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At least 415 records · Page 23Linked to original sources
PubMed1986

Serum thyroxine and seasonal fattening of free-living Piute ground squirrels, Spermophilus mollis (Rodentia: Sciuridae).

Serum thyroxine and body composition of free-living Piute ground squirrels were examined during the season of above-ground activity. Serum thyroxine titers were 2-10 times higher than those reported in laboratory studies on other species. Among juveniles, both body size and lipid content were negatively correlated with thyroxine, whereas these variables were not significantly correlated among adults. Significant sex differences in serum thyroxine were observed for both age groups. Results suggest that the seasonal cycle of body weight is driven by an underlying metabolic cycle but that individual fattening schedules are determined by environmental conditions.

Animals↗
PubMed1987

Caecal size and function in the rock elephant shrew Elephantulus myurus (Insectivora, Macroscelididae) and the Namaqua rock mouse Aethomys namaquensis (Rodentia, Muridae).

1. The relative size of the digestive organs and the function of the caeca of an insectivorous elephant shrew Elephantulus myurus (Macroscelididae) and of a herbivorous rodent Aethomys namaquensis (Muridae) were compared. 2. Both species had similar body mass but A. namaquensis had a significantly heavier total digestive tract, full stomach, and caecum and a longer large intestine and caecum than E. myurus. 3. Both species had similar total volatile fatty acid (VFA) concentration and VFA % composition although A. namaquensis had a significantly higher % of n-butyric acid. Both had a similar caecal NH3-N concentration. 4. The presence of a functional caecum in E. myurus supports the view that Macroscelididae have evolved from ancestral herbivores and not from insectivores.

Animals↗
PubMed1989

Variation in renal structure and urine concentrating capacity among ground squirrels of the Spermophilus townsendii complex (Rodentia: Sciuridae).

Renal structure and urine concentrating capacity varied significantly among nine populations of desert ground squirrels representing four closely related taxa. Variation in renal structure was weakly associated with taxonomic grouping. Urine concentrating capacity was not correlated with standard measures of habitat were aridity, but it was correlated with soil salinity. Maximum urine osmolalities for one population from the most saline habitat were among the highest documented for sciurid rodents. Results do not support the hypothesis that hibernating sciurids have poor renal efficiency.

Animals↗
PubMed1989

The effects of increased dietary cellulose on the anatomy, physiology and behaviour of captive water voles, Arvicola terrestris (L.) (Rodentia: Microtinae).

1. Wild water voles and captives on high fibre diets had significantly longer and heavier digestive tracts (especially the caecum) than captives fed a low fibre diet. 2. Increasing dietary cellulose increased food intake, faecal output and metabolic rate, and decreased digestibility. Some but not all added cellulose was digested. 3. The passage of food through the digestive tract was significantly faster on the diet with added cellulose. 4. Coprophagy included eating directly from the anus and eating faecal pellets from the floor of the cage. The frequency of the latter type increased significantly for animals on a high fibre diet.

Animals↗
PubMed1979

Protein variation and systematics of three subgenera of Malayan rats (Rodentia: Muridae, genus Rattus Fischer).

1. Nine erythrocyte proteins coded by a separate locus each were analysed in and among seven Malayan species of Rattus belonging to three subgenera. 2. Electrophoretic data obtained confirm the specific status of the seven taxa and divide the seven species into three groups which correspond with Ellerman's (1949) subgenera Stenomys, Maxomys and Leopoldamys. 3. A comparative study together with 11 other species of Malayan Rattus previously analysed show that, with few exceptions, the overall relationships among the 18 species based on electrophoretic data correspond well with conclusions based on morphological evidence. 4. Malayan species of Rattus are relatively very diverse genetically (S = 0.27, range 0.01-0.94).

Acid Phosphatase↗
PubMed2004

Origin and developmental fate of vestigial tooth primordia in the upper diastema of the field vole (Microtus agrestis, Rodentia).

OBJECTIVE: Odontogenesis in voles is a convenient model to test hypotheses on tooth development generated from investigations in the mouse. Similar to other rodents, the functional dentition of the vole includes a toothless diastema. At its mesial end, a vestigial tooth bud has been found in the upper jaw of vole embryos. The aim of this study was to analyse the developmental dynamics of vestigial tooth structures in the upper diastema of the field vole and to compare it with the situation in the mouse. DESIGN: The development of odontogenic structures in the upper diastema of the field vole was investigated using serial histological sections and three-dimensional (3D) computer-aided reconstruction. RESULTS: A transient continuous dental lamina in the upper diastema of the field vole extended mesially to the first molar primordium, but was not continuous with the dental lamina in the incisor region. At its mesial limit, a large vestigial tooth primordium was regularly present. A further distinct vestigial bud was located mesially to the first molar primordium. The segmentation of the dental lamina suggested a potential to give rise to further vestiges in the upper diastema of the vole. CONCLUSIONS: In the prospective diastema of the vole exists as in the mouse a continuous dental lamina. Beside the prominent vestigial tooth bud in the mesial diastema, a further large bud was transiently located in front of the molars. The incorporation of dental epithelium into the first upper molar (M(1)) primordium in the vole differs from that in the mouse.

Animals↗
PubMed2006

Phenotypic plasticity in response to low quality diet in the South American omnivorous rodent Akodon azarae (Rodentia: Sigmodontinae).

We studied the responses in the omnivorous rodent A. azarae submitted to a low quality diet at morphological, physiological and biochemical levels. At short term, a decrease in body mass occurred. A later increase in food consumption constituted a strategy that allowed a temporal recovery of physical condition. However, hyperphagia appeared not to be enough to maintain physical condition after 30 days of low quality diet consumption. At the morphological level, an increase in length (9%) of the anterior portion of the gut occurred, the part of the gut where digestion and absorption take place. A decrease in small intestine weight could be related with the long-term impairment of body condition. Inhibition of sucrase specific activity in small intestine would indicate a down-regulation of sucrase-isomaltase complex. Total maltase specific activity in small intestine was not affected suggesting an up-regulation of sucrase-independent maltase specific activity. A down-regulation of protease specific activity in small intestine occurred in response to low quality diet. The specific activity of disaccharidases in caecum and large intestine was down-regulated. The strategies and constraints at different levels of A. azarae upon low quality diet are discussed.

Adaptation, Physiological↗
PubMed2004

Renal physiology of two southern African Mastomys species (Rodentia: Muridae): a salt-loading experiment to assess concentrating ability.

Aspects of renal physiology were examined to test the hypothesis that two cryptic species of the genus Mastomys (Mastomys natalensis and Mastomys coucha) are geographically separated by differences in aridity tolerance. Laboratory-bred females of each species were subjected to different levels of salinity in their water source (distilled water, 0.9% NaCl, and 1.5% NaCl; 10 conspecifics in each group) from weaning until sexual maturity. Individuals of the two species exhibited similar rates of water consumption and urine production. The salinity treatments caused sodium diuresis in both species, evident in increased urine volume, decreased osmolality and increased osmotic output. Urine concentration, kidney mass and kidney relative medullary area (RMA) did not differ between species. The results of our study do not support the hypothesis that differences in osmoregulatory ability separate these two cryptic species. Nor do they support the use of salt loading to elicit maximum urine concentrations in mammals.

Animals↗
PubMed2004

Phenotypic flexibility of digestive morphology and physiology of the South American omnivorous rodent Akodon azarae (Rodentia: Sigmodontinae).

We have determined the occurrence of responses at different levels (morphological, physiological and biochemical) in the omnivorous rodent Akodon azarae upon cold acclimation (15 degrees C). A short-term enhancement in food consumption appeared to account for the maintenance of both mass and body composition. At the morphological level, the main response was an increase in the dimensions of small intestine, which constitutes the section of the gut where absorption and secretion take place. An increase in sucrase specific activity was only found in small intestine. Sucrose independent maltase activity was very low since 99.8% of total maltase activity was due to sucrase-isomaltase (SI) complex. Protease specific activities were not affected. The fact that resting metabolic rates determined at 15 and 23 degrees C were similar in cold acclimated animals suggests a change in lower critical temperature. In conclusion, our results show that A. azarae exhibits different strategies to support cold environment that could lead to an enhancement in digestion and absorption efficiency. Furthermore, this work suggests that low temperature is an independent cue of other environmental factors to trigger the strategies allowing the maintenance of body condition in A. azarae.

Animals↗
PubMed2005

Cadmium and lead concentrations in Skrjabinotaenia lobata (Cestoda: Catenotaeniidae) and in its host, Apodemus sylvaticus (Rodentia: Muridae) in the urban dumping site of Garraf (Spain).

The present study evaluates the parasitological model constituted by the wood mouse (Apodemus sylvaticus) and its intestinal cestode (Skrjabinotaenia lobata) as a potential bioindicator of Cd and Pb in the urban dumping site of Garraf near the city of Barcelona (Spain) and in Begues (reference site). Tissues and respective S. lobata specimens of 38 wood mice captured in Garraf and Begues were analyzed for Cd and Pb by means of ICP-MS. Higher cadmium levels in S. lobata were found only in respect to the muscular levels of their hosts. Nevertheless, lead levels were 8.5-, 53.2- and 81.4-fold higher in S. lobata than kidney, liver and muscle levels of A. sylvaticus from Garraf, respectively. Thus, the proposed model seems to be a promising bioindicator to evaluate environmental lead exposure in terrestrial habitats. In addition, all available data on lead bioaccumulation by cestode parasites of terrestrial mammals are generally discussed.

Animals↗
PubMed2005

Evidence for the existence of two distinct species: Psammomys obesus and Psammomys vexillaris within the sand rats (Rodentia, Gerbillinae), reservoirs of cutaneous leishmaniasis in Tunisia.

A thorough taxonomic knowledge about putative animal reservoirs of transmissible diseases is an absolute prerequisite to any ecological investigation and epidemiological survey of zoonoses. Indeed, accurate identification of these reservoirs is essential for predicting species-specific population outbreaks and therefore to develop accurate ecological control strategies. The systematic status of sand rats (genus Psammomys) remains unclear despite the pivotal role of these rodents in the epidemiology of Zoonotic Cutaneous Leishmaniasis (ZCL) disease as sand rats are the main known reservoir hosts of the protozoan parasite Leishmania major. In the present work, we expose morphological, biochemical, genetic and cytogenetic evidence supporting the identification of at least two cryptic species within the genus Psammomys in Tunisia. First, significant morphometric differences were observed and were correlated associated with external features and biogeographic origins. Second, differences in patterns of two isoenzymic systems (Glutamate Oxaloacetate Transaminase (GOT) and 6-PhosphoGluconate Dehydrogenase (6PGD)) were found, which makes it possible to amount these isoenzyme characters to two diagnostic loci. Third, based on the mitochondrial cytochrome b (cyt b) gene, a high magnitude of genetic distance (13.89%) was also observed. Fourth, cytogenetic analysis showed that these two populations groups differ in their diploid chromosome numbers, i.e. 2N=46 versus 2N=48. We consider that all these variations are enough important to be considered as demonstrative and we propose that these two lineages should be considered as two distinct species that we refer to the fat sand rat Psammomys obesus Cretzschmar, 1828 and the thin sand rat Psammomys vexillaris Thomas, 1925. Implications of such results on the eco-epidemiology of ZCL in Tunisia are discussed.

Animals↗
PubMed2004

Toxoplasma gondii and mast cell interactions in vivo and in vitro: experimental infection approaches in Calomys callosus (Rodentia, Cricetidae).

In the present work, we studied some qualitative and quantitative characteristics of mast cells located in the peritoneal cavity, submandibular and dorsal lymph nodes and ileum of Calomys callosus experimentally infected by Toxoplasma gondii. In uninfected animals, the majority of mast cells had similar ultra-structural characteristics, including several cytoplasmic granules with homogeneous and electron dense contents. However, after 1 h of infection, a significant influx of mast cells into peritoneal cavity was observed. The number of mast cells in this compartment decreased progressively in infected animals, and was significantly lower than the number of mast cells in control animals after 48 h of infection. Mast cells from infected animals or from purified suspensions that were infected in vitro presented significant morphological modifications, suggesting a degranulation process: cytoplasmic granules with electron dense content, fusion of the cytoplasmic granules, intracytoplasmic channels, cytoplasmic granules with flocculent material, plasma membrane rupture and granule contents in the extracellular environment. A remarkable increase in the influx of neutrophils toward the peritoneal cavity of the infected animals was observed after 12 h of infection. Moreover, this event occurred after the mast cell degranulation process took place. The relative increase in the number of mast cells and neutrophils was also followed by an increase in the number of macrophages, but there was a significant decrease in lymphocyte influx. After 48 h of infection, the parasite had spread from the peritoneal cavity to all organs examined. Also, mast cells from these organs showed evident morphological alterations, indicating the presence of the degranulation process. These results suggest that mast cells are deeply involved with the acute phase of the inflammatory response in this experimental model.

Animals↗
PubMed2005

Involvement of pre- and post-synaptic serotonergic receptors of dorsal raphe nucleus neural network in the control of the sweet-substance-induced analgesia in adult Rattus norvegicus (Rodentia, Muridae).

In order to investigate the effects of monoaminergic mechanisms of the dorsal raphe nucleus on the elaboration and control of sweet-substance-induced antinociception, male albino Wistar rats weighing 180-200 g received sucrose solution (250 g/L) for 14 days as their only source of liquid. After the chronic consumption of sucrose solution, each animal was pretreated with unilateral microinjection of methiothepin mesylate (5.0 microg/0.2 microL), or methysergide maleate (5.0 microg/0.2 microL) in the dorsal raphe nucleus. Each rat consumed an average of 15.6g sucrose/day. Their tail withdrawal latencies in the tail-flick test were measured immediately before and after this treatment. An analgesia index was calculated from the withdrawal latencies before and after the pharmacological treatment. The blockade of serotonergic receptor in the dorsal raphe nucleus with methysergide after the chronic intake of sucrose decreased the sweet-induced antinociception. However, microinjections of methiothepin in the dorsal raphe nucleus did not cause a similar effect on the tail-flick latencies after the chronic intake of sucrose solution, increasing the sweet-substance-induced analgesia. These results indicate the involvement of serotonin as a neurotransmitter in the sucrose-produced antinociception. Considering that the blockade of pre-synaptic serotonergic receptors of the neural networks of the dorsal raphe nucleus with methiothepin did not decrease the sweet-substance-induced antinociception, and the central blockade of post-synaptic serotonergic receptors decreased the sucrose-induced analgesia, the modulation of the release of serotonin in the neural substrate of the dorsal raphe nucleus seems to be crucial for the organization of this interesting antinociceptive process.

Analgesia↗
PubMed2006

Learning-induced axonal remodeling: evolutionary divergence and conservation of two components of the mossy fiber system within Rodentia.

Damage to the hippocampal formation results in profound impairments in spatial navigation in rats and mice leading to the widely accepted assumption that the hippocampal cellular and molecular memory mechanisms of both genera are conserved. Recently our group has shown in two rat strains that hippocampal-dependent training in the water maze specifically induces robust 'sprouting' of granule cell suprapyramidal mossy fiber axon terminal fields. Here we sought to investigate whether the pronounced remodeling of adult hippocampal circuitry observed in the rat is also present in the mouse motivated by the thought that subsequent studies using genetically-engineered mice could then be implemented to explore the molecular mechanisms underlying training-dependent axonal growth in adult rodents. However, in contrast to Wistar rats, no changes in the Timm's-stained area of mossy fiber terminal fields (MFTFs) were observed in C57BL/6J or 129Sv/EmsJ inbred wild-type mice after water maze training. Neither extending the duration of training nor scaling down the size of the apparatus was able to induce sprouting in mouse mossy fiber pathways. Though there may be similarities in the ultimate output of the hippocampus of rats and mice as inferred from lesion studies, the current results, as well as differences in learning and memory characteristics between the two genera, suggest that the way in which the component circuitry functions is likely to be different; a not too surprising conclusion given the substantial evolutionary distance between them (>20 million years). The present findings afford an opportunity for uncovering linkages between evolutionarily significant alterations in hippocampal circuitry in relation to genera-specific information storage requirements.

Analysis of Variance↗
PubMed2006

Trichostrongylina (Nematoda) parasitic in Phyllotis sp. (Rodentia: Sigmodontinae) from Argentina, with description of three new species.

The Trichostrongylina parasitic in the leaf-eared mouse Phyllotis sp. (Sigmodontinae) from the Province of Catamarca, Argentina are studied. Three new species of Stilestrongylus Freitas, Lent and Almeida, 1937 (Heligmosomoidea: Heligmonellidae: Nippostrongylinae) are described. Stilestrongylus andalgala n. sp. is distinguished from the most closely related species S. moreli Diaw, 1976 parasitic in Auliscomys boliviensis from Bolivia, by the absence of a common trunk of right rays 2 and 3, by left ray 4 shorter than ray 5, and by the shape of the female tail, without a mucron. Stilestrongylus catamarca n. sp. is distinguished from all the other species in the genus by hypertrophied rays 2, larger than rays 3, and from the closely related species Stilestrongylus barusi Durette-Desset, 1971, parasitic in Sigmodontomys alfari from Colombia, by right ray 4 longer than ray 5 and left ray 4 shorter than ray 5, by a larger spicule length/body length ratio (22.6% vs. 7.2%), and by the presence of a mucron on the female tail. Stilestrongylus gracielae n. sp. most closely resembles Stilestrongylus azarai Durette-Desset and Sutton, 1985, parasitic in Akodon azarae and in Graomys griseoflavus, and Stilestrongylus franciscanus Digiani and Durette-Desset, 2003, also parasitic in G. griseoflavus, both from Argentina. These latter differ from the new species by the right lobe of the caudal bursa: in S. azarai rays 4, 5 and 6 arise at same level from their common trunk and in S. franciscanus right rays 4 and 5 diverge at their distal extremity. Lamanema chavezi Becklund, 1963 (Molineoidea: Molineinae), a parasite of South American camelids, is reported in rodents for the second time.

Animals↗
PubMed2005

Do dispersing non-reproductive female Damaraland mole-rats, Cryptomys damarensis (Rodentia: Bathyergidae) exhibit spontaneous or induced ovulation?

The Damaraland mole-rat is a eusocial, subterranean rodent that exhibits a seasonal breeding. Non-reproductive females show physiological suppression of reproduction whilst in the confines of the natal colony. This study set out to investigate whether dispersing female Damaraland mole-rats exhibit induced or spontaneous ovulation. Fifteen non-reproductive females were removed from their natal colonies and housed individually for a period of 6 weeks. During this period urine was collected from all animals every second day. After this initial period the animals were divided into 3 groups. Females were subjected to 1 of 3 trials: a control group housed separately without a male, allowed non-physical contact, or placed in direct physical contact with vasectomized males. Urine was collected for a further 5 weeks, and urinary progesterone profiles established. All three groups showed a significant difference in urinary progesterone concentrations between the two treatment periods indicating initiation of follicular development in all animals following removal from the colony. Histological results further revealed that at least one animal in the control group and five of the six animals in the vasectomized group had corpora lutea present in the ovaries showing that ovulation has taken place. All groups had similar numbers of Graafian follicles, indicating that all females were likely to ovulate in the near future. This finding suggests that females are capable of spontaneous ovulation, but the act of coitus may advance the onset of ovulation in this arid dwelling mole-rat.

Adaptation, Physiological↗
PubMed2005

Cataleptic activity of the denatured venom of the social wasp Agelaia vicina (Hymenoptera, Vespidae) in Rattus norvegicus (Rodentia, Muridae).

Catalepsy is a state of immobility, commonly experienced by patients with chronic use of many antiparkisonism and neuroleptic drugs. Recently, catatonia has been considered as an evolutionary-based fear response. The cataleptogenic effects of the low molecular weight compounds from the venom of the social wasp A. vicina (AdAv) were reported in rodents. Intracerebroventricular injections of AdAv in highest dose reduced the locomotor activity of Wistar rats in the open field and induced ataxia and catalepsy within 10 min. This effect could be observed up to 30 min after injections. Lower doses of denatured venom injected in brain ventricles also reduced the locomotor activity of the rats but did not induce catalepsy. The cataleptic effects of the intracerebrally administered AdAv were antagonized by the peripheral (intraperitoneal) pretreatment with theophylline and ketamine. Moreover, the central effects of the AdAv were compared to those elicited by the neuroleptic drug haloperidol (intraperitoneally administered), whose cataleptic effects were also antagonized by theophylline and ketamine. However, the association of haloperidol and denatured venom was reverted by theophylline but not by ketamine. These findings suggest that A. vicina venom may affect neural substrates involved with catalepsy in the central nervous system.

Analysis of Variance↗