Phytoplankton population dynamics of a small reservoir: physical/biological coupling and the time scales of community change

This paper describes the day-to-day changes in species compositionthat resulted from intermittent wind mixing of the surface watersof a small reservoir. Two major scales of community change weredetected: a short-term (>1 day) scale associated with theredistribution of cells within the basin, and a 5–14-dayscale associated with growth responses. The physical scalesof change were found to be almost identical to the biologicalscales: wind stress caused changes in the temperature gradientof surface waters at scales of a day, and major vertical mixingevents occurred at scales of 10–14 days. The presenceof buoyant species ensured that rapid advection of populationsfollowed wind events. Community change was a function of bothadvection and growth, so that both real and apparent changesin abundance occurred. The observed seasonal succession wasboth a true succession and a changing sequence of populationsdependent on horizontal advection of water within the basin.Consistent stratification was present throughout the summerperiod and phytoplankton diversity was low. Even so, the seasonalsuccession was best described as a series of allogenic perturbationsfollowed by biological restructuring of the community. Dailysampling was necessary to document fully the mechanisms drivingthe seasonal succession of species.     

Effects of in vivo ultrasound hyperthermia on natural killer cell cytotoxicity in the hamster

The effects of in vivo ultrasound irradiation of the spleen on immunological functions were assessed with an in vitro natural killer (NK) cell cytotoxic assay. Anesthetized hamsters were exposed to 1 MHz ultrasound at intensity levels currently being used clinically for therapeutic diathermy and hyperthermia (1-5 W/cm2, for 500 sec with constant beam scanning). Hyperthermic levels in the spleen ranged from 38-43 degrees C. Significant depression of natural killer (NK) cell activity was seen 4 h after spleen irradiation as compared to sham irradiated and normal animals. A return towards normal levels was observed in experimental groups at 24 h after exposure. Sham and normal animals were not significantly different in NK activity, indicating no significant stress-related immunosuppressive effects due to handling. Differential leukocyte counts taken for each exposure condition showed significant lymphopenia at 4, 8, and 16 h after exposure, near normal levels at 24 h, and complete recovery by 48 h. The number of circulating mononuclear cells at 4 h showed a dose-related suppression as the exposure intensities were increased.     

Chromosome 8 breakpoint far 3'' of the c-myc oncogene in a Burkitt''s lymphoma 2;8 variant translocation is equivalent to the murine pvt-1 locus.

The 2;8 variant translocation of human Burkitt's lymphomas is closely related cytogenetically to the t(6;15) of murine plasmacytomas; both involve a reciprocal exchange between the Ig kappa locus and a band region indistinguishable from that bearing the c-myc oncogene. To define their molecular relationship, we have compared cloned chromosome 8 DNA from the t(2;8) breakpoint in the human Burkitt's lymphoma JBL2 with cloned DNA from the murine pvt-1 locus, the major chromosome 15 breakpoint region in murine t(6;15). DNA sequencing and Southern blot analysis shows that these two regions are homologous. Thus the t(2;8) in JBL2 is the molecular equivalent of many murine t(6;15). The murine pvt-1 locus lies an unknown distance 3' of c-myc; analysis of DNA from several tumours with c-myc amplification reveals that pvt-1 is co-amplified in at least one case, placing pvt-1 approximately 100-500 kb 3' of c-myc. The significance of these results with respect to the role of pvt-1 in tumorigenesis is discussed.     

Inhibition of exogenous NADH oxidation in plant mitochondria by chlorotetracycline in the presence of calcium ions

Chlorotetracycline inhibits the uncoupled oxidation of exogenous NADH by Jerusalem artichoke (Helianthus tuberosus L.) mitochondria extensively (over 80%) and rapidly (inhibition complete in 10 s) in the presence of added Ca²⁺. Half-maximal inhibition is observed at 15 μM chlorotetracycline in the presence of 2 mM Ca²⁺. The oxidation of succinate is only affected marginally by chlorotetracycline plus Ca²⁺. The inhibition of NADH oxidation and the fluorescence of CTC are well correlated. Mn²⁺ is the only other cation which shows an (increased) inhibition in the presence of chlorotetracycline. The inhibition by Ca²⁺ and chlorotetracycline disappears at acid pH, and the pH optimum in their presence is 6.4. The inhibition caused by other lipid-soluble Ca²⁺-chelators is not reversible or is enhanced by the addition of excess Ca²⁺. In contrast, inhibition caused by relatively water-soluble chelators is completely reversed by added Ca²⁺. It is suggested that a neutral 1:2 complex is formed between Ca²⁺ and chlorotetracycline which can substitute for Ca²⁺ bound at sites in the lipophilic phase of the inner mitochondrial membrane, which are essential for the activity of the external NADH dehydrogenase.     

Incidence of antibiotic-resistant Escherichia coli in milk produced in the west of Scotland

Antibiotic-resistant Esch. coli were found in 10.6% of milk samples collected from 998 farms in the west of Scotland. The incidence of both Esch. coli and antibiotic-resistant Esch. coli in milk was higher when the cattle were housed day and night than when they were outdoors. Of the 1125 Esch. coli isolates tested 22.2% were antibiotic resistant and of these 42.4% were resistant to more than one antibiotic. Escherichia coli carrying up to six resistance determinants were isolated. The possible implications to animal and human health are discussed.     

Menstrual cycle patterns of hormones and sexual behavior in gorillas

Oppositely sexed pairs of gorillas were tested behaviorally during the menstrual cycle to determine the relationship between hormone concentrations of the female and the frequency of sexual activity by the pair. Five females were tested individually during two cycles with each of two males, but serum samples for hormone assay were obtained from each female only during the first cycle of testing. There was no clear relationship between hormones and behavior for the single cycle in which the serum samples were obtained, with the exception that no copulations occurred after the early luteal phase, when progesterone was greater than 5 ng/ml. Normalized behavioral data from all four test cycles for all pairs suggested that female-solicited copulations were restricted primarily to the periovulatory period. Male sexual initiative (by one of the males) accounted for most copulations temporally dissociated from the periovulatory period. Normalized hormone data for all of the females suggested that (1) attractivity was associated with estradiol concentrations during the follicular phase, (2) proceptivity with estradiol and testosterone at midcycle, whereas (3) receptivity was not associated with hormone patterns or cycle phase. The data suggest that hormones are one of several variables that contribute to the regulation of sexual behavior in gorillas.     

Metabolism of arachidonic acid and prostanoids in human endometrial stromal cells in monolayer culture

In the present investigation, we compared the metabolism of arachidonic acid in human endometrial stromal cells maintained in monolayer culture with that in human decidual tissues. By gas-chromatographic analysis, the distribution of arachidonic acid in glycerophospholipids and in the neutral lipids of decidual tissues and stromal cells in culture was similar. After the addition of [14C]arachidonic acid to the culture medium, steady-state conditions with respect to radioactive labeling of the lipids of the cells were attained after 24 h, except for phosphatidylethanolamine and neutral lipids. The percentage distribution of [14C]arachidonic acid in the lipids of the cells in culture was as follows: phosphatidylcholine, 41%; phosphatidylserine, 5%; phosphatidylinositol, 19%; phosphatidylethanolamine, 22%; neutral lipids, 11%. This distribution of arachidonic acid among the lipids is similar to that in decidual tissue, except for that in phosphatidylethanolamine. The amount of radioactivity in phosphatidylethanolamine continued to increase up to 72 h whereas that in neutral lipids declined after a maximum amount was present at 4 h. In the cells in monolayer culture, [14C]prostaglandin E2 and [14C]prostaglandin F2 alpha were produced from [14C]arachidonic acid, as is true in superfused decidual tissue. The similarities in arachidonic acid metabolism in these cells to that in decidual tissue are supportive of the proposition that endometrial stromal cells in monolayer culture are an appropriate model for the study of the regulation of arachidonic acid release and prostaglandin formation by endometrium and decidua vera.     

Nutrient control of brain neurotransmitter synthesis and function

Dietary fluctuations in nutrient availability are factors in the regulation of brain function. Until recently the prevailing view was that brain biochemistry and function were influenced by diet only when biochemical and clinical evidence of nutrient deficiency was present. It is now clear, however, that the brain is sensitive and responsive to diet composition. Preliminary data show that variation in vitamin and mineral nutrient intakes over ranges that are considered to maintain normal nutritional status may impact on brain biochemistry, owing to their many coenzyme roles. Furthermore, the synthesis of at least five brain neurotransmitters, namely serotonin, the catecholamines, acetylcholine, histamine, and glycine responds to dietary fluctuations in availability of their nutrient precursors, tryptophan, tyrosine, choline, histidine, and threonine, respectively. Not only are these biochemical events altered by normal variations in diet composition, but considerable evidence now exists to show that the brain uses this information to regulate many functions. Future studies can be expected to continue to elucidate the links between diet, brain neurotransmission, and brain function, and to exploit the application of these links in understanding the function of the brain under normal and disease conditions.