvae is a complex biotic interaction, potentially involving exploitation competition, sand throwing (i.e., interference competition), cannibalism and intra-guild predation. We investigated the short-term behavioral and developmental responses of the strict sit-and-wait antlion predator Myrmeleon hyalinus to sand disturbance (i.e., quantification of the impact of severe sand throwing), and to con- and hetero-specific competition by a larger sit-and-pursue antlion species Lopezus fedtschenkoi. We found that antlions subjected to sand disturbances reduced their pit construction activity and relocated less often. Furthermore, the reduction in pit construction activity was stronger among antlions subjected to disturbances prior to feeding. Almost no death occurred during the sand disturbance experiment, but as expected, disturbances caused reductions in the relative growth rates of antlions. This negative effect was stronger in the group exposed to sand disturbances prior to feeding. The presence of the sit-and-pursue competitor led to reductions both in pit construction and in relocation activities of M. hyalinus. Although the per-capita food supply was identical in both experiments, only 48% of M. hyalinus larvae survived the competition experiment, and this pattern was consistent between the con- and hetero-specific treatments. However, in the presence of hetero-specific competitors, the relative growth rate of surviving larvae was significantly lower than that measured in the presence of con-specific competitors. Our study demonstrates that investigating the different components of complex biotic interactions can markedly improve our understanding of how these different factors interact to influence the behavior and life history of organisms.