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PubMed2003

Glycero- versus sphingo-phospholipids: correlations with human and non-human mammalian lens growth.

The human lens differs from other mammalian lenses in its very slow growth and unusual phospholipid composition of its cell membranes. Dihydrosphingomyelins (DHSMs) make up about half of all phospholipids in adult human fiber membranes. In all other membranes, sphingomyelins(SMs) with a trans double bond in their backbone, are prevalent. In our quest to understand the biological implications of such elevated DHSM levels, we analyzed membranes from various regions of human, elephant, giraffe, polar bear, pig and cow lenses. The levels of DHSMs were minor in non-human lens membranes. A strong correlation was observed between growth rate and relative contents of phosphatidylcholines(PCs) in epithelia and outer cortical fibers. Sphingomyelins became increasingly predominant in differentiated fibers and this increase was age dependent. Indeed, nuclear fiber membranes of aged non-human mammals were composed, almost exclusively, of (SMs). Although human lens membranes followed comparable compositional trends, the magnitude of the changes was much smaller. We postulate that the high relative contents of DHSMs provide a biochemically inert matrix in which only small amounts of PCs and SMs and their metabolites, known to promote and arrest growth, respectively, are present. This compositional difference is proposed to contribute to the slow multiplication and elongation of human lens cells.

Adolescent↗
PubMed2002

Endocrine patterns associated with reproduction in the Nile hippopotamus (Hippopotamus amphibius) as assessed by fecal progestagen analysis.

The hippopotamus (Hippopotamus amphibius) is a popular zoo animal and an integral part of wetland ecosystems in its native continent of Africa. However, information about the reproductive physiology of the hippopotamus is limited compared to the other megaherbivores of Africa such as the elephant and the rhinoceros. This study is the first to report on the endocrine patterns associated with ovulation and pregnancy in the Nile hippopotamus. Fecal samples were collected 3 times per week from female hippopotami (N = 9) housed in captivity in Florida. Progesterone metabolites were extracted from the feces with 80% MeOH and quantified using a progestagen EIA. Fecal progestagen analysis indicated hippopotami had a cycle length of 35.3 +/- 1.3 days and ovulated throughout the year. Fecal progestagen concentrations during pregnancy (N = 11 pregnancies) were higher on average (833.5 +/- 115.2 ng/g; P < 0.05) than those observed during non-pregnant luteal phases (309.5 +/- 20.9 ng/g) and remained elevated throughout gestation. Fecal progestagen analysis revealed the onset of puberty in three females between 3 and 4 years of age and all conceived by their fourth cycle. Lactational suppression of ovulation during nursing was usually, but not always, observed and lasted for 33.9 +/- 1.8 weeks. The observed calving interval in females with lactational anovulation was 17 months. The majority of births (63.6%) occurring during the summer rainy season and the inconsistency of lactational anovulation suggested the possibility of environmental influences on reproduction.

Aging↗
PubMed2003

A newly-identified lineage of Schistosoma.

Because of their role in causing schistosomiasis, flukes of the genus Schistosoma are the best known of all digeneans. The genus has traditionally been divided into four familiar species groups. Here we report on three poorly known species of Schistosoma, one of which, Schistosoma hippopotami, is known from the hippopotamus, one of which is provisionally identified as Schistosoma edwardiense, another hippo parasite, and a third that has not previously been described. All were collected from freshwater snails obtained from Lake Edward, western Uganda, the type locality for both known hippo schistosomes. The three different kinds of schistosome cercariae differ from one another in size, and all are readily differentiated by their long tail stems from the cercariae of human-infecting species. Furthermore, each was recovered from a different genus of snail host, Biomphalaria sudanica, Bulinus truncatus or Ceratophallus natalensis. Molecular analysis, based on 8350 bases of combined nuclear and mitochondrial DNA, groups these three long tail-stem cercariae into a well supported clade that does not associate with any of the recognised species groups. The placement of this clade, basal to all African species plus several Asian species, suggests that there has been an ancient association between Schistosoma and hippos. This new African Schistosoma clade advocates the need for further modification of the traditional species group-based classification. Two of the four species groups are paraphyletic. It also suggests that Schistosoma has been remarkably plastic with respect to adapting to snail hosts-three distantly related genera of planorbid snails have been exploited by worms within a single clade. Finally, it adds a new layer of complexity to deciphering the origins of Schistosoma, often considered to be African but recently challenged as being Asian. In the late Cenozoic the distribution of hippo species straddled both Africa and Asia and they may have provided a means for the introduction of blood flukes to Africa.

Animals↗
PubMed1998

Pneumocystis carinii in wildlife.

Pneumocystis carinii is a eukaryotic organism capable of causing life-threatening pneumonia (PCP) in immunocompromised hosts. Despite intensive investigation in human and laboratory animal hosts, information on the occurrence and nature of infections in wild animals is scarce, although characterisation of infections in wild-animal populations may help to elucidate the life-cycle and transmission of this elusive organism. Due to the interspecific differences in prevalence and intensity of P. carinii infection, and to the antigenic and genetic diversity of P. carinii organisms originating from various host species, which may affect the infectivity and pathogenicity of these organisms, we should be cautious when making generalisations about the nature of P. carinii infection. This review summarises the present state of knowledge on the occurrence of P. carinii in wild mammals in their natural habitats, and briefly discusses various characteristics of P. carinii infection important for understanding the distribution and abundance of this organism. Some aspects of P. carinii infection in wild hosts of particular interest for future research in this field will also be discussed.

Animals↗
PubMed2002

A model for time-dependent flow in (giraffe jugular) veins: uniform tube properties.

Computations are reported for a one-dimensional model of time-dependent flow in collapsible tubes representing long mammalian veins. The tubes are taken to have uniform intrinsic properties and we concentrate on the effect of longitudinal gravity. The main application is to the jugular vein of the upright giraffe, with given inflow rate from the head, a given pressure, slightly above the external, atmospheric pressure, at the downstream (vena caval) end, and a variety of initial conditions. We show that: (i) previously calculated steady flows are the long time limits of unsteady computations, although only after a considerable time in which slowly-decaying waves and elastic jumps propagate up and down, (ii) steady flows are indeed not found when the steady-flow analysis shown them not to exist, although the consequent unsteadiness is of such small amplitude as to be practically unimportant, (iii) the time taken for the flow to become steady when the neck is raised from the horizontal or the head-down position can be several seconds longer than the neck-raising time itself (3-7s). We also find that roll-waves do not develop despite having been previously predicted for long collapsible tubes. Further application is made to the effect of postural changes on human neck and leg veins.

Animals↗
PubMed1985

On the mathematics of digesta flow kinetics.

A unifying mathematical analysis of the use of compartmental models with and without time lags is given, with particular reference to the use of such models for digesta movement along the gastro-intestinal tract of the ruminant. First the generalized compartmental model without time lags is developed, and then it is shown how discrete time lags may be incorporated into this formalism. The important relationship between distributed lags, especially the gamma-distributed time lags, and the equivalent compartmental scheme, is emphasized. It is shown how distributed time lags can be included in a general compartmental model. The treatment covers, as special cases, some widely used models, and shows their relationship to each other and to other possible models. Finally a compartmental interpretation is outlined for a recently proposed double-exponential model.

Animals↗
PubMed1970

Onchocerciasis.

Explore the source record for details and available documents.

Africa↗
PubMed2006

Sensory control of extraocular muscles.

The role of sensory receptors in eye muscles is not well understood, but there is physiological and clinical evidence for the presence of proprioceptive signals in many areas of the central nervous system. It is unclear which structures generate these sensory signals, and which central neural pathways are involved. Three different types of receptors are associated with eye muscles: (1) muscle spindles, (2) palisade endings, and (3) Golgi tendon organs, but their occurrence varies wildly between species. A review of their organization shows that each receptor is mainly confined to a morphologically separate layer of the eye muscle. The palisade endings - which are unique to eye muscles, are associated with the global layer; and they have been found in all mammals studied so far. Their function is unknown. The muscle spindles, if they are present in a species, lie in the orbital layer, or at its junction to the global layer. Golgi tendon organs appear to be unique to artiodactyls (i.e., sheep and goats, etc.); they lie in an outer distal marginal layer of the eye muscle, called the "peripheral patch layer" in sheep. The specific association between palisade endings and the multiply innervated type of muscle fibers of the global layer has led to the hypothesis that together they may act as a sensory receptor, and provide a source of central proprioceptive signals. But other interpretations of the morphological evidence do not support this role.

Afferent Pathways↗
PubMed2002

Cryopreservation of gametes and embryos of non-domestic species.

Many species of mammals are threatened or endangered. Methods of assisted reproduction that are being used with increasing frequency to produce offspring of domestic animals and humans are often viewed as offering innovative ways to reproduce non-domestic species as well. Uncounted millions of live young of domestic or laboratory species have been produced from gametes and embryos stored at -70 degrees C or below, sometimes for as long as 25 to 35 yrs. Such methods of cryopreservation are now being applied with increasing frequency and urgency to preserve gametes and embryos of non-domestic and threatened species to establish "genome resource banks" or "frozen zoos." But levels of success to produce live young from such cryopreserved gametes or embryos vary considerably from species to species, as well as from individual to individual. It is sometimes thought that differences among species in fundamental characteristics of their gametes may determine the efficacy of cryopreservation and the production of live young. However, it may not be that ineffective cryopreservation is responsible for low success rates. Rather, the limiting factor may be insufficient information and knowledge of the most basic reproductive biology of such non-domestic species. Even standard methods of cryopreservation may be completely adequate to act as a "temporary" expedient to preserve germplasm of non-domestic species to permit time to acquire a fuller understanding of the biology and behavior of non-domestic species.

Animals↗
PubMedDate not supplied

Ultrastructural observations on the placenta of the alpaca (Lama pacos).

The alpaca is one of the four South American species of the family Camelidae. Its placenta, like that of other camelids, is diffuse and epitheliochorial in type. The chorionic epithelium is thrown into unbranched villi or folds which are closely apposed to corresponding undulations of the uterine epithelium, and the fetal-maternal interface consists of an intricate interdigitation of fetal and maternal microvilli. In late gestation both chorionic and uterine epithelia are deeply indented by placental capillaries, so that the minimum intercapillary distance across the diffusion pathway may be as little as 2 microns. This distance appears to be less than that found in the epitheliochorial placenta of any other species of domestic ungulate in late gestation: it may be one of several adaptations to pregnancy at high altitude. Delivery of the fetal membranes occurs some 45 minutes after the birth of the fetus. The placenta is non-deciduate.

Amnion↗