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PubMed1987

Fibrinogen levels in mammals suffering from bacterial infections.

In a retrospective survey of fibrinogen levels and neutrophil counts in 388 blood samples from mammals suffering from bacterial infection, the combined results of the two tests provided positive confirmation of infection in a greater percentage of samples than did the results of either test alone. In Perissodactyla, Artiodactyla and Proboscidea, the fibrinogen level was abnormal more often than the neutrophil count. It was concluded that a fibrinogen estimation is a valuable addition to routine haematological screening procedures in mammals.

Animals↗

PubMed2007

Hypoxia tolerance in mammals and birds: from the wilderness to the clinic.

All mammals and birds must develop effective strategies to cope with reduced oxygen availability. These animals achieve tolerance to acute and chronic hypoxia by (a) reductions in metabolism, (b) the prevention of cellular injury, and (c) the maintenance of functional integrity. Failure to meet any one of these tasks is detrimental. Birds and mammals accomplish this triple task through a highly coordinated, systems-level reconfiguration involving the partial shutdown of some but not all organs. This reconfiguration is achieved through a similarly complex reconfiguration at the cellular and molecular levels. Reconfiguration at these various levels depends on numerous factors that include the environment, the degree of hypoxic stress, and developmental, behavioral, and ecological conditions. Although common molecular strategies exist, the cellular and molecular changes in any given cell are very diverse. Some cells remain metabolically active, whereas others shut down or rely on anaerobic metabolism. This cellular shutdown is temporarily regulated, and during hypoxic exposure, active cellular networks must continue to control vital functions. The challenge for future research is to explore the cellular mechanisms and conditions that transform an organ or a cellular network into a hypometabolic state, without loss of functional integrity. Much can be learned in this respect from nature: Diving, burrowing, and hibernating animals living in diverse environments are masters of adaptation and can teach us how to deal with hypoxia, an issue of great clinical significance.

Animals↗

PubMed1990

Body size, medullary thickness, and urine concentrating ability in mammals.

B. H. Blake (Comp. Biochem. Physiol. A Comp. Physiol. 58: 413-419, 1977.) and W. A. Calder and E. J. Braun (Am. J. Physiol. 244 (Regulatory Integrative Comp. Physiol. 13): R601-R606, 1983.) have predicted that urine concentrating ability of mammals should decline with increasing body mass (M, in kg) as M-0.08. Edwards (29), on the other hand, speculated that concentrating ability should be independent of body mass. Using information compiled from the literature for 245 species of mammals, I examined the scaling of urine concentrating ability with body mass. Maximum urine concentration (Uosm, in mosmol/kgH2O) declined exponentially with body mass as Uosm = 2,564 M-0.097, and generally only the smallest species (less than 400 g) could produce urine with an osmolality greater than 4,000 mosmol/kgH2O. Medullary thickness (MT, in mm) and, therefore, the length of the loop of Henle, increased with body mass as MT = 8.147 M0.129. The thickness of the medulla relative to the size of the kidney (RMT), however, declined with body size (RMT = 5.408 M-0.108). The relative thickness of the medulla accounted for only 59% of the variability among species in concentrating ability, indicating that there are other morphological or physiological factors that significantly influence urine concentrating ability.

Animals↗

PubMed1992

Scaling of bodily proportions in adult terrestrial mammals.

To model body shape, a data base was constructed for body, forelimb, and hindlimb length, surface area, and girth, each as a function of body weight, in a diversity of mammals. These data were submitted to linear least-squares regression analysis. In addition, data on the partitioning of weight and surface area among the body segments (head-trunk, forelimbs, and hindlimbs) were collected. These data imply a relatively constant partitioning of body weight and surface area among the body segments. The regression parameters and the body segment data were used to build and test a model of bodily proportions. The model consists of three classes of cylinders, each specified by a length and a diameter, representing the three classes of body segments. The parameters of the model were constrained to enforce geometric similarity (constant shape). The model was found to agree reasonably well with an independent subset of the data. It is concluded that adult land mammals do exhibit geometric similarity over a substantial weight range.

Animals↗

PubMed1995

August Krogh Lecture. The renal concentrating mechanism in insects and mammals: a new hypothesis involving hydrostatic pressures.

Water moves from compartments of higher to compartments of lower water potential. Osmotically active solutes and negative hydrostatic pressure both lower water potential by stretching the hydrogen bonds between water molecules (Hammel-Scholander hypothesis). In trees the negative hydrostatic pressure in the sap is balanced by the osmotic pressure of the leaves. In response to differences in water potential, water flows across biological membranes through water-filled pores. Protein molecules, aquaporins, forming hourglass-shaped pores have been identified, cloned, and located in plasma membranes in mammalian as well as other tissues. Water molecules flow single file through aquaporins. Insects concentrate the urine in the rectum. Mammals concentrate the urine in the collecting ducts in the inner medulla. In both, a compartment with a high osmotic concentration is created through ion transport. Both have a muscular coat surrounding the tissue, which shows peristaltic contractions. In insects it is the muscular layer around the rectum; in mammals it is the renal pelvic wall that surrounds the papilla. Mechanisms are proposed whereby these peristaltic contractions, through the creation of positive and negative hydrostatic pressures in the tissues, can lead to hyperosmotic excreta.

Animals↗

PubMed1997

Cellular energy utilization and molecular origin of standard metabolic rate in mammals.

The molecular origin of standard metabolic rate and thermogenesis in mammals is examined. It is pointed out that there are important differences and distinctions between the cellular reactions that 1) couple to oxygen consumption, 2) uncouple metabolism, 3) hydrolyze ATP, 4) control metabolic rate, 5) regulate metabolic rate, 6) produce heat, and 7) dissipate free energy. The quantitative contribution of different cellular reactions to these processes is assessed in mammals. We estimate that approximately 90% of mammalian oxygen consumption in the standard state is mitochondrial, of which approximately 20% is uncoupled by the mitochondrial proton leak and 80% is coupled to ATP synthesis. The consequences of the significant contribution of proton leak to standard metabolic rate for tissue P-to-O ratio, heat production, and free energy dissipation by oxidative phosphorylation and the estimated contribution of ATP-consuming processes to tissue oxygen consumption rate are discussed. Of the 80% of oxygen consumption coupled to ATP synthesis, approximately 25-30% is used by protein synthesis, 19-28% by the Na(+)-K(+)-ATPase, 4-8% by the Ca2(+)-ATPase, 2-8% by the actinomyosin ATPase, 7-10% by gluconeogenesis, and 3% by ureagenesis, with mRNA synthesis and substrate cycling also making significant contributions. The main cellular reactions that uncouple standard energy metabolism are the Na+, K+, H+, and Ca2+ channels and leaks of cell membranes and protein breakdown. Cellular metabolic rate is controlled by a number of processes including metabolic demand and substrate supply. The differences in standard metabolic rate between animals of different body mass and phylogeny appear to be due to proportionate changes in the whole of energy metabolism. Heat is produced by some reactions and taken up by others but is mainly produced by the reactions of mitochondrial respiration, oxidative phosphorylation, and proton leak on the inner mitochondrial membrane. Free energy is dissipated by all cellular reactions, but the major contributions are by the ATP-utilizing reactions and the uncoupling reactions. The functions and evolutionary significance of standard metabolic rate are discussed.

Adenosine Triphosphate↗

PubMed1997

Physiology of diving of birds and mammals.

This review concentrates on the physiological responses, and their control, in freely diving birds and mammals that enable them to remain submerged and sometimes quite active for extended periods of time. Recent developments in technology have provided much detailed information on the behavior of these fascinating animals. Unfortunately, the advances in technology have been insufficient to enable physiologists to obtain anything like the same level of detail on the metabolic rate and physiological adjustments that occur during natural diving. This has led to much speculation and calculations based on many assumptions concerning usable oxygen stores and metabolic rate during diving, in an attempt to explain the observed behavior. Despite their shortcomings, these calculations have provided useful insights into the degree of adaptations of various species of aquatic birds and mammals. Many of them, e.g., ducks, smaller penguins, fur seals, and Weddell seals, seem able to metabolize aerobically, when diving, at approximately the same (if not greater) rate as they do at the surface. Their enhanced oxygen stores are able to support aerobic metabolism, at what would not be considered unusually low levels, for the duration of the dives, although there are probably circulatory readjustments to ensure that the oxygen stores are managed judiciously. For other species, such as the larger penguins, South Georgian shag, and female elephant seals, there is a general consensus that they must either be reducing their aerobic metabolic rate when diving, possibly by way of regional hypothermia, and/or producing ATP, at least partly, by anaerobiosis and metabolizing the lactic acid when at the surface (although this is hardly likely in the case of the female elephant seals). Circulation is the proximate regulator of metabolism during aerobic diving, and heart rate is the best single indicator of circulatory adjustment. During voluntary dives, heart rates range from extreme bradycardia to well above resting, reflecting metabolic performance. Efferent cardiac control is largely parasympathetic. Reflex cardiorespiratory responses are modulated by conditioning and habituation, but reflexes predominate during extended dives and during recovery, when gas exchange is maximized.

Adenosine Triphosphate↗

PubMed2000

Arealization of the neocortex in mammals: genetic and epigenetic contributions to the phenotype.

The neocortex is composed of areas that are functionally, anatomically and histochemically distinct. In comparison to most other mammals, humans have an expanded neocortex, with a pronounced increase in the number of cortical areas. This expansion underlies many complex behaviors associated with human capabilities including perception, cognition, language and volitional motor responses. In the following review we consider data from comparative studies as well as from developmental studies to gain insight into the mechanisms involved in arealization, and discuss how these mechanisms may have been modified in different lineages over time to produce the remarkable degree of organizational variability observed in the neocortex of mammals. Because any phenotype is a result of the complex interactions between genotypic influences and environmental factors, we also consider environmental, or epigenetic, contributions to the organization of the neocortex.

Animals↗

PubMed2002

Sex chromosomes and sex determination in weird mammals.

Weird mammals are of two types. Highly divergent mammals, such as the marsupials and monotremes, have informed us of the evolutionary history of the Y chromosome and sex-determining gene, and the recently specialized rodents can help us predict its future. The Y chromosome has had a short but eventful history, and is already heading briskly for oblivion. It originated as a homologous partner of the X when it acquired a sex-determining gene (not necessarily SRY). Most of the genes on the Y, even those with a male-specific function, evolved from genes now on the X. At the mercy of a high rate of variability and the forces of drift and selection, the Y has lost genes at a rate of 3-6 genes/million years, sparing those that acquired critical male-specific functions. Even these genes have disappeared from one mammalian lineage or another as their functions were usurped by genes elsewhere in the genome. The mammalian testis-determining gene, SRY, is a typical Y-borne gene. It arose by truncation of a gene (SOX3) on the X that is expressed in brain development, and it may work by interacting with (inhibiting?) related genes, including SOX9. Variant sex-determining systems in rodents show that the action of SRY can change, as it evidently has in the mouse, and SRY can be inactivated, as in akodont rodents, or even completely superseded, as in mole voles.

Animals↗

PubMed2002

Convergences in the modular and areal organization of the forebrain of mammals: implications for the reconstruction of forebrain evolution.

Early efforts to reconstruct the course of the evolution of the human brain relied on comparing the brains of a few related mammals with brains at successively higher levels of complexity. This Clark or ladder of levels approach is now seen as having limited usefulness in that species are not easily assigned to levels, and extant mammals are now recognized as mosaics of primitive and derived features. In addition, direction of change does not necessarily proceed from simple to complex, small to large, or diffuse to differentiated. A modern cladistic approach reconstructs the brains of ancestors by identifying brain characters within and across phylogenetic groups (clades), and uses parsimony or likelihood to infer direction of change and distinguish ancestral features from independently evolved convergences. Unfortunately, an idealized cladistic approach is often difficult to realize because characters may be hard to identify and validate, key species may be unavailable for study, and broadly based comparative studies can be costly, poorly funded, and labor intensive. Thus, many investigators pursue a truncated approach that is superficially Clark-like but conceptually cladistic. A truncated approach that relies on the extensive study of a few species may compensate for weaknesses by including niche-matched species that offer the opportunity to estimate the likelihood of similar brain features evolving as convergent adaptations. Because inferences about the brains of the primate ancestor are often made from the brains of tree shrews, we compare the brains of squirrel-like tree shrews with the brains of diurnal squirrels, and suggest that many of the primate-like features of the visual system of tree shrews arose independently of those in primates.

Animals↗

PubMedDate not supplied

UV-Absorbing compounds in the aqueous humor from aquatic mammals and various non-mammalian vertebrates.

OBJECTIVE: To evaluate the absorbance of ultraviolet radiation (UVR) in the aqueous humor of various animal species in relation to the ambient radiation of their respective habitats, and to identify substances responsible for this absorbance. Representatives of all five classes (fish, amphibian, reptile, bird, and mammal) have been tested. METHODS: Absorbance was recorded using a spectrophotometer. The ascorbic and uric acid concentrations were determined by HPLC, and the amino acid profiles with an automatic analyzer. Screening for potential UV-absorbing substances was performed by HPLC and a total of 12 species were examined, 7 of them birds. RESULTS: UV-absorbing substances in the aqueous humor were proteins, tryptophan, tyrosine and ascorbic and uric acid. In addition, an unknown UV-absorbing component present in bird aqueous humor caused a high, red-shifted UV-absorbance spectrum, particularly in tentatively heavily exposed species such as goose when migrating at 10,000 m altitude. By comparison, the UV absorbance above the 288-nm wavelength was low in the aqueous humor of fish, frogs, aquatic mammals and two ground-living birds. The crocodile, whose aqueous humor contained significant amounts of both ascorbic and uric acid, revealed a concentration mechanism for ascorbic acid. CONCLUSIONS: The UV absorbance of aqueous humor varies considerably from one species to the next, and independent of class. It is noteworthy that the species being at highest risk for high-dose UV exposure, the migrating goose, showed the most red-shifted spectrum.

Absorption↗

PubMed2006

Genomic imprinting in plants and mammals: how life history constrains convergence.

In both flowering plants and mammals, DNA methylation is involved in silencing alleles of imprinted genes, but surprising differences in imprinting control are emerging between the two taxa which may be traced to differences in their life cycles. Imprinted gene expression in plants occurs in the endosperm, a separate fertilisation product which transmits nutrients to the embryo and does not contribute a genome to the next generation. Regulation of expression of the known imprinted genes in Arabidopsis involves a cascade of gene expression beginning in the gametophyte, a haploid life phase interposed between the meiotic products and the gametes, which evolved from free-living organisms that constitute the dominant life phase of lower plants. Although the gametophytes of flowering plants are highly reduced they still express large numbers of genes, perhaps reflecting their evolutionary legacy, and which may now be recruited for control of imprinting. Strikingly, the genes at the top of the expression cascade appear to be specifically activated by demethylation, rather than targeted for silencing. Unlike in mammals, there is no evidence for global resetting of methylation in plants, and although imprinting involves the activity of a maintenance methyltransferase, de novo methyltransferases do not appear to be required. Plants do not set aside a germline; instead the cells that undergo meiosis to produce gametophytes differentiate in the adult plant during flower development. Both the late differentiation of the lineage producing germ cells, and the extent of gene expression during the haploid phase, may be incompatible with global resetting of methylation. Resetting may be unnecessary in any case because the adult plant expresses imprinted loci either biallelically or not at all, suggesting there is no chromosomal memory of parent-of-origin in the lineage that produces the gametophytes. Thus several features of the plant life cycle may account for the different strategies used by plants and animals to regulate parent-specific gene expression.

Animals↗

PubMed1988

Size and shape of the cerebral cortex in mammals. II. The cortical volume.

The geometry of the brain and cerebral cortex in mammals has been studied from an evolutionary perspective and is described in mathematical terms. The volume of the cerebral cortex, in contrast to the cortical surface area, scales to brain volume in a similar way, irrespective of the degree of cortical folding. Among mammals, Cetacea form a subgroup, in that their volumetric data fit an isometric model better than an allometric model. An index of corticalization is presented which contains information about both the mass of interconnective nerve fibers and the degree of intracortical processing. It is shown, furthermore, that a semilogarithmic equation appropriately describes the relationship between mean cortical thickness and brain volume. Finally, allometric equations between brain volume and cortical parameters, which can be used for predictive purposes, are presented.

Animals↗

PubMed1985

Rates of brain development in mammals including man.

The paper considers the absolute rates at which the brain grows in different mammals and the relative rates of growth for the various subareas. It concludes that the various mammals are much more similar in the rates of growth of the brain than of the body. The rate of growth of the human brain is within the range of variation expected. Indirect evidence is presented that the different mammalian orders may differ in the relative rates of growth of the neocortex and other brain areas.

Aging↗

PubMed1987

Distribution of elastic system fibers in the peripheral nerves of mammals.

Various nerves of 6 representative species of mammals (including the human) were studied by the comparative association of the selective staining methods of light microscopy with the ultrastructural observation after tannic acid-glutaraldehyde fixation, which provided a reliable means of characterizing the different elastic system fibers. Although mature elastic fibers are not present in nerves, elastic-related fibers are frequently observed: oxytalan fibers are found mainly in the endoneurium, whereas elaunin fibers predominate in the epineurium. These fibers are longitudinally disposed, in a parallel orientation to the axons. The fact that these findings were consistently observed in the nerves of all species studied argues strongly in favor of the existence of a uniform structural pattern of distribution of elastic system fibers in nerves as a general phenomenon in mammals.

Animals↗

PubMed1995

Somatotropic dysregulation in old mammals.

In old mammals, including humans, the spontaneous growth hormone (GH) secretory pattern is markedly reduced resulting in lower amounts of GH released over 24 h, and the GH response to administration of GH-releasing hormone (GHRH) is reduced. In agreement with these in vivo findings, an impaired responsiveness to GHRH is evident in the pituitary of old male and female rats in vitro, and this is linked with a diminished stimulation of adenylate cyclase by GHRH. The poor GH responsiveness to GHRH in old mammals, which in the rat is coupled to a defective number of GHRH receptors in the somatotrophs, is likely due to a primary deficiency of GHRH availability, as implied by the diminished GHRH immunoreactivity and gene expression in and GHRH release from the hypothalamus of old rats. Attempts have been made to stimulate the sluggish somatotrophic function in elderly humans and dogs using GHRH; in either species positive results were obtained though, overall, it would seem that the GHRH hypofunction does not entirely account for the GH hyposecretory state during ageing. Concerning somatostatin, although the expression of this peptide decreases with age in the rat hypothalamus, secretion and activity of this hormone is increased, resulting in an altered relationship between GHRH and somatostatin gene expression and secretion. It is likely that defects, especially in catecholaminergic and cholinergic neurons, are instrumental in altering specific peptidergic neurons. Reportedly, catecholamines induce GH release by stimulating GHRH neurons and inhibiting somatostatin-releasing neurons; acetylcholine stimulates GH release via muscarinic receptors, in this way inhibiting the action of somatostatin neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed2004

From mouse to whale: a universal scaling relation for the PR Interval of the electrocardiogram of mammals.

BACKGROUND: On the ECG, the PR interval measures the time taken by an electrical impulse generated in the sinoatrial node to propagate from atria to ventricles. From mouse to whale, the PR interval increases approximately 10(1), whereas body mass (BM) augments approximately 10(6). Scaling of many biological processes (eg, metabolic rate, life span, aortic diameter) is described by the allometric equation Y=Y(0) x BM(b), where Y is the biological process and b is the scaling exponent that is an integer multiple of 1/4. Hierarchical branching networks have been proposed to be the underlying mechanism for the 1/4 power allometric law. METHODS AND RESULTS: We first derived analytically the allometric equation for the PR interval. We assumed that the heart behaves as a set of "fractal-like" networks that tend to minimize propagation time across the conducting system while ensuring a hemodynamically optimal atrioventricular activation sequence. Our derivation yielded the relationship PR proportional, variant BM1/4. We subsequently obtained previously published values of PR interval, heart rate, and BM of 541 mammals representing 33 species. Double-logarithmic analysis demonstrates that PR interval increases as heart rate decreases, and both variables relate to BM following the 1/4 power law. Most important, the best fit for PR versus BM is described by the equation PR=53 x BM0.24. Hence, the empirically determined exponent (0.24) is close to 1/4, as predicted. CONCLUSIONS: We have demonstrated that the PR interval of mammals scales as the 1/4 power of the BM, following the universal law for allometric scaling to ensure an optimal atrioventricular activation sequence.

Algorithms↗

PubMed2006

Eleven ancestral gene families lost in mammals and vertebrates while otherwise universally conserved in animals.

BACKGROUND: Gene losses played a role which may have been as important as gene and genome duplications and rearrangements, in modelling today species' genomes from a common ancestral set of genes. The set and diversity of protein-coding genes in a species has direct output at the functional level. While gene losses have been reported in all the major lineages of the metazoan tree of life, none have proposed a focus on specific losses in the vertebrates and mammals lineages. In contrast, genes lost in protostomes (i.e. arthropods and nematodes) but still present in vertebrates have been reported and extensively detailed. This probable over-anthropocentric way of comparing genomes does not consider as an important phenomena, gene losses in species that are usually described as "higher". However reporting universally conserved genes throughout evolution that have recently been lost in vertebrates and mammals could reveal interesting features about the evolution of our genome, particularly if these losses can be related to losses of capability. RESULTS: We report 11 gene families conserved throughout eukaryotes from yeasts (such as Saccharomyces cerevisiae) to bilaterian animals (such as Drosophila melanogaster or Caenorhabditis elegans). This evolutionarily wide conservation suggests they were present in the last common ancestors of fungi and metazoan animals. None of these 11 gene families are found in human nor mouse genomes, and their absence generally extends to all vertebrates. A total of 8 out of these 11 gene families have orthologs in plants, suggesting they were present in the Last Eukaryotic Common Ancestor (LECA). We investigated known functional information for these 11 gene families. This allowed us to correlate some of the lost gene families to loss of capabilities. CONCLUSION: Mammalian and vertebrate genomes lost evolutionary conserved ancestral genes that are probably otherwise not dispensable in eukaryotes. Hence, the human genome, which is generally viewed as being the result of increased complexity and gene-content, has also evolved through simplification and gene losses. This acknowledgement confirms, as already suggested, that the genome of our far ancestor was probably more complex than ever considered.

Animals↗