Acceleration of recovery from sciatic nerve damage by the ACTH(4–9) analog Org 2766: Different routes of administration

Functional recovery following a sciatic nerve crush in rats was investigated by measuring the reflex withdrawal of the hindpaw to a hot air stream. The ACTH(4–9) analog Org 2766 accelerated recovery when administered subcutaneously (two-daily injections: 10 μg/animal; minipumps: 20–40 μg/animal per 24 hr; biodegradable microspheres: 40 μg/animal per 24 hr), but oral administration (1.5–20 mg/animal daily, in the drinking water; 1.5–15 mg/animal daily, by gavage) was not effective.     

Survival, Gap Formation, and Recovery Dynamics in Grassland Ecosystems Exposed to Heat Extremes: The Role of Species Richness

A field experiment was performed in which the richness of perennial grasses (S) was varied in model ecosystems exposed to a simulated heat wave (free air temperature increase and drought). The proportion of individuals that survived the heat wave decreased with S, which could be ascribed to higher water consumption in the species-rich systems. Higher transpiration at high diversity was also observed in other studies using functional groups and could have originated from increased leaf area, less intense stomatal closure, or a combination of both. The increased tiller number per plant that we observed, while leaf area per tiller remained constant, suggests that an enhanced leaf area index was most likely responsible. However, competitive interactions also seemed to play a role in the influence of S on survival. Regrowth of the surviving individuals, expressed as leaf area per living plant after a recovery period following the heat wave, increased with S, most likely due to the dominance of productive species, which was facilitated by the additional space yielded by more intense gap formation at higher S (due to higher plant mortality). Species richness affected both the size and density of the gaps. Mean size increased exponentially with S, while density increased at low S but decreased at higher S when connectance of the gaps occurred. Size distribution of the gaps was not affected. Received 18 January 2000; accepted 31 May 2001.     

Quantitative Determination of Polyethylene Glycol Based upon Its Salting Out and Partitioning of a Dye into the Resulting Aqueous Two-Phase System

A method is described that allows quantitative determination of polyethylene glycol (PEG) concentrations by spectrophotometric measurement of fluorescein dye absorbance after its partitioning into an aqueous two-phase system containing mPEG (M_r 5 kDa) in the upper phase and ammonium sulfate in the lower phase. The absorbance decrease of fluorescein in the lower phase is directly proportional to the mPEG concentration, with two proportionality constants equal to 4.42 × 10⁵ and 2.84 × 10⁵ M⁻¹ cm⁻¹ in the range of 0-0.4 and 0.4-1 μM, respectively. This experimental technique can be extended to PEGs of other molecular weights by means of calibration curves that give for each size of PEG the adequate proportionality constants. The results indicate that the quantitative determination is not affected by the presence of many substances such as proteins, reducing agents, and salts, at the usual concentrations.     

Ecology of testate amoebae communities from aquatic habitats in the Zackenberg area (Northeast Greenland)

A total of 67 taxa, belonging to 15 genera, were recorded from aquatic samples collected in Zackenberg (Northeast Greenland). Most taxa belong to the genera Difflugia, Centropyxis, Nebela and Euglypha. Trinema lineare showed the highest relative abundance. Seven taxa were recorded for the first time in the Arctic. A TWINSPAN classification reveals two groups, reflecting a local geographical distinction. In the ponds of the old Zackenberg delta area (group 1), two assemblages were found: the Paraquadrula globulosa-Cyphoderia perlucidus assemblage and the Difflugiella crenulata-Cryptodifflugia compressa assemblage. The lakes, the pools and ponds east of the Zackenberg river (group 2) also harbour two assemblages: the Trinema enchelys-Euglypha sp.1 assemblage and the Centropyxis aerophila-Difflugia globulosa assemblage. Although the lakes are chemically unique, having extremely low values for turbidity, colour, SiO²⁻ ₂, Cl⁻ and hardness, this is not reflected in the characteristic testacean communities. Accepted: 24 April 1999     

Small‐scale spatial associations between Artemisia frigida and Potentilla acaulis at different intensities of sheep grazing

Questions: The formerly overgrazed Inner Mongolia steppe was subject to retrogressive succession. Today, Artemisia frigida and Potentilla acaulis are two dominant species in different phases of successive degradation. To investigate the impact of grazing intensity on spatial community structure, we investigated the small‐scale spatial association between A. frigida and P. acaulis at zero, light, medium and heavy sheep grazing, and proposed factors involved in the spatial associations between these two species along a grazing intensity gradient. Location: The Inner Mongolia Grassland Ecosystem Research Station of the Chinese Academy of Sciences. Methods: Four grazing intensities were selected: zero, light (1.33 sheep/ha), medium (4.0 sheep/ha) and heavy (6.7 sheep/ha). After 13 years of grazing three 2 m × 2 m quadrats with 100 × 100 cells of size 2 cm × 2 cm were randomly selected in each treatment in July and August 2002. The presence of A. frigida and P. acaulis in each cell was recorded and the positions of the individuals were mapped using Cartesian coordinates in each quadrat. The small‐scale spatial associations between A. frigida or P. acaulis were quantified with the L₁₂(d), J₁₂(d) functions (both derived from K₁₂(d), the former indicating the type of the spatial association, the latter indicating the strength of the spatial association), using Monte Carlo simulations. Results: A. frigida was negatively associated with P. acaulis at short distances (0–100 cm) under zero and light grazing, and negatively or independently under medium and heavy grazing. Increasing grazing intensities suppressed the peak negative associations. More intense grazing enhanced the tendency towards independent distribution of these two species. Conclusions: The small‐scale spatial associations between A. frigida and P. acaulis were significantly different at four different intensities of sheep grazing. Grazing disturbance, clonal growth habit of species, and interspecific competition are the main factors leading to a difference of spatial associations between these two species at different grazing intensities.     

Reproductive Ecology of Understory Species in a Tropical Montane Forest in Costa Rica1

The reproductive ecology of nine hermaphroditic understory species in a tropical montane Quercus forest was studied at two sites (2300 and 2600 m elev.) in the Cordillera de Talamanca, Costa Rica. Flower life span, studied in six species, averaged 4.4 d. This is longer than flower life spans found in the Monteverde cloud forest (2.7 d) and comparable to flower life spans found for arctic and alpine species. We studied the breeding system in five species and found no self-incompatible species. Four species proved self-compatible, and three of these showed autogamy. The main diurnal insect pollinator was the bumblebee Bombus ephippiatus. Natural fruit set was low (8-32%) in six species with few seeds per fruit, while two many-seeded species showed a high rate of fruit set (90 and 96%). The incidence of pre–dispersal seed predation was high; the percentage of seeds infested in four species ranged from 8 to 56 percent.     

Effects of elevated atmospheric carbon dioxide on gas exchange and growth of white clover

Effects of rising atmospheric CO₂ concentrations on gas exchange, growth and productivity were investigated on an important grassland species, Trifolium repens L. cv. Blanca. Pure stands of this species were cultivated over an entire growing season in small acrylic greenhouses with an artificial atmosphere of ±367 or ±620 ppm CO₂, respectively. Effects on growth and development were examined in a functional growth analysis, while consequences for gas exchange were determined by photosynthesis and transpiration measurements on canopy level. The stands were regularly clipped for production assessment. Canopies grown at high CO₂ levels showed an average increase in productivity of almost 75%. Growth analysis indicated development of a larger foliage area as the major cause, particularly in the first days of regrowth after cutting. The growth advantage that began in this stage was maintained or bettered during the following weeks. The difference between gas exchange measurements expressed per unit leaf area and per unit ground area suggested that changes in net photosynthesis and respiration did not contribute to the increase in total yield. Transpiration declined under high CO₂ if expressed on a leaf area basis but total canopy transpiration was at least as large as in ambient CO₂ due to the larger leaf area. Water-use efficiency calculations on the summer data indicated a 35% improvement with a doubling of CO₂ concentration.     

Estradiol- and estriol-binding in human benign prostatic hyperplasia.

Binding of the natural estrogens, estradiol and estriol, was investigated, in 34 samples of human benign prostatic hypertrophy (BPH) tissue, using Scatchard analysis and agar gel electrophoresis. Saturation binding analysis using a wide range of concentrations of both ligands resulted in curvilinear Scatchard plots. This confirmed the presence of two binding forms for estradiol: a true estrogen receptor, and a protein with lower affinity and higher capacity. Both binding species were also demonstrated and quantified with estriol. The electrophoretic process, after incubation at low and high ligand concentrations also resulted in separation, for both estrogens, of two binding peaks. They are probably two distinct forms of the low affinity, high capacity binding measured by Scatchard. The procedure used in our laboratory was not able to provide accurate determination of the concentrations of these binding forms. Possible modifications to alleviate these drawbacks are discussed.     

Steroid receptors in the human prostate. 2. Some properties of the estrophilic molecule of benign prostatic hypertrophy.

Some physicochemical properties of the estrophilic ‘receptor’ of human benign prostatic hypertrophy were examined by agar gel electrophoresis. 1) Competition analyses revealed the high selectivity of the molecule for the naturally occurring estrogens but not for representatives of other classes of steroid hormones (androgens, corticosteroids, progesterone). This, coupled with the failure of an estrogen ‘receptor’-rich extract to exhibit detectable tissue specific binding of (³H) 5α-dihydrotestosterone suggests that prostatic androgen and estrogen receptors may have separate identities. 2) The molecule proved highly resistant to enzyme attack, a stability conferred by estradiol-17β rather than by the thiol reagent dithiothreitol. Its proteinaceous nature was finally demonstrated when extract was exposed to enzymes at 0°C prior to steroid addition. 3) Initial complex formation between estrogen and its ‘receptor’ protein was rapid and reached a plateau after 4 hours. Binding was greater at 0°C than 37°C.