Characterization of a Leishmania tropica antigen that detects immune responses in Desert Storm viscerotropic leishmaniasis patients.

A chronic debilitating parasitic infection, viscerotropic leishmaniasis (VTL), has been described in Operation Desert Storm veterans. Diagnosis of this disease, caused by Leishmania tropica, has been difficult due to low or absent specific immune responses in traditional assays. We report the cloning and characterization of two genomic fragments encoding portions of a single 210-kDa L. tropica protein useful for the diagnosis of VTL in U.S. military personnel. The recombinant proteins encoded by these fragments, recombinant (r) Lt-1 and rLt-2, contain a 33-amino acid repeat that reacts with sera from Desert Storm VTL patients and with sera from L. tropica-infected patients with cutaneous leishmaniasis. Antibody reactivities to rLt-1 indicated a bias toward IgG2 in VTL patient sera. Peripheral blood mononuclear cells from VTL patients produced interferon gamma, but not interleukin 4 or 10, in response to rLt-1. No cytokine production was observed in response to parasite lysate. The results indicate that specific leishmanial antigens may be used to detect immune responses in VTL patients with chronic infections.

Residual delay maps unveil global patterns of atmospheric nonlinearity and produce improved local forecasts

We use residual-delay maps of observational field data for barometric pressure to demonstrate the structure of latitudinal gradients in nonlinearity in the atmosphere. Nonlinearity is weak and largely lacking in tropical and subtropical sites and increases rapidly into the temperate regions where the time series also appear to be much noisier. The degree of nonlinearity closely follows the meridional variation of midlatitude storm track frequency. We extract the specific functional form of this nonlinearity, a V shape in the lagged residuals that appears to be a basic feature of midlatitude synoptic weather systems associated with frontal passages. We present evidence that this form arises from the relative time scales of high-pressure versus low-pressure events. Finally, we show that this nonlinear feature is weaker in a well regarded numerical forecast model (European Centre for Medium-Range Forecasts) because small-scale temporal and spatial variation is smoothed out in the grided inputs. This is significant, in that it allows us to demonstrate how application of statistical corrections based on the residual-delay map may provide marked increases in local forecast accuracy, especially for severe weather systems.

Rapid transition in the structure of a coral reef community: The effects of coral bleaching and physical disturbance

Coral reef communities are in a state of change throughout their geographical range. Factors contributing to this change include bleaching (the loss of algal symbionts), storm damage, disease, and increasing abundance of macroalgae. An additional factor for Caribbean reefs is the aftereffects of the epizootic that reduced the abundance of the herbivorous sea urchin, Diadema antillarum. Although coral reef communities have undergone phase shifts, there are few studies that document the details of such transitions. We report the results of a 40-month study that documents changes in a Caribbean reef community affected by bleaching, hurricane damage, and an increasing abundance of macroalgae. The study site was in a relatively pristine area of the reef surrounding the island of San Salvador in the Bahamas. Ten transects were sampled every 3–9 months from November 1994 to February 1998. During this period, the corals experienced a massive bleaching event resulting in a significant decline in coral abundance. Algae, especially macroalgae, increased in abundance until they effectively dominated the substrate. The direct impact of Hurricane Lili in October 1996 did not alter the developing community structure and may have facilitated increasing algal abundance. The results of this study document the rapid transition of this reef community from one in which corals and algae were codominant to a community dominated by macroalgae. The relatively brief time period required for this transition illustrates the dynamic nature of reef communities.

Desert dust suppressing precipitation: A possible desertification feedback loop

The effect of desert dust on cloud properties and precipitation has so far been studied solely by using theoretical models, which predict that rainfall would be enhanced. Here we present observations showing the contrary; the effect of dust on cloud properties is to inhibit precipitation. Using satellite and aircraft observations we show that clouds forming within desert dust contain small droplets and produce little precipitation by drop coalescence. Measurement of the size distribution and the chemical analysis of individual Saharan dust particles collected in such a dust storm suggest a possible mechanism for the diminished rainfall. The detrimental impact of dust on rainfall is smaller than that caused by smoke from biomass burning or anthropogenic air pollution, but the large abundance of desert dust in the atmosphere renders it important. The reduction of precipitation from clouds affected by desert dust can cause drier soil, which in turn raises more dust, thus providing a possible feedback loop to further decrease precipitation. Furthermore, anthropogenic changes of land use exposing the topsoil can initiate such a desertification feedback process.

A dendrodendritic reciprocal synapse provides a recurrent excitatory connection in the olfactory bulb

Neuronal synchronization in the olfactory bulb has been proposed to arise from a diffuse action of glutamate released from mitral cells (MC, olfactory bulb relay neurons). According to this hypothesis, glutamate spills over from dendrodendritic synapses formed between MC and granule cells (GC, olfactory bulb interneurons) to activate neighboring MC. The excitation of MC is balanced by a strong inhibition from GC. Here we show that MC excitation is caused by glutamate released from bulbar interneurons located in the GC layer. These reciprocal synapses depend on an unusual, 2-amino-5-phosphonovaleric acid-resistant, N-methyl-d-aspartate receptor. This type of feedback excitation onto relay neurons may strengthen the original sensory input signal and further extend the function of the dendritic microcircuit within the main olfactory bulb.

Protein kinase A-independent modulation of ion channels in the brain by cyclic AMP.

Ion channels underlying the electrical activity of neurons can be regulated by neurotransmitters via two basic mechanisms: ligand binding and covalent modification. Whereas neurotransmitters often act by binding directly to ion channels, the intracellular messenger cyclic AMP is thought usually to act indirectly, by activating protein kinase A, which in turn can phosphorylate channel proteins. Here we show that cyclic AMP, and transmitters acting via cyclic AMP, can act in a protein kinase A-independent manner in the brain. In hippocampal pyramidal cells, cyclic AMP and norepinephrine were found to cause a depolarization by enhancing the hyperpolarization-activated mixed cation current, IQ (also called Ih). This effect persisted even after protein kinase A activity was blocked, thus strongly suggesting a kinase-independent action of cyclic AMP. The modulation of this current by ascending monoaminergic fibers from the brainstem is likely to be a widespread mechanism, participating in the state control of the brain during arousal and attention.