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At least 937 records · Page 52Linked to original sources
PubMed1988

The distribution of 5-hydroxytryptamine in the gastrointestinal tract of reptiles, birds and a prototherian mammal. An immunohistochemical study.

The distribution of 5-hydroxytryptamine in the gut of several species of birds and reptiles, and of a prototherian mammal, the platypus, was studied using a monoclonal antibody. 5-Hydroxytryptamine-like immunoreactivity was found in enterochromaffin cells and, in birds, in thrombocytes. Immunoreactivity was not found in enteric neurons fixed immediately after dissection. A detailed study was made on one avian species, the budgerigar. Following incubation of intestine in physiological solution, immunoreactivity was found in nerve fibres in the gut wall that was more marked after incubation with the monoamine oxidase inhibitor pargyline. These fibres took up exogenous 5-hydroxytryptamine. Similar fibres were found in the intestinal nerves and in perivascular plexuses on mesenteric arteries. Both the uptake of 5-hydroxytryptamine and the appearance of neuronal immunoreactivity after incubation were inhibited by the amine uptake inhibitors desmethylimipramine or fluoxetine. Fibres taking up 5-hydroxytryptamine were damaged by pretreatment with 6-hydroxydopamine. It was concluded that the fibres showing immunoreactivity after incubation were adrenergic fibres that had taken up 5-hydroxytryptamine released in vitro from enterochromaffin cells or thrombocytes. These, and more limited observations made on the other species, suggest that birds, reptiles and prototherian mammals lack enteric neurons that use 5-hydroxytryptamine as a transmitter substance.

Animals↗
PubMed1996

The uptake and effects of lead in small mammals and frogs at a trap and skeet range.

This study was performed to evaluate the bioavailability and effects of lead in wildlife at a trap and skeet range. The total lead concentration in a composite soil sample (pellets removed) was 75,000 micrograms/g dry weight. Elevated tissue lead concentrations and depressed ALAD activities in small mammals and frogs indicate that some of the lead deposited at the site is bioavailable. Mean tissue lead concentrations (micrograms/g dry wt.) in white-footed mice (Peromyscus leucopus) at the range liver = 4.98, kidney = 34.9, femur = 245) were elevated (P < 0.01) 5- to 64-fold relative to concentrations in mice from a control area. Tissue lead concentrations in the only shorttail shrew (Blarina brevicauda) captured at the range (liver = 34.1, kidney = 1506, femur = 437) were elevated 35- to 1038-fold. Femur lead concentrations in green frogs (Rana clamitans) at the range (1,728 micrograms/g) were elevated nearly 1000-fold, and the lead concentration in a pooled kidney sample (96.2 micrograms/g) was elevated 67-fold. There was significant depression of blood ALAD activity in mice (P = 0.0384) and depression of blood and liver ALAD activity in frogs (P < 0.001). Hematological and histopathological lesions associated with lead toxicosis were observed in some animals. Hemoglobin concentrations were reduced 6.7% in mice (P = 0.0249), but hematocrit was not significantly affected in mice or frogs. Intranuclear inclusions were present in the renal proximal tubular epithelium of two of the mice and the shrew that were captured at the range, and necrosis of the tubular epithelium was also evident in one of the mice. Kidney:body weight ratios were similar in range and control mice. Soil ingestion may be a significant route of lead uptake in small mammals at the range. However, the tendency of lead to concentrate in the bones rather than in more digestible soft tissues may minimize food chain uptake of lead by predators, especially raptors that regurgitate undigestible material.

Animals↗
PubMed1980

The pineal gland of equatorial mammals. I. The pinealocytes of the Malaysian Rat (Rattus sabanus).

The ultrastructure of the pinealocytes of the Malaysian rat (Rattus sabanus), a mammal inhabiting a zone near the equator where the annual variations of daylength are inconspicuous, was examined and compared with that of pinealocytes of other mammals. On the basis of the presence of granular vesicles, only one population of pinealocytes was found. A large number of granular vesicles and vesicle-crowned rodlets is characteristic of the pinealocytes of this equatorial species. Vesicle-crowned rodlets are especially numerous in the endings of the pinealocyte processes and; they most often found in direct topographical connection with the perivascular spaces. The physiological significance of the presence of such large amounts of vesicle-crowned rodlets and of the secretory process characterized by the formation of granular vesicles is discussed.

Animals↗
PubMed1987

The early development of the heart of Tupaia belangeri, with reference to other mammals.

The development of the heart of Tupaia belangeri from the first endothelial-lined lumina to the cardiac loop is described in 20 embryos with 2 to 14 somites, from ontogenetic days 11 and 12. Bilateral endocardial tubes transporting blood are found in the 8-somite embryo; in the middle cardiac plate, angioblasts and angiocysts are located between them. In the 9-somite embryo, formation of the cardiac loop has started, the endocardial tubes approach each other closely, most of the angiocysts have been incorporated by the expanding endocardial tubes, and fusion of the endocardial lumina has started in the cono-truncal area. Apparently, much of the endocardial cardiac loop found in the 9-somite embryo has been produced by the disproportionate lengthening of a segment of the endocardial tubes, which is very short in the 8-somite embryo. In the 13-somite embryo the endocardial tubes have largely fused, but tube-like strands of endothelia, remnants of the original endothelial walls separating them, form a "palisade" and mark the original boundary between them. Myoepicardial differentiations of the splanchnopleure begin separately on both sides of the embryo and gradually spread craniad until they coalesce in the midline, in front of the anterior intestinal portal. The caudal portions of the endocardial tubes with initial myoepicardial and cardiac jelly differentiations do not contribute to the definitive heart. The anterior intestinal portal is very broad in Tupaia. Contradictions in the literature as to the bilaterality of cardiac primordia of eutherian mammals are discussed. The hypothesis is developed that bilateral endocardial tubes and bilateral myoepicardial differentiations of the splanchnopleure develop in species with a large yolk-sac, relatively late closure of the foregut, and a broad anterior intestinal portal (e.g., Tupaia, ferret, and cat, etc.). This is probably the primitive condition in eutherian mammals. In species with a small yolk-sac and/or reversal of germ layers (man, rodents), the foregut and anterior intestinal portal are formed earlier, the heart primordium reaches its median position ventral to the foregut in the angiocyst-stage, and the first endocardial lumina appear close to the midline. In these species, the primordium of the endocardium seems to be plexiform and without clear evidence for bilaterality.

Animals↗
PubMed1990

Oxygen transport in the blood of arctic mammals: adaptation to local heterothermia.

The oxygen binding of whole blood from humans and two arctic mammals, reindeer and muskox, has been studied as a function of carbon dioxide and temperature. All bloods display a marked Bohr effect with Bohr coefficients in the range -0.44- -0.73. The Bohr effect is more pronounced at 20 degrees C. The temperature sensitivity of reindeer and muskox blood expressed by the apparent heat of oxygenation, delta H, is almost three times lower than that of human HbA under the same experimental conditions. This thermodynamic difference gives special benefits to arctic mammals with large heterothermy by safeguarding oxygen unloading at very low ambient temperatures.

Acclimatization↗
PubMed1985

Eye-specific segregation of optic afferents in mammals, fish, and frogs: the role of activity.

Eye-specific patches or stripes normally develop in the visual cortex and superior colliculus of many (but not all) mammals and are also formed, after surgically produced binocular innervation, in the optic tectum of fish and frogs. The segregation of ocular dominance patches or columns has been studied using a variety of anatomical pathway-tracing techniques, by electrophysiological recording of postsynaptic units or field potentials, and by the 2-deoxyglucose method following visual stimulation of only one eye. In the tectum of both fish and frogs and in the cortex and colliculus of mammals, eye-specific patches develop from initially diffuse, overlapping projections. Of the various mechanisms that might cause such segregation, the evidence favors an activity-dependent process that stabilizes synapses from the same eye because of their correlated activity. First, several environmental manipulations affect the segregation of afferents in visual cortex: strabismus and alternate monocular exposure apparently enhance segregation, whereas dark rearing slows the segregation process, and monocular deprivation causes the experienced eye to form larger patches at the expense of those of the deprived eye. Second, blocking activity in both eyes is effective in preventing the segregation both in the tectum of fish and frog and in the visual cortex of cat. With the eyes blocked, alternate stimulation of the optic nerves permits the segregation of ocular dominance, at least onto single cells in the cat visual cortex. These findings are discussed in terms of an activity-dependent stabilization of those synapses having correlated activity (those from neighboring ganglion cells within one eye) but not of those lacking correlated activity (those from left and right eyes). We suggest that the eye-specific patches represent a compromise between total segregation of the projections from the two eyes and the formation of a single continuous retinotopic map across the surface of the cortex or tectum.

Animals↗
PubMedDate not supplied

Effect of soil pollution with metallic lead pellets on lead bioaccumulation and organ/body weight alterations in small mammals.

Using small mammals as bioindicators, the bioavailable status and ecotoxicity of lead was investigated in an acidic sandy soil environment polluted with metallic lead pellets from shotgun ammunition. Average concentrations of lead in kidney, liver and bone tissue of wood mice (Apodemus sylvaticus), bank voles (Clethrionomys glareolus), and shrews (Sorex araneus) were strongly elevated, compared to tissue levels of conspecifics collected from an adjacent unpolluted area. All shrews and some bank voles collected from the shooting range exceeded the critical renal Pb concentration of 25 micrograms/g dry weight, considered diagnostic of lead intoxication in mammals. The geometric mean renal Pb concentration in shrews was 270 micrograms/g dry weight, with an upper range of more than 1,000 micrograms/g. The population of shrews and bank voles from the shooting range also showed a significantly increased average relative kidney weight (kidney-to-body weight ratio), which is indicative of lead poisoning. The results suggest that metallic lead pellets deposited in an acidic sandy soil are transformed to a chemical form of lead, probably Pb2+, which is toxic to organisms and which can readily enter the terrestrial food chain.

Analysis of Variance↗
PubMed1993

Effects of air pollution on passerine birds and small mammals.

The effects produced by emissions from coal-fired power plants, including mainly SO2, NOx and particulates, on natural populations and caged specimens of birds and small mammals were studied. The field-captured species used to evaluate these effects were passerine birds: Parus major (coal tit) and Emberiza cia (rock bunting), and the rodent Apodemus sylvaticus (wood mouse). In parallel to this study on animals captured in the field, we used other animals, Mus musculus (house mouse) and Carduelis carduelis (goldfinch) which were placed in cages near the source of pollution. Some of the animals were killed and their tracheas were removed and prepared for conventional optic studies (1000x) and electron microscopy (TEM and SEM). The results show that atmospheric air pollutants from coal-fired power plants produce alterations in the tracheal epithelium. In passerine birds, an increase in the mucus which covers the tracheal epithelium, shortening of the cilia, and increase in the number of secretory granules and vesicles were observed. In mammals, variation of the uniformity of the pseudostratified epithelium with a wide stratum of mucus, shortening of the cilia, and increase in the number of secretory granules were observed.

Air Pollutants↗
PubMed1977

The pineal gland of nocturnal mammals. I. The pinealocytes of the bat (Nyctalus noctula, Schreber).

The ultrastructure of the pinealocytes of noctule bats, mammals which live most of the time in darkness or very low light intensities, was examined and compared with the pinealocytes of other mammals. Two different populations of pinealocytes (I and II) were observed. They differ in general aspect, in location and especially in their content of cell organelles involved in synthetic processes. Mitochondria, ribosomes, lysosomes and lipid inclusions were present in the perikaryon of pinealocytes of both populations. In the pinealocytes of population I some granular vesicles, of presumed Golgi origin, and some other structures were observed. Pinealocytes of population II are characterized by many glycogen granules, more or less associated with a large vacuolar system. Moreover, some small vacuoles originating from cisterns of the granular endoplasmic reticulum and containing flocculent material of a moderate electron density are described. The possibility is discussed that these small vacuoles are involved in one of the secretory processes of the pineal gland while the granular vesicles of the pinealocyte of the population I are the products of another.

Animals↗
PubMed1976

Functional aspects of hemoglobin evolution in the mammals.

Comparative studies of red cells 2, 3 Diphosphoglycerate (DPG) and its effect on hemoglobin oxygen affinity from a taxonomically diverse set of mammals indicate two anomalous groups: members of the superfamilies Bovoidea (Actiodactyla) and Feloidea (Carnivora). In both taxa all of the individuals assayed had very low or unmeasurable quantities of DPG and red cell lysates with little, if any, DPG effect as measured by the change in oxygen affinity in the absence and presence of the phosphate. However, in both groups compensatory changes have occurred in hemoglobin structure and function so as to reduce the native oxygen affinity and thus cause them to resemble the hemoglobins of DPG-utilizing mammals as they occur in the setting of the red cell. We conclude that this parallelism of function is the result of convergent evolution.

Amino Acid Sequence↗
PubMed1977

On urea formation in marine mammals.

Ornithine carbamoyltransferase (EC 2.1.3.3) has been determined in homogenates of liver of the sei whale (Balaenoptera borealis), the bottle-nose dolphin (porpoise) (Tursiops truncatus) and California sea lion (Zalophus californianus). These marine mammals show levels of this ornithine-urea cycle enzyme which are typical of terrestrial mammals.

Animals↗
PubMed1991

The molecular evolution of ZFY-related genes in birds and mammals.

We report the isolation and nucleotide sequence determination of clones derived from five ZFY-related zinc-finger genes from birds and mammals. These sequences are analyzed with reference to the previously published human genes, ZFX and ZFY, and mouse genes, Zfx, Zfa, Zfy-1, and Zfy-2. The analysis indicates that ZFY-related genes are highly conserved in birds and mammals, and that the rate of nucleotide substitution in the Y-linked genes is not as high as predicted. However, the mouse Zfy-1 and Zfy-2 genes are markedly divergent members of the ZFY gene family; we suggest this relates to X-inactivation of the mouse gene Zfx.

Amino Acid Sequence↗
PubMed1976

Distribution of HEOD (dieldrin) in mammals: III. Transport--transfer.

A mathematical model simulating the blood transport and tissue residue distributions of the highly toxic and highly lipid soluble pesticide dieldrin in mammals is presented. This model is a significant improvement over our previously published preliminary model for dieldrin distribution in mammals. The assumptions and working hypotheses of the model are presented and used in generating a set of differential equations based upon mass balance principles. Two simulation cases are examined. The first simply demonstrates the gross features of: 1) Transport limiting conditions; 2) equal transport-equal membrane transfer conditions, and 3) membrane transfer limit conditions. The second studies a single tissue (the blood-brain barrier case) example of the above mentioned conditions. All simulations made were conducted for a hypothetical mature male rate of the average Wistar type eating food ad lib.

Animals↗
PubMed2000

Dimorphic features of the different alpha-containing GABA-A receptor subtypes in the cortico-basal ganglia system of two distantly related mammals (hedgehog and rat)

This investigation represents a first study dealing with the dimorphic differences of the main alpha-containing gamma-aminobutyric acid (GABA(A)) receptors in the brain of two distantly related mammals (hedgehog and rat). The labeling of these receptors in the presence of zolpidem (highly selective benzodiazepine agonist) and under the different degree of GABA(A)/benzodiazepine allosteric coupling activities accounted for a heterogeneous colocalization of alpha1-enriched and of alpha2/3-enriched and alpha5-enriched GABA(A) receptors in some areas of the cortico-basal ganglia system (including the important ventrolateral thalamic station) of both mammalian sexes. In the hedgehog, the greatest (P<0.001) GABA-dependent reduction of zolpidem inhibition constants was mostly registered in alpha1- and/or alpha5-enriched areas, such as the frontoparietal cortex lamina III (235%), ventrolateral thalamic nucleus (128%), and substantia nigra pars reticulata (110%) of the male. However, the greatest reductions in the rat were instead detected in the male substantia nigra pars reticulata (192%) and female striatum (120%), areas which are enriched either by the colocalization of alpha1- with alpha2/3-subunits or by all three alpha-subunits. These results support the contention that a sex-related alpha-containing GABA(A) receptor sensitivity constitutes an important element in the execution of skilled motor activities during the different socio-sexual behaviors of the two mammals.

Animals↗
PubMed2005

The alpha-globin gene family of an Australian marsupial, Macropus eugenii: the long evolutionary history of the theta-globin gene and its functional status in mammals.

Comparative evolutionary analyses of gene families among divergent lineages can provide information on the order and timing of major gene duplication events and evolution of gene function. Here we investigate the evolutionary history of the alpha-globin gene family in mammals by isolating and characterizing alpha-like globin genes from an Australian marsupial, the tammar wallaby, Macropus eugenii. Sequence and phylogenetic analyses indicate that the tammar alpha-globin family consists of at least four genes including a single adult-expressed gene (alpha), two embryonic/neonatally expressed genes (zeta and zeta'), and theta-globin, each orthologous to the respective alpha-, zeta-, and theta-globin genes of eutherian mammals. The results suggest that the theta-globin lineage arose by duplication of an ancestral adult alpha-globin gene and had already evolved an unusual promoter region, atypical of all known alpha-globin gene promoters, prior to the divergence of the marsupial and eutherian lineages. Evolutionary analyses, using a maximum likelihood approach, indicate that theta-globin, has evolved under strong selective constraints in both marsupials and the lineage leading to human theta-globin, suggesting a long-term functional status. Overall, our results indicate that at least a four-gene cluster consisting of three alpha-like and one beta-like globin genes linked in the order 5'-zeta-alpha-theta-omega-3' existed in the common ancestor of marsupials and eutherians. However, results are inconclusive as to whether the two tammar zeta-globin genes arose by duplication prior to the radiation of the marsupial and eutherian lineages, with maintenance of exon sequences by gene conversion, or more recently within marsupials.

Amino Acid Sequence↗
PubMed2001

The comparative genomics of polyglutamine repeats: extreme differences in the codon organization of repeat-encoding regions between mammals and Drosophila.

Polyglutamine repeats within proteins are common in eukaryotes and are associated with neurological diseases in humans. Many are encoded by tandem repeats of the codon CAG that are likely to mutate primarily by replication slippage. However, a recent study in the yeast Saccharomyces cerevisiae has indicated that many others are encoded by mixtures of CAG and CAA which are less likely to undergo slippage. Here we attempt to estimate the proportions of polyglutamine repeats encoded by slippage-prone structures in species currently the subject of genome sequencing projects. We find a general excess over random expectation of polyglutamine repeats encoded by tandem repeats of codons. We nevertheless find many repeats encoded by nontandem codon structures. Mammals and Drosophila display extreme opposite patterns. Drosophila contains many proteins with polyglutamine tracts but these are generally encoded by interrupted structures. These structures may have been selected to be resistant to slippage. In contrast, mammals (humans and mice) have a high proportion of proteins in which repeats are encoded by tandem codon structures. In humans, these include most of the triplet expansion disease genes.

Animals↗
PubMed2001

Episodic evolution of protein hormones in mammals.

Pituitary growth hormone (GH) and prolactin have been shown previously to display a pattern of evolution in which episodes of rapid change are imposed on a low underlying basal rate (near-stasis). This study was designed to explore whether a similar pattern is seen in the evolution of other protein hormones in mammals. Seven protein hormones were examined (with the common alpha-subunit of the glycoprotein hormones providing an additional polypeptide for analysis)--those for which sequences from at least four eutherian orders are available with a suitable non-eutherian outgroup. Six of these (GH, prolactin, insulin, parathyroid hormone, glycoprotein hormone alpha-subunit, and luteinizing hormone beta-subunit) showed markedly variable evolutionary rates in each case with a pattern of a slow basal rate and bursts of rapid change, the precise positions of the bursts varying from protein to protein. Two protein hormones (follicle-stimulating hormone beta-subunit and thyroid-stimulating hormone beta-subunit) showed no significant rate variation. Based on the sequences currently available, and pooling data from all eight proteins, the phase of slow basal change occupied about 85% of the sampled evolutionary time, but most evolutionary change (about 62% of the substitutions accepted) occurred during the episodes of rapid change. It is concluded that, in mammals at least, a pattern of prolonged periods of near-stasis with occasional episodes of rapid change provides a better model of evolutionary change for protein hormones than the one of constant evolutionary rates that is commonly favored. The mechanisms underlying this episodic evolution are not yet clear, and it may be that they vary from one group to another; in some cases, positive selection appears to underlie bursts of rapid change. Where gene duplication is associated with a period of accelerated evolution this often occurs at the end rather than the beginning of the episode. To what extent the type of pattern seen for protein hormones can be extended to other proteins remains to be established.

Animals↗