Insufficient nitrogen supply from symbiotic fixation reduces seasonal crop growth and nitrogen mobilization to seed in highly productive soybean crops

Nitrogen (N) supply can limit the yields of soybean [Glycine max (L.) Merr.] in highly productive environments. To explore the physiological mechanisms underlying this limitation, seasonal changes in N dynamics, aboveground dry matter (ADM) accumulation, leaf area index (LAI) and fraction of absorbed radiation (fAPAR) were compared in crops relying only on biological N₂ fixation and available soil N (zero-N treatment) versus crops receiving N fertilizer (full-N treatment). Experiments were conducted in seven high-yield environments without water limitation, where crops received optimal management. In the zero-N treatment, biological N₂ fixation was not sufficient to meet the N demand of the growing crop from early in the season up to beginning of seed filling. As a result, crop LAI, growth, N accumulation, radiation-use efficiency and fAPAR were consistently higher in the full-N than in the zero-N treatment, leading to improved seed set and yield. Similarly, plants in the full-N treatment had heavier seeds with higher N concentration because of greater N mobilization from vegetative organs to seeds. Future yield gains in high-yield soybean production systems will require an increase in biological N₂ fixation, greater supply of N from soil or fertilizer, or alleviation of the trade-off between these two sources of N in order to meet the plant demand.     

Cholinergic neuromodulation of inhibitory interneurons facilitates functional integration in whole-brain models

Segregation and integration are two fundamental principles of brain structural and functional organization. Neuroimaging studies have shown that the brain transits between different functionally segregated and integrated states, and neuromodulatory systems have been proposed as key to facilitate these transitions. Although whole-brain computational models have reproduced this neuromodulatory effect, the role of local inhibitory circuits and their cholinergic modulation has not been studied. In this article, we consider a Jansen & Rit whole-brain model in a network interconnected using a human connectome, and study the influence of the cholinergic and noradrenergic neuromodulatory systems on the segregation/integration balance. In our model, we introduce a local inhibitory feedback as a plausible biophysical mechanism that enables the integration of whole-brain activity, and that interacts with the other neuromodulatory influences to facilitate the transition between different functional segregation/integration regimes in the brain.     

Development and Evaluation of Sustained-Release Etoposide-Loaded Poly(ε-Caprolactone) Implants

Poly(ε-caprolactone) implants containing etoposide, an important chemotherapeutic agent and topoisomerase II inhibitor, were fabricated by a melt method and characterized in terms of content uniformity, morphology, drug physical state, and sterility. In vitro and in vivo drug release from the implants was also evaluated. The cytotoxic activity of implants against HeLa cells was studied. The short-term tolerance of the implants was investigated after subcutaneous implantation in mice. The original chemical structure of etoposide was preserved after incorporation into the polymeric matrix, in which the drug was dispersed uniformly. Etoposide was present in crystalline form in the polymeric implant. In vitro release study showed prolonged and controlled release of etoposide, which showed cytotoxicity activity against HeLa cells. After implantation, good correlation between in vitro and in vivo drug release was found. The implants demonstrated good short-term tolerance in mice. These results tend to show that etoposide-loaded implants could be potentially applied as a local etoposide delivery system.     

Effects of Timing of Dexamethasone Treatment on the Outcome of Collagenase-Induced Intracerebral Hematoma in Rats

The effect of timing in providing dexamethasone treatment after intracerebral hematoma was evaluated in rats with hematoma induced by a subcortical collagenase injection. Male Sprague–Dawley rats (n = 30; body weight, 185 to 230 g) received dexamethasone (1 mg/kg) intraperitoneally at 2 h, 4 h, or 6 h (1 group per time point) after intracerebral collagenase injection, with another dose (1 mg/kg) administered at 24 h after collagenase injection. Neurologic examinations and rotarod treadmill tests were used to evaluate motor behavior before and at 24 and 48 h after intracerebral injection. Rats were euthanized after the last behavioral test. Brains were evaluated for hematoma size, number of penumbral necrotic neurons, neutrophils within the hematoma, and astrocytic response. Compared with the control and other treatment groups, rats treated with dexamethasone at 2 and 24 h after intracerebral collagenase injection scored significantly better on neurologic exams and rotarod tests. Hematoma volume was significantly smaller in all treated groups than in the control group but did not differ between treatment groups. Fewer neutrophils were seen in the perihematoma region of all treated rats compared with controls, but the number of necrotic neurons was decreased significantly only in the group treated with dexamethasone at 2 and 24 h. These results indicate that a 1-mg/kg dose of dexamethasone is beneficial for treatment of intracerebral hemorrhage, particularly if administered early after the hemorrhagic insult.Traumatic cerebral hemorrhages, which in veterinary patients are caused mainly by automobile accidents and falls, are diagnostic and therapeutic challenges.¹⁵ Animal models have played an important role in elucidating the cascade of cellular and biochemical events occurring after traumatic brain injury.⁷ These models have helped to elucidate various aspects of the pathogenesis and treatment of intracranial hemorrhaging. Among these, the collagenase-induced intracerebral hematoma model¹⁴ is highly reproducible and shows many characteristics of the intracerebral hemorrhagic process in mammals. In addition, the short- and long-term histologic and behavioral changes associated with this model have been evaluated.^5,6 Compared with the blood infusion model, the collagenase model causes greater primary injury that occurs distal to the hematoma, and neurologic deficits resolve less rapidly over time, making the collagenase model more appealing for long-term studies.¹²The efficacy of corticosteroids for the treatment of brain hemorrhages has been evaluated in different experimental studies with conflicting results.^3,8-11 Administration of corticosteroids at 1 h after hematoma induction is beneficial for the treatment of this condition.^10,11,16 Although these studies have promising results, the interval between trauma and treatment might greatly influence the response to corticosteroid treatment. The aim of this study was to assess the motor performance and histopathology associated with dexamethasone treatment at 2, 4, and 6 h after hematoma induction in the intracranial collagenase rat model. A second dexamethasone dose was administered 24 h after collagenase injection.     

Eosin fluorescence changes during Rb+ occlusion in the Na+/K(+)-ATPase

We used suspensions of partially purified Na(+)/K(+)-ATPase from pig kidney to compare the effects of Rb(+), as a K(+) congener, on the time course and on the equilibrium values of eosin fluorescence and of Rb(+) occlusion. Both sets of data were collected under identical conditions in the same enzyme preparations. The incubation media lacked ATP so that all changes led to an equilibrium distribution between enzyme conformers with and without bound eosin and with and without bound or occluded Rb(+). Results showed that as Rb(+) concentration was increased, the equilibrium value of fluorescence decreased and occlusion increased along rectangular hyperbolas with similar half-maximal values. The time courses of attainment of equilibrium showed an initial phase which was so quick as to fall below the time resolution of our rapid-mixing apparatus. This phase was followed by the sum of at least two exponential functions of time. In the case of fluorescence the fast exponential term accounted for a larger fraction of the time course than in the case of occlusion. Comparison between experimental and simulated results suggests that fluorescence changes express a process that is coupled to Rb(+) occlusion but that is completed before occlusion reaches equilibrium.     

Influence of trophic status and conductivity on zooplankton composition in lakes and ponds of Torres del Paine National Park (Chile)

The Torres del Paine National Park is located in the southern Chilean Patagonia. This park has numerous and heterogeneous lakes and ponds with different trophic status and zooplankton composition. The aim of this study was to analyze the influence of trophic status and conductivity on zooplankton assemblages in lakes and ponds within the Torres del Paine National Park. The water bodies described in the present study were previously classified in three groups. The first group consisted of large, deep and oligotrophic lakes with fish populations, low zooplankton species diversity and high predominance of calanoid copepods of small body size. The second group contained small mesotrophic lakes with fish populations and relatively high predominance of small sized daphnids. The third group consisted of fishless ponds of different trophic status, wide conductivity gradient and with zooplankton species of relatively large body size. The results show that Daphnids abundance was directly related to chlorophyll-a concentration and inversely associated with conductivity. Calanoids abundance was also directly associated with conductivity.