The structural organization of the kidney of the desert rodent Psammomys obesus.

The architecture of the desert rodent Psammomys obesus has been studied by means of standard histologic procedures and by single nephron injections. As other rodent kidneys (rat, mouse), the Psammomys kidney consists of two types of nephrons, 66% short looped and 34% long looped nephrons. The cortex is composed of 4 to 5 layers of glomeruli, which lie closely put together, the glomeruli often touch each other. The superficial and the midcortical glomeruli give rise to short looped neophrons, the juxtamedullary to long looped nephrons. In the strongly developed medulla the inner stripe shows the most striking pattern. It consists of two distinct compartments, that of the giant vascular bundles and that of the interbundle regions. The giant vascular bundles consist of about 8 to 14% arterial vasa recta and 39 to 47% venous vasa recta; furthermore they include the thin descending limbs of the short loops of Henle which amount to 44 to 51% of the bundle structures. The tubules of the interbundle regions surround the bundles in a regular pattern. The inner zone is almost completely surrounded by the renal pelvis; the long broad papilla protrudes into the ureter. The thin descending limbs of short looped nephrons traverse the inner stripe inside the giant vascular bundles. Leaving the bundles they turn back within the inner stripe; their ascending limbs lie in the interbundle region. Both limbs of the long loops of Henle run in the interbundle region, together with the ascending limbs of the short loops and the collecting ducts. The long loops penetrate deeply the inner zone. Many bends are found near the tip of the papilla. The renal pelvis has a very specialized form. It penetrates the inner stripe with many complexely shaped extensions, which surround the giant vascular bundles. Large parts of the bundles with their thin walled structures are thus separated from the pelvic urine only by a single layer of cuboidal epithelium. The possible functional importance of the described specializations of the Psammomys kidney (giant vascular bundles, large inner zone, special shape of the renal pelvis) for the urine concentrating and urea recyclng mechanisms is discussed.     

Urinary concentrating mechanism in the desert rodent Psammomys obesus.

The mechanism by which osmolality rises in fluid in the juxtamedullary descending limb was examined in Psammomys obesus by micropuncture of the left renal papilla. The concentration of Na, Cl, K, Mg, and phosphorus was determined by electron probe; Cl concentration by both probe and the microcoulometric technique of Ramsay et al. (J. Exp. Biol. 32: 822--829, 1955). The mean urine-to-plasma ultrafiltrate (U/P) osmolality was 5.5 +/- 0.46 (SE). In 43 samples obtained from the end-descending limb in 16 animals, mean values were: tubule fluid-to-plasma ultrafiltrate (TF/P) osmolality, 3.64 +/- 0.30; (TF/P)In, 6.96 +/- 0.52; (TF/P)Na, 3.53 +/- 0.27; (TF/P)Cl-e, 4.11 +/- 0.37 (-e is electron probe determination); and (TF/P)Cl-r, 4.25 +/- 0.37 (-r is determination by method of Ramsay). In terms of percentage of filtered ion remaining at the end-descending limb, Na was 54 +/- 3.7%, Cl-e was 61 +/- 3.6%, and Cl-r was 63 +/- 4.0%. The percentage of filtered chloride remaining averaged 80% or more in three animals, equalled or slightly exceeded 100% in six individual descending limb samples, and in all animals was a function of loop fluid osmolality (y = 8.61x + 31.9, r = 0.66, P less than 0.01). The results are most consistent with the thesis that both water extraction and transepithelial NaCl addition contribute to the rise in osmolality of fluid in the descending limb of the Psammomys.     

The vascular organization of the kidney of Psammomys obesus.

Summary The vascular organization of the kidney of Psammomys obesus has been studied by injecting silicone rubber into the renal arterial and venous vessels and by standard histological techniques.Whereas the cortical vasculature is not principally different from that of other species, the medullary vessels show some unique features in the Psammomys. In the outer stripe, the vasa efferentia of juxtamedullary glomeruli give rise to primary vascular bundles which, in the transitional region between the outer and inner stripes, fuse to form secondary and, finally, giant vascular bundles.In the inner stripe exist two clearly separated vascular compartments that of the giant bundles and that of the interbundle region. The latter is supplied by arterial vasa recta originating from the upper part of the vascular bundles at the entrance to the inner stripe. In the lower portion, the separation of the two compartments is enhanced by vessel-free rims around the bundles (the rims contain descending, limbs of long loops only) and by protrusions of the renal pelvis.The inner zone is supplied exclusively by the vasa recta descending throughout the inner stripe within the vascular bundles. They splay out of the bundles at the transitions from outer to inner medulla, and descend individually as straight unbranched vessels. Many of them do not split up into capillaries before they reach the tip of the papilla.The venous drainage of the inner zone is ensured by venous vasa recta ascending individually up to the border between the inner zone and the inner stripe. They all enter the giant vascular bundles within which they traverse the inner stripe. The venous vessels draining the interbundle, region of the inner stripe do not join the bundles but ascend directly to the outer stripe. Thus, the circulations of the, outer and inner medullary zones are totally separated from each other.In the outer stripe venous vasa recta from the bundles and from the interbundle areas are mixed together. Most of them ascend high into the cortex within the medullary rays in close apposition to tubules, and empty into interlobular veins.     

The ultrastructure of the nephrons of the desert rodent (Psammomys obesus) kidney II. Thin limbs of henle of long-looped nephrons

Long nephrons are derived from juxtamedullary glomeruli. In their descent through the outer medulla toward the inner medulla, the thin descending limbs (TDLs) of long loops of Henle are consistently excluded from the vascular bundles and occupy the interbundle region. The outer medullary segment of long TDLs (Type II epithelium) is elaborately developed with numerous cellular interdigitations. microvilli, and a cytoplasm well equipped with numerous organelles. The inner medullary segment of these long TDLs is characterized by yet another epithelium that is markedly reduced from its Type II predecessor and is designated as Type III epithelium. It is a very low, flattened epithelium with few cytoplasmic details. In a cross section of the inner medullary TDL, the Type III epithelium appears poorly interdigitated, with only two to four cell processes and their junctional complexes. Shortly before the bend of a long loop of Henle, the epithelium is again altered to one that is well-interdigitated and better equipped with cytoplasmic organelles (Type IV epithelium). It persists through the actual bend of the loop and throughout the entire thin ascending limb (TAL), until the latter's transition to the distal tubule at the level of the inner/outer medullary border. We conclude that the Type II epithelium of the outer medullary segments of long TDLs in Psammomys is suitably constructed for involvement in energized transport of solutes. The possibility for a similar role in the Type IV epithelium of the bends and TALs is not excluded by our data. However, the Type III epithelium of the inner medullary segments of long TDLs is most suitably constructed for the concentration of its luminal fluids via water extraction. A comparison between these epithelial types and their permeabilities in various species is presented.     

Lipogenesis in the sand rat (Psammomys obesus)

Synthesis of fatty acids was measured in the liver and in epididymal adipose tissue of sand rats and albino rats. In chow-fed sand rats the rate of hepatic lipogenesis, as measured by the incorporation of 3H2O into fatty acids, was four- to sevenfold higher than in albino rats and in sand rats on a low-calorie saltbush diet. The contribution of [14C]glucose to lipogenesis in sand rat liver was lower than in albino rats. In fed sand rats lipogenesis incorporating 3H2O was stimulated by casein but not by glucose. In adipose tissue, lipogenesis measured 1 h after administration of 3H2O was much lower in sand rats than in albino rats. In vitro incorporation of [14C]glucose or acetate into adipose tissue fatty acids was negligible. In adipose tissue, uptake of very-low-density lipoproteins (VLDL) and lipoprotein lipase activity were sevenfold higher than in albino rats. Activities of NADP-malate dehydrogenase, acetyl CoA carboxylase, and fatty acid synthetase were considerably higher in the liver of chow-fed sand rats than in albino rats. It was concluded that obesity in sand rats originates from hepatic lipogenesis without a significant contribution of local fatty acid synthesis in adipose tissue.     

The histopathology of naturally-occurring cutaneous leishmaniasis in the reservoir host, Psammomys obesus

Ears from infected Psammomys obesus, the gerbil reservoir host of Leishmania major, were histopathologically studied. The histopathology was a chronic localized infection consisting of an epithelioid granuloma with greatly increased populations of mast cells, melanocytes and melanophores; ulceration was present and parasites were always very few and inside parasitophorus vacuoles.     

Hyperhomocysteinemia and myocardial remodeling in the sand rat,Psammomys obesus

ObjectiveNumerous studies have shown that a methionine-rich diet induces hyperhomocysteinemia (Hhcy), a risk factor for cardiovascular diseases. The objective of the present study was to determine the involvement of Hhcy in cardiac remodeling in the sand rat Psammomys obesus.Materials and methodsAn experimental Hhcy was induced, in the sand rat Psammomys obesus, by intraperitoneal injection of 300 mg/kg of body weight/day of methionine for 1 month. The impact of Hhcy on the cellular and matricial structures of the myocardium was analyzed with histological techniques (Masson trichrome and Sirius red staining). Immunohistochemistry allowed us to analyze several factors involved in myocardial remodeling, such as fibrillar collagen I and III, metalloproteases (MMP-2 and -9) and their inhibitors (TIMP-1 and -2), TGF-β1 and activated caspase 3.ResultsOur results show that Hhcy induced by an excess of methionine causes, in the myocardium of Psammomys obesus, a significant accumulation of fibrillar collagens I and III at the interstitial and perivascular scales, indicating the appearance of fibrosis, which is associated with an immuno-expression increase of TGF-β1, MMP-9 and TIMP-2 and an immuno-expression decrease of MMP-2 and TIMP-1. Also, Hhcy induces apoptosis of some cardiomyocytes and cardiac fibroblasts by increasing of activated caspase 3 expression. These results highlight a remodeling of cardiac tissue in hyperhomocysteinemic Psammomys obesus.     

Freeze-fracture studies on the thin limbs of Henle's loop in Psammomys obesus

The thin limbs of short and long loops of Henle of the desert rodent Psammomys obesus were studied by freeze-fracture techniques. Intercellular junctions and internal membrane characteristics of thin-limb epithelia are of interest with regard to the high urine-concentrating capacity of this animal. The epithelium of the descending thin limbs of short loops is remarkably undifferentiated and equipped with multistrand tight junctions. In the descending thin limb of long loops, two segments are to be distinguished. The upper parts are characterized by an extensive cellular interdigitation and single-strand tight junctions. Thus, the paracellular pathways are prominent from two aspects: the junctional belt is elongated by interdigitation, and its apico-basal depth is shallow. The transition from the upper to the lower part appears to be abrupt, as indicated by the change in intramembrane particle density. The lower parts are characterized by a noninterdigitating epithelium with junctions consisting of few, but always more than two, strands. In addition, this thin-limb segment is characterized by regularly distributed infoldings of the basal cell membrane. The ascending thin limbs are established by an interdigitating epithelium, with junctions generally consisting of one strand. Once again, the elongated junctional belt is shallow. This study presents further evidence that remarkable species differences occur among thin-limb epithelia, especially concerning the descending thin limbs of long loops. Those differences may well explain discrepant functional findings concerning the transport properties of this segment in various species.     

The histogenesis of hepatoma occurring spontaneously in a strain of sand rats (Psammomys obesus).

Spontaneous hepatomas and hepatic preneoplastic changes were observed in sand rats (Psammomys obesus) from two colonies. Both colonies originated from 10 sand rats captured in the Judean desert in 1969. At the age of 6 months, and increasing in multiplicity with advancing age, histologic examination revealed nodules containing hepatocytes characterized by hyperbasophilia, accumulation of glycogen, eosinophilic cytoplasm, or a mixture of these cells. In animals over 25 months old hepatocellular carcinoma was diagnosed. The histologic changes described here were reported to be characteristic of chemical hepatomagenesis in rats. No external chemical carcinogen could be demonstrated in our animal colonies, and a hereditary predisposition to tumor formation is presumed. Identity of hepatic carcinogenesis, irrespective of etiology in distantly related rodents, ie, the laboratory rat and the sand rat, which in reality is a gerbil, supports the assumption of the existence of a general law governing hepatic carcinogenesis.     

Ecoepidemiology of leishmaniases in Syria. 3. Leishmania major infection in Psammomys obesus provides clues to life history of the rodent and possible control measures.

Collections of Psammomys obesus from near Damascus, Syria in May 1990 and November 1991 contained animals of all ages. Both series had a high prevalence of Leishmania major infection. Lesions were small in November and large in May. Assuming the two collections were representative of typical years, it is inferred that the breeding season is between October and May: there is high winter mortality of animals born early in the breeding season, but high survival of their parents, and there is high mortality in summer of animals aged between 17 and around 20 months. Transmission in summer is, therefore, between old adults shortly before their death and young adults born in late winter or spring. Juvenile animals are not exposed to the infection. If these findings are confirmed it should be relatively easy to break this tenuous cycle.     

The structural organization of the kidney of Typhlonectes compressicaudus (Amphibia, Gymnophiona)

Summary The structural organization of the kidney ofTyphlonectes compressicaudus (Amphibia, Gymnophiona) was studied by light microscopic (LM) examination of serial paraffin and semithin Epon sections. The kidney is slender and quite long and has a mesonephric segmental construction; the excretory duct (Wolffian duct), running along the lateral side of the kidney, segmentally receives the terminal trunks of the collecting duct system. The nephron has the following parts: renal corpuscle, neck segment, proximal tubule, intermediate segment, distal tubule and connecting tubule. The distal tubule is located in a ventromedial (central) zone of the kidney; all other tubular segments lie in a dorsolateral (peripheral) zone. The renal corpuscles are found at the border between these two zones.The renal corpuscle is very large; its urinary pole faces the peripheral zone. A small proportion of neck segments receive either a nephrostomal duct or a blind branch. The proximal tubule is a thick, highly convoluted tubule. The intermediate segment is ciliated and makes a few coils. The distal tubule is composed of three portions: a highly convoluted part in the central zone, subsequently an attachment site with the renal corpuscle and a short postattachment-part. The connecting tubule and the collecting duct have a heterogeneous epithelium consisting of light and dark cells. The collecting duct is distinguished by dilated intercellular spaces. The Wolffian duct has a pseudostratified epithelium.The present study correlates the course and segmentation of the renal tubule ofTyphlonectes. The tubule has three major convolutions. The first occurs in the proximal tubule in the peripheral zone; the second is established by the distal tubule and occurs in the central zone; the third is formed by the connecting tubule and is found in the peripheral zone.Research fellow of the Alexander von Humboldt foundation: home address: Department of Anatomy, Faculty of Medicine, University of Tokyo, Tokyo 113, Japan     

Enzyme histochemistry of the sand rat pancreas (Psammomys obesus) after different caloric food]

In a complex investigation were evidenced 12 selected enzymes (oxidoreductases and hydrolases) in the pancreas of normoglycemic sand rats (Psammomys obesus). The sand rat developed a spontaneous diabetic metabolism by holding in the vivarium. The material based of animal groups that were fooded ad libitum or after defined dietetic regimes. The topochemical pattern of enzymes in the Langerhans' islets and exocrine acini can be compared between the sand rat groups and with the good investigated model of the Wistar rat. Because enzymhistochemical investigations of the sand rat pancreas absented, were the results compared with the rare specific observations of other animals and the man and the changed metabolic level were discussed under the especially food situation and in diabetes mellitus.     

Immunohistochemical detection of somatostatin in the islet-organ of sand rats (Psammomys obesus) (author's transl)

Islets of Langerhans were investigated with the indirect immunofluorescence technique for somatostatin. Fluorescence was observed in cells which are by number and localization typical "D-cells". somatostatin-like immunoreactivity was also present in few cells of the exocrine part of pancreas.     

Occurrence of somatostatin-like immunoreactivity (SLI) in the dorsal hippocampus of the sand rat (Psammomys obesus).

Somatostatin-like immunoreactivity (SLI) was demonstrated in neurons of the dorsal hippocampus of the sand rat by means of the immunofluorescence technique.     

Quantitative histologic studies of the gonads of sand rats (Psammomys obesus) during the development of diabetes mellitus]

Quantitative-histological investigations (point counting method) are pointed out in 27 male and 15 female sand rats. The animals are divided in the IGT (impaired glucose tolerance), the diabetic and the control group. The LEYDIG cells are in the IGT-group increased, and in the diabetic group decreased. The female sand rats are characterized by the tendency of increase of size and number of follicles in the IGT-group. Corpora lutea are reduced but atretic follicles are increased in the diabetic group. The ovaries are greater in diabetic sand rats.