Kidney function in the Spinifex hopping mouse, Notomys alexis

Notomys alexis (Spinifex hopping mouse) is found in the arid zone of Australia. The structure and function of the kidneys allow this species to conserve water. This study investigated the rate at which N. alexis can reduce urine volume and increase the concentration of electrolytes and solutes when water deprived. It also looked at the response to rehydration, following a period of water deprivation. The laboratory mouse, Mus musculus domesticus, was used for comparison. N. alexis is able to reduce urine volume and increase urine concentration more rapidly than M. m. domesticus when water deprived. This appears to occur prior to any measurable changes in plasma electrolyte concentrations and is not due to reductions in glomerular filtration rate. Gradual water deprivation over a period of 10 days allowed N. alexis to adjust so that urine composition was similar in many ways to animals that had ad libitum access to water, whereas M. m. domesticus required significant water supplementation to maintain body weight at 85% of initial body weight. Ability to concentrate urine rapidly is characteristic of a well-insulated renal medulla [Bankir, L., DeRouffignac, C., 1985. Urinary concentrating ability: insights from comparative anatomy. Am. J. Physiol. 249, R643-666]. However, a well-insulated medulla is normally associated with slow dilution of urine when animals are rehydrated. N. alexis was able to produce dilute urine very rapidly following rehydration of water deprived animals. Physiological control of renal function appears to be complex. Although M. m. domesticus is able to produce concentrated urine, it is unable to survive without free water and responds more slowly to water deprivation.     

Mating behaviour and insemination in the hopping mouse (Notomys alexis)

Hopping mice have extremely small testes and a reduced complement of male accessory sex glands. Nevertheless, greater than 1000 spermatozoa populate the isthmus of the oviduct after each insemination and a range of morphological types is found similar to that in the male tract. When females are primed with gonadotrophins they sometimes lock with more than one of the males within the group and in the present study two inseminations sometimes took place at the one oestrus. There is thus the possibility for intermale sperm competition within the female tract of these animals.     

Isolation of the mite Myocoptes musculinus Koch from the Spinifex Hopping mouse (Notomys alexis)

This paper reports on the isolation and identification of the fur-clasping mite, Myocoptes musculinus, from the faeces of the Spinifex Hopping mouse (Notomys alexis). This investigation adds to the sparse records of ectoparasites collected from native Australian murids.     

The distribution of renal hyaluronan and the expression of hyaluronan synthases during water deprivation in the Spinifex hopping mouse, Notomys alexis

Hyaluronan (HA) is a glycosaminoglycan that is synthesized by a family of enzymes called hyaluronan synthases (HASs), of which there are three isoforms (HAS1, 2 and 3) in mammals. The HASs have different tissue expression patterns and function, indicating that synthesis of HA and formation of the HA matrix may be regulated by various factors. The HA matrix has an important role in renal water handling and the production of a concentrated urine. We investigated the distribution of HA and the expression of HAS1, HAS2 and HAS3 mRNAs in the kidney of the Spinifex hopping mouse, Notomys alexis, a native Australian desert rodent that is reported to produce the most concentrated urine of any mammal. After periods of three, seven and fourteen days of water deprivation, the distribution of renal HA changed considerably, and there was a general down-regulation of HAS mRNA expression. It is proposed that the regulation of HA synthesis by the different HAS isoforms during water deprivation in N. alexis, could be influenced by the molecular mass of the HA chains produced by each isoform, followed by the rate at which the individual HAS produces HA.     

The distribution of renal hyaluronan and the expression of hyaluronan synthases during water deprivation in the Spinifex hopping mouse, Notomys alexis.

Hyaluronan (HA) is a glycosaminoglycan that is synthesized by a family of enzymes called hyaluronan synthases (HASs), of which there are three isoforms (HAS1, 2 and 3) in mammals. The HASs have different tissue expression patterns and function, indicating that synthesis of HA and formation of the HA matrix may be regulated by various factors. The HA matrix has an important role in renal water handling and the production of a concentrated urine. We investigated the distribution of HA and the expression of HAS1, HAS2 and HAS3 mRNAs in the kidney of the Spinifex hopping mouse, Notomys alexis, a native Australian desert rodent that is reported to produce the most concentrated urine of any mammal. After periods of three, seven and fourteen days of water deprivation, the distribution of renal HA changed considerably, and there was a general down-regulation of HAS mRNA expression. It is proposed that the regulation of HA synthesis by the different HAS isoforms during water deprivation in N. alexis, could be influenced by the molecular mass of the HA chains produced by each isoform, followed by the rate at which the individual HAS produces HA.     

Environmental factors and reproduction in the female hopping mouse, Notomys alexis.

Australian hopping mice (Notomy alexis) were subjected to short or long photoperiods, different social environments and/or water deprivation. The age at which vaginal opening and first oestrus occurred was delayed by short photoperiods and by the absence of male proximity. Water deprivation prevented normal maturation. The normal 7 to 8 day oestrous cycle was prolonged by short photoperiods or water deprivation. Animals deprived of water had lighter body, ovarian and uterine weights, and follicular growth seemed to be impaired. No differences in organ weights were found between animals in the two photoperiods. The significance of the findings is discussed.     

Organization of testicular interstitial tissue of an Australian rodent,the spinifex hopping mouse,Notomys alexis

Summary The organization of testicular interstitial tissue of the spinifex hopping mouse, Notomys alexis differs from that of other rodents. It comprises between 10.3% and 17.3% (average 15.0%) of the total testicular volume, and is variable in its organization both at different locations within the testis of the one animal and among different individuals. Abundant, closely packed Leydig cells are usually present; however, in some regions large, thick-walled blood vessels and extensive peritubular lymphatic spaces, often lacking an endothelium adjacent to the Leydig cells, are also prominent. The Leydig cells in contact with the large blood vessels and lymphatics, unlike those in regions where lymph is sparse, are not densely packed and sometimes contain numerous lipid droplets. Ultrastructure of Leydig cells is typical of steroid-producing cells; however, mitochondria are often extremely large, unusual in shape or bizarely arranged in relation to one another. Also electrondense bodies displaying a paracrystalline-like internal structure of parallel, electron-dense filaments arranged in a lattice pattern occur in the cytoplasm of many cells. The significance of these unusual ultrastructural features and the organization of the interstitial tissue remain to be determined conclusively, but may relate to steroid synthesis, secretion and uptake.     

Quantitative estimation of islet tissue of pancreas in water rat (Hydromys chrysogaster)

Pancreases from three male and three female adult water rats ( Hydromys chrysogaster ) were studied. Estimations of islet tissue mass and of individual cell types were made on paraffin sections of Bouin-fixed tissue taken from head, neck, body and tail regions of the pancreas of each animal. Islet tissue mass was assessed using a linear scanning technique (Carpenter & Lazarow, 1962) on sections stained with haematoxylin and eosin. Specific cell types were assessed using a point-intercept method (Weibel, Kistler & Scherle, 1966) on sections stained with aldehyde-fuchsin for beta (β) cells, phosphotungstic acid haematoxylin for alpha (α) cells and an immunoperoxidase method for somatostatin for delta ( δ ) cells. Positive regional differences noted were a greater percentage proportion of islet tissue in the tail region and a lower proportion of a cells in the head region. Alpha cells were peripherally situated in the islets.
These results show some elements of agreement with a previously proposed hypothesis (Bonner-Weir & Weir, 1979) regarding the general pattern of arrangement of the mammalian endocrine pancreas.     

Ultrastructure of the epithelial cells of the ventral prostate from the hopping mouse Notomys alexis

The large ventral prostate of the hopping mouse has abundant secretory units whose epithelial cells vary in height and which often have nuclei in the apical region of the cell. TEM observations indicated two epithelial cell types in which some unusual features occurred. Type A cells had granular endoplasmetic reticulum (GER) whose membranes often formed intracytoplasmic confronting cisternae. Type B cells had more fragmented and vesiculated GER with sparse ribosomes and less frequently also intracytoplasmic confronting confronting cisternae. In the latter cells, two types of granules were found, one of which was derived from the Golgi and the other possibly directly from the GER. Type A cells only had one type of granule present. A highly convoluted membrane was also found at the basal region in many of the cells. The significance of these unusual ultrastructural features has yet to be ascertained.     

Quantitative estimation of islet tissue of pancreas in adult Grey kangaroos (Macropus fuliginosus)

Six Grey kangaroos, both male and female, were shot and weighed. The pancreas was isolated, weighed and samples fixed in Bouin's solution. Using a linear scanning technique (Carpenter & Lazarow, 1962) the mean islet tissue mass was estimated in head, neck, body and tail regions. A uniform distribution was found in all regions. The relationship between pancreas weight and body weight and islet mass in relation to body weight were calculated. Sections stained with aldehyde-fuchsin (Gomori, 1950), Mallory's phosphotungstic acid haemotoxylin and modified Davenport's technique (Epple, 1967) were prepared. Using a Wild-M501 semiautomatic sampling microscope and a Weibel graticule (Weibel et al., 1966) the percentage volume of β cells, α cells and δ cells were estimated respectively in the head, neck, body and tail regions of the six samples. The α cells or glucagon-producing cells were the most predominant as these macropodid marsupials are well adapted to dealing with hypoglycemic conditions. They were uniformly distributed in all regions.     

Copulatory behaviour and coagulum formation in the female reproductive tract of the Australian hopping mouse, Notomys alexis

Hopping mice were examined to study two interrelated questions: (1) when groups of adults of both sexes are kept together in one cage in the laboratory is there evidence that the females copulate with only one male, and (2) is a copulatory plug formed in the female tract after ejaculation? The findings indicate that a female will sometimes lock with more than one male in the group during an oestrous period induced by administration of exogenous gonadotrophins, and that a small 'plug' of soft material forms post coitum in the more caudal parts of the female tract. Individuals of this species, therefore, do not appear to be strictly monogamous, at least in this artificial laboratory situation. Although a coagulum is formed, this is quite different from the typical hard copulatory plug that occurs in common laboratory murids; it may possibly reduce sperm backflow from the lower region of the female reproductive tract.     

Quantitative estimation of pancreatic polypeptide (PP) cells of islet tissue of pancreas in Australian mammals

Pancreases from three male and three female echidnas ( Tachyglossus aculeatus ), possums ( Trichosurus vulpecula ), grey kangaroos ( Macropus fuliginosus ), spinifex hopping mice ( Notomys alexis ) and water rats ( Hydromys chrysogaster ) were studied using a point-intercept method and Weibel graticule (Weibel, Kistler & Scherle, 1966) on sections stained by an immunoperoxidase method for pancreatic polypeptide (PP). PP cells were assessed in the head, neck, body and tail regions. There was a greater percentage proportion of PP cells in the head than in the other regions of echidna, possum and water rat. PP cells were not identified in grey kangaroo and spinifex hopping mouse, although control sections were positive.
These results show some agreement with a previously proposed hypothesis (Bonner-Weir & Weir, 1979) concerning the distribution of cell types in the mammalian endocrine pancreas.     

The effect of water deprivation on the expression of atrial natriuretic peptide and its receptors in the spinifex hopping mouse,Notomys alexis

This study investigated the mRNA expression of the atrial natriuretic peptide (ANP) system (peptide and receptors) during water deprivation in the spinifex hopping mouse, Notomys alexis, a native of central and western Australia that is well adapted to survive in arid environments. Initially, ANP, NPR-A and NPR-C cDNAs (partial for receptors) were cloned and sequenced, and were shown to have high homology with those of rat and mouse. Using a semi-quantitative multiplex PCR technique, the expression of cardiac ANP mRNA and renal ANP, NPR-A, and NPR-C mRNA was determined in 7- and 14-day water-deprived hopping mice, in parallel with control mice (access to water). The levels of ANP mRNA expression in the heart remained unchanged, but in the kidney ANP mRNA levels were increased in the 7-day water-deprived mice, and were significantly decreased in the 14-day water-deprived mice. NPR-A mRNA levels were significantly higher in 7-day water-deprived mice while no change for NPR-A mRNA expression was observed in 14-day water-deprived mice. No variation in NPR-C mRNA levels was observed. This study shows that water deprivation differentially affects the expression of the ANP system, and that renal ANP expression is more important than cardiac ANP in the physiological adjustment to water deprivation.     

Vocalizations of Australian hopping mice (Rodentia: Notomys)

The four species of hopping mouse studied, N. alexis, N. cervinus, N. fuscus and N. mitchellii , were found to have a basic repertoire of eight more or less discrete vocalizations: three in the young—the calls produced in the nest, ultrasonic pipping given when removed from the nest and a high intensity (pain) squeal—and five in the adult—a low intensity pip given during mutual grooming, a high intensity (pain) squeal, a medium intensity squeak given when "annoyed", twittering given during aggressive chases and ultrasonic pipping given during non-aggressive encounters. The calls of the different species varied in structure and in pitch. No vocalizations were associated with threat or fighting. Calls given in the nest by suckling young are well developed and the intensity of such calls appears to mirror the general motivational state of the caller. It is suggested that these calls may act to maintain maternal behaviour in the mother.     

The metabolism of phenol in a desert rodent Notomys alexis.

1. Phenol is rapidly metabolized in the desert rodent Notomys alexis; sulphate and glucuronide conjugates being formed.2. The circulating half-life of phenolic metabolites is similar in N. alexis to laboratory mice. This contrasts with comparable data for salicylate turnover.3. After injection, the tissue distribution of phenolic metabolites is highest in liver, lung and kidney.4. In this species, phenol is rapidly conjugated to soluble form and a low rate of water turnover does not correlate with differences in phenol metabolism from those generally observed in mammals.     

Inheritance studies of glucose phosphate isomerase, transferrin and esterases in the Australian hopping mice Notomys alexis, N. cervinus, N. mitchellii and N. fuscus (Rodentia: Muridae)

Electrophoretic variation in glucose phosphate isomerase was found in N. alexis, N. cervinus and N. fuscus. Inheritance was apparently Mendelian with two co-dominant alleles; heterozygotes possessed a triple-banded phenotype. High intra-specific electrophoretic variability was found in all species for transferrin. Most of the variation was attributable to variation in the number of attached moieties, probably sialic acid. In N. alexis however, a second pattern of transferrin variation was found that followed a Mendelian pattern of codominant inheritance. In all four species, considerable variability was found in three zones of esterase activity, but the pattern of inheritance was not elucidated.     

Cytological organization of the seminiferous epithelium in the Australian rodents Pseudomys australis and Notomys alexis

Absolute and relative testis mass of two species of conilurine rodents, the plains rat (Pseudomys australis) and the hopping mouse (Notomys alexis), were markedly different. In plains rats the testis comprised approximately 3% of body mass while in hopping mice they rarely accounted for more than 0.2%. In both species, 8 cellular associations, or cycle stages, were recognized in the seminiferous epithelium. The relative frequencies, and hence durations, of Stages I to VIII were 5.1, 7.0, 12.5, 10.5, 5.4, 25.9, 4.4 and 29.0% of one cycle for plains rats (N = 14), and 20.4, 10.9, 9.6, 8.1, 5.1, 20.4, 14.7 and 10.8% for laboratory-bred hopping mice (N = 35). Generally, the relative durations of the cycle stages were very similar between plains rat individuals, but were variable between hopping mice. Also, organization of the seminiferous epithelium was less rigid in hopping mouse testes, and several anomalies were observed. These included: the occurrence of 2-4 cellular associations in about 20% (range 11.3-33.9%) of tubular cross-sections, deviations in cellular composition in certain cycle stages from that usually observed, and an increased incidence of degenerating cells, together with the presence of multinucleated "giant' cells, within the seminiferous epithelium.     

Urea metabolism in isolated perfused lungs of the laboratory rat and of a desert rodent, Notomys alexis

1. Using the isolated perfused lung preparation we have demonstrated a low-activity ureolytic enzyme present in rodent lung tissue. The enzyme shares four characteristic features with jack bean urease (EC 3.5.1.5). 2. Ureolytic activity was inhibited by fluoride ions and methionine hydroxamic acid; using the latter inhibitor, the I50 value and maximum inhibition were similar to those reported for jack bean urease. The apparent Km for rat lung urease was similar to the plasma urea level. 3. The low level of urease activity in the rat lung and in that of Notomys alexis, a desert rodent, suggests that the enzyme is not involved in urea excretion, rather that pulmonary ammonia production may influence fluid balance at the alveolus.