Identification of neural circuits by imaging coherent electrical activity with FRET-based dyes.

We show that neurons that underlie rhythmic patterns of electrical output may be identified by optical imaging and frequency-domain analysis. Our contrast agent is a two-component dye system in which changes in membrane potential modulate the relative emission between a pair of fluorophores. We demonstrate our methods with the circuit responsible for fictive swimming in the isolated leech nerve cord. The output of a motor neuron provides a reference signal for the phase-sensitive detection of changes in fluorescence from individual neurons in a ganglion. We identify known and possibly novel neurons that participate in the swim rhythm and determine their phases within a cycle. A variant of this approach is used to identify the postsynaptic followers of intracellularly stimulated neurons.     

Two forms of sensitization of the local bending reflex of the medicinal leech

Sensitization of the local bending reflex of the medicinal leech Hirudo medicinalis was studied in a semi-intact preparation in which behavioral and electrophysiological recordings were made simultaneously. 1. Sensitization of local bending could be produced in two ways: by repeated stimulation of the mechanoreceptor sensitive to pressure (the P cell), and by stimulation of the mechanoreceptor sensitive to noxious stimuli (the N cell). 2. Both forms of sensitization produced a central neuronal change, measured as an increase in the number of stimulus-evoked action potentials in cell 3 (an excitor of dorsal longitudinal muscles). 3. Intracellular stimulation of serotonin-containing neurons 21 and 61 mimicked the sensitizing stimuli, but stimulation of the Retzius cell, which also contains serotonin, did not. 4. Stimulation of the Leydig cell, which releases octopamine, decreased the strength of local bending.     

Structural verification of 15-oxo-13,14-dihydrothromboxane B2

The mass spectra of three stable isotope derivatives are presented to confirm ion assignments in the spectrum of the methoxime, trimethylsilyl ether, methyl ester from 15-oxo-13,14-dihydrothromboxane B2.     

Selenium Species and Their Distribution in Freshwater Fish from Argentina

The distribution and speciation of selenium (Se) in freshwater fish (muscle and liver tissue) from lakes in Argentina was investigated. Three introduced species, brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss) and brook trout (Salvelinus fontinalis), and one native species, creole perch (Percichthys trucha), were investigated. Values for total selenium in muscle ranged from 0.66 to 1.61 μg/g, while in the liver, concentrations were much higher, from 4.46 to 73.71 μg/g on a dry matter basis. Separation of soluble Se species (SeCys₂, selenomethionine (SeMet), SeMeSeCys, selenite and selenate) was achieved by ion exchange chromatography and detection was performed by inductively coupled plasma–mass spectrometry. The results showed that in fish muscle, from 47 to 55 % of selenium was soluble and the only Se species identified was SeMet, which represented around 80 % of soluble Se, while in the liver, the amount of soluble Se ranged from 61 to 76 % and the percentage of species identified (SeMet and SeCys₂) was much lower and ranged from 8 to 17 % of soluble Se.     

Shift work,circadian gene variants and risk of breast cancer

Circadian (clock) genes have been linked with several functions relevant to cancer, and epidemiologic research has suggested relationships with breast cancer risk for variants in NPAS2, CLOCK, CRY2 and TIMELESS. Increased breast cancer risk has also been observed among shift workers, suggesting potential interactions in relationships of circadian genes with breast cancer. Relationships with breast cancer of 100 SNPs in 14 clock-related genes, as well as potential interactions with shift work history, were investigated in a case–control study (1042 cases, 1051 controls). Odds ratios in an additive genetic model for European-ancestry participants (645 cases, 806 controls) were calculated, using a two-step correction for multiple testing: within each gene through permutation testing (10,000 permutations), and correcting for the false discovery rate across genes. Interactions of genotypes with ethnicity and shift work (<2 years vs ≥2 years) were evaluated individually. Following permutation analysis, two SNPs (rs3816360 in ARNTL and rs11113179 in CRY1) displayed significant associations with breast cancer and one SNP (rs3027188 in PER1) was marginally significant; however, none were significant following adjustment for the false discovery rate. No significant interaction with shift work history was detected. If shift work causes circadian disruption, this was not reflected in associations between clock gene variants and breast cancer risk in this study. Larger studies are needed to assess interactions with longer durations (>30 years) of shift work that have been associated with breast cancer.     

Approximations for the hitchhiking effect caused by the evolution of antimalarial-drug resistance

An analytically feasible, deterministic model for the spread of drug resistance among human malaria parasites, which incorporates all characteristics of the complex malaria-transmission cycle was introduced by Schneider and Kim (Theor. Popul Biol, 2010). The model accounts for the fact that only a fraction of infected hosts receive drug treatment and that hosts can be co-infected by differently many parasites. Furthermore, the model also incorporates host heterogeneity. Antimalarial-drug resistance is assumed to be caused by a single locus with two alleles—a sensitive one and a resistance one. The most important result for this model is that an analytical solution for the frequencies of a linked neutral biallelic locus exists. However, the exact solution does not admit an explicit form, and cannot straightforwardly be interpreted in terms of the model parameters. Here, we establish simple approximations for the equilibrium frequency at the neutral locus. Under the assumption that the resistant allele is initially rare—the biologically most relevant assumption in this context—and that recombination is weak, the approximations become similar to the approximations in the standard hitchhiking model. However, there are crucial differences. In particular, because of the high degree of selfing among malaria parasites in their sexual phase, a genome-wide reduction of relative heterozygosity occurs if selection is sufficiently strong. It turns out that the approximations are accurate even if the recombination rates are not small and the resistant allele is initially not very rare. The main advantage of our approximations is that they are easy to interpret in terms of model parameters. Moreover, they allow to make predictions of the size of the valley of reduced heterozygosity around the selected locus for given model parameters. Reversely, for a given reduction of heterozygosity, it is possible to identify the corresponding parameters. Moreover, we will show that incorporating host heterogeneity leads to an increased hitchhiking effect.