Forage variation in brood-rearing areas used by pacific black brant geese on the Yukon-Kuskokwim delta, Alaska

1 We investigated the effects of grazing by black brant geese on Carex subspathacea lawns on the Yukon-Kuskokwim delta, Alaska.
2 We compared variation in growth and forage quality in both grazed and temporarily exclosed sites to determine responses of C. subspathacea to grazing at landscape scales within two nesting colonies that had experienced different population dynamics over recent decades.
3 Landscapes differed in forage quality, grazing patterns, and in the effect grazing had on C. subspathacea forage characteristics. We found no effect of grazing on net above-ground primary productivity ( NAPP ) over a wide range of natural grazing intensities at the landscape scale.
4 No differences in forage quality, NAPP , or response of C. subspathacea growth rates to grazing pressures could be detected between colonies. This suggests that goose grazing does not have deleterious effects on C. subspathacea in this ecosystem.
5 It has been suggested that gosling growth rates are sensitive to seasonal declines in forage availability and quality. Spatial variation in forage quality and availability per sampled area exceeded seasonal variation in these characteristics and is likely to have dramatic effects on gosling growth and recruitment rates.     

Side chain conjugation prevents bacterial 7-dehydroxylation of bile acids

The effect of side chain conjugation on 7-dehydroxylation of bile acids has been investigated. C24-bile acids and their glycine and taurine conjugates and keto bile acids were incubated with pure strains of Eubacterium sp. VPI 12708. Bile acids of the 5 alpha- or 5 beta-series with a free terminal carboxyl group and a 3 alpha, 7 alpha-dihydroxy system were very effectively 7 alpha-dehydroxylated, whereas 7 beta-hydroxy bile acids resisted 7-dehydroxylation. Oxo bile acids were metabolized at the oxygen function also. Glycine- and taurine-conjugated bile acids were neither deamidated nor 7-dehydroxylated by the bacteria. Thus, side chain conjugation prevents 7-dehydroxylation of bile acids by Eubacterium sp. VPI 12708.     

Direct embryotoxicity of cocaine in rats: effects on mitochondrial activity, cardiac function, and growth and development in vitro

Day 10 rat embryos were exposed to cocaine HCl (10-100 microM) in vitro in 20% (designated normoxic) and 10-12% (designated moderately hypoxic) oxygen and examined the following day. In normoxia, it caused prompt and significant decreases in heart rates and significant reductions in measures of growth and development and diameters of the vitelline arteries. In moderate hypoxia, cocaine exposure resulted in axially asymmetric defects reported previously only in embryos exposed to extreme hypoxia or to hypoxia generated by redox cyclers. Day 10 or 11 embryos or isolated hearts from the latter stage were incubated with cocaine under normoxic conditions. Acute and significant concentration-dependent decreases in heart rates occurred on day 10. The rates in day 11 embryos and in isolated hearts from day 11 embryos were less sensitive than those on day 10. Cocaine also significantly inhibited the activity of the terminal electron transport system of the mitochondria of embryos. Maternal cocaine exposure has been associated with uterine vasoconstriction and decreases in fetal oxygenation. The latter has been shown to stimulate glucose uptake. We hypothesize that placental vasoconstriction limits the ability of embryos to meet the increased glucose demands induced by hypoxia. The developmental toxicity of nutrient and oxygen deprivation is further enhanced by significant decreases of mitochondrial activity. We propose therefore that compromised energy supplies form the basis of the developmental toxicity of cocaine.     

Studies of pyridine nucleotide oxidizing enzymes from human neutrophils

An NADH cytochrome c reductase has been identified in plasma membrane fractions from neutrophils in addition to the superoxide producing NADPH oxidase which has been extensively studied by other investigators. Activation of neutrophils resulted in increased enzyme activities but to different degrees; the NADH cytochrome c reductase increased 2 fold in specific activity and the NADPH oxidase 30 fold. Treatment of the plasma membrane fraction with sonication and differential centrifugation yielded a particulate fraction (R2) with a 2 fold increase in specific activities of both enzymes and concentrations of cytochrome b and FAD. The cytochrome b in the preparation was not reduced under anaerobic conditions by either NADH or NADPH. Treatment of preparations of R2 with deoxycholate or potassium thiocyanate separated the two enzymes yielding particulate preparations with only NADPH oxidase or NADH cytochrome c reductase activity, respectively.     

Iron deficiency in the rat: biochemical studies of fetal metabolism

The effects of dietary-induced iron deficiency on fetal and maternal metabolism were studied in the rat. Concentrations of phenylalanine, but not tyrosine, were significantly elevated in plasma from iron-deficient maternal and fetal rats at day 20 of gestation with individual fetal plasma levels of phenylalanine as high as 10 mg per 100 ml. Concentrations of total 5-hydroxyindole compounds were significantly decreased in brain tissue from iron-deficient fetuses (day 20 of gestation), suggesting that synthesis of the compounds may be inhibited by iron deficiency. Mitochondrial NADH oxidase activity was markedly decreased (60%) in homogenates of fetuses at day 14 of gestation and may account for the high fetal resorption rate and small fetal size observed in the rat in iron deficiency.     

Pattern of human motoneuron activity during voluntary muscular contraction

The pattern of motor unit activity of the rectus femoris muscle during isometric contraction was studied. Interspike interval sequences were analyzed. At frequencies below 8–10/sec the interval histograms were asymmetrical (long intervals predominated), the standard deviation was high and depended on the mean interval, and adjacent intervals were independent. At frequencies above 10–13/sec the interval distribution became normal in type, the standard deviation was low and independent of the mean interval duration, and negative correlation was found between adjacent intervals. During brief contraction specific for this particular (fast) muscle the activity of most neurons was of the second type, while during prolonged contraction it was of the first type. The change from activity of the first to the second type took place approximately when, with an increase in frequency, spikes began to appear against the background of after-hyperpolarization. A hypothesis is put forward to the effect that after-hyperpolarization creates the rhythm of activity (low variability of the intervals), and that the duration of after-hyperpolarization is correlated with the lower limit of working frequencies of the motoneurons. The motoneuron is regarded as performing not only a summating, but also a damping function, reducing the effect of random fluctuations of the synaptic inflow and coding information for transmission as a mean frequency.Institute of Problems of Information Transmission, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 3, No. 6, pp. 609–619, November–December, 1971.     

Division Delay Induced in Escherichia coli by Near-Ultraviolet Radiation

Beams of near-ultraviolet radiation at several principal emission lines of a mercury arc were isolated with a grating monochromator and directed upon cell suspensions. During subsequent incubation at room temperature in Nutrient Broth, the population was studied by removing samples and obtaining cell numbers and cell size distributions with an electronic cell counter. Division delay without lethality was observed. The shapes of the dose-response curves for induction, the doses of near-ultraviolet radiation required, and the action spectrum for division delay were found to be similar to those for growth delay (in broth) and for photoprotection. These findings indicate that all three effects, division delay, growth delay, and photoprotection, are induced by a common type of critical event. Changes in cell size distribution in the culture during incubation in Nutrient Broth after near-ultraviolet irradiation are very similar for control and irradiated populations, although these changes occur at a much later time in the irradiated population. This indicates that, in Nutrient Broth, the population recovers completely from the inhibition of growth and division, thus justifying use of the term "delay," and suggesting that the damage is nongenetic.