Beyond carbon flux partitioning: Carbon allocation and nonstructural carbon dynamics inferred from continuous fluxes

Carbon (C) allocation and nonstructural carbon (NSC) dynamics play essential roles in plant growth and survival under stress and disturbance. However, quantitative understanding of these processes remains limited. Here we propose a framework where we connect commonly measured carbon cycle components (eddy covariance fluxes of canopy CO₂ exchange, soil CO₂ efflux, and allometry-based biomass and net primary production) by a simple mass balance model to derive ecosystem-level NSC dynamics (NSC_i ), C translocation (dC_i ), and the biomass production efficiency (BPE_i ) in above- and belowground plant (i = agp and bgp) compartments. We applied this framework to two long-term monitored loblolly pine (Pinus taeda) plantations of different ages in North Carolina and characterized the variations of NSC and allocation in years under normal and drought conditions. The results indicated that the young stand did not have net NSC flux at the annual scale, whereas the mature stand stored a near-constant proportion of new assimilates as NSC every year under normal conditions, which was comparable in magnitude to new structural growth. Roots consumed NSC in drought and stored a significant amount of NSC post drought. The above- and belowground dC_i and BPE_i varied more from year to year in the young stand and approached a relatively stable pattern in the mature stand. The belowground BPE_bgp differed the most between the young and mature stands and was most responsive to drought. With the internal C dynamics quantified, this framework may also improve biomass production estimation, which reveals the variations resulting from droughts. Overall, these quantified ecosystem-scale dynamics were consistent with existing evidence from tree-based manipulative experiments and measurements and demonstrated that combining the continuous fluxes as proposed here can provide additional information about plant internal C dynamics. Given that it is based on broadly available flux data, the proposed framework is promising to improve the allocation algorithms in ecosystem C cycle models and offers new insights into observed variability in soil-plant-climate interactions.

Urban warming increases the temperature sensitivity of spring vegetation phenology at 292 cities across China

Urban spring phenology changes governed by multiple biological and environmental factors significantly impact urban ecosystem functions and services. However, the temporal changes in spring phenology (i.e., the start of the vegetation growing season, SOS) and the magnitude of SOS sensitivity to temperature in urban settings are not well understood compared with natural ecosystems. Therefore, we explored warming impacts on SOS across 292 rural and urban areas from 2001 to 2016. We found that warming occurred in 79.9% of urban areas and 61.3% of rural areas. This warming advanced SOS in 78.3% of the urban settings and 72.8% of the rural areas. The accelerated rate of SOS in urban settings was significantly higher (-0.52 ± 0.86 days/year) than in rural areas (-0.09 ± 0.69 days/year). Moreover, SOS was significantly more sensitive to warming in urban areas (-2.86 ± 3.57 days/°C) than in rural areas (-1.57 ± 3.09 days/°C), driven by urban-rural differences in climatic (precipitation, temperature, and warming speed) and vegetation factors. Precipitation contributed the most had the highest relative importance for controlling SOS, at 45% and 63% for urban and rural areas, respectively. These findings provide a new understanding of the impacts of urbanization and climate change on vegetation phenology. Moreover, our results have implications for urban environment impacts on ecosystems and human health.

COSORE: A community database for continuous soil respiration and other soil-atmosphere greenhouse gas flux data

Globally, soils store two to three times as much carbon as currently resides in the atmosphere, and it is critical to understand how soil greenhouse gas (GHG) emissions and uptake will respond to ongoing climate change. In particular, the soil-to-atmosphere CO₂ flux, commonly though imprecisely termed soil respiration (R_S ), is one of the largest carbon fluxes in the Earth system. An increasing number of high-frequency R_S measurements (typically, from an automated system with hourly sampling) have been made over the last two decades; an increasing number of methane measurements are being made with such systems as well. Such high frequency data are an invaluable resource for understanding GHG fluxes, but lack a central database or repository. Here we describe the lightweight, open-source COSORE (COntinuous SOil REspiration) database and software, that focuses on automated, continuous and long-term GHG flux datasets, and is intended to serve as a community resource for earth sciences, climate change syntheses and model evaluation. Contributed datasets are mapped to a single, consistent standard, with metadata on contributors, geographic location, measurement conditions and ancillary data. The design emphasizes the importance of reproducibility, scientific transparency and open access to data. While being oriented towards continuously measured R_S , the database design accommodates other soil-atmosphere measurements (e.g. ecosystem respiration, chamber-measured net ecosystem exchange, methane fluxes) as well as experimental treatments (heterotrophic only, etc.). We give brief examples of the types of analyses possible using this new community resource and describe its accompanying R software package.

Using δ13C and δ18O to analyze loblolly pine (Pinus taeda L.) response to experimental drought and fertilization

Drought frequency and intensity are projected to increase throughout the southeastern USA, the natural range of loblolly pine (Pinus taeda L.), and are expected to have major ecological and economic implications. We analyzed the carbon and oxygen isotopic compositions in tree ring cellulose of loblolly pine in a factorial drought (~30% throughfall reduction) and fertilization experiment, supplemented with trunk sap flow, allometry and microclimate data. We then simulated leaf temperature and applied a multi-dimensional sensitivity analysis to interpret the changes in the oxygen isotope data. This analysis found that the observed changes in tree ring cellulose could only be accounted for by inferring a change in the isotopic composition of the source water, indicating that the drought treatment increased the uptake of stored moisture from earlier precipitation events. The drought treatment also increased intrinsic water-use efficiency, but had no effect on growth, indicating that photosynthesis remained relatively unaffected despite 19% decrease in canopy conductance. In contrast, fertilization increased growth, but had no effect on the isotopic composition of tree ring cellulose, indicating that the fertilizer gains in biomass were attributable to greater leaf area and not to changes in leaf-level gas exchange. The multi-dimensional sensitivity analysis explored model behavior under different scenarios, highlighting the importance of explicit consideration of leaf temperature in the oxygen isotope discrimination (Δ18Oc) simulation and is expected to expand the inference space of the Δ18Oc models for plant ecophysiological studies.

An extractive removal step optimized for a high-throughput α-cellulose extraction method for δ13C and δ18O stable isotope ratio analysis in conifer tree rings

Stable isotope ratios (δ13C and δ18O) of tree-ring α-cellulose are important tools in paleoclimatology, ecology, plant physiology and genetics. The Multiple Sample Isolation System for Solids (MSISS) was a major advance in the tree-ring α-cellulose extraction methods, offering greater throughput and reduced labor input compared to traditional alternatives. However, the usability of the method for resinous conifer species may be limited by the need to remove extractives from some conifer species in a separate pretreatment step. Here we test the necessity of pretreatment for α-cellulose extraction in loblolly pine (Pinus taeda L.), and the efficiency of a modified acetone-based ambient-temperature step for the removal of extractives (i) in loblolly pine from five geographic locations representing its natural range in the southeastern USA, and (ii) on five other common coniferous species (black spruce (Picea mariana Mill.), Fraser fir (Abies fraseri (Pursh) Poir.), Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), Norway spruce (Picea abies (L.) Karst) and ponderosa pine (Pinus ponderosa D.)) with contrasting extractive profiles. The differences of δ13C values between the new and traditional pretreatment methods were within the precision of the isotope ratio mass spectrometry method used (±0.2‰), and the differences between δ18O values were not statistically significant. Although some unanticipated results were observed in Fraser fir, the new ambient-temperature technique was deemed as effective as the more labor-consuming and toxic traditional pretreatment protocol. The proposed technique requires a separate acetone-inert multiport system similar to MSISS, and the execution of both pretreatment and main extraction steps allows for simultaneous treatment of up to several hundred microsamples from resinous softwood, while the need of additional labor input remains minimal.

Greening China naturally

China leads the world in afforestation, and is one of the few countries whose forested area is increasing. However, this massive "greening" effort has been less effective than expected; afforestation has sometimes produced unintended environmental, ecological, and socioeconomic consequences, and has failed to achieve the desired ecological benefits. Where afforestation has succeeded, the approach was tailored to local environmental conditions. Using the right plant species or species composition for the site and considering alternatives such as grassland restoration have been important success factors. To expand this success, government policy should shift from a forest-based approach to a results-based approach. In addition, long-term monitoring must be implemented to provide the data needed to develop a cost-effective, scientifically informed restoration policy.

Short-course raltegravir intensification does not reduce persistent low-level viremia in patients with HIV-1 suppression during receipt of combination antiretroviral therapy

BACKGROUND

Combination antiretroviral therapy suppresses but does not eradicate human immunodeficiency virus type 1 (HIV-1) in infected persons, and low-level viremia can be detected despite years of suppressive antiretroviral therapy. Short-course (28-day) intensification of standard antiretroviral combination therapy is a useful approach to determine whether complete rounds of HIV-1 replication in rapidly cycling cells contribute to persistent viremia. We investigated whether intensification with the integrase inhibitor raltegravir decreases plasma HIV-1 RNA levels in patients receiving suppressive antiretroviral therapy.

METHODS

Subjects (n = 10) with long-term HIV-1 suppression receiving combination antiretroviral regimens had their regimens intensified for 4 weeks with raltegravir. Plasma HIV-1 RNA level was determined before, during, and after the 4-week intensification period, using a sensitive assay (limit of detection, 0.2 copies of HIV-1 RNA/mL of plasma). A 4-week intensification course was chosen to investigate potential HIV-1 replication in cells with relatively short (approximately 1-14-day) half-lives.

RESULTS

There was no evidence in any subject of a decline in HIV-1 RNA level during the period of raltegravir intensification or of rebound after discontinuation. Median levels of HIV-1 RNA before (0.17 log10 copies/mL), during (0.04 log10 copies/mL), and after (0.04 log10 copies/mL) raltegravir intensification were not significantly different (P > .1 for all comparisons in parametric analyses). High-performance liquid chromatography and mass spectroscopy experiments confirmed that therapeutic levels of raltegravir were achieved in plasma during intensification.

CONCLUSIONS

Intensification of antiretroviral therapy with a potent HIV-1 integrase inhibitor did not decrease persistent viremia in subjects receiving suppressive regimens, indicating that rapidly cycling cells infected with HIV-1 were not present. Eradication of HIV-1 from infected persons will require new therapeutic approaches.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT00618371.

Poplar plantation has the potential to alter the water balance in semiarid Inner Mongolia

Poplar plantation is the most dominant broadleaf forest type in northern China. Since the mid-1990s plantation was intensified to combat desertification along China's northwestern border, i.e., within Inner Mongolia (IM). This evoked much concern regarding the ecological and environmental effects on areas that naturally grow grass or shrub vegetation. To highlight potential consequences of large-scale poplar plantations on the water budget within semiarid IM, we compared the growing season water balance (evapotranspiration (ET) and precipitation (PPT)) of a 3-yr old poplar plantation (Kp(3)) and a natural shrubland (Ks) in the Kubuqi Desert in western IM, and a 6-yr old poplar plantation (Bp(6)) growing under sub-humid climate near Beijing. The results showed that, despite 33% lower PPT at Kp(3), ET was 2% higher at Kp(3) (228 mm) as compared with Ks (223 mm) in May-September 2006. The difference derived mainly from higher ET at the plantation during drier periods of the growing season, which also indicated that the poplars must have partly transpired groundwater. Estimated growing season ET at Bp(6) was about 550 mm and more than 100% higher than at Kp(3). It is estimated that increases in leaf area index and net radiation at Kp(3) provide future potential for the poplars in Kubuqi to exceed the present ET and ET of the natural shrubland by 100-200%. These increases in ET are only possible through the permanent use of groundwater either directly by the trees or through increased irrigation. This may significantly change the water balance in the area (e.g., high ET at the cost of a reduction in the water table), which renders large-scale plantations a questionable tool in sustainable arid-land management.

Acute time to response in the Treatment for Adolescents with Depression Study (TADS)

OBJECTIVE

To examine the time to response for both pharmacotherapy and psychotherapy in the Treatment for Adolescents with Depression Study (TADS).

METHOD

Adolescents (N = 439, ages 12 to 17 years) with major depressive disorder were randomized to fluoxetine (FLX), cognitive-behavioral therapy (CBT), their combination (COMB), or pill placebo (PBO). Defining response as very much improved or much improved on the Clinical Global Impression-Improvement Scale (CGI-I), survival analyses using Cox proportional hazards models, and Kaplan-Meier curves were conducted to evaluate time to first response and time to stable response for subjects receiving pharmacotherapy (COMB, FLX, PBO) as well as for subjects receiving CBT (COMB, CBT). Direct comparisons between pharmacotherapy and CBT were not made because of differences in visit schedules.

RESULTS

Based on pharmacotherapist CGI-I scores, COMB and FLX showed faster onset of benefit than PBO on time to response and time to stable response (p < .001), and COMB was faster than FLX on time to stable response (p = .034). The probability of sustained early response was approximately threefold greater for COMB than PBO, twofold greater for FLX than PBO, and 1.5-fold greater for COMB than FLX. On the psychotherapist CGI-I scores, both first response and stable response occurred faster in COMB than CBT (p < .001), with a probability of sustained early response approximately threefold greater for COMB than CBT.

CONCLUSIONS

In the acute treatment of depressed adolescents, FLX and COMB accelerate response relative to PBO, and COMB accelerates response relative to CBT alone.

Insulin glargine or NPH combined with metformin in type 2 diabetes: the LANMET study

AIMS/HYPOTHESIS

In type 2 diabetic patients we compared 9 months of combination therapy with insulin glargine and metformin with 9 months of NPH insulin combined with metformin. The primary focus was changes in HbA(1c); secondary focus was diurnal glucose profiles and symptomatic hypoglycaemia.

METHODS

In this investigator-initiated open, parallel-group clinical trial involving seven centres, 110 insulin-naive type 2 diabetic patients with poor glycaemic control (HbA(1c) >or=8.0%) on oral hypoglycaemic agents (90% using sulfonylurea plus metformin) were randomised to receive bedtime insulin glargine with metformin (G+MET) or bedtime NPH with metformin (NPH+MET) for 36 weeks. The patients were taught how to self-adjust their insulin dose and use a modem to send the results of home glucose monitoring to treatment centres. The goal was to achieve a fasting plasma glucose (FPG) of 4.0 to 5.5 mmol/l in both groups.

RESULTS

During the last 12 weeks, FPGs averaged 5.75+/-0.02 and 5.96+/-0.03 mmol/l (p<0.001) and insulin doses were 68+/-5 and 70+/-6 IU/day (0.69+/-0.05 and 0.66+/-0.04 IU kg(-1) day(-1), NS) in the G+MET and NPH+MET groups, respectively. At 36 weeks, mean HbA(1c) was 7.14+/-0.12 and 7.16+/-0.14%, respectively (NS). Symptomatic, but not confirmed symptomatic, hypoglycaemia was significantly lower during the first 12 weeks in the G+MET group (4.1+/-0.8 episodes/patient-year) than in the NPH+MET group (9.0+/-2.3 episodes/patient-year, p<0.05), but not significantly different thereafter. Glucose levels before dinner were higher in the NPH+MET group (10.1+/-0.3 mmol/l) than in the G+MET group (8.6+/-0.3 mmol/l, p=0.002) throughout the 36-week study. With regard to baseline characteristics such as initial glycaemia or C-peptide, there was no difference between patients who achieved good glycaemic control (HbA(1c) <7.0%) and those who did not. Differences were seen in the following: between study centres, weight gain during the run-in period and insulin therapy, and FPG during the last 12 weeks (5.7+/-0.2 vs 6.7+/-0.3 mmol/l for patients reaching vs those not reaching target, p<0.01).

CONCLUSIONS/INTERPRETATION

Good glycaemic control can be achieved with both G+MET and NPH+MET. Use of G+MET reduces symptomatic hypoglycaemia during the first 12 weeks and dinner time hyperglycaemia compared with NPH+MET.

Amyloid beta-peptide(1-42) and hydrogen peroxide-induced toxicity are mediated by TRPM2 in rat primary striatal cultures

Amyloid beta-peptide (Abeta) is the main component of senile plaques which characterize Alzheimer's disease and may induce neuronal death through mechanisms which include oxidative stress. To date, the signalling pathways linking oxidant stress, a component of several neurodegenerative diseases, to cell death in the CNS are poorly understood. Melastatin-like transient receptor potential 2 (TRPM2) is a Ca(2+)-permeant non-selective cation channel, which responds to increases in oxidative stress levels in the cell and is activated by oxidants such as hydrogen peroxide. We demonstrate here that Abeta and hydrogen peroxide both induce death in cultured rat striatal cells which express TRPM2 endogenously. Transfection with a splice variant that acts as a dominant negative blocker of TRPM2 function (TRPM2-S) inhibited both hydrogen peroxide- and Abeta-induced increases in intracellular-free Ca(2+) and cell death. Functional inhibition of TRPM2 activation by the poly(ADP-ribose)polymerase inhibitor SB-750139, a modulator of intracellular pathways activating TRPM2, attenuated hydrogen peroxide- and Abeta-induced cell death. Furthermore, a small interfering RNA which targets TRPM2, reduced TRPM2 mRNA levels and the toxicity induced by hydrogen peroxide and Abeta. These data demonstrate that activation of TRPM2, functionally expressed in primary cultures of rat striatum, contributes to Abeta- and oxidative stress-induced striatal cell death.

The role of TRPM channels in cell death

Transient receptor potential (TRP) channels of the melastatin-like family (TRPM) play critical roles in mediating cellular responses to a wide range of physiological stimuli that, under certain situations, can induce cell death. To date, two TRPM family members, TRPM2 and TRPM7, have been implicated directly as central components of cell death pathways. TRPM2, a Ca(2+)-permeant, non-selective cation channel, senses and responds to oxidative stress levels in the cell. TRPM7 is required for cell viability and has been proposed recently to mediate stress-induced cell death in the central nervous system. We review here the evidence for the involvement of these TRPM channels in cell death processes and discuss the mechanisms by which TRPM channel activation occurs. The ability to attenuate expression levels and functionality of these channels is necessary to understand the involvement of TRPM in cell death and we evaluate current approaches for modulation of TRPM channel function. Finally, we discuss the possibility that TRPM channels may provide therapeutic targets for degenerative diseases involving oxidative stress-related pathologies including diabetes and Alzheimer's disease.

Flufenamic acid is a pH-dependent antagonist of TRPM2 channels

Like a number of other TRP channels, TRPM2 is a Ca(2+)-permeable non-selective cation channel, the activity of which is regulated by intracellular and extracellular Ca(2+). A unique feature of TRPM2 is its activation by ADP-ribose and chemical species that arise during oxidative stress, for example, NAD(+) and H(2)O(2). These properties have lead to proposals that this channel may play a role in the cell death produced by pathological redox states. The lack of known antagonists of this channel have made these hypotheses difficult to test. Here, we demonstrate, using patch clamp electrophysiology, that the non-steroidal anti-inflammatory compound flufenamic acid (FFA) inhibits recombinant human TRPM2 (hTRPM2) as well as currents activated by intracellular ADP-ribose in the CRI-G1 rat insulinoma cell line. All concentrations tested in a range from 50 to 1000 microM produced complete inhibition of the TRPM2-mediated current. Following FFA removal, a small (typically 10-15%) component of current was rapidly recovered (time constant approximately 3 s), considerably longer periods in the absence of FFA produced no further current recovery. Reapplication of FFA re-antagonised the recovered current and subsequent FFA washout produced recovery of only a small percentage of the reblocked current. Decreasing extracellular pH accelerated FFA inhibition of TRPM2. Additional experiments indicated hTRPM2 activation was required for FFA antagonism to occur and that the generation of irreversible antagonism was preceded by a reversible component of block. FFA inhibition could not be induced by intracellular application of FFA. ADP-ribose activated currents in the rat insulinoma cell line CRI-G1 were also antagonised by FFA with concentration- and pH-dependent kinetics. In contrast to the observations made with hTRPM2, antagonism of ADP-ribose activated currents in CRI-G1 cells could be fully reversed following FFA removal. These experiments suggest that FFA may be a useful tool antagonist for studies of TRPM2 function.

Inhibition of TRPM2 channels by the antifungal agents clotrimazole and econazole

TRPM2 is a Ca(2+)-permeable non-selective cation channel that uniquely is activated by intracellular ADP-ribose. To date, only one pharmacological blocker of this channel, namely flufenamic acid (FFA), has been described. Here we demonstrate, using patch clamp electrophysiology, that the antifungal imidazoles clotrimazole and econazole inhibit ADP-ribose-activated currents in HEK-293 cells expressing recombinant human TRPM2 (hTRPM2). For both compounds, all concentrations in a range from 3 microM to 30 microM produced an essentially complete inhibition of the TRPM2-mediated current. The rate of current antagonism was dependent on the concentration applied, with higher concentrations producing faster block. In addition, decreasing extracellular pH accelerated inhibition of TRPM2 by both clotrimazole and econazole; extracellular alkalisation produced the converse effect. Additional experiments indicated hTRPM2 activation was required for the antagonism of either compound to develop, and that neither compound blocked from the intracellular face of the plasma membrane. ADP-ribose-activated whole-cell and single-channel currents in the rat insulinoma cell-line CRI-G1 were also antagonised by clotrimazole. Contrary to the observations made with hTRPM2, antagonism in CRI-G1 cells could be largely reversed following clotrimazole removal. These experiments suggest that imidazole antifungals may be useful tool antagonists for future studies of TRPM2 function.

Differentiation of bipolar CG-4 line oligodendrocytes is associated with regulation of CREB, MAP kinase and PKC signalling pathways

Undifferentiated bipolar CG-4 cell line oligodendrocytes provide a model system for the O-2A progenitor cell from which oligodendrocytes are derived both in vivo and in vitro. The exchange of neuroblastoma conditioned basal media for basal media causes differentiation of undifferentiated bipolar CG-4 cells into multipolar oligodendrocyte-like cells whilst replacement with basal media containing 20% foetal bovine serum favours the formation of type-2 astrocyte-like cells. Here, we demonstrate that activation of these differentiation pathways correlates with distinct changes both in cell metabolism and in signal transduction. Exchange of neuroblastoma conditioned media for basal media correlates with stimulation of basal metabolic activity, reduced phosphorylation of p44/42 MAP kinase and reduced phosphorylation of the transcription factor CREB. In contrast, differentiation with basal medium containing 20% foetal bovine serum (FBS), into type 2 astrocyte-like cells, correlates with reduction in basal metabolic activity, increased phosphorylation of p44/42 MAP kinase and increased phosphorylation of the transcription factor CREB. Inhibition of protein kinase C blocked both the metabolic and morphological changes associated with differentiation towards mature multipolar oligodendrocyte-like cells. Inhibition of PKA and MEK did not effect metabolic activity. The rapid return of neuroblastoma conditioned basal media to cells treated with basal media, increased phosphorylation of CREB and MAP kinase. These results demonstrate that protein kinase C and p44/42 MAP kinase signalling pathways are modulated during bipolar CG-4 cell differentiation and demonstrate that the transcription factor CREB may play a pivotal role in differentiation along oligodendrocyte-or astrocyte-lineages.

Heparin-induced thrombocytopenia: bovine versus porcine heparin in cardiopulmonary bypass surgery

BACKGROUND

Studies have demonstrated a high incidence of antibodies to heparin/platelet factor 4 complexes, the antigen in heparin-induced thrombocytopenia, in patients after cardiopulmonary bypass surgery. In many hospitals, beef lung heparin has been used historically for cardiopulmonary bypass, and there has been reluctance to change to porcine heparin despite concerns of an increased incidence of heparin-induced thrombocytopenia in patients receiving bovine heparin.

METHODS

A prospective randomized trial comparing bovine and porcine heparin in cardiopulmonary bypass surgery was conducted. Presurgery and postsurgery heparin antibody formation was studied using the serotonin release assay and a heparin/platelet factor 4 enzyme-linked immunosorbent assay.

RESULTS

Data available on 98 patients, randomized to receive either bovine or porcine heparin, revealed no significant difference in patient positivity by serotonin release assay (12% in both groups) or by the heparin/platelet factor 4 enzyme-linked immunosorbent assay (29% with porcine and 35% with bovine heparin) postoperatively. There were no significant differences between preoperative and postoperative platelet counts or thromboembolic complications.

CONCLUSIONS

Our study does not support the belief that bovine heparin is more likely than porcine heparin to induce the development of antibodies to heparin/platelet factor 4.

Radiofrequency transmission to monitoring devices in the operating room: a simulation study

We evaluated radiofrequency (RF) transmission to various monitoring devices using circuits that simulated potentially hazardous conditions for patients in the operating room. Right heart ejection fraction (REF) pulmonary artery catheters, transesophageal atrial pacing stethoscopes, and temperature-sensing esophageal stethoscopes were subjected to RF transmission from an electrosurgery unit. Peak voltage and spark intensity were measured in circuits between the electrocautery dispersive pad and conductive elements of the various medical devices. All monitoring devices with an exposed conductive surface were found to have induced voltages and even spark generation. The ranking for peak voltage from least to most was as follows: disrupted esophageal stethoscope (620 volts), the transesophageal pacemaker (640 volts), and the REF pulmonary artery catheter (PAC) (680 volts). Peak voltage measurements of the REF PAC significantly decreased from 388 +/- 23 to 142 +/- 22 volts (P < 0.0001, Student's t-tests) in a fluid medium compared to air. In a fluid medium, peak voltage significantly decreased from 142 +/- 22 to 85 +/- 15 volts (P < 0.0001, Student's t-tests) when the REF PAC was connected to the cardiopulmonary monitor.

Protein kinase C activation by 12-0-tetradecanoylphorbol 13-acetate in CG-4 line oligodendrocytes stimulates turnover of choline and ethanolamine phospholipids by phospholipase D and induces rapid process contraction

Treatment of [3H]-choline- or [14C]-ethanolamine-labelled undifferentiated bipolar and differentiated multipolar CG-4 line oligodendrocytes with 12-0-tetradecanoylphorbol 13-acetate (TPA) to activate protein kinase C stimulated the release of choline or ethanolamine metabolites to the medium over controls. Ro31-8220, a PKC inhibitor, reduced TPA-stimulated release of choline- and ethanolamine-metabolites to basal levels. TPA treatment of both bipolar and multipolar cells caused rapid contraction of processes leaving rounded up cells: this effect was blocked by Ro31-8220. After 12-15 h exposure to TPA, bipolar undifferentiated CG-4 line cells extended short processes again and the cells became multipolar. Nocodozole, an agent which disrupts microtubules and caused CG-4 line cells to round up, caused increased choline or ethanolamine-metabolite release to the medium over basal levels suggesting that some release during TPA-treatment might occur due to process fragmentation. However, the transphosphatidylation reaction confirmed that phospholipase D was active in these cells. Exposure of bipolar undifferentiated CG-4 line cells to TPA resulted in down-regulatation of PKC-alpha and PKC-beta which could not be detected by Western blotting after a few hours; PKC-epsilon was down-regulated much more slowly but PKCs delta, zeta and iota were not influenced by 48 h exposure of cells to TPA. Formation of phosphatidylethanol in the transphosphatidylation reaction was markedly reduced in TPA down-regulated cells indicating a role for PKCs alpha and beta in phospholipase D activation in CG-4 line oligodendrocytes.

The interplay between climate change, forests, and disturbances

Climate change affects forests both directly and indirectly through disturbances. Disturbances are a natural and integral part of forest ecosystems, and climate change can alter these natural interactions. When disturbances exceed their natural range of variation, the change in forest structure and function may be extreme. Each disturbance affects forests differently. Some disturbances have tight interactions with the species and forest communities which can be disrupted by climate change. Impacts of disturbances and thus of climate change are seen over a board spectrum of spatial and temporal scales. Future observations, research, and tool development are needed to further understand the interactions between climate change and forest disturbances.

Association between variants at the GABAAbeta2, GABAAalpha6 and GABAAgamma2 gene cluster and alcohol dependence in a Scottish population

A role for the GABA/benzodiazepine receptor complex in alcohol dependence syndrome has been suggested by several lines of evidence. To elucidate the role of GABAA subunits in human alcohol dependence syndrome, we identified polymorphisms in the GABAAbeta2 and GABAAalpha6 receptor subunit genes on 5q33 and assessed their potential contribution in an association study, together with a NciI RFLP at the GABAAgamma2 receptor subunit gene. One hundred and eight alcohol-dependent subjects and 54 unrelated controls were recruited from Scotland. Two novel genetic markers were identified at the GABAAbeta2 and GABAAalpha6 receptor subunit genes and examined for association with the alcohol dependence syndrome and subgroups of subjects with Korsakoff's psychosis and without Korsakoff's psychosis, together with a NciI RFLP at the GABAAgamma2 receptor subunit gene. The chi2 tests demonstrated associations between all alcohol-dependent subjects (not stratified) and the BanI RFLP at the GABAAbeta2 receptor subunit gene (P = 0.015), and the AlwNI RFLP at the GABAAalpha6 receptor gene (P = 0.013). Significant associations were also found between the alcohol-dependent subjects with Korsakoff's psychosis and the BanI RFLP (P = 0.039) and the AlwNI RFLP (P = 0.003). Haplotype analysis also provided evidence of association when all alcohol-dependent subjects (P = 0.013) and the subjects with Korsakoff's psychosis (P = 0.007) were compared with controls. Our findings provide evidence for a role for the GABAA receptor subunit cluster on chromosome 5q33 in susceptibility to the alcohol dependence syndrome and Korsakoff's psychosis.

The effects of endomorphin-1 and endomorphin-2 in CHO cells expressing recombinant mu-opioid receptors and SH-SY5Y cells

1 Endomorphin-1 and -2 (E-1/E-2) have been proposed as endogenous ligands for the mu-opioid receptor. The aims of this study are to characterize the binding of E-1/E-2 and the subsequent effects on cyclic AMP formation and [Ca2+]i levels in SH-SY5Y and Chinese hamster ovary (CHO) cells expressing endogenous and recombinant mu-opioid receptors. 2 E-1 displaced [3H]-diprenorphine ([3H]-DPN) binding in CHO micro and SH-SY5Y membranes with pKi values of 8.02+/-0.09 and 8.54+/-0.13 respectively. E-2 displaced [3H]-DPN binding in CHOmu and SH-SY5Y cells with pKi values of 7.82+/-0.11 and 8.43+/-0.13 respectively. E-1/E-2 bound weakly to CHOdelta and CHOkappa membranes, with IC50 values of greater than 10 microM. 3 In CHOmu cells, E-1/E-2 inhibited forskolin (1 microM) stimulated cyclic AMP formation with pIC50 values of 8.03+/-0.16 (Imax = 53.0+/-9. 3%) and 8.15+/-0.24 (Imax = 56.3+/-3.8%) respectively. In SH-SY5Y cells E1/E2 inhibited forskolin stimulated cyclic AMP formation with pIC50 values of 7.72+/-0.13 (Imax=46.9+/-5.6%) and 8.11+/-0.31 (Imax = 40.2+/-2.8%) respectively. 4 E-1/E-2 (1 microM) increased [Ca2+]i in fura-2 loaded CHOmu cell suspensions in a thapsigargin sensitive and naloxone reversible manner. Mean increases observed were 106+/-28 and 69+/-6.7 nM respectively. In single adherent cells E-1/E-2 (1 microM) increased [Ca2+]i with a mean 340/380 ratio change of 0.81+/-0.09 and 0.40+/-0.08 ratio units respectively. E-1/E-2 failed to increase intracellular calcium in CHOdelta, CHOkappa and SH-SY5Y cells. 5 These data show that E-1/E-2 bind with high affinity and selectivity to mu-opioid receptors and modulate signal transduction pathways typical of opioids. This provides further evidence that these two peptides may be endogenous ligands at the mu-opioid receptor.

Expression and characterisation of human and rat CRF2alpha receptors

Rat and human CRF2alpha receptors were expressed in CHO-pro5 cells and stable cell lines generated. Each receptor was characterised using [125I][tyr0]sauvagine and results compared to CRF1 receptors expressed in the same parental cell line. Under identical assay conditions, [125I][tyr0]sauvagine labelled both CRF1 and CRF2alpha receptors with high affinity. The level of expression varied from 103 fmol/mg membrane protein to 1842 fmol/mg membrane protein (rat CRF1 receptors and rat CRF2 receptors, respectively). It was possible to establish robust scintillation proximity assays (SPA) using wheat germ agglutinin (WGA) SPA beads to trap membrane protein. The success of the SPA assay format was dependent on the level of receptor expression observed. The rank order of affinities of a series of peptide CRF receptor agonists and antagonists was similar to that described in the literature for the two receptor subtypes as determined using radioligand binding and cAMP accumulation. No pharmacological differences were apparent between rat and human cloned receptors with the exception of alpha-helical CRF-(9-41). This peptide exhibited 10-fold higher affinity for rat CRF2alpha receptors as compared to human CRF2alpha receptors. PD 173307, PD 173602 and PD 174239 exhibited high affinity and selectivity for human CRF1 receptors, and as such represent useful tools for probing CRF receptor function.

Bombesin-like peptides depolarize rat hippocampal interneurones through interaction with subtype 2 bombesin receptors

1. Whole-cell patch-clamp recordings were made from visually identified hippocampal interneurones in slices of rat brain tissue in vitro. Bath application of the bombesin-like neuropeptides gastrin-releasing peptide (GRP) or neuromedin B (NMB) produced a large membrane depolarization that was blocked by pre-incubation with the subtype 2 bombesin (BB2) receptor antagonist [D-Phe6, Des-Met14]bombesin-(6-14)ethyl amide. 2. The inward current elicited by NMB or GRP was unaffected by K+ channel blockade with external Ba2+ or by replacement of potassium gluconate in the electrode solution with caesium acetate. 3. Replacement of external NaCl with Tris-HCl significantly reduced the magnitude of the GRP-induced current at -60 mV. In contrast, replacement of external NaCl with LiCl had no effect on the magnitude of this current. 4. Photorelease of caged GTPgammaS inside neurones irreversibly potentiated the GRP-induced current at -60 mV. Similarly, bath application of the phospholipase C (PLC) inhibitor U-73122 significantly reduced the size of the inward current induced by GRP. 5. Reverse transcription followed by the polymerase chain reaction using cytoplasm from single hippocampal interneurones demonstrated the expression of BB2 receptor mRNA together with glutamate decarboxylase (GAD67). 6. Although bath application of GRP or NMB had little or no effect on the resting membrane properties of CA1 pyramidal cells per se, these neuropeptides produced a dramatic increase in the number and amplitude of miniature inhibitory postsynaptic currents in these cells in a TTX-sensitive manner.

Substratum of pleiotrophin (HB-GAM) stimulates rat CG-4 line oligodendrocytes to adopt a bipolar morphology and disperse: primary O-2A progenitor glial cells disperse similarly on pleiotrophin

Pleiotrophin (HB-GAM), an extracellular matrix-associated protein with a high content of basic amino acid residues, is expressed in the central nervous system during late pre- and early post-natal development and promotes neurite outgrowth in vitro. Here, we show that, on a substratum of pleiotrophin formed from a 5 or 10 microg/ml solution, undifferentiated rat CG-4 line oligodendrocytes adopt a bipolar morphology and disperse over the substratum, as we have previously shown with poly-L-lysine (Rumsby et al. Neurosci. Res. Commun. 23:101-109, 1998). On pleiotrophin substrata formed from coating solutions of 1 microg/ml and below, CG-4 line cells form aggregates and do not disperse, as is also the case with poly-L-lysine. The same dispersing effect is observed with rat primary 0-2A progenitor glial cells on pleiotrophin substrata from solutions of 5 and 10 microg/ml: 0-2A cells aggregate together on pleiotrophin substrata formed from lower concentrations and do not disperse. A pleiotrophin substratum enhances proliferation of CG-4 line oligodendrocytes and primary 0-2A progenitor glial cells. The results show that pleiotrophin provides a substratum that can influence progenitor oligodendrocyte morphology, aid cell dispersion, and perhaps also enhance progenitor oligodendrocyte cell growth.

Anatomical and functional characterisation of a dopaminergic system in the suprachiasmatic nucleus of the neonatal Siberian hamster

In altricial rodents, maternal influences entrain the developing circadian system in the perinatal period before the capacity to respond directly to photic cues develops. The aim of these studies was to investigate the potential role of dopamine in this process in the Siberian hamster. An initial study investigated the ontogeny of retinal innervation of the suprachiasmatic nuclei (SCN) by using cholera toxin B subunit as a tracer. This revealed that retinal fibres first innervate the SCN on postnatal day 3 (PD3), and ingrowth of fibres is extensive by PD6. In situ hybridisation studies revealed the presence of D1-dopamine receptor (D1-R) mRNA in the SCN on PD2, and levels of expression were similar in PD6 pups and adult hamsters. Immunocytochemical staining for tyrosine hydroxylase revealed abundant catecholaminergic fibres within the ventromedial zone of the SCN from the day of birth through PD20; however, in contrast, few fibres were present in adult SCN. Dopamine-beta-hydroxylase-immunoreactive fibres were absent from the neonatal and adult SCN, suggesting that the fibres in the SCN are dopaminergic. The function of this dopaminergic system was investigated by determining the effects of D1-R agonists on the expression of the immediate-early gene c-fos in the SCN. This was assessed in pups ages PD1- PD5 by in situ hybridisation and immunocytochemical localisation of its protein product. No induction was seen in the SCN, in marked contrast to studies in the developing rat. A final series of studies investigated dopaminergic function by determining whether a D1-agonist could induce phosphorylation of Ca2+/cyclic AMP response element-binding protein (CREB) on Ser133. Hypothalamic slices containing SCN taken from PD1 and PD2 hamsters were treated with D1-R agonists, and levels of phosphorylated CREB were assayed by Western blots. Phosphorylation of CREB was stimulated by D1-R agonists in both Syrian and Siberian hamster hypothalamus, but the response was far greater in Syrian hamster tissue (+138%+/-28%) than in Siberian hamster tissue (+43%+/-11%). Although the anatomical studies demonstrate the existence of a dopaminergic system in the SCN of the early postnatal Siberian hamster, the unresponsiveness of c-fos expression and the relative lack of phosphorylation of CREB after D1-R activation suggests a diminished role for dopamine in the regulation of circadian events during the postnatal period in this species.

Corticotropin-releasing factor type 1 and type 2alpha receptors regulate phosphorylation of calcium/cyclic adenosine 3',5'-monophosphate response element-binding protein and activation of p42/p44 mitogen-activated protein kinase

CRF exerts a key neuroregulatory control on the function of the hypothalamic-pituitary-adrenal axis. These effects are thought to be mediated primarily through activation of Gs-coupled plasma membrane receptors. In the present study, we investigated the effects of activation of CRF receptors by sauvagine on signaling pathways that converge on phosphorylation of the transcription factor calcium/cAMP response element-binding protein (CREB). Studies were undertaken using CHO cell lines transfected with either rat CRF-1 or CRF-2alpha receptors. Signaling pathways were investigated using immunocytochemical, Western blot, and imaging techniques. Treatment with sauvagine increased phosphorylation of p42/p44, but not of p38 or stress-activated protein kinase (SAPK)/JUN N-terminal kinase (JNK) mitogen-activated protein (MAP) kinases correlating with increased p42/p44 MAP kinase activity. Mobilization of intracellular Ca2+ stores was observed in cells treated with high concentrations (100 nM, 1 microM) of sauvagine. A time- and dose-dependent increase in phosphorylation of the transcription factor CREB was observed in cultures treated with sauvagine. Phosphorylation of CREB occurred at lower concentrations of sauvagine than those required to mobilize intracellular calcium stores, and phosphorylation was not blocked by the mitogen-activated protein kinase kinase inhibitor PD98059 at a concentration (1 microM) that fully inhibited phosphorylation of MAP kinase. Cotreatment of cultures with the protein kinase A inhibitor H89 (10 microM) blocked fully the stimulatory actions of sauvagine (0.1 nM, 1 nM) on phosphorylation of CREB, but not those on phosphorylation of MAP kinase. Phosphorylation of MAP kinase was partially blocked by the phosphoinositide 3-kinase inhibitor LY294002 (5 microM) and by the phosphoinositide-phospholipase C inhibitor U73122 (10 microM). These data demonstrate that cAMP-, Ca2+-, and MAP kinase-dependent signaling pathways are activated by stimulation of CRF-1 and CRF-2alpha receptors. However, in these cells, only protein kinase A-dependent pathways contribute significantly to enhanced phosphorylation of CREB. These represent the first reported observations of CRF receptor-mediated phosphorylation of the transcription factor CREB and activation of MAP kinase signal transduction pathways.

Glutamatergic induction of CREB phosphorylation and Fos expression in primary cultures of the suprachiasmatic hypothalamus in vitro is mediated by co-ordinate activity of NMDA and non-NMDA receptors

Exposure of Syrian hamsters to light 1 h after lights-off rapidly (10 min) induced nuclear immunoreactivity (-ir) to the phospho-Ser133 form of the Ca2+/cAMP response element (CRE) binding protein (pCREB) in the retinorecipient zone of the suprachiasmatic nuclei (SCN). Light also induced nuclear Fos-ir in the same region of the SCN after 1 h. The glutamatergic N-methyl-D-aspartate (NMDA) receptor blocker MK801 attenuated the photic induction of both factors. To investigate glutamatergic regulation of pCREB and Fos further, tissue blocks and primary cultures of neonatal hamster SCN were examined by Western blotting and immunocytochemistry in vitro. On Western blots of SCN tissue, the pCREB-ir signal at 45 kDa was enhanced by glutamate or a mixture of glutamatergic agonists (NMDA, amino-methyl proprionic acid (AMPA), and Kainate (KA)), whereas total CREB did not change. Glutamate or the mixture of agonists also induced a 56 kDa band identified as Fos protein in SCN tissue. In dissociated cultures of SCN, glutamate caused a rapid (15 min) induction of nuclear pCREB-ir and Fos-ir (after 60 min) exclusively in neurones, both GABA-ir and others. Treatment with NMDA alone had no effect on pCREB-ir. AMPA alone caused a slight increase in pCREB-ir. However, kainate alone or in combination with NMDA and AMPA induced nuclear pCREB-ir equal to that induced by glutamate. The effects of glutamate on pCREB-ir and Fos-ir were blocked by antagonists of both NMDA (MK801) and AMPA/KA (NBQX) receptors. In the absence of extracellular Mg2+, MK801 blocked glutamatergic induction of Fos-ir. However, the AMPA/KA receptor antagonist was no longer effective at blocking glutamatergic induction of either Fos-ir or pCREB-ir, consistent with the model that glutamate regulates gene expression in the SCN by a co-ordinate action through both NMDA and AMPA/KA receptors. Glutamatergic induction of nuclear pCREB-ir in GABA-ir neurones was blocked by KN-62 an inhibitor of Ca2+/Calmodulin (CaM)-dependent kinases, implicating Ca2+-dependent signalling pathways in the glutamatergic regulation of gene expression in the SCN.

Stimuli which entrain the circadian clock of the neonatal Syrian hamster in vivo regulate the phosphorylation of the transcription factor CREB in the suprachiasmatic nucleus in vitro

Photic resetting of the adult mammalian circadian clock in vivo is associated with phosphorylation of the Ser133 residue of the calcium/cyclic AMP response-element binding-protein (CREB) in the retinorecipient region of the suprachiasmatic nucleus (SCN). Western blotting and immunocytochemistry were used to investigate whether agonists known to reset the clock of neonatal hamsters in vivo are also able to influence the phosphorylation of CREB in the suprachiasmatic hypothalamus in vitro. Antisera raised against synthetic CREB peptide sequences were used to differentiate between total CREB and the Ser133 phosphorylated form of CREB (pCREB). Western blot analysis of proteins isolated from suprachiasmatic tissue of 1-day-old Syrian hamsters revealed bands at approximately 45 kDa corresponding to total CREB and pCREB. Treatment of the tissue with a mixture of glutamatergic agonists [N-methyl-D-aspartate (NMDA), amino-methyl proprionic acid (AMPA) and kainate, all at 1 microM], or native glutamate (1 microM) had no effect on the total CREB signal, but increased the pCREB signal, indicative of agonist-stimulated phosphorylation of CREB on Ser133. A similar effect was seen following treatment of the suprachiasmatic blocks with either dopamine (1 microM) or forskolin (1 microM). Simultaneous treatment with melatonin (1 microM) significantly attenuated stimulation by forskolin. The effect of the agonists on nuclear pCREB-immunoreactivity (-ir) was investigated in primary cultures which contained a mixture of cell types characteristic of the suprachiasmatic nuclei in vivo. Basal expression of nuclear total CREB-ir was high, whereas expression of pCREB-ir was low. Treatment with glutamate (1 microM) or dopamine (1 microM) had no effect on total CREB-ir, but increased pCREB-ir in approximately 50 and 30% of cells, respectively, whereas forskolin (1 microM) increased pCREB-ir in almost all cells (> 90%). The effects of all three agonists were rapid (< 15 min), and dose and time dependent. Melatonin reversed the effects of forskolin in mixed cultures, but not in pure astrocyte cultures. Dual-immunocytochemistry (ICC) revealed that glutamate (1 microM) increased nuclear pCREB-ir in cells immunoreactive for microtubule-associated protein II (MAP II-ir), but not other cells, indicating an effect predominantly on neurons. This occurred equally in gamma-amino butyric acid (GABA)-ir and non-GABA-ir neurons. Dopamine (1 microM) was more selective, increasing pCREB-ir only in GABA-ir neurons, whereas forskolin increased pCREB-ir in all cells. The specific stimulation of pCREB-ir in GABA-ir neurons by dopamine was reversed by melatonin, but melatonin had no effect on the increase in pCREB-ir induced in GABA-ir neurons by glutamate. These results demonstrate that agonists known to entrain the circadian clock in vivo modulate phosphorylation of CREB in GABA-ir neurons derived from the neonatal suprachiasmatic nuclei.

Ability of heart rate variability to predict prognosis in patients with advanced congestive heart failure

We analyzed heart rate variability from normal RR intervals in patients with advanced congestive heart failure. Although most patients had decreased HRV, patients with a life-threatening cardiac event or death (n = 8) within 18 months had significantly lower heart rate variability than those who did not (n = 18), which may have value in determining prognosis in this population.

Melatonin-sensitive, serum-stimulated signalling in ovine pars tuberalis

In primary cultures of ovine pars tuberalis (oPT), serum acts through melatonin-sensitive mechanisms independent of cyclic AMP to increase the phosphorylation of the Ca2+/cyclic AMP response element binding protein (CREB). Immunocytochemical and biochemical assays were used to characterize the active components of serum and the signalling pathways through which they and melatonin function in oPT. The stimulatory effect of serum was heat-labile, sensitive to precipitation by methanol, and required components with a mass greater than 10 KDa implicating peptide or protein factors as the active agent. Serum increased the cytosolic free Ca2+ concentration ([Ca2+]i) of oPT cells. Serum also enhanced the release of [3H]-choline and [3H]-arachidonic acid from prelabeled cells, demonstrating that factors present in serum increase the breakdown of cellular phospholipids. This effect, however, was not blocked by melatonin (1 microM). Serum also caused a dose-dependent increase in levels of immediate early gene immunoreactivity, confirming that factors in serum have the ability to control transcription in the oPT. Down-regulation of protein kinase C (PKC) by treatment with 12-0-tetradecanoylphorbol-13-acetate (TPA, 100 nM) or treatment with a specific PKC inhibitor (RO-31-8220, 1 microM), did not affect protein kinase A-mediated stimulation of CREB phosphorylation. However, down-regulation of PKC blocked the acute stimulatory effects of TPA (100 nM) and of serum (1%). Moreover, RO-31-8220 abolished the stimulatory effect of TPA (100 nM) and strongly attenuated that of serum (1%). These results demonstrate that serum increases the phosphorylation of CREB by stimulating cyclic AMP-independent, PKC-dependent, signalling pathways within the oPT. PKC may be activated through increased phospholipid catabolism and/or raised [Ca2+]i.

Prevalence of heparin-associated antibodies without thrombosis in patients undergoing cardiopulmonary bypass surgery

BACKGROUND

Patients with cardiovascular disease almost invariably receive heparin before cardiopulmonary bypass surgery, which places them at risk of developing heparin-associated antibodies with a risk of thromboembolic complications. This study was designed to determine the prevalence of heparin-induced antibodies in patients before and after cardiopulmonary bypass surgery.

METHODS AND RESULTS

Plasma from 111 patients was tested before surgery and 5 days after surgery for heparin-dependent platelet-reactive antibodies with a 14C-serotonin-release assay (SRA) and for antibodies to heparin/platelet factor 4 complexes with an ELISA. Heparin exposure after surgery was minimized. Heparin-dependent antibodies were detected before surgery in 5% of patients with SRA and 19% of patients with ELISA. By the fifth postoperative day, there was a marked increase in patients positive on the SRA or ELISA (13% and 51%, respectively; P < .01 for each). Patients who had received heparin therapy earlier in their hospitalization were more likely to have a positive ELISA before surgery (35%; P = .017) and a positive ELISA (68%; P = .054) or SRA (30%; P = .002) after surgery. However, there was no difference in the prevalence of thrombocytopenia or thromboembolic events between the antibody-positive and-negative groups.

CONCLUSIONS

Approximately one fifth of patients undergoing cardiopulmonary bypass surgery have heparin-induced platelet antibodies detectable before the procedure as a result of prior heparin exposure, and many more develop antibodies after surgery. The absence of an association between these antibodies and thromboembolic complications in this study may be, in part, attributable to careful avoidance of heparin after surgery. The high prevalence of heparin-induced antibodies in this setting suggests that these patients may be at risk of developing thrombotic complications with additional heparin exposure.

Elevation of cyclic AMP levels in mouse embryonic stem cells by insulin related peptides

The preimplantation mammalian embryo has been shown to respond to exogenous insulin-like growth factors and insulin itself, however, the most quantitatively important source of these peptides and the receptors through which they exert their effects are unclear. Whilst the type 1 insulin-like growth factor (IGF) receptor is believed to act primarily through tyrosine phosphorylation of the substrate protein alpha IRS-1, evidence for a signalling role for the type 2 receptor is disputed, some evidence pointing to mediation through G protein-dependent calcium ion flux. We have examined the response of murine embryonic stem cells, as a model for the cells of the preimplantation embryo, to IGF-I, IGF-II, insulin and analogs of IGF-II: R6 IGF-II and des (1-6) IGF-II. In response to all of these peptides, except R6 IGF-II, elevation of intracellular cyclic AMP occurs. As R6 IGF-II binds with higher affinity to the type 2 receptor than canonical IGF-II or IGF-I, and insulin fails to interact, this suggests that the elevation of cyclic AMP in response to the other insulin related peptides (IRPs) is not through the type 2 receptor. We conclude that either the type 1 receptor has a previously uncharacterized direct or indirect effect on intracellular cyclic AMP levels, or that there is a further, as yet uncharacterized, receptor active in embryonic stem cells.

Phosphorylation of CREB in ovine pars tuberalis is regulated both by cyclic AMP-dependent and cyclic AMP-independent mechanisms

This study used a combination of Western blotting and immunocytochemistry to test whether signalling pathways independent of cyclic AMP have the potential to induce phospho-CREB (pCREB)-like immunoreactivity (-ir) in the oPT. Western blot analysis of extracts of primary cultures of oPT using an antiserum against CREB, revealed a major band of CREB-ir at 44 KDa. The intensity of this band did not vary systematically with treatment. In extracts from untreated cells, Western blot analysis revealed a major band of pCREB-ir at 42 KDa which was not sensitive to agonist treatment. Treatment of cells with forskolin (10(-6) M) increased the intensity of a number of other pCREB-ir bands at between ca. 38 and 44 KDa. The band at 44 KDa probably represented native pCREB whilst the other bands induced by forskolin probably represented pCREB-like proteins. Melatonin (10(-6) M) alone had no effect on pCREB-ir, but it did inhibit the effect of forskolin on the ca. 38 and 44 KDa pCREB-ir bands. Treatment with lamb serum (1%) consistently increased the intensity of the ca. 38 and 44 KDa pCREB-ir bands relative to control cells, as assessed by Western blot. However, Western blot analysis did not reveal a consistent effect of melatonin on the pCREB-ir response to serum. The effect of serum on pCREB-ir in oPT cells was characterized further by immunocytochemical analysis. In contrast to experiments utilizing Western blotting, untreated cells did not possess detectable pCREB-ir. In serum-starved oPT and oPD cultures, treatment with serum induced exclusively nuclear pCREB-ir. A large majority of oPT cells (> or = 90%) were sensitive to serum (1%), and serum caused a time- and dose-dependent increase of nuclear pCREB-ir. Melatonin attenuated the response to serum in the oPT. This inhibition of the response to serum was not apparent in the oPD, demonstrating that the effect of melatonin was specific for a tissue known to express melatonin receptors. In oPT cultures, physiological concentrations of melatonin (10(-9) M) partially reversed (ca. 70%) the inductive effect of 0.1% serum on nuclear pCREB-ir. However, in contrast to studies applying forskolin, the induction of pCREB-ir by serum occurred in the absence of measurable changes in the concentration of cyclic AMP, indicating that components of serum are able to stimulate the phosphorylation of CREB in the oPT through mechanisms independent of cyclic AMP. Both adenosine and prostaglandin E2 (PGE2) also induced nuclear pCREB-ir in the absence of increased levels of cyclic AMP. These results demonstrate that transcriptional activities in the oPT which are under the control of CREB may be modulated by convergent cyclic AMP-dependent and cyclic AMP-independent pathways. Regulation of these pathways by melatonin and other factors present in serum may be an important control-point in the generation of seasonal neuroendocrine cycles.

Mental stress--induced myocardial ischemia and cardiac events

OBJECTIVE

To assess the clinical significance of mental stress-induced myocardial ischemia in patients with coronary artery disease (CAD).

DESIGN AND SETTING

Cohort study in outpatients in a tertiary care teaching hospital assessed at baseline and followed up for up to 5 years.

SUBJECTS

A total of 126 volunteer patients (112 men, 14 women; mean age, 59 years) with documented CAD and exercise-induced myocardial ischemia.

OUTCOME MEASURES

Patients underwent baseline mental stress and exercise testing using radionuclide ventriculography and 48-hour Holter monitoring. Patients were subsequently contacted by mailed questionnaires or telephone to document cardiac events, including death, nonfatal myocardial infarction, and cardiac revascularization procedures. Logistic regression and Cox proportional hazards models were used to examine the prognostic value of the ischemic measures after adjusting for such potential confounding factors as age, baseline left ventricular ejection fraction (LVEF), and history of myocardial infarction.

RESULTS

Twenty-eight patients (22%) experienced at least 1 cardiac event. Baseline mental stress-induced ischemia was associated with significantly higher rates of subsequent cardiac events (odds ratio, 2.8; 95% confidence interval [CI], 1.0-7.7; P < .05). The LVEF change during mental stress was significantly related to event-free survival (risk ratio [RR], 2.4; 95% CI, 1.12-5.14; P = .02), controlling for age, history of prior myocardial infarction, and baseline LVEF. This relationship remained significant after controlling for electrocardiogram (ECG)-defined ischemia during exercise (RR, 2.2; 95% CI, 1.01-4.81; P < .05). The RR for ECG-defined ischemia during exercise testing was 1.9 (95% CI, 0.95-3.96; P = .07) and the RR for ambulatory ECG ischemia was 0.75 (95% CI, 0.35-1.64; P = .47).

CONCLUSIONS

The presence of mental stress-induced ischemia is associated with significantly higher rates of subsequent fatal and nonfatal cardiac events, independent of age, baseline LVEF, and previous myocardial infarction, and predicted events over and above exercise-induced ischemia. These data suggest that the relationship between psychological stress and adverse cardiac events may be mediated by the occurrence of myocardial ischemia.

A randomized factorial trial of reperfusion strategies and aspirin dosing in acute myocardial infarction. The DUCCS-II Investigators

The focus of new research efforts to improve the morbidity and mortality associated with acute myocardial infarction (AMI) has turned to adjuvant agents that show promise of improving outcomes following coronary thrombolysis. We enrolled 162 patients with AMI in a randomized trial comparing front-loaded tissue-plasminogen activator (t-PA) plus weight-adjusted heparin with anisoylated plasminogen streptokinase activator complex (APSAC) without heparin as well as standard-dose (325 mg) and low-dose (81 mg) aspirin. The primary end point was an in-hospital morbidity profile; secondary end points were clinical and angiographic potency and hemorrhagic events. Selected sites performed an electrocardiographic substudy to determine the time to 50% ST-segment recovery and the time to steady state. Although the trial was terminated when the Global Utilization of Streptokinase and t-PA for Occluded Coronary Arteries-I trial showed that t-PA had a significant mortality advantage over streptokinase, important trends were evident. Patients given t-PA and heparin were better anticoagulated (p = 0.001), yet AP-SAC-treated patients had more bleeding complications. The primary end point favored t-PA (25.4% vs 31.3%), and the secondary end points were similar in both groups. In the electrocardiographic substudy, the t-PA group achieved both 50% ST-segment recovery and steady-state recovery sooner than the APSAC group. Patients taking low-dose aspirin had lower in-hospital mortality and less recurrent ischemia but more strokes than the standard-dose aspirin group. Thus, this trial demonstrated trends favoring front-loaded t-PA with weight-adjusted heparin over APSAC without heparin in the treatment of AMI. The use of low-dose aspirin did not appear to impose a loss of protection from adverse events, nor did standard-dose aspirin increase serious bleeding.

FosB in the suprachiasmatic nucleus of the Syrian and Siberian hamster

The suprachiasmatic nucleus (SCN) generates circadian rhythms of behavior and hormone secretion in mammals, and integrates responses to light and nonphotic stimuli to synchronize such rhythms with the external environment. Previous studies have demonstrated a close association between the induction of the immediate early gene (IEG) c-fos in the SCN by light and phase shifts of circadian rhythms induced by light, but nonphotic stimuli (e.g., arousal), which also cause phase shifts, do not increase c-fos expression in the SCN. Because c-fos is now known to be a member of a large family of IEGs which can regulate transcription and thus cellular function, the aim of the current study was to determine whether induction of another member of this immediate early gene family, fosB, is associated with photic and nonphotic phase shifts. An antiserum that recognizes a unique peptide sequence derived from FosB was produced so that the expression of fosB could be investigated in cells within the SCN by immunocytochemical detection of its protein product. The regional distribution of FosB-immunoreactive (ir) cells in the SCN of Syrian and Siberian hamsters was broadly similar to that for c-Fos-ir cells. However, whereas c-fos expression in the SCN was constitutively low, but could be massively induced by light at particular circadian phases, FosB-ir cells were present at all circadian phases studied, irrespective of photic stimulation, and light only produced marginal increases in the number of FosB-ir cells compared with nonstimulated controls. Moreover, blockade of glutamatergic neurotransmission by pretreatment of hamsters with the NMDA receptor antagonist MK801 significantly reduced photic induction of c-Fos-ir cells, but did not influence the number of FosB-ir cells in the SCN. Finally, an arousing nonphotic stimulus known to cause phase advances in wheel-running behavior in Syrian hamsters did not alter significantly the number of FosB-ir cells in the SCN. These observations indicate that light and nonphotic stimuli are not potent regulators of fosB expression in the SCN. However, because fosB and c-fos can be present in the SCN at the same time after a light pulse, these studies indicate the potential for interactions with each other and with members of the Jun family in the regulation of the circadian timing system.

The inhibitory action of melatonin in the ovine pars tuberalis is not dependent on changes in plasma membrane potential

Treatment of ovine pars tuberalis (oPT) cultures with forskolin activates adenylyl cyclase, leading to increased levels of cyclic AMP, activation of protein kinase A, phosphorylation of the calcium/cyclic AMP response-element binding protein and the increased synthesis and secretion of several proteins. Simultaneous treatment with melatonin inhibits or reverses these effects of forskolin. In the neonatal rat pituitary, the inhibitory effects of melatonin are mediated by changes in membrane potential. This study therefore investigated whether the inhibitory action of melatonin in oPT cultures is also dependent on the modulation of plasma membrane potential. Treatment of cultures with the ionophore valinomycin selectively permeabilised the cell plasma membrane to potassium, thereby causing membrane hyperpolarisation. In cultures of oPT, valinomycin inhibited in a concentration-dependent manner (maximal effect 2 microM) the stimulatory action of forskolin (1 microM) on intracellular levels of cyclic AMP, indicating that the activity of adenylyl cyclase in this tissue is sensitive to hyperpolarisation of the plasma membrane. However, increasing the extracellular concentration of potassium from 5 mM to 100 mM, which would depolarise the plasma membrane, had no effect on the inhibitory action of melatonin (1 microM) in forskolin-stimulated cultures. This indicated that melatonin could be effective in cells with sustained depolarisation. To test directly whether integrity of the plasma membrane is essential for melatonin to inhibit adenylyl cyclase, cultures were treated with the cholesterol-chelating agent saponin (50 micrograms/ml). Saponin increased cellular permeability to trypan blue and enhanced the release of the cytoplasmic enzyme lactate dehydrogenase to the extracellular medium, demonstrating that cell plasma membranes had been permeabilised, thereby abolishing membrane polarity.(ABSTRACT TRUNCATED AT 250 WORDS)

Melatonin regulates the phosphorylation of CREB in ovine pars tuberalis

This study investigated whether melatonin could modulate the phosphorylation of the calcium/cyclic AMP response-element binding-protein (CREB) within primary cell cultures of ovine pars tuberalis (oPT) and pars distalis (oPD). Gel shift assays confirmed the presence of nuclear factors able to alter the electrophoretic mobility of a 32P-labelled CRE oligonucleotide. Two shifted bands were observed probably due to monomer and dimer binding to the CRE. Each band was supershifted by antisera directed against both CREB and the phosphorylated form of CREB (P-CREB), consistent with a specific role of CREB proteins in transcriptional regulation. To study the physiological role of CREB, the nuclear immunoreactivity for P-CREB was followed in primary cultures of oPT given different pharmacological treatments. Cells stimulated with forskolin responded with a robust time- and dose-dependent increase in nuclear phospho-CREB immunoreactivity (P-CREB-ir), confirming that activation of this transcription factor occurred through the cyclic AMP-PKA pathway. Maximal stimulation was achieved within 15 min and persisted for up to 1 h. Treatment with melatonin alone did not alter basal P-CREB-ir levels, yet melatonin inhibited the forskolin-induced increase in P-CREB-ir in a dose-dependent manner (IC50 of between 10(-10) M and 10(-8) M melatonin when tested against 1 microM forskolin). In contrast, in primary cultures of oPD, melatonin failed to block forskolin-stimulated increases in either the content of cyclic AMP or the intensity of nuclear P-CREB-ir, confirming that the action of melatonin upon P-CREB-ir is tissue specific. These results demonstrate that, consistent with its inhibitory effect on the activation of PKA within oPT, melatonin prevents or reverses the phosphorylation of CREB induced by activation of the cyclic AMP signal transduction pathway. Therefore melatonin has the potential to regulate gene expression in the oPT by acting upon the CREB transcription factor. However, this paper also shows that 12-O-tetradecanoylphorbol-13-acetate (TPA) which activates PKC also leads to the phosphorylation of CREB in oPT cells, suggesting the potential involvement of other signal transduction pathways in the transcriptional regulation of these cells.

Phospholipases and melatonin signal transduction in the ovine pars tuberalis

The potential role of phospholipases in mediating melatonin-dependent inhibition of adenylyl cyclase was investigated in pars tuberalis (PT) cultures. The phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) stimulated the release of choline metabolites and increased the transphosphatidylation reaction. The calcium ionophore A23187 stimulated the release of arachidonic acid from cultures. These observations demonstrate phospholipase A and D activities within PT. Phosphatidic acid inhibited forskolin-stimulated production of cyclic AMP both in PT cells and in membrane preparations. This indicates that melatonin could inhibit adenylyl cyclase by increasing phosphatidic acid levels through activation of cellular phospholipases. Melatonin did not stimulate the release of arachidonic acid or choline from PT cultures, nor did it increase intracellular levels of hydrophobic second messengers or stimulate transphosphatidylation. Therefore melatonin does not stimulate phospholipase A and D pathways in PT cells. However, these pathways are present in the PT and their activation could potentially modulate the cellular actions of melatonin.