Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Life Cycle”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37Linked to original sources
PubMedDate not supplied

[Life-cycle of Renicola lari J. Timon-David, 1933 (Trematoda, Renicolidae) (author's transl)].

This paper deals with life-cycle of Renicola lari J. Timon-David, 1933. Description and illustration are given. Sporocyst development occurs inside the visceral mass of Cerithium mediterraneum and C. Rupestre (Mollusca Prosobranchia). Cercariae are planktonic; they are swallowed up by the second intermediate host, Atherina hepsetus and A. boyeri (Teleostean fishes). Cercariae perforate intestine wall. Metacercariae are encysted in liver. Adult flukes have been recovered in kidneys of uninfected Larus argentatus and L. ridibundus after exerimental contamination with naturally infected fishes. Cercariae of Renicola lari differ from Plagiorchid type cercariae by the following characters : stylet lacking ; very large excretory bladder ; they develop into metacercariae in fishes. Cercariae of R. lari seem to Rhodometope type cercariae ; they have the same excretory bladder. Cercariae of R. lari differ from Rhodometope cercariae in lacking fins on their tail.

Animals↗
PubMed1986

The life-cycle research productivity of mathematicians and scientists.

Declining research productivity with age is implied by economic models of life-cycle human capital investment but is denied by some recent empirical studies. The purpose of the present study is to provide new evidence on whether a scientist's output generally declines with advancing age. A longitudinal data set has been compiled for scientists and mathematicians at six major departments, including data on age, salaries, annual citations (stock of human capital), citations to current output (flow of human capital), and quantity of current output measured both in number of articles and in number of pages. Analysis of the data indicates that salaries peak from the early to mid-60s, whereas annual citations appear to peak from age 39 to 89 for different departments with a mean age of 59 for the 6 departments. The quantity and quality of current research output appear to decline continuously with age.

Adult↗
PubMedDate not supplied

Nutrition and the life cycle: nutrition and the school child.

This is the third in this series of articles examining nutrition and the life cycle. The first considered current thinking regarding nutrition in pregnancy (Vol 9(17): 1133-8), and the second discussed nourishing the infant, particularly in relation to weaning (Vol 9(21): 2205-16). This article considers nutrition and the older child. The school years are characterized by increasing independence from parents and exposure to values from outside the home. After being neglected for some years, childhood nutrition is again giving cause for concern. Some children are not eating enough, or not the right nutrients at the right time, while others are becoming overweight, with possible severe long-term effects on their health. Many of these problems are not related to poverty, but rather to changes in lifestyle. Some older children, however, are undernourishing themselves in an attempt to obtain a particular body shape. The last two articles in this series will review nutrition in adulthood and in older years.

Adolescent↗
PubMed1987

Heartwater. The development and life cycle of Cowdria ruminantium in the vertebrate host, ticks and cultured endothelial cells.

Various aspects of the development and life cycle of Cowdria ruminantium are discussed. C. ruminantium is transmitted transstadially by certain Amblyomma species. Apparently organisms initially develop in the gut epithelial cells of ticks and subsequent stages of C. ruminantium invade and develop in the salivary gland acini cells of the vector. Stages at which transmission to the final host are attained appear to be coordinated with the feeding cycle of the ticks and the vertebrate host is infected via salivary glands of the tick. In the vertebrate host, ticks and cultured endothelial cells, different morphological forms of C. ruminantium (electron-dense and reticulated forms) are found. Organisms enter cells through a process resembling phagocytosis and reticulated forms of the organisms appear to be the main vegetative stage. In the vertebrate host, organisms proliferate in vascular endothelial cells, neutrophils, macrophages and reticulo-endothelial cells.

Animals↗
PubMed2005

Aploparaksis demshini n. sp. (Cestoda: Hymenolepididae), a parasite of the woodcock Scolopax rusticola Linnaeus, and its life-cycle.

Aploparaksis demshini n. sp. is described from a woodcock Scolopax rusticola L. from different parts of the Palaearctic (Lithuania, Karelia, the Urals, Primorskiy Kray). It differs from the most similar species A. belopolskajae Bondarenko, 1988, a parasite of snipes Gallinago spp., in the form and length of the rostellar hooks and the smaller cirrus, and from two other similar species, A. clavata Spasskaya, 1966 and A. schilleri Webster, 1955, by having an embryophore with polar thickenings and a spindle-shaped cirrus. The life-cycle of the parasite was studied under experimental conditions. The metacestodes were commonly located under the chlorogogenous tissue of the intestine of the earthworms Eisenia foetida(Savigny), Dendrobaena octaedra (Savigny) and E. nordenskioldi(Eisen), and in the wall of the intestine of the enchytraeid Briodrilus arcticus(Bell). The metacestodes exhibit a pattern of postembryonal development typical for the cysticercoid modification termed an 'ovoid diplocyst'.

Animals↗
PubMed2000

Temperature effects on embryonic development and the life cycle of Diphyllobothrium dendriticum.

Diphyllobothrium dendriticum eggs collected from hamster faeces were incubated at 10 or 20 degrees C, or maintained at 4 degrees C for 11-30 months. On day 65, 20-50% of eggs failed to hatch at 10 degrees C and 42-51% did not hatch by day 21 at 20 degrees C. Our study indicates that eggs begin to hatch in mid-August and persist until October in many lakes within the natural range of D. dendriticum. Our results demonstrate that eggs stored at 4 degrees C will hatch, suggesting they can persist in the environment for long periods and contribute to the D. dendriticum life cycle in high Arctic lakes by hatching months or years after release.

Animals↗
PubMed2001

Analysis of Borrelia burgdorferi gene expression during life cycle phases of the tick vector Ixodes scapularis.

Borrelia burgdorferi exists in nature via an enzootic cycle whereby the organism must adapt to the diverse environmental conditions provided inside the arthropod transmission vector and the mammalian reservoir hosts. B. burgdorferi genes shown to be regulated by temperature, pH and/or cell density during the organism's growth in culture medium were assayed for expression during various stages of the tick feeding cycle by reverse transcription-polymerase chain reaction (RT-PCR). ospA, ospC, flaB, erpA/I/N, erpB/J/O, rev and mlpA, were transcriptionally active following the larval and nymphal stages of feeding as determined by qualitative RT-PCR. During tick resting periods between feedings, ospC, mlpA and rev transcription were undetectable, in contrast to ospA, flaB, erpA/I/N and erpB/J/O. bba64, a gene induced by environmental changes in culture and expressed during mammalian infection, was not detectable during any of the tick life cycle phases. Quantitative PCR to determine B. burgdorferi genome equivalents in these tick samples using DNA co-purified with the RNA allowed an estimation of gene expression relative to the numbers of B. burgdorferi present in the ticks. Although the spirochete totals varied widely between individual tick pools of fed, replete nymphs, the relative expression ratios between individual target genes following a nymphal feed were comparable. Similarly, borrelial gene transcription from the larval feeding and the nymphal feeding were observed and compared. These findings analogize B. burgdorferi gene expression observed by environmental stimuli in vitro with the transcriptional activity occurring during the organism's infectious cycle within the tick.

Animals↗
PubMed2003

Parasite mitochondria as drug target: diversity and dynamic changes during the life cycle.

Parasites have developed a wide variety of physiological functions to survive within the specialized environments of the host. Regarding energy metabolism, which represents an essential factor for survival, parasites adapt low oxygen tension in host mammals using metabolic systems that differ substantially from those of the host. Most parasites do not use free oxygen available within the host, but employ systems other than oxidative phosphorylation for ATP synthesis. Furthermore, parasites display marked changes in mitochondrial morphology and components during the life cycle, and these represent very interesting elements of biological processes such as developmental control and environmental adaptation. The enzymes in parasite-specific pathways offer potential targets for chemotherapy. Cyanide-insensitive trypanosome alternative oxidase (TAO) is the terminal oxidase of the respiratory chain of long slender bloodstream forms of the African trypanosome, which causes sleeping sickness. Recently, the most potent inhibitor of TAO to date, ascofuranone, was isolated from the phytopathogenic fungus, Ascochyta visiae. The inhibitory mechanisms of ascofuranone have been revealed using recombinant enzyme. Parasite-specific respiratory systems are also found in helminths. The NADH-fumarate reductase system in mitochondria form a final step in the phosphoenolpyruvate carboxykinase (PEPCK)-succinate pathway, which plays an important role in anaerobic energy metabolism for the Ascaris suum adult. Enzymes in this system, such as NADH-rhodoquinone reductase (complex I) and rhodoquinol-fumarate reductase (complex II), form promising targets for chemotherapy. In fact, a specific inhibitor of nematode complex I, nafuredin, has been found in mass-screening using parasite mitochondria.

Amino Acid Sequence↗
PubMed2003

Potencies of estrogenic compounds in in vitro screening assays and in life cycle tests with zebrafish in vivo.

The objective of this study was to compare the estrogenic potency of environmental estrogens at two testing tiers: at the initial level of in vitro screening assays, and at the level of definitive fish reproduction tests in vivo. The in vitro tests included a recombinant yeast estrogen receptor (ER) assay, a competitive radioreceptor assay using the hepatic ER of carp (Cyprinus carpio), and assays on vitellogenin induction in cultured hepatocytes of rainbow trout (Oncorhynchus mykiss) and carp. In vivo, full life cycle tests with zebrafish (Danio rerio) were performed, using fertilization success as estrogen-sensitive reproductive endpoint. The test compounds included the natural estrogen 17beta-estradiol (E2) (only applied in the in vitro assays); the synthetic estrogen ethynylestradiol (EE2); and two xenoestrogens, 4-tert-octylphenol (OP) and bisphenol A (BPA). Among the in vitro assays, differences were observed in the relative ranking of the test substances, and in the absolute sensitivity (EC50 values), although the interassay differences of EC50 values were within one order of magnitude. The in vivo activity of the test compounds was not accurately predicted by the in vitro assays, with respect to neither sensitivity nor ranking. The in vitro assays tended to overestimate the relative potency of the xenoestrogens; i.e. the ratio between the activity of the reference compound, EE2, and that of the test compound. The best prediction of the in vivo fish test results was obtained from the recombinant yeast assay.

Animals↗
PubMed2001

Life cycle of Ixodes pacificus (Acari: Ixodidae): timing of developmental processes under field and laboratory conditions.

The developmental timing of Ixodes pacficus Cooley & Kohls, the primary vector of the Lyme disease spirochete and the agent of human granulocytic ehrlichiosis in the far-western United States, was determined under field and laboratory conditions. During their seasonal peaks of abundance, each of the three parasitic stages of L. pacificus, both fed and unfed, was placed inside silk-screen packets. These packets were apportioned between four topographic exposures of two hilltop sites in northwestern California. The sites differed in vegetational composition and elevation: the first (elevation 390 m) was dominated by woodland-grass, the second (elevation 914 m) by chaparral. The timing of oviposition, larval eclosion, molting, and mortality were recorded in the field every 2-3 wk for 2.5 yr. Microenvironmental temperatures were measured on all four exposures at both sites. Accelerated developmental rates of all three stages were correlated with warmer soil temperatures and the time of placement in the field. In the laboratory, replete female I. pacificus maintained under uniform environmental conditions sustained constant preovipositional and prehatch periods independent of date-of-feeding. In the field, all unfed stages survived through one active feeding season with most larvae and nymphs remaining in behavioral diapause between late summer and early spring. No life stage survived through two active feeding periods which suggests that cohorts do not overlap. We concluded that I. pacificus takes a minimum of 3 yr to complete its life cycle in northwestern California.

Animals↗
PubMed2005

Effects of the pyrethroid esfenvalerate on life-cycle traits and population dynamics of Chironomus riparius--importance of exposure scenario.

Field populations of aquatic organisms, particularly those inhabiting flowing waters, likely are exposed to short pulses of pesticides following periods of spray drift, surface runoff, or drain flow. In the present study, we investigated the effect of pulse exposures of a pyrethroid insecticide, esfenvalerate, on survival, development, and reproduction of the midge, Chironomus riparius. The first experiment was designed to simulate the exposure of settling larvae to a waterborne pulse of esfenvalerate. A second experiment simulated exposure of larvae entering a sediment that had been exposed previously to a waterborne pulse of esfenvalerate. A third experiment simulated exposure of sediment-inhabiting larval populations to a waterborne pulse of esfenvalerate and examined whether population density influenced the response of C. riparius. Our results indicate that even very brief (i.e., 1-h) exposures to environmentally realistic concentrations of esfenvalerate during early larval life can have measurable effects on larval survival and developmental rates. For those individuals that survived a pulse exposure early in life, however, there appeared to be no lasting effects of esfenvalerate on their subsequent egg laying or egg viability. Thus, brief exposure to environmentally realistic concentrations of pesticides can have measurable effects on freshwater invertebrate populations, but whether such effects occur depends on the details of the exposure regime. In addition, population density may influence the responses of life-cycle traits and, thereby, population-level impacts of pesticides.

Animals↗
PubMedDate not supplied

Self-harm behaviors across the life cycle: a pilot study of inpatients with borderline personality disorder.

The purpose of this study was to explore, throughout the life cycle, the prevalence of self-harm behaviors among psychiatric inpatients with and without borderline personality disorder (BPD). Psychiatric inpatients with BPD (n = 43) were compared to those without BPD (n = 40) with regard to self-reported self-harm behaviors during their lifetime. The mean number of self-harm behaviors, including high-lethal behaviors (i.e., suicide attempts, cutting oneself, overdosing), among those with BPD dramatically increased between the ages of 18 and 24 years and was sustained through ages 50 to 59 years. Non-BPD patients showed a similar pattern, but the means were notably less. These data suggest that the behavioral "burn out" theory of personality disorders does not necessarily occur among inpatients with BPD.

Adolescent↗
PubMedDate not supplied

Morphology and infraciliature of a marine scuticociliate with a polymorphic life cycle: Urocryptum tortum n. gen., n. comb.

A new genus and species combination are proposed for Urocryptum tortum n. gen., n. comb., a scuticociliate with a polymorphic life cycle. This marine ciliate was isolated from a sample taken at Gokasho Bay in Mie Prefecture (Japan). Specimens from different phases of the growth cycle were examined in vivo and with two silver staining techniques. Three life-history stages were observed: an exponential growth phase stage (trophont), a stationary phase stage (tomite), and finally a resting stage (cyst). The exponential growth form is laterally flattened and ovoid; it has 20-24 somatic kineties (SK) and a typical complement of scuticociliate oral structures. Polykinetid 1 (Pk1) has two longitudinal files of 6 kinetosomes (Ks); sometimes one or two additional kinetosomes are located anteriorly. Polykinetid 2 (Pk2) has two files of 6 or 7 Ks; a third file of three widely spaced kinetosomes is located on its right side, as well as a small curved row of 5 Ks positioned on the right hand side of the posterior end of Pk2. Polykinetid 3 (Pk3) has 3 rows of 4, 5, and 7 Ks's perpendicular to the haplokinety (Hk) or paroral membrane. The stationary growth phase cell is spindle-shaped and has a similar number of SK that are much more closely spaced than in exponentially growing specimens. Oral infraciliary structures are reduced in size, having fewer kinetosomes and being positioned more anteriorly in the cell. Pk1 is composed of two files of 5-Ks, Pk2 has only two files of 6-7 Ks, and Pk3 has two to three rows of 3-4 Ks. The Hk is displaced anteriorly and becomes straight, losing the shape typical of exponential growth phase cells. Cysts are pyriform with a wide cyst wall; no infraciliary structures were visible.

Animals↗
PubMed2004

The life cycle of crime guns: a description based on guns recovered from young people in California.

STUDY OBJECTIVE: We describe the life cycle of crime guns recovered from young people-the movement of those guns from manufacture to criminal use-and identify associations between the characteristics of those guns and their possessors, purchasers, sellers, and places of origin. METHODS: This is a cross-sectional study of data from gun ownership tracing records compiled by the Bureau of Alcohol, Tobacco, Firearms and Explosives for 2,121 crime guns recovered in California from persons younger than 25 years and traced in 1999. Purchaser and seller data for handguns were updated when possible by linking to California handgun sales records. RESULTS: The 2,121 traced guns were recovered from 1,717 young people. Guns recovered from persons aged 21 to 24 years were most frequently also purchased by persons aged 21 to 24 years; those recovered from persons younger than 18 years were most often purchased by persons aged 45 years or older. Small-caliber handguns made up 41.0% of handguns recovered from persons younger than 18 years but 25.2% of handguns recovered from persons aged 21 to 24 years. The median time from sale to recovery (commonly called time to crime) for all guns was 6.4 years (interquartile range 2.7 to 12.4 years). A time to crime of less than 3 years, suggesting deliberate gun trafficking, was observed for 17.3% of guns recovered from persons younger than 18 years but 34.6% of guns recovered from persons aged 21 to 24 years. Ten retailers who sold 10 or more traced guns accounted for 13.1% of all guns traced to a retailer. Handguns whose purchaser and possessor were the same person were more likely than others to be large-caliber semiautomatic pistols (29.3% and 11.7%, respectively); their median time to crime was 0.2 years (69 days). CONCLUSION: Analysis of crime-gun ownership traces reveals patterns that may help refine gun violence prevention efforts and render them more effective.

Adolescent↗
PubMed1996

Biological rhythms in the human life cycle and their relationship to functional changes in the suprachiasmatic nucleus.

Biological rhythms play a prominent role in the human life cycle. The endogenous rhythms are entrained by the environment and have an astronomical counterpart which is obvious for daily, monthly, and yearly rhythms, and may possibly also be present in weekly rhythms. Circadian rhythms are present in, e.g. testosterone levels, spontaneous birth, strokes, and death from cardiovascular causes. Circaseptan rhythms are present in, e.g. spontaneous birth, 17-ketosteroid levels, myocardial infarctions, and strokes. The relationship of these rhythms with the suprachiasmatic nucleus (SCN) has not yet been established. Circatrigintan rhythms, such as the menstrual cycle, have so far not been associated with the SCN. Circannual rhythms are present in, e.g. mood, suicides, reproduction, birth weight, sleep and season of birth of psychiatric patients. The human SCN shows strong circadian and circannual fluctuations in the number of neurons expressing vasopressin. The vasopressin and VIP cell population of the SCN develop late, i.e. for a major part postnatally. After the age of 50 the amplitudes of circadian and circannual fluctuations of the vasopressin cell numbers are reduced whereas the number of vasopressin expressing neurons decreases after the age of 80 and do so even more and earlier in Alzheimer's disease. Sex differences are present in the shape of the vasopressin subnucleus of the SCN and in the vasoactive intestinal polypeptide (VIP) cell number. The sex differences in the SCN, the doubling of the number of vasopressin neurons in the SCN of homosexual men, and a variety of animal experimental observations indicate that the SCN is involved in sexual behavior and reproduction. The exact role of the SCN in these processes is subject to current research.

Circadian Rhythm↗
PubMed2000

Transient chaotic mixing during a baroclinic life cycle.

We discuss how atmospheric eddies affect transport and mixing of tracers at midlatitudes. To this purpose, we study baroclinic life cycles in a simple dynamical model of the atmosphere. We consider the trapping properties of the developing eddies and the characteristics of meridional transport, and we identify regions of increased mixing. Although the flow is in principle three-dimensional, we illustrate how some of the concepts developed in the study of two-dimensional chaotic advection provide useful information on tracer dynamics in more complicated flows. (c) 2000 American Institute of Physics.

Journal Article↗
PubMed1990

Controls in the papillomavirus life cycle.

Papillomaviruses cause neoplasia of epithelia and subepidermal fibroblasts which may progress to certain forms of malignancies. During the viral life cycle, papillomavirus genomes receive, process and generate signals. Transcription factors binding to their enhancer carry information about tissue specificity and hormonal regulation, while other factors in the cornified layer of the epidermis activate capsid protein production. Furthermore, products of the viral E2 and E1 genes constitute feedback signals that modulate viral transcription and replication. Proteins derived from the genes E5, E6 and E7 modulate cellular homeostasis so as to induce neoplatic transformation. A molecular understanding of these regulatory events may form a prerequisite for a causal therapy of papillomavirus-induced malignancies.

Epithelium↗
PubMedDate not supplied

[The life cycl of Maritrema pyrenaica Deblock et Combes, 1965, a parasite of insectivorous micromammals in the Pyrences (author's transl)].

The life cycle of Maritrema pyrenaica is described. M. pyrenaica develops to the sporocyst stage in the snail Bythinella reyniesii. The xiphidio-cercaria, monostomous, anenterous in type, is liberated in water and actively penetrates a Crustacea Gammarus pulex where it encysts. From the point of view of epidemiology, the focuses of M. pyrenaica are divided into two different areas: the area where the parasites multiply (that we call "l'endemiotope") coinciding with the Bythinella biotope and the area limited to the length of the river where the Vertebrate is parasitized.

Animals↗