Proportions of mammalian-type and reptilian-type nephrons in the kidneys of two passerine birds

We compared the proportions of mammalian-type and reptilian-type nephrons in the kidneys of two species of passerine birds. The desert house sparrow (Passer domesticus) is relatively well adapted for water conservation, whereas the white-crowned sparrow (Zonotrichia leucophrys) is more mesic adapted. The two species do not differ in body mass, but the kidneys of P. domesticus are significantly smaller than those of Z. leucophrys. Associated with its smaller size, the house sparrow kidney has significantly fewer glomeruli (35,700 per kidney) than does the white-crowned sparrow kidney (53,000 per kidney). The medullary cones, which contain the loops of Henle of the mammalian-type nephrons, are significantly longer in house sparrows than in white-crowned sparrows (2.2 vs. 1.9 mm). The number of medullary cones, the number of nephrons per medullary cone, and, hence, the number of mammalian-type nephrons do not differ between the two species. The smaller number of nephrons in the kidney of the house sparrow therefore represents a smaller number of reptilian-type nephrons. Desert house sparrows have 18% mammalian-type nephrons, whereas white-crowned sparrows have 10% mammaliantype nephrons. The relative reduction of reptilian-type nephrons in P. domesticus may reduce the flow of dilute urine through the collecting ducts, thereby permitting a greater concentration gradient to be established along the length of the medullary cones.     

Evidence for a new type of juxtamedullary nephron in the rabbit kidney

The microanatomy of a unique type of juxtamedullary nephrons has been studied in the rabbit kidney by means of corrosion casts, scanning electron microscopy and the air cast method. The nephrons described in this paper are located in the outer stripe of the outer medulla and are the only nephrons that are not arranged radially within the kidney. They differ from other juxtamedullary nephrons in the morphology and course followed by the proximal tubule and by the close relationship that they establish with the arcuate vessels. The glomerulus of these nephrons is supplied by a short afferent arteriole that arises directly from the arcuate artery. Because of the special characteristics of these nephrons we have named them 'arcuate nephrons'. The morphology, spatial relationships and vascularization of the arcuate nephrons suggest that these nephrons differ functionally from the other juxtamedullary nephrons. Possible developmental factors responsible for the special microanatomy of the arcuate nephrons are analyzed.     

Modifications of the genital kidney proximal and distal tubules for sperm transport in Notophthalmus viridescens (Amphibia,Urodela, Salamandridae)

Male salamanders use nephrons from the genital kidney to transport sperm from the testicular lobules to the Wolffian duct. The microstructure of the epithelia of the genital kidney proximal tubule and distal tubule was studied over 1 year in a population of Notophthalmus viridescens from Crawford and Pike counties in central Missouri. Through ultrastructural analysis, we were able to support the hypothesis that the genital kidney nephrons are modified to aid in the transportation of sperm. A lack of folding of the basal plasma membrane, in both the genital kidney proximal and distal tubules when compared to the pelvic kidney proximal and distal tubules, reduces the surface area and thus likely decreases the efficiency of reabsorption in these nephron regions of the genital kidney. Ciliated epithelial cells are also present along the entire length of the genital kidney proximal tubule, but are lacking in the epithelium of the pelvic kidney proximal tubule. The exact function of these cilia remains unknown, but they may aid in mixing of seminal fluids or the transportation of immature sperm through the genital kidney nephrons. Ultrastructural analysis of proximal and distal tubules of the genital kidney revealed no seasonal variation in cellular activity and no mass production of seminal fluids throughout the reproductive cycle. Thus, we failed to support the hypothesis that the cellular activity of the epithelia lining the genital kidney nephrons is correlated to specific events in the reproductive cycle. The cytoplasmic contents and overall structure of the genital and pelvic kidney epithelial cells were similar to recent observations in Ambystoma maculatum, with the absence of abundant dense bodies apically in the epithelial cells lining the genital kidney distal tubule. J. Morphol. 275:914–922, 2014. © 2014 Wiley Periodicals, Inc.     

Modification of genital kidney nephrons for sperm transport in a plethodontid salamander,Eurycea longicauda

Salamanders possess kidneys with two distinct regions: a caudal pelvic portion and cranial genital portion. Nephrons of the pelvic region are responsible for urine formation and transport. Nephrons of the genital region transport sperm from testes to Wolffian ducts; however, nephrons of the genital region possess all the same functional regions found in pelvic kidney nephrons that are involved with urine formation and transport (renal corpuscles, proximal tubules, distal tubules, and collecting ducts). Morphological similarities between pelvic and genital regions stimulated past researchers to hypothesize that nephrons of genital kidneys possess dual function; that is, sperm transport and urine formation/transport. Considering size of glomeruli is directly related to the total amount of blood plasma filtered into the Bowman's space, we tested the hypothesis that nephrons of genital kidneys have reduced urine formation function by comparing glomerular size between nephrons of pelvic and genital kidney regions in Eurycea longicauda with general histological techniques. Light microscopy analysis revealed that glomeruli of pelvic kidneys were significantly larger than those measured from genital kidneys. Transmission electron microscopy analysis also revealed modifications in genital kidney nephrons when compared to pelvic kidney nephrons that suggested a decrease in urine formation function in genital kidneys. Such modifications included a decrease in basal and lateral plasma membrane folding in genital kidney proximal and distal tubules compared to that of pelvic kidney proximal and distal tubules. Genital kidney proximal tubules were also ciliated, which was not observed in pelvic kidney proximal tubules. In conclusion, although structurally similar at the histological level, it appears that nephrons of genital kidneys have decreased urine formation function based on glomerular size comparison and nephron ultrastructure.     

The testicular sperm ducts and genital kidney of male Ambystoma maculatum (Amphibia,Urodela, Ambystomatidae)

The ducts associated with sperm transport from the testicular lobules to the Wolffian ducts in Ambystoma maculatum were examined with transmission electron microscopy. Based on the ultrastructure and historical precedence, new terminology for this network of ducts is proposed that better represents primary hypotheses of homology. Furthermore, the terminology proposed better characterizes the distinct regions of the sperm transport ducts in salamanders based on anatomy and should, therefore, lead to more accurate comparisons in the future. While developing the above ontology, we also tested the hypothesis that nephrons from the genital kidney are modified from those of the pelvic kidney due to the fact that the former nephrons function in sperm transport. Our ultrastructural analysis of the genital kidney supports this hypothesis, as the basal plasma membrane of distinct functional regions of the nephron (proximal convoluted tubule, distal convoluted tubule, and collecting tubule) appear less folded (indicating decreased surface area and reduced reabsorption efficiency) and the proximal convoluted tubule possesses ciliated epithelial cells along its entire length. Furthermore, visible luminal filtrate is absent from the nephrons of the genital kidney throughout their entire length. Thus, it appears that the nephrons of the genital kidney have reduced reabsorptive capacity and ciliated cells of the proximal convoluted tubule may increase the movement of immature sperm through the sperm transport ducts or aid in the mixing of seminal fluids within the ducts. © J. Morphol., 2013. © 2012 Wiley Periodicals, Inc.     

Microscopic anatomy of the triton kidney

The structure of the nephron, length of all its segments and the renal architectonics as a whole have been studied in the newt (Triturus vulgaris L.) by means of microdissection and microinjection methods. The microinjection of latex or lissamine green is performed into the blood vessels and nephrons. In one kidney 85-95 nephrons are counted, their number is not the same along the kidney length and increases in the caudal direction. There are nephrons of the ventral, intrarenal and medial populations. The length of the former is 2.7 times as great as that of the latter. A relative length of the nephron segments changes slightly. In all the ventral nephrons a nephrostome is detected. A specific peculiarity of the newt nephron that differs it from that in other vertebrates is the presence of a long distal segment, heterogeneous by its structure. Superficial canaliculi of the kidney are strictly oriented: medially to the renal corpuscles there are loops of the first part of the distal segment, they are vascularized out of the efferent veins system; laterally to the renal corpuscles the loops of the proximal, connective and second part of the distal segments are localized; they receive their blood from some branches of the afferent vein.     

Rat metanephric organ culture in terato-embryology

The development of the permanent mammalian kidney, or metanephros, depends on mesenchymal-epithelial interactions, leading to branching morphogenesis of the ureteric bud that forms the collecting ducts and to conversion of the metanephric mesenchyme into epithelium that forms the nephrons. Rat metanephric organ culture in which these interactions are maintained is a valuable in vitro model system for investigating normal and abnormal renal organogenesis. Methods were designed to evaluate either the capacity of the ureteric bud to branch or that of the mesenchyme to form nephrons. Both are based on specific staining of the ureteric bud and the glomeruli with lectins. Using this approach, we have shown that retinoids are potent stimulating factors of nephrogenesis, acting through an increase in the branching capacity of the ureteric bud. On the other hand, several drugs such as gentamicin and cyclosporin A were found to reduce the number of nephrons formed in vitro. While gentamicin affects the early branching pattern of the ureteric bud, cyclosporin may affect the capacity of the mesencyme to convert into epithelium. This methodology therefore appears a potentially useful tool for toxicological studies new drugs.     

Analysis of Nephron Composition and Function in the Adult Zebrafish Kidney

The zebrafish model has emerged as a relevant system to study kidney development, regeneration and disease. Both the embryonic and adult zebrafish kidneys are composed of functional units known as nephrons, which are highly conserved with other vertebrates, including mammals. Research in zebrafish has recently demonstrated that two distinctive phenomena transpire after adult nephrons incur damage: first, there is robust regeneration within existing nephrons that replaces the destroyed tubule epithelial cells; second, entirely new nephrons are produced from renal progenitors in a process known as neonephrogenesis. In contrast, humans and other mammals seem to have only a limited ability for nephron epithelial regeneration. To date, the mechanisms responsible for these kidney regeneration phenomena remain poorly understood. Since adult zebrafish kidneys undergo both nephron epithelial regeneration and neonephrogenesis, they provide an outstanding experimental paradigm to study these events. Further, there is a wide range of genetic and pharmacological tools available in the zebrafish model that can be used to delineate the cellular and molecular mechanisms that regulate renal regeneration. One essential aspect of such research is the evaluation of nephron structure and function. This protocol describes a set of labeling techniques that can be used to gauge renal composition and test nephron functionality in the adult zebrafish kidney. Thus, these methods are widely applicable to the future phenotypic characterization of adult zebrafish kidney injury paradigms, which include but are not limited to, nephrotoxicant exposure regimes or genetic methods of targeted cell death such as the nitroreductase mediated cell ablation technique. Further, these methods could be used to study genetic perturbations in adult kidney formation and could also be applied to assess renal status during chronic disease modeling.     

Entry of nephrons into the collecting duct network of the avian kidney: A comparison of chickens and desert quail

The avian kidney contains a population of nephrons with and without loops of Henle. How the collecting ducts of this heterogeneous population of nephrons merge to exit as single ducts from the medullary cones has been uncertain. The results of this study show that the collecting duct tree begins with the coalescence of the distal tubules of pairs of loopless nephrons. These primary collecting ducts receive output from only loopless nephrons. Primary collecting ducts fuse in pairs and become secondary collecting ducts. They receive the distal tubules of transition nephrons. Pairs of secondary collecting ducts fuse and become tertiary collecting ducts. Tertiary collecting ducts receive the distal tubules of looped nephrons. Thus, the fluid from all nephron types comingles as it passes through the medullary cone. The results of this study also show that the anatomical arrangement of medullary cones does not permit the output from one medullary cone to enter a second medullary cone. Thus, all the medullary cones function as parallel units. This anatomical organization of the avian kidney affects its ability to produce a urine hyperosmotic to the plasma. © 1993 Wiley-Liss, Inc.     

Microanatomy of the renal cortex in the domestic fowl

Two aspects of the avian renal cortical microanatomy previously were unclear. The precise in situ folding patterns and orientations of the nephrons with respect to the other cortical elements had not been demonstrated. It also was not known whether certain nephron segments are supplied exclusively by either the arterial or the portal blood flow. In the present study, a new casting compound was developed to allow selective examination of the cortical components by light microscopy. Cortical nephrons at the surface of the kidney were serially sectioned and reconstructed in order to determine: (a) their relationships to the vasculature and collecting ducts; (b) the location and characteristics of the tubule segments; and (c) the primary and secondary folding patterns of the tubules. The anatomical findings were documented individually and then summarized in a comprehensive diagram of the superficial cortical microanatomy. In addition, an in vivo method was used to determine the extent of portal blood distribution to the nephron segments. It was demonstrated that renal portal blood suffuses all of the segments except for the loops of Henle.     

Kidney regeneration through nephron neogenesis in medaka

Although renal regeneration is limited to repair of the proximal tubule in mammals, some bony fish are capable of renal regeneration through nephron neogenesis in the event of renal injury. We previously reported that nephron development in the medaka mesonephros is characterized by four histologically distinct stages, generally referred to as condensed mesenchyme, nephrogenic body, relatively small nephron, and the mature nephron. Developing nephrons are positive for wt1 expression during the first three of these stages. In the present study, we examined the regenerative response to renal injury, artificially induced by the administration of sublethal amounts of gentamicin in adult medaka. Similar to previous reports in other animals, the renal tubular epithelium and the glomerulus of the medaka kidney exhibited severe damage after exposure to this agent. However, kidneys showed substantial recovery after gentamicin administration, and a significant number of developing nephrons appeared 14 days after gentamicin administration (P < 0.01). Similarly, the expression of wt1 in developing nephrons also indicated the early stages of nephrogenesis. These findings show that medaka has the ability to regenerate kidney through nephron neogenesis during adulthood and that wt1 is a suitable marker for detecting nephrogenesis.     

Morphological and flow cytometric characterization of leukocytes from the notothenioid teleosts Dissostichus eleginoides, Notothenia coriiceps, and Trematomus hansoni

To date, the adaptive immune response of the notothenioid fishes of the Sub- and High-Antarctic has received little attention. Here we characterize leukocyte preparations derived from head (pronephric) kidney, spleen, and intestine of three notothenioid species, Dissostichus eleginoides, Notothenia coriiceps, and Trematomus hansoni. Cells were collected from head kidney, spleen, and intestine, and were fixed in paraformaldehyde and analyzed by flow cytometry and optical microscopy. The three species displayed typical leukocyte populations composed of lymphocytes, granulocytes, monocytes/macrophages and thrombocytes with a peculiar organ distribution and peculiar flow cytometric patterns. This work represents the first characterization of cells involved in immune reactions in the investigated species.     

The primary localization of ascorbate and its synthesis in the kidneys of acipenserid (Chondrostei) and teleost (Teleostei) fishes

The kidneys of the rainbow trout Oncorhynchus mykiss, the channel catfish Ictalurus punctatus (both Teleostei), and the white sturgeon, Acipenser transmontanus (Chondrostei) displayed similar profiles of ascorbate distribution irrespective of the capability of synthesizing ascorbic acid. The head kidney was found to be the richest in ascorbate, whereas the trunk kidney showed significantly lower ascorbate levels in all three species. The head kidney richness in ascorbate was correlated with the localization of the cortical and chromaffin tissues known to accumulate ascorbate in some fish and mammals. Based on ascorbate concentration, it was possible to distinguish the head from the trunk kidney in salmonids and sturgeons which have an antero-posterior-fused kidney. The absence of l-gulonolactone oxidase activity in the kidneys of the channel catfish and the rainbow trout was asserted biochemically. We also confirmed that the ascorbic acid-synthesizing enzyme exists in white sturgeon kidney, and found that the enzyme distribution was inversely correlated with ascorbate concentrations. An active transport of ascorbate might exist in the head kidney of both acipenserids and the teleosts in order to maintain this vitamin at high concentrations. This report suggests a link between ascorbate concentration and its physiological functions in kidneys of lower vertebrates.Abbreviations AA ascorbic acid - TAA total ascorbic acid - DHA dehydroascorbic acid - DCIP dichloroindophenol - EDTA ethylenediaminetetra-acetic acid - GLO l-gulonolactone oxidase     

Effects of chlorpyrifos exposure on kidney Notch2-Jagged1 pathway of early prenatal embryo

Aims: To evaluate the effects of this insecticide on the embryonic development of kidney and to assess the important role of Notch2–Jagged1 pathway in this duration. Methods and results: Chlorpyrifos (CPF) 5 mg/kg/d were administrated on gestation 7.5–11.5 day by subcutaneous injection. On gestation 16.5 day, the normal embryo kidney developed through S shape duration to the original kidney, which had the nephrons and could start to secret the urine. But for the CPF‐treated mice, the embryo kidney developed much more slowly, they did not show the S shape and the nephrons. The Notch2–Jagged1 pathway should be expressed stronger in the normal embryo kidney on gestation 16.5 day, but for the CPF‐treated mice we found the obvious weak pathway staining. Conclusions : CPF broke the Notch2–Jagged1 pathway during the embryo kidney development, and the Notch2–Jagged1 pathway plays an important role in the S shape to original kidney formation duration. Birth Defects Res (Part B) 92:97–101, 2011. © 2011 Wiley‐Liss, Inc.     

Structure of the glomerular capillaries of the domestic chicken and desert quail

The glomerular capillary architecture of nephrons that include a loop of Henle (looped) and those that lack the loop (loopless) nephrons was examined qualitatively and quantitatively by electron microscopy in Gallus gallus and Callipepla gambelii. The glomerular capillaries of looped nephrons form a dichotomously branched network, while those of loopless nephrons are arranged loosely, and the majority are unbranched. There was no significant difference in the diameter of the glomerular capillaries between looped and loopless nephrons; however, in all cases the diameter of the afferent arteriole was significantly larger than that of the efferent arteriole. Based on size alone, the predicted blood flow rate in the efferent arteriole in 20% that of the afferent arteriole in G. gallus and 7% that of the afferent arteriole in C. gambelii. There was no significant difference in the volume density (Vv) of the glomerular capillaries between looped and loopless nephrons. However, the surface area density (Sv) of the glomerular capillaries in loopless nephrons of C. gambelii was significantly larger than for the looped nephrons, and for the loopless nephrons in G. gallus. This suggests that there may be a decrease in blood flow rate along the glomerular capillaries of the loopless nephrons in C. gambelii. Overall, the results indicate that the avian glomerular capillaries are less complex than those of mammals. Reasons may be that either avian blood is more viscous than that of mammals or that avian erythrocytes may be unable to fit physically through a tight intertwining network of capillaries due to the presence of a nucleus, which limits the tank-treading ability of avian erythrocytes. © 1995 Wiley-Liss, Inc.     

Relative thickness of the renal medulla in birds

The intraspecific mean length of medullary cones in avian kidneys is analogous to medullary thickness in the mammalian kidney. Hence, relative medullary thickness (based upon kidney volume) can be calculated for birds as was done in mammals years ago. Comparative figures are given for 26 species from nine avian orders. The organizational pattern of cortex and medulla in the bird kidney is reviewed, and a simplified diagram of this relationship is presented. With some exceptions, urine concentrating ability and relative medullary thickness are directly proportional in mammals. Contrarily, no similar trend was evident in birds when current information on water economy was compared to relative medullary thickness in various species. There are a number of factors (such as the respective functional roles of reptilian and mammalian-type nephrons, interspecific variations in ion transport, etc.) which require study before the significance of relative thickness in the avian medulla can be evaluated more thoroughly.     

The sexual segment of hemidactylus turcicus and the evolution of sexual segment location in squamata

The kidneys of the Mediterranean Gecko, Hemidactylus turcicus (Gekkonidae), were investigated using light and electron microscopy with the primary focus placed on morphology of the sexual segment of the kidney. The nephrons of male H. turcicus are composed of five distinct regions: 1) a renal corpuscle and glomerulus, 2) a proximal convoluted tubule, 3) an intermediate segment, 4) a distal convoluted tubule, and 5) the sexual segment of the kidney/collecting duct. Female H. turcicus is similar but lack a sexual segment of the kidney. The sexual segment of the kidney is hypertrophied during the months of March through August, which corroborates previous reports of reproductive activity. During inactive months, the sexual segment of the kidney is nondiscernable from the collecting ducts. The sexual segment consists of tall columnar epithelial cells with basally positioned nuclei. Perinuclear Golgi complexes and rough endoplasmic reticulum are present. Secretory granules, which fill the apices of the epithelial cells, are electron dense and released into the lumen by a merocrine secretory process. Narrow intercellular canaliculi separate each epithelial cell and are sealed by tight junctions at the luminal aspect. Basally, leukoctyes are observed within the intercellular canaliculi and outside the basal lamina. Mast cells can be found just outside the basal lamina in close association with renal capillaries. The sexual segment of the kidney of H. turcicus is similar to that of three unrelated lizards for which ultrastructure was investigated with secretion mode being the major difference Also, H. turcicus is similar to most other lizards in that complete regression occurs during reproductive inactivity, but differs in this trait from the skink, Scincella lateralis, and most snakes which display a hypertrophied sexual segment of the kidney throughout the entire year. Although some unique similarities appear during the optimization, no direct patterns or directions are observed, and only the molecular based phylogeny resolves the ancestral condition of the Squamata as the sexual segment of the kidney being observed in the distal convoluted tubule, collecting duct, and ureter. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

Ultrastructure of the kidney of the newt

In the newt [Triturus vulgaris (J.)] kidney a zone of single nephrons is distinguished, where there are ten nephrons, connected with the paramesonephral (Müller's) canal, and another zone of the renal mass; in the latter the main part of nephrons is situated, which are connected with the ureter by means of collecting tubules. In these zones of the kidney ultrastructure of epitheliocytes in the proximal and distal parts is different. The renal corpuscles of the epithelial cell in the cervical and in the intermediate parts are similar in both zones. In the zone of the single nephrons a specific peculiarity of epitheliocytes in the proximal and in the distal parts of the canaliculi is presence of numerous secretory granules in their cytoplasm. The canalicular epitheliocytes in the renal mass zone are different in the terminal and in the initial parts of the canaliculi: the former contains more mitochondria, and the area of the basolateral parts of plasmolemma is greater than those in the latter. These results are in accordance with the level of sodium ions transport in these parts of the canaliculus.