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PubMed1983

Receptive-field properties in reptilian optic tectum: some comparisons with mammals.

The receptive-field properties of single cells in the optic tectum of Iguana iguana were studied using the same procedures as have been used in this laboratory in studying its mammalian homologue, the superior colliculus. Surprisingly, despite some species-specific characteristics, the range of physiological properties of tectal and superior collicular cells appeared to be strikingly similar. This observation is not consistent with the notion that functional differences between these structures evolved as a consequence of the tremendous elaboration of mammalian neocortex and its involvement in sensory processes. The internal organization of visual tectal receptive fields was observed to be very much like that described in mammals. This included a similar distribution of on-off areas, the presence of both spatial summation and spatial inhibition within the excitatory receptive-field borders, suppressive areas just beyond these borders, and a marked tendency for habituation. In addition, many cells showed distinct directional preferences that were strongly influenced by the velocity of movement through the receptive field. Furthermore, the receptive fields of bimodal and trimodal cells showed topographic correspondences as in mammals, although the sizes of the fields were often large, thereby emphasizing the lack of an exact register between modalities. In contrast to the findings in mammals, however, a preference for stationary over moving stimuli was observed in most neurons, and specializations in iguana tectal cells representing the fovea were noted that have not been described in other species. These foveal specializations include a distinct preference for stationary over moving stimuli, the absence of directional selectivity, and the presence of a majority of cells responding at light onset only. It is suggested that the similarities in the organization and response properties of cells of the optic tectum and superior colliculus reflect the retention of ancestral characteristics through various levels of vertebrate evolution. Furthermore, the subtle species differences in the properties of these cells appear to reflect adaptations to specific ecological pressures rather than general evolutionary trends.

Animals↗

PubMed2004

B chromosomes in populations of mammals.

B chromosomes (Bs) have been found in 55 out of 4629 living species of mammals. The summarized data show great variability in types of mammalian Bs, including differences in size, shape and molecular composition. This variability extends to the origin, mode of transmission and population dynamics. In general, B chromosomes in mammals do not differ from Bs found in other animal or plant species, but some peculiarities do exist. Most species in which Bs are found are widespread. Some data support the view that Bs may contribute to the successful expansion of some of these species, but it is possible that Bs are just more easily scored in them due to their frequent occurrence. Most of these species are also characterized by cycling fluctuations of abundance and characteristic social organization that produce conditions favorable for Bs to spread. All areas of research on Bs in mammals suffer from lack of data, emphasizing the necessity for intensified research on the molecular structure and ways of maintenance of Bs in populations.

Animals↗

PubMed2004

The evolution of drug-activated nuclear receptors: one ancestral gene diverged into two xenosensor genes in mammals.

BACKGROUND: Drugs and other xenobiotics alter gene expression of cytochromes P450 (CYP) by activating the pregnane X receptor (PXR) and constitutive androstane receptor (CAR) in mammals. In non-mammalian species, only one xenosensor gene has been found. Using chicken as a model organism, the aim of our study was to elucidate whether non-mammalian species only have one or two xenosensors like mammals. RESULTS: To explore the evolutionary aspect of this divergence, we tried to identify additional xenobiotic sensing nuclear receptors in chicken using various experimental approaches. However, none of those revealed novel candidates. Ablation of chicken xenobiotic receptor (CXR) function by RNAi or dominant-negative alleles drastically reduced drug-induction in a chicken hepatoma cell line. Subsequently, we functionally and structurally characterized CXR and compared our results to PXR and CAR. Despite the high similarity in their amino acid sequence, PXR and CAR have very distinct modes of activation. Some aspects of CXR function, e.g. direct ligand activation and high promiscuity are very reminiscent of PXR. On the other hand, cellular localization studies revealed common characteristics of CXR and CAR in terms of cytoplasmic-nuclear distribution. Finally, CXR has unique properties regarding its regulation in comparison to PXR and CAR. CONCLUSION: Our finding thus strongly suggest that CXR constitutes an ancestral gene which has evolved into PXR and CAR in mammals. Future studies should elucidate the reason for this divergence in mammalian versus non-mammalian species.

Journal Article↗

PubMed2006

In silico identification of opossum cytokine genes suggests the complexity of the marsupial immune system rivals that of eutherian mammals.

BACKGROUND: Cytokines are small proteins that regulate immunity in vertebrate species. Marsupial and eutherian mammals last shared a common ancestor more than 180 million years ago, so it is not surprising that attempts to isolate many key marsupial cytokines using traditional laboratory techniques have been unsuccessful. This paucity of molecular data has led some authors to suggest that the marsupial immune system is 'primitive' and not on par with the sophisticated immune system of eutherian (placental) mammals. RESULTS: The sequencing of the first marsupial genome has allowed us to identify highly divergent immune genes. We used gene prediction methods that incorporate the identification of gene location using BLAST, SYNTENY + BLAST and HMMER to identify 23 key marsupial immune genes, including IFN-gamma, IL-2, IL-4, IL-6, IL-12 and IL-13, in the genome of the grey short-tailed opossum (Monodelphis domestica). Many of these genes were not predicted in the publicly available automated annotations. CONCLUSION: The power of this approach was demonstrated by the identification of orthologous cytokines between marsupials and eutherians that share only 30% identity at the amino acid level. Furthermore, the presence of key immunological genes suggests that marsupials do indeed possess a sophisticated immune system, whose function may parallel that of eutherian mammals.

Journal Article↗

PubMed2006

What explains the trot-gallop transition in small mammals?

The transition from trot to gallop in quadruped mammals has been widely hypothesized to be a strategy to minimize the energetic costs of running. This view, however, has been challenged by some experimental evidence suggesting instead that this transition might be triggered by mechanical cues, and would occur when musculoskeletal stresses reach a certain critical value. All previous experiments to test those hypotheses have used relatively large species and their results, therefore, may not be applicable to small mammals. In this study we evaluated the effect of carrying loads on the locomotor energetics and gait transitions of the rodent Octodon degus running on a treadmill. Metabolic rate and cost of transport increased about 30% with a 20% increment in body mass. This increment was higher than expectations based on other mammals, where energy consumption increases in proportion to the added mass, but similar to the response of humans to loads. No abrupt change of energy consumption between gaits was observed and therefore no evidence was found to support the energetic hypothesis. The trot-gallop transition speed did not vary when subjects were experimentally loaded, suggesting that the forces applied to the musculoskeletal system do not trigger gait transition.

Animals↗

PubMed1999

Energetics of locomotion by the Australian water rat (Hydromys chrysogaster): a comparison of swimming and running in a semi-aquatic mammal.

Semi-aquatic mammals occupy a precarious evolutionary position, having to function in both aquatic and terrestrial environments without specializing in locomotor performance in either environment. To examine possible energetic constraints on semi-aquatic mammals, we compared rates of oxygen consumption for the Australian water rat (Hydromys chrysogaster) using different locomotor behaviors: swimming and running. Aquatic locomotion was investigated as animals swam in a water flume at several speeds, whereas water rats were run on a treadmill to measure metabolic effort during terrestrial locomotion. Water rats swam at the surface using alternate pelvic paddling and locomoted on the treadmill using gaits that included walk, trot and half-bound. Water rats were able to run at twice their maximum swimming velocity. Swimming metabolic rate increased with velocity in a pattern similar to the 'humps' and 'hollows' for wave drag experienced by bodies moving at the water surface. Metabolic rate increased linearly during running. Over equivalent velocities, the metabolic rate for running was 13-40 % greater than for swimming. The minimum cost of transport for swimming (2.61 J N-1 m-1) was equivalent to values for other semi-aquatic mammals. The lowest cost for running (2.08 J N-1 m-1) was 20 % lower than for swimming. When compared with specialists at the extremes of the terrestrial-aquatic continuum, the energetic costs of locomoting either in water or on land were high for the semi-aquatic Hydromys chrysogaster. However, the relative costs for H. chrysogaster were lower than when an aquatic specialist attempts to move on land or a terrestrial specialist attempts to swim.

Animals↗

PubMed2001

Similitude in the cardiovascular system of mammals.

Scaling laws governing the cardiovascular system of mammals are discussed in the present review in a manner emphasizing their experimental basis. Specific attention is given to the well-known experimental laws requiring the rate of oxygen consumption and the heart rate of mammals to vary with body mass raised to the powers 3/4 and -1/4, respectively. This review involves reconsideration and further discussion of the previous work of the writer in which these and other scaling relationships were developed from fundamental considerations. The predicted scaling laws remain unchanged from the earlier work, but alternative assumptions leading to the laws are used so as to provide additional insight. The scaling laws are shown to have their origin in the basic design of the cardiovascular system and in the basic processes involved in its working. Modification of the design assumptions of the system to account for known differences in the relative heart masses of mammals and birds is shown to lead to the scaling laws for rate of oxygen consumption and heart rate of birds.

Animals↗

PubMed2005

Small mammals of Chapada dos Veadeiros National Park (Cerrado of Central Brazil): ecologic, karyologic, and taxonomic considerations.

This work is based on a survey of small mammals carried out in the Chapada dos Veadeiros National Park, a natural reserve located in the mountains of the Planalto Central Goiano in the Cerrado of Central Brazil. The 227 specimens collected represented six marsupial and 13 rodent species. Taxonomic, karyologic, and ecologic considerations are present and discussed in the present work. Our data reflected the faunal heterogeneity with respect to both elevation and vegetation because only eight of the 19 species were collected at both high and low elevations. The composition of the small mammal fauna of the park is influenced by predominance of forest formations at low elevations and cerrado with rupestrian areas at high elevations. Presence of endemic species and one undescribed demonstrated that the cerrado has an endemic fauna and a little known diversity of small mammals.

Altitude↗

PubMed1993

Vitamin D hydroxylases and their regulation in a naturally vitamin D-deficient subterranean mammal, the naked mole rat (Heterocephalus glaber).

The vitamin D hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) is generated by a series of hydroxylation steps in the liver and kidneys. We investigated whether naturally vitamin D-deficient subterranean mammals (naked mole rats, Heterocephalus glaber) employ the same enzymatic pathways, and whether these are regulated in a similar manner to that established for other mammals. Vitamin D3-25-hydroxylase in the liver and both 25-hydroxyvitamin D3-1-hydroxylase and 25-hydroxyvitamin D3-24 hydroxylase (1-OHase and 24-OHase) in the kidney were detectable in mole rats. As expected for vitamin D-deficient mammals, the 1-OHase activity predominated over the 24-OHase. After mole rats received a supraphysiological supplement of vitamin D3, 1-OHase activity was suppressed and 24-OHase activity was enhanced. Irrespective of vitamin D status, forskolin (a protein kinase A activator) and dibutyryl cyclic AMP did not alter the activity of either 1-OHase or 24-OHase. These findings suggest that the response of renal hydroxylases to parathyroid hormone was blunted. Phorbol esters, 12-O-tetradecanoylphorbol 13-acetate (TPA) and 1-oleoyl-2-acetylglycerol (OAG) (protein kinase C activators), suppressed 1-OHase activity. 24-OHase activity was induced by TPA but not by OAG. These effects were similar to those illicited by vitamin D3 supplementation but were additive in that they increased the responses shown in vitamin D-replete mole rats. These data confirm that naturally vitamin D-deficient mole rats can convert vitamin D3 to the hormone, 1,25(OH)2D3.(ABSTRACT TRUNCATED AT 250 WORDS)

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗

PubMed2005

Hepatic porphyria induced by the herbicide tralkoxydim in small mammals is species-specific.

Tralkoxydim is the active ingredient in a postemergent herbicide used in cereal crops. During preregistration trials, tralkoxydim was observed to cause hepatic porphyria and cholestasis in laboratory mice. Porphyria was not seen in similarly exposed rats or hamsters, but data were not collected regarding the susceptibility of any wild small mammal species to the tralkoxydim-induced porphyria. To address this data gap, we exposed small mammals to tralkoxydim, to 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC; a known porphyrinogenic chemical), or to sunflower oil alone. We studied small mammal species that might be exposed following agricultural applications of the herbicide, including the white-footed mouse (Peromyscus leucopus), the deer mouse (P. maniculatus), and the meadow vole (Microtus pennsylvanicus). Because of their known susceptibility to both tralkoxydim- and DDC-induced porphyria, commercially supplied Mus musculus (CD-1 Swiss mice) were exposed as positive-control animals. We also exposed offspring of wild-caught M. musculus to compare their responses to those of the commercially supplied animals. Potential hepatotoxicity was determined by assessing the accumulation of liver protoporphyrin. Of the species tested, only M. musculus was susceptible to the porphyrinogenic action of tralkoxydim, and no significant accumulation of protoporphyrin was observed in any of the other species exposed to the herbicide.

Animals↗

PubMed1983

Spirochetes in Ixodes dammini and mammals from Connecticut.

Spirochetes were observed in the midguts of 35% of 147 motile Ixodes dammini from three locations in Lyme and East Haddam, Connecticut. Positive ticks were removed from eastern chipmunks (Tamias striatus), raccoons (Procyon lotor), white-footed mice (Peromyscus leucopus), and a red squirrel (Tamiasciurus hudsonicus). Spirochetes were isolated in fortified Kelly's medium from nine questing or partially engorged I. dammini adults and nymphs and from the bloods of a raccoon and a white-footed mouse. Connecticut isolates from ticks and mammals were serologically indistinguishable from the original Shelter Island, New York strain when cross-tested by immunofluorescence against their mouse antisera. Sera from eight patients diagnosed as having Lyme disease contained antibodies to spirochetes isolated from ticks and mammals. Our finding of serologically and morphologically indistinguishable spirochetes in a raccoon, white-footed mouse and ticks suggests that closely related serotypes are present in wild mammals commonly parasitized by I. dammini, and further supports the claim that a spirochete is involved in the etiology of Lyme disease.

Animals↗

PubMed2001

Serologic evidence of influenza A infection in marine mammals of arctic Canada.

A serologic survey of influenza A antibodies was undertaken on 1,611 blood samples from five species of marine mammals collected from Arctic Canada from 1984-98. Sampling was done in 24 locations throughout the Canadian Arctic encompassing Sachs Harbor (72 degrees N, 125 degrees W), Northwest Territories in the west to Loks Land (63 degrees N, 64 degrees W), Nunavut in the east, to Eureka (80 degrees N, 86 degrees W), Nunavut in the north to Sanikiluaq (56 degrees N, 79 degrees W), Nunavut in the south. A competitive ELISA using a monoclonal antibody (Mab) against influenza A nucleoprotein (NP) was used. Five of 418 (1.2%) belugas (Delphinapterus leucas) and 23 of 903 (2.5%) ringed seals (Phoca hispida) were serologically positive. None of the 210 walruses (Odobenus rosmarus rosmarus), 76 narwhals (Monodon monoceros) and four bowhead whales (Balaena mysticetus) had detectable antibodies to influenza A. Positive belugas were identified from communities on southeast Baffin Island while positive ringed seals came from communities in the eastern, western and high Arctic. Virus isolation attempts on lung tissue from a seropositive beluga were unsuccessful. We believe that influenza A infection in marine mammals is sporadic, the infection is probably self-limiting, and it may not be able to be maintained in these animals. Although the predominant hemagglutinin (H) type was not determined and therefore the pathogenicity of the strains to humans is unknown, the hunting and consumption of marine mammals by the Inuit, may put them at risk for influenza A infection.

Animals↗

PubMed1998

Twenty years of trace metal analyses of marine mammals in Alaska: evaluation and summation.

The compilation of existing data on contaminants in the marine food chain is essential in addressing concerns regarding the magnitude of potential human exposures and in the evaluation of subsistence food safety. This paper presents a summary of studies on trace metals in tissues of Alaska marine mammals from the 1970s to the present, along with derived mean tissue trace metal concentrations. The derived mean can serve as a norm against which future monitoring results may be compared, and may be used to estimate human exposure to trace metals through the consumption of marine mammals. Additionally, the variation among studies in the reported mean tissue concentrations has been described through a derived standard deviation. Sufficient analytical and methodological details were available to derive means and standard deviations for tissues in bearded seal, bowhead whale, beluga whale, fur seal, harbor seal, Pacific walrus, and ringed seal. A high concordance between trace metal values reported in tissues (i.e., liver, kidney, muscle) was observed despite significant differences in reported sampling and analytical methodologies. Consistent with other reviews of trace metal concentrations in marine species, the standard deviation of tissue metal concentrations was generally < or = 100% of the reported mean. Significant gaps in available information remain, particularly for muscle tissues and for methylmercury, despite the considerable efforts to monitor marine mammal species in Alaska.

Alaska↗

PubMed1999

[Analysis of correlation between some parameters depending on cell proliferation and life span of "stationary phase aging" cultures and maximum life span of mammals].

Earlier we developed a "stationary phase aging" model and introduced a definition of life span of "stationary phase aging" cell cultures. In this model the cells grow after seeding in flasks without subcultivation and medium change. They reach cell saturation density, stop dividing, gradually degrade ("stationary phase aging") and perish. By the term "culture life span" we designate the time from cell seeding until culture death. We designate the culture as dead when the number of living cells is less than 10 per cent of their number at saturation density of cell culture. The life span of transformed Chinese hamster cells was found to be proportional to the duration of their growth from cell seeding up to saturation density, as well as to the number of cell culture doublings and to be inversely proportional to the velocity of cell culture doubling for the same growth period. Maximum life span of mammals is known to be proportional to pregnancy duration and to the age at puberty. We found that maximal life span of mammals was proportional to the number of cell population doublings and inversely proportional to the velocity of cell population doubling during embryonal period or for the time from zygote to growth termination. The dependences for cell cultures and for mammals are analogous to each other.

Aging↗

PubMedDate not supplied

[Parasite-host relationship of flies and small mammals in the Omsk region].

A generalized analysis of data on a flea fauna, range of their hosts in various natural zones, and features of parasite-host relationships between fleas and small mammals obtained in the Omsk province during long term researches in 1963-1997 is given. 35 flea species are recorded. The most mass species both on animals and in their nest is Ctenophthalmus assimilis; the numerous species are Amalareus penicilliger, Megabothros rectangulatus, M. walkeri, Peromyscopsylla silvatica, Ctenophthalmus unciatus, Palaropsylla sorecis, Doratopsilla birulai, Neopsylla pleskei, Hystrichopsylla talpae; the usual species--Ceratopsyllus garei, M. calcarifer, M. turbidus, Frontopsylla elata, Amphipsylla sibirica, A. kuznetzowi, Peromyscopsylla dasycnema, Radinopsylla integella, Catalagia dacenkoi. Other species are less numerous or infrequent. The general infection rate of the flea populations on rodents and insectivores makes 30.4%. For certain species it reaches 65.1% (on red-backed vole Cletrionomys rutilus), for regular groups--86.9% (on shrews of the genus Sorex). The greatest variety of the flea populations is observed on Microtus arvalis, the least one--on Sorex caecutiens and S. daphaenodon. In the nests of small mammals the variety of fleas is significantly lower. Based on the index of flea species relative "loyalty" to small mammals and their nest we have recognized 6 groups of fleas.

Animals↗

PubMed1975

Biochemical studies on mammalian cardiac muscles: I. distribution pattern of myoglobin in different chambers of the heart of some mammals.

The myoglobin content of atria and ventricles of hearts of some mammals has been studied. The hearts of various mammals exhibit variations in their myoglobin concentration in contrast to earlier reports on various mammals. A definite gradation in the distribution pattern of myoglobin in mammalian cardiac muscles with Left atrium less than Right atrium less than Right ventricle less than Left ventricle, is discernible. There seems to be a close correlation of ventricular myocardium and their functional requirements.

Animals↗

PubMed2001

Differential Gene Expression Following Noise Trauma in Birds and Mammals.

Acoustic overstimulation has very different outcomes in birds and mammals. When noise exposure kills hair cells in birds, these cells can regenerate and hearing will recover. In mammals, however, the hair cell loss, and resulting hearing loss, is permanent. Changes in gene expression form the basis for important biological processes, including repair, regeneration, and plasticity. We are therefore using a battery of molecular approaches to identify and compare changes in gene expression following noise trauma in birds and mammals. Both differential display and subtractive hybridisation were used to identify genes whose expression increased in the chick basilar papilla immediately following exposure to an octave band noise (118 dB, centre frequency 1.5 kHz) for 4-6 hr. Among those upregulated genes were two involved in actin signalling: the CDC42 gene encoding a Rho GTPase, and WDR1, which encodes a protein involved in actin dynamics. A third gene, UBE3B, encodes an E3 ubiquitin ligase involved in protein turnover. A fourth gene encodes a cystein-rich secreted protein that may interact with calcium channels. To examine the mammalian response, gene microarrays on nylon membranes (Clontech Atlas Gene Arrays) were used to examine global changes in gene expression 30 minutes after TTS (110 dB broadband noise 50% duty cycle) or PTS (125 dB, 100% duty cycle) noise overstimulation (each for 90 minutes) in the rat cochlea. Several genes, including classic immediate early response genes such as c-fos, EGR1/NGFI-A, and NGFI-B, were upregulated at this early time point following the PTS exposure, but were not upregulated following the TTS exposure.

Journal Article↗

PubMed2003

Exposure of small mammals, in particular the wood mouse Apodemus sylvaticus, to pesticide seed treatments.

Field exposure of small mammals to fungicide-treated wheat seed was investigated over three weeks following drilling on fields near York, United Kingdom. Seed consumption by small mammals trapped on and immediately adjacent to the drilled fields was quantified by measuring the amount of seed in the stomach. In addition, exposure to one seed-treatment, fluquinconazole, was quantified by measuring residues of the fungicide in the stomach, liver, and intestine. The wood mouse, Apodemus sylvaticus, was the dominant species caught on the fields and the only species found to have consumed measurable quantities of seed. Voles, Microtus agrestis and Clethrionomys glareolus, were caught in small numbers, almost exclusively in the field hedge, and showed no evidence of having consumed seed. Stomach-contents analysis revealed that more than 80% of animals trapped in the hedge adjacent to the field had consumed no wheat seed, whereas 98% had consumed less than 10% (by stomach volume). Ninety percent of animals trapped on the field had consumed seed, although 90% of these animals had less than 20% seed in the stomach. Residues of the fungicide in the stomach, intestine, and liver were lower than would be expected for the amount of seed consumed, possibly because of dehusking of the seeds by mice. The relevance of these findings when assessing exposure (and risk) posed by seed treatments to wild mammals is discussed.

Animals↗