Running on an incline.

Seven male subjects ran at 3.0 m/s on a motorized treadmill including a force platform under the tread. The subjects ran at each of five treadmill inclinations: +0.17, +0.077, 0, -0.077, and -0.17 radians. The position of the subjects' legs were read from ciné films (100 frames/s). Results of the film and force plate analysis generally corroborated the "hanging triangle" hypothesis, which postulates that the angle between the leg and the vertical upon foot strike does not change as the treadmill is tipped up or down. A mathematical model of running, in which the leg is represented as a nonlinear spring, made satisfactory predictions of the way many parameters of running change with the treadmill angle, including the length of the leg at touchdown and liftoff and the peak leg force in the middle of a step. The peak leg force reaches a maximum at a treadmill angle near -0.12 radians, close to the downhill angle where other authors have found a minimum in the rate of oxygen consumption.     

The CDK4/6 Inhibitor Abemaciclib Induces a T Cell Inflamed Tumor Microenvironment and Enhances the Efficacy of PD-L1 Checkpoint Blockade

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Three-year study of benthic algal spring bloom development in a small, Danish lowland stream

Seasonal development of benthic algae was studied over a three-year period in a small, nutrient-rich lowland stream to investigate inter-annual variation in the algal spring bloom and differences in algal biomass regulation on two different substrata: fine-grained sediments and stones. The algal spring bloom was initiated when irradiance at the sediment surface exceeded 7 mol photons m^-2 d^-1 and mean water velocity was concomitantly below the threshold for bed load transport in the stream. Large inter-annual and substratum-dependent differences in peak algal biomass were observed, thus suggesting that different parameters regulate algal biomass development on the two substrata. On fine-grained sediments algal biomass development was predominantly coupled to light availability, while on stony substrata algal composition and peak biomass might be affected by invertebrate grazing.     

On the mechanisms of the growth-promoting effect of prostaglandins in hepatocytes: The relationship between stimulation of DNA synthesis and signaling mediated by adenylyl cyclase and phosphoinositide-specific phospholipase C

While many observations indicate that prostaglandins may act as positive regulators of hepatocyte proliferation, the underlying mechanisms are not known. We have examined some of the signal pathways in the growth response induced by prostaglandins in hepatocytes, with particular focus on adenylyl cyclase and phosphoinositide-specific phospholipase C. Adult rat hepatocytes were cultured as primary monolayers in serum-free medium in the presence of EGF and insulin. PGE₂ or PGF_2α (added 0-3 h after plating) enhanced the incorporation of [³H]-thymidine into DNA (measured at 50 h); at 100 γM the stimulation was about threefold. PGI₂ and PGD₂ also showed significant but smaller stimulatory effects. No significant increase in the level of cyclic AMP (cAMP) was detected in response to any of the prostaglandins. Low concentrations of glucagon (0.1-10 nM), a potent activator of hepatic adenylyl cyclase, or 8-bromo-cAMP (0.1-10 γM) enhanced the DNA synthesis. When 8-bromo-cAMP was used in maximally effective concentrations, no further stimulation was obtained by combining it with glucagon, whereas the effects of PGE₂ and 8-bromo-cAMP were completely additive. All the prostaglandins also showed additivity with the effect of glucagon on the DNA synthesis. PGE₂, PGF_2α, PGI₂, and PGD₂ increased intracellular inositol-1,4,5-trisphosphate (InsP₃), with a relative order of efficacy roughly corresponding to their activity as stimulators of DNA synthesis. Increases in cytosolic free Ca²⁺, as measured in single cells, were elicited in a majority of the hepatocytes by all these prostaglandins at 1 γM. Supramaximal concentrations of vasopressin, a strong activator of phospholipase C in hepatocytes, acted additively with PGE₂ on the DNA synthesis. Pretreatment of the hepatocytes with a concentration of pertussis toxin that prevented the inhibitory effect of PGE₂ on glucagon-induced cAMP accumulation did not abolish the ability of PGE₂ to stimulate the DNA synthesis. The results do not support a role for adenylyl cyclase activation in the stimulatory effect of prostaglandins on hepatocyte growth. While the data are compatible with an involvement of phosphoinositide-specific phospholipase C in the growth-promoting effect of prostaglandins in cultured rat hepatocytes, they suggest this may not be the sole mechanism. © 1995 Wiley-Liss, Inc.     

The spatial structure of the gene pool of a viviparous population of Poa alpina - environmental controls and spatial constraints

Bjømstad, O. N., Iversen, A. & Hansen, M. 1995. The spatial structure of the gene pool of a viviparous population of Poa alpina — environmental controls and spatial constraints. — Nord. J. Bot. 15: 347–354. Copenhagen. ISSN 0107–055X.
Because both the genetic make-up and the environmental conditions of a population are spatially autocorrelated, it is difficult to infer processes of selection or drift for population genetic mappings. We propose a methodology based on partial Mantel techniques and partial autocorrelation techniques to separate the action of these processes. The method is applied to data on Poa alpina to indicate that isolation-by-distance (drift) is the main process inducing positive autocorrelation at the scale of diaspore dispersal (< 100m). The pattern at larger distances is more consistent with selection.     

Estrogens and non-estrogenic ovarian influences combine to promote the recruitment and decrease the turnover of new neurons in the adult female canary brain

The higher vocal center (HVC) of the songbird forebrain exhibits persistent neurogenesis in adulthood, particularly in a region of the mediocaudal neostriatum that is associated with a subventricular layer of estrogen receptive cells. We asked whether estrogens might influence adult neurogenesis, by assessing the effect of ovariectomy on HVC neuronal production in the adult female canary. Fifteen 1-year-old females were separated into groups of ovariectomized, estradiol-replaced ovariectomized, and gonadally intact birds. To label dividing cells and their progency, the birds were given [³H]thymidine for 8 days, killed 32 days later, and their brains autoradiographed. A significant rise was noted in the number of HVC neurons per section in estradiol-treated birds relative to the untreated control birds. The number of [³H]-thymidine-labeled HVC neurons was also higher in the estrogen-treated birds; however, the neuronal labeling index (LI) did not vary as a function of estradiol replacement, as the total number of HVC neurons rose in parallel with the added new neurons. In contrast, the neuronal LI did rise as a result of ovariectomy, and this ovariectomy-associated increase in the LI was not reversed by estradiol. Among non-neuronal cell types, the endothelial LI was higher in estrogen-treated birds than in their untreated counterparts, suggesting estrogen-associated angiogenesis. Radioimmunoassay confirmed that serum estradiol was reduced in the castrated birds. Since estrogen appeared to promote the survival of [³H]thymidine⁺ neurons, we next sought to determine whether estrogen acted directly on the newly generated neurons, or rather indirectly through an intermediary cell population. To this end, we asked whether the new neurons or their precursors expressed estrogen receptor immunoreactivity (ER-IR). Five adult male canaries were given [³H]thymidine for periods ranging from 2 to 28 days, killed at varying times up to 3 weeks therafter, then probed for ER-IR and autoradiographed. [³H]thymidine⁺ cells displayed no detectable ER-IR within their first 4 weeks of postmitotic life. Rather, during migration from the ventricular zone (VZ), the new neurons traversed a layer of mitotically quiescent, ER⁺ subventricular cells. Double labeling for ER-IR and cell-type selective antigens confirmed that these ER⁺ cells were neurons. These results indicate that the early survival of new neurons in the adult songbird HVC is promoted by estrogen, and may be mediated by the estrogen-stimulated paracrine release of neurotrophic agents by ER-IR subventricular neurons. Our data suggest that estrogen's promotion of neuronal survival may operate concurrently with an estrogen-independent ovarian suppression of neuronal mitogenesis.     

Oxidation and Assimilation of Atmospheric Methane by Soil Methane Oxidizers

The metabolism of atmospheric methane in a forest soil was studied by radiotracer techniques. Maximum (sup14)CH(inf4) oxidation (163.5 pmol of C cm(sup-3) h(sup-1)) and (sup14)C assimilation (50.3 pmol of C cm(sup-3) h(sup-1)) occurred at the A(inf2) horizon located 15 to 18 cm below the soil surface. At this depth, 31 to 43% of the atmospheric methane oxidized was assimilated into microbial biomass; the remaining methane was recovered as (sup14)CO(inf2). Methane-derived carbon was incorporated into all major cell macromolecules by the soil microorganisms (50% as proteins, 19% as nucleic acids and polysaccharides, and 5% as lipids). The percentage of methane assimilated (carbon conversion efficiency) remained constant at temperatures between 5 and 20(deg)C, followed by a decrease at 30(deg)C. The carbon conversion efficiency did not increase at methane concentrations between 1.7 and 1,000 ppm. In contrast, the overall methane oxidation activity increased at elevated methane concentrations, with an apparent K(infm) of 21 ppm (31 nM CH(inf4)) and a V(infmax) of 188 pmol of CH(inf4) cm(sup-3) h(sup-1). Methane oxidizers from soil depths with maximum methanotrophic activity respired approximately 1 to 3% of the assimilated methane-derived carbon per day. This apparent endogenous respiration did not change significantly in the absence of methane. Similarly, the potential for oxidation of atmospheric methane was relatively insensitive to methane starvation. Soil samples from depths above and below the zone with maximum atmospheric methane oxidation activity showed a dramatic increase in the turnover of the methane assimilated (>20 times increase). Physical disturbance such as sieving or mixing of soil samples decreased methane oxidation and assimilation by 50 to 58% but did not alter the carbon conversion efficiency. Ammonia addition (0.1 or 1.0 (mu)mol g [fresh weight](sup-1)) decreased both methane oxidation and carbon conversion efficiency. This resulted in a dramatic decrease in methane assimilation (85 to 99%). In addition, ammonia-treated soil showed up to 10 times greater turnover of the assimilated methane-derived carbon (relative to untreated soil). The results suggest a potential for microbial growth on atmospheric methane. However, growth was regulated strongly by soil parameters other than the methane concentration. The pattern observed for metabolism of atmospheric methane in soils was not consistent with the physiology of known methanotrophic bacteria.     

Phototrophic growth in the lumostat: a photo-bioreactor with on-line optimization of light intensity

A novel approach is described for the growth of phototrophic microorganisms in batch culture in laboratory-scale photo-bioreactors. Pure CO₂ is added separately to the aeration gas in a closed loop and the rate of photosynthetic activity is monitored continuously by recording the amount of CO₂ added in order to maintain constant pH. These activity measurements are used to control the intensity of illumination by varying the voltage applied to a bank of fluorescent tubes. The intensity of illumination is maintained at the value giving the maximal rate of photosynthesis while photoinhibition due to excess light is avoided. Since the light intensity received by the individual cells is maintained at the optimal value we term the device a lumostat.Measurements of photosynthetic activity by monitoring CO₂ addition were in excellent agreement with off-line measurements of cell carbon as long as corrections were made for diffusion loss through the walls of the tubing. Exponential growth of a thermophilic strain of the cyanobacteriumSynechococcus was obtained for 7 generations with maximum cell densities of 8 × 10⁷ cells mL^–1. The productivity of the lumostat is superior to that of batch cultures at any fixed light intensity.     

Cytochemical localization of myrosinase (β-thioglucosidase) in root tips ofSinapis alba

Summary A method for electron microscopic cytochemical localization of a-thioglucosidase (myrosinase) has been developed. Since sulphate is one of the products of the hydrolysis of sinigrin by myrosinase, it was felt that if the incubation was carried out in the presence of Pb⁺⁺-ions an insoluble precipitate of electron-dense PbSO₄ would be formed at the reaction sites. Following formaldehyde fixation a few different cell organelles in the extreme root tip ofSinapis alba showed reaction specificity for myrosinase but following glutaraldehyde fixation the enzymatic activity was inhibited. Biochemical tests of the isolated enzyme showed complete inhibition of the myrosinase by glutaraldehyde. Variations in the substrate concentration and incubation time indicated that the enzyme was confined to the dilated cisternae of the endoplasmic reticulum and in a limited extent to the mitochondria.     

RELEASE OF [3H]GAMMA-AMINOBUTYRIC ACID FROM GLIAL CELLS IN RAT DORSAL ROOT GANGLIA.

Abstract— Desheathed rat dorsal root ganglia were incubated in a medium containing amino-oxyacetic acid and [³H]GABA. Under these conditions, [³H]GABA is taken up exclusively by the satellite glial cells in the ganglia. Efflux of [³H]GABA from the tissue was measured after passing the ganglia through a series of wash solutions. The spontaneous efflux of radioactivity, mostly [³H]GABA, was more rapid in the absence of amino-oxyacetic acid in the incubation and wash media.
Raising the potassium concentration in the wash media caused an increase in the efflux of [³H]GABA. This increase was sigmoidally related to the potassium concentration in the wash media, reaching a maximum at 64 m m -K⁺. The releasing effect of K⁺ was inhibited by removing calcium from the media. Reducing the calcium and raising the magnesium concentration in the wash solutions inhibited the increased efflux of [³H]GABA due to 64 m m -K⁺ by 48 per cent, while 5 mM-La³⁺ and diphenylhydantoin (0·005 and 0·5 m m ) had no effect on this increase.
Only a small increase in the efflux of [¹⁴C]glutamate was produced by 64 m m -K⁺ and it had no effect upon the effluxes of [³H]glycine, [³H]alanine or [³H]leucine. The efflux of lactate dehydrogenase was similarly unaffected by 64 mM-K⁺. The results suggest that glial cells in spinal ganglia can respond to depolarizing concentrations of potassium by releasing GABA in a calcium-dependent process.