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At least 1,081 records · Page 60Linked to original sources
PubMed2003

Abnormal spermatogenesis at low temperatures in the Japanese red-bellied newt, Cynops pyrrhogaster: possible biological significance of the cessation of spermatocytogenesis.

In newt testis, spermatocytes never appear during winter, because secondary spermatogonia die by apoptosis just before meiosis. In the current study, we examined the effect of low temperatures on spermatogenesis. Incubation of newts at low temperatures (8, 12, 15 degrees C) induced defects in spermatogenesis in a temperature-dependent manner. At 8 degrees C, multinucleated giant cells (MGCs) were observed in spermatocytes and spermatogenesis never proceeded beyond meiosis. Although spermatocytes completed meiotic divisions at 12 degrees C, severe cell death was observed in the spermatids. At 15 degrees C both normal and abnormal spermiogenesis were observed. Under these conditions, impaired meiotic synapsis/recombination and down-regulation of the expression of the DMC1 protein, which play pivotal roles in meiotic pairing in eukaryotes, were also observed. Furthermore, to examine the quality of the sperm produced at low temperature for supporting development, artificial insemination was performed. The eggs inseminated with spermatozoa derived from newts kept at 15 degrees C demonstrated a restricted developmental capacity, even though these spermatozoa had an equal capacity for carrying out fertilization to those kept at 22 degrees C. These results suggest that meiosis at low temperatures cause the production of abnormal spermatozoa. Conservation and the significance of this phenomenon in poikilothermic vertebrates living in the temperate zones are also discussed.

Animals↗
PubMed2001

Signal generation and clarification: use of case-control data.

Case-control surveillance systems are useful for 'signal' generation, i.e., signaling potential previously unidentified adverse effects of drugs. Two systems currently in operation, the Slone Epidemiology Unit's Case-Control Surveillance and the Birth Defects Study, have monitored drug effects since 1976. With extensive information on the diagnoses and covariates, the systems have the capacity to carry out in-depth analyses in which the outcome measure is more specifically defined and in which confounding is controlled, thus reducing the possibility of false alarms.

Case-Control Studies↗
PubMed1989

Surgical treatment of epilepsy: opportunities for research into basic mechanisms of human brain function.

Numerous technological developments in neurology have increased the ability to localize structural and functional abnormalities within the human brain. Such techniques have contributed to a renewed interest in resective surgical treatment for medically refractory partial seizures. Enhanced capacity to carry out detailed in vivo and in vitro measurements of neuronal activity in patients, during the course of presurgical evaluation and following surgical resection, now offers unprecedented opportunities for invasive research into normal and abnormal human cerebral function. Electrophysiological, microanatomical, biochemical and behavioral studies can be carried out without presenting undue risk or discomfort to the patient. Such research in a clinical setting presents difficulties in experimental design for the basic neuroscientist. Problems are reduced in clinical programs where diagnostic and surgical procedures are carried out in a standardized fashion according to specific protocols. The UCLA clinical protocol for anterior temporal lobectomy, based on presurgical evaluation with stereotactically implanted depth electrodes, is particularly amenable to the integration of basic research projects. This protocol and related ongoing research projects are described.

Brain Mapping↗
PubMed1994

Famine, revolt, and the dynastic cycle: population dynamics in historic China.

"Historians have long noticed that population declines in ancient China often coincided with dynasty changes, and that most of these declines were the result of internecine wars which, in turn, were often initiated by famine or density pressure. Since the interactions between density pressure, internecine wars, and dynasty changes cannot be explained by the traditional age-specific density-dependent population structure, we propose to use a bandit/peasant/ruler occupation-specific population model to interpret the dynamic socio-economic transitions of ancient Chinese population, and provide econometric support to our model. We also highlight the rich dynamics of the composition of human population, a factor which was often neglected in previous research on general populations."

Asia↗
PubMed1986

Changing patterns of population distribution in Zimbabwe.

"This paper critically evaluates the causes and consequences of changes in population distribution in Zimbabwe during the colonial period and since independence in 1980. Five main aspects of population geography are examined. Firstly...the history of tenure policies is outlined. Secondly, the distribution of the African population as revealed in the 1982 census is described and major changes between the census years of 1962, 1969, and 1982 are discussed. Thirdly, changing patterns of settlement and land use within the peasant farming areas (Communal Lands) are examined in the context of increasing population pressures. Fourthly, trends in the...urbanisation of the African population are described. Fifthly, post-independence development policies directed at effecting changes in the distribution of population are discussed with particular reference to the land resettlement programme."

Africa↗
PubMed1994

Evidence that the intrinsic membrane protein LHCII in thylakoids is necessary for maintaining localized delta mu H+ energy coupling.

This work tested the hypothesis that thylakoid localized proton-binding domains, suggested to be involved in localized delta mu H(+)-driven ATP formation, are maintained with the involvement of several membrane proteins, including the LHCII (Laszlo, J.A., Baker, G.M., and Dilley, R.A. (1984) Biochim. Biophys. Acta 764, 160-169), which comprises about 50% of the total thylakoid protein. The concept we have in mind is that several membrane proteins cooperate to shield a localized proton diffusion pathway from direct contact with the lumen, thus providing a physical barrier to H+ equilibration between the sequestered domains and the lumen. A barely mutant, chlorina f2, that lacks Chl b and does not accumulate some of the LHCII proteins, was tested for its capacity to carry out localized-proton gradient-dependent ATP formation. Two previously developed assays permit clear discrimination between localized and delocalized delta mu H+ gradient-driven ATP formation. Those assays include the effect of a permeable buffer, pyridine, on the number of single-turnover flashes needed to reach the energetic threshold for ATP formation and the more recently developed assay for lumen pH using 8-hydroxy-1,3,6-pyrene trisulfonic acid as a lumenally loaded pH-sensitive fluorescent probe. By those two criteria, the wild-type barley thylakoids revealed either a localized or a delocalized energy coupling mode under low- or high-salt storage conditions, respectively. Addition of Ca++ to the high-salt storage medium caused those thylakoids to maintain a localized energy-coupling response, as previously observed for pea thylakoids.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1990

The tragedy of the commons: twenty-two years later.

The authors take up the hypothesis originally proposed by Garrett Hardin that resources held in common, such as oceans, rivers, air, and parklands, are bound to be subject to massive degradation. Specifically, they "examine the accumulated evidence pertaining to common-property resource management and provide a critique of the conventional theory expounded by Hardin." They conclude that recent evidence suggests that users of such resources are able to restrict access to them and establish rules among themselves for their sustainable use.

Conservation of Natural Resources↗
PubMed1985

Self-renewal capacity of murine hemopoietic stem cells under internal contamination with 239Pu and 241Am.

The self-renewal capacity of murine pluripotent hemopoietic stem cells (CFU-S) of vertebral bone marrow was studied under conditions of short-term and long-term internal contamination with 239Pu or 241Am in female mice. Measurement of the CFU-S self-renewal capacity was carried out using double transplantation assay. To evaluate the production of differentiated progeny of stem cells average erythroblast numbers/visible spleen colony and 59Fe-uptake/colony were computed. The marrow cellularity/vertebra and the number of CFU-S/vertebra were decreased and affected more by 239Pu than by 241Am. The production of erythroblasts per a single CFU-S and the 59Fe-uptake/colony were reduced, similarly the numbers of secondary spleen colonies and of secondary CFU-S in primary colonies. The above changes resulting from impaired functions of surviving CFU-S were more serious with 241Am than with 239Pu. The biological effects of plutonium and americium appeared independent of the phase of contamination.

Alpha Particles↗
PubMed1994

[Agrarian overpopulation and household structure in Saguenay (1881-1931)].

"Our paper investigates the effect of land shortage in the Saguenay region [of Quebec, Canada,] upon the household structures, more precisely on the frequency of a) complex structures, b) celibacy, c) cohabitation with strangers (non-relatives). The data come from 28 parish censuses of the period 1881-1931. For each of these three indicators, findings show that the saturation of arable land did not entail significant changes." (SUMMARY IN ENG)

Agriculture↗
PubMed1982

Isolation of Chinese hamster ovary cells with reduced unscheduled DNA synthesis after UV irradiation.

A simple procedure has been worked out to obtain UV-sensitive mutants of Chinese hamster ovary (CHO) cells. In this procedure, conventional mutagenesis is followed by BrdU--light treatment to enrich the population for UV-sensitive cells. Colonies that are allowed to form subsequently are duplicated by replica plating and screened on the master plate for their UV sensitivity and their capacity to carry out UV-induced DNA repair synthesis. Putative mutants are isolated from the replica. With this combination of methods, we succeeded in isolating CHO mutants with an 85-95% reduced level of UV-induced DNA synthesis in combination with an increased UV sensitivity.

Animals↗
PubMed2002

Cell-adhered conjugated linoleic acid regulates isomerization of linoleic acid by resting cells of Propionibacterium freudenreichii.

The microbiological isomerization of linoleic acid (LA) to conjugated linoleic acid (CLA) was studied in resting cell suspensions of a propionibacterium and micellar LA to identify factors critical in the isomerization efficiency. These suspensions, containing cells 5x10(10) colony-forming units ml(-1) and 510 micro g LA ml(-1), isomerized about 90% of LA to CLA. However, the yield was not improved with higher amounts of micellar LA, suggesting that the cells had a fixed capacity to carry out the isomerization. This was explained by the fact that the CLA formed had a tendency to accumulate in the cell mass rather than in the aqueous micellar phase during the isomerization. Concomitantly, cell viability and isomerization rates were gradually reduced. Upon cessation of the reaction, about 46% of all the CLA formed was in the cell material. This accumulation to the cells was prevented by adding the detergent in excess to that required for micellization of LA. Then the cells remained viable, but the rate of isomerization was drastically lowered, due to impaired availability of LA from the fortified micellar phase to the cells. It was concluded that the phase distribution of substrate and product plays a critical role in the microbiological production of CLA.

Enzyme Inhibitors↗
PubMed2006

Insights into central and peripheral factors affecting the "oxidative performance" of skeletal muscle in aging.

During exercises with relatively small muscle masses, limitations to exercise performance by the cardiovascular system should be significantly reduced, allowing one to fully-test the "oxidative potential" of the investigated muscles. Ten elderly males (E, 77.8 +/- 2.9 years [x +/- SD]) and eight young controls (Y, 26.6 +/- 3.0) underwent incremental exercises to voluntary exhaustion on a dynamic leg-extension (dominant limb) machine (knee-extension, KE) and on a cycloergometer (CYCLO). During KE the load was increased every 3 min to loads corresponding to 20, 40 and 60% of the force of one-repetition maximum (1RM). The following variables were determined (vastus lateralis muscle): concentration changes of deoxygenated haemoglobin and myoglobin (Delta[deoxy(Hb + Mb)]) by near-infrared spectroscopy (NIRS), expressed as percentage of the maximal value obtained during transient limb ischemia, and taken as an index of O2 extraction; root mean square (RMS) and median power frequency (MDF) by electromyography. The total lifted load during KE and peak workload during CYCLO were lower in E versus Y (620.4 +/- 321.9 kg vs. 1347.4 +/- 458.7; 113.5 +/- 23.9 W vs. 224.3 +/- 41.0, respectively). During CYCLO Delta[deoxy(Hb + Mb)] peak (i.e. the value determined at exhaustion) was lower in E (44.5 +/- 17.7%) versus Y (67.1 +/- 22.9), whereas during KE Delta[deoxy(Hb + Mb)] peak was higher in E (56.8 +/- 20.9%) versus Y (38.6 +/- 15.8). "Thresholds", that is abrupt increases in RMS slopes, were detected in Y but not in E, suggesting less recruitment or a preferential atrophy of type 2 fibers in the elderly. These findings, associated with the preserved capacity of O2 extraction, suggest a shift towards oxidative metabolism in skeletal muscles of 78 year-old subjects, which could preserve, at least in part, their capacity to carry out exercise.

Adult↗