Reverse Shifts Research Articles

Mannitol for acute traumatic brain injury.

Mannitol is sometimes dramatically effective in reversing acute brain swelling, but its effectiveness in the on-going management of severe head injury remains open to question. There is evidence that, in prolonged dosage, mannitol may pass from the blood into the brain, where it might cause reverse osmotic shifts that increase intracranial pressure. To assess the effects of different mannitol therapy regimens, of mannitol compared to other intracranial pressure (ICP) lowering agents, and to quantify the effectiveness of mannitol administration given at other stages following acute traumatic brain injury. The review drew on the search strategy for the Injuries Group as a whole. We checked reference lists of trials and review articles, and contacted authors of trials. Randomised trials of mannitol, in patients with acute traumatic brain injury of any severity. The comparison group could be placebo-controlled, no drug, different dose, or different drug. Trials where the intervention was started more than eight weeks after injury, and cross-over trials were excluded. The reviewers independently rated quality of allocation concealment and extracted the data. Relative risks (RR) and 95% confidence intervals (CI) were calculated for each trial on an intention to treat basis. Overall there were few eligible trials. In the pre-operative management of patients with acute intracranial haemorrhage the administration of high-dose mannitol resulted in reduced mortality (RR=0.55; 95%CI 0.36, 0.84) and reduced death and severe disability (RR=0.58; 95%CI 0.45, 0.74) when compared with conventional-dose mannitol. One trial compared ICP-directed therapy to 'standard care' (RR for death= 0.83; 95%CI 0.47,1.46). One trial compared mannitol to pentobarbital (RR for death = 0.85; 95% CI 0.52, 1.38). No trials compared mannitol to other ICP-lowering agents. One trial tested the effectiveness of pre-hospital administration of mannitol against placebo (RR for death=1.75; 95% CI 0.48, 6.38). High-dose mannitol appears to be preferable to conventional-dose mannitol in the pre-operative management of patients with acute intracranial haematomas. However, there is little evidence about the use of mannitol as a continuous infusion in patients with raised intracranial pressure in patients who do not have an operable intracranial haematoma. Mannitol therapy for raised ICP may have a beneficial effect on mortality when compared to pentobarbital treatment. ICP-directed treatment shows a small beneficial effect compared to treatment directed by neurological signs and physiological indicators. There are insufficient data on the effectiveness of pre-hospital administration of mannitol to preclude either a harmful or a beneficial effect on mortality.

Unringing the Bell: Can Industries Reverse Unfavorable Institutional Shifts Triggered by their Own Mistakes?

I present a study of the US chemical industry's unified efforts to reverse an unfavorable institutional shift triggered by the transgressions of one of its members. I measure changes in the industry's institutional environment from 1980 to 2000. I find that the industry's collective efforts did not directly improve institutional conditions confronting individual firms, but did help buffer firms from financial losses that commonly arise when their rivals suffer crises.

The evolution of agriculture in beetles (Curculionidae: Scolytinae and Platypodinae).

Beetles in the weevil subfamilies Scolytinae and Platypodinae are unusual in that they burrow as adults inside trees for feeding and oviposition. Some of these beetles are known as ambrosia beetles for their obligate mutualisms with asexual fungi--known as ambrosia fungi--that are derived from plant pathogens in the ascomycete group known as the ophiostomatoid fungi. Other beetles in these subfamilies are known as bark beetles and are associated with free-living, pathogenic ophiostomatoid fungi that facilitate beetle attack of phloem of trees with resin defenses. Using DNA sequences from six genes, including both copies of the nuclear gene encoding enolase, we performed a molecular phylogenetic study of bark and ambrosia beetles across these two subfamilies to establish the rate and direction of changes in life histories and their consequences for diversification. The ambrosia beetle habits have evolved repeatedly and are unreversed. The subfamily Platypodinae is derived from within the Scolytinae, near the tribe Scolytini. Comparison of the molecular branch lengths of ambrosia beetles and ambrosia fungi reveals a strong correlation, which a fungal molecular clock suggests spans 60 to 21 million years. Bark beetles have shifted from ancestral association with conifers to angiosperms and back again several times. Each shift to angiosperms is associated with elevated diversity, whereas the reverse shifts to conifers are associated with lowered diversity. The unusual habit of adult burrowing likely facilitated the diversification of these beetle-fungus associations, enabling them to use the biomass-rich resource that trees represent and set the stage for at least one origin of eusociality.

THE EVOLUTION OF AGRICULTURE IN BEETLES (CURCULIONIDAE: SCOLYTINAE AND PLATYPODINAE)

Beetles in the weevil subfamilies Scolytinae and Platypodinae are unusual in that they burrow as adults inside trees for feeding and oviposition. Some of these beetles are known as ambrosia beetles for their obligate mutualisms with asexual fungi—known as ambrosia fungi—that are derived from plant pathogens in the ascomycete group known as the ophiostomatoid fungi. Other beetles in these subfamilies are known as bark beetles and are associated with free-living, pathogenic ophiostomatoid fungi that facilitate beetle attack of phloem of trees with resin defenses. Using DNA sequences from six genes, including both copies of the nuclear gene encoding enolase, we performed a molecular phylogenetic study of bark and ambrosia beetles across these two subfamilies to establish the rate and direction of changes in life histories and their consequences for diversification. The ambrosia beetle habits have evolved repeatedly and are unreversed. The subfamily Platypodinae is derived from within the Scolytinae, near the tribe Scolytini. Comparison of the molecular branch lengths of ambrosia beetles and ambrosia fungi reveals a strong correlation, which a fungal molecular clock suggests spans 60 to 21 million years. Bark beetles have shifted from ancestral association with conifers to angiosperms and back again several times. Each shift to angiosperms is associated with elevated diversity, whereas the reverse shifts to conifers are associated with lowered diversity. The unusual habit of adult burrowing likely facilitated the diversification of these beetle-fungus associations, enabling them to use the biomass-rich resource that trees represent and set the stage for at least one origin of eusociality.Corresponding Editor: S. Pitnick

Alternative stable states of macrophytes versus phytoplankton in two interconnected impoundments of the New Danube (Vienna, Austria)

Natural dynamic processes leading to a shift from algal to macrophyte domination in the two impoundments of the New Danube flood-relief channel are associated with and explained by a theory of bi-stable states. Changes are largely caused by alterations of water level and hence the retention times of the impoundments. Implications for water quality evaluation are discussed using the concept of potential water column concentrations of phosphorus. Calculations indicate the importance of macrophytes as structures that can buffer nutrient concentrations, via uptake and storage in plant tissues Results are contrasted with similar hut anthropogenically-induced forward and reverse shifts in the nearby Old Danube seepage lake, and implications for lake management are discussed.

Chemical reduction of the water splitting enzyme system of photosynthesis and its light-induced reoxidation characterized by optical and mass spectrometric measurements: A basis for the estimation of the states of the redox active manganese and of water in the quaternary oxygen-evolving S-state cycle

The chemical reduction and over-reduction of the water-splitting enzyme and its subsequent light-induced reoxidation was followed by simultaneous measurements of (i) UV and (ii) electrochromic absorption changes, accompanied (iii) by O 2 measurement and (iv) mass spectrometric analysis of the evolved 15N 2 and 15N 2O of the applied reductant, 15NH 2OH. (1) On this reversible pathway, the measured four characteristics attributed to changes of Mn valences, surplus charges, water oxidation and oxidation of the reductant are quantitatively coupled with each other. (2) Treatment with NH 2OH (or NH 2NH 2) leads to a three-digit reverse shift of O 2 evolution and UV and electrochromic absorption changes. This is interpreted as the reduction of the enzyme in the dark from the S 1 state via the S 0 and the overreduced S −1 state to the superreduced state, S −2. (3) S −2 is stable for hours. (4) S −2 is a terminal state, not further reducible without being deactivated. (5) Each step on this reversible pathway from state S 1 to S −2 is accompanied by a 1 2- 15 N 2 evolution from 15NH 2OH interpreted as a three-electron reduction of state S 1 which is in accordance with the three-digit reverse shifts. (6) The results are explained by a reversible reduction of 3 redox-active Mn ions. Based on the obtained data, the possible valence states of these photooxidizable Mn ions in state S −2 to S 3 have been estimated. (7) Irreversible deactivation of S −2 with release of Mn into the solution is coupled with an approx. 1- 15N 2O evolution from 15NH 2OH. (8) The electrochromic changes indicate at pH 7 a surplus charge at S −1, S 2 and S 3. This is explained by an H + release of approx. 2:1:0:1 with the 1:1:1:1 electron extraction in the S −1 → S 0 → S 1 → S 2 → S 3 transition. On this basis, the possible states of the water derivatives up to S 3 have been estimated. (9) The results are compared with information obtained from UV-difference spectra and XAS, EPR and NMR measurements.

The effect of DC polarization on the magnitude and phase of the CM harmonics

Rectification processes must play an important role in the mechanical to neural transduction process in the auditory system since intracellular recording has demonstrated large DC receptor potentials for sinusoidal acoustic stimuli in inner haircells [I. J. Russell, and P. M. Sellick, Nature 267, 858–860 (1977)]. Any rectification process would not only generate DC potentials but also would generate even harmonic distortion. The magnitude and phase of the CM fundamental and harmonics were measured in scale media of the first turn of the guinea pig cochlea using digital signal‐processing techniques. The data suggest that the even order harmonics are the sum of two separate components which are 180° out of phase at low acoustic frequencies. One component dominates at low SPL and the other at high SPL. Positive DC polarization shifts the transition of the two components to lower SPL and a reverse current shifts the transition to higher SPL. The results are consistent with our recent hypothesis that the hairc...

The Calculation of Proportional Counter Energy Deposition Spectra from Experimental Data: II. Very Small Energy Losses and High Energy Delta Rays

BS>It is shown that a convolution technique, developed by Kellerer can be used to generate energy deposition spectra, by either forward or reverse shifts, for many pathlengths from a limited set of experimental data for low energy fast protons ( approximates 45 MeV) corresponding to pathlengths of radiobiological interest. For medium energy fast protons ( approximates 600 MeV) the method fails if shifts based upon the expected average energy losses are used as the base for these calculations. However, if shifts based on an experimental determination of the average energy loss in the volume of interest are used then good agreement with experiment is obtained. This reflects the effect of energy transport into and out of the counter volume by high energy secondary particles, resulting in a significant loss of energy from the volumes in which the measurements have been made and the high probability for a significant number of incident particles not undergoing collisions over the test pathlength. This results in experimental values of average energy which are different than those calculated using stopping power theory. (auth)

Effect of angiotonin on the distribution of sodium, potassium and water in the rat.

STUDIES of ‘Pitressin’ in the bilaterally nephrectomized rat have shown that this extract causes a shift of sodium and water out of the extracellular fluid while potassium moves in1. These movements are related to the pressor effect of the extract. Similar shifts are also associated with the pressor effects of epinephrine and norepinephrine2,3. With all these agents, reverse shifts occur during the decline of the blood pressure back to normal. Based on our interpretation of these and other similar experiments, we have suggested the theory that the regulation of blood pressure depends, inter alia, on the sodium transfer systems4. We have considered potassium to be of less importance than sodium in this regulation, since shifts of this ion are usually considerably less in total amount. This idea is supported by the present findings with angiotonin (hypertensin) in which sodium shifts were not accompanied by any inverse shift of potassium.