The Influence of Spike Rate and Stimulus Duration on Noradrenergic Neurons

We model spiking neurons in locus coeruleus (LC), a brain nucleus involved in modulating cognitive performance, and compare with recent experimental data. Extracellular recordings from LC of monkeys performing target detection and selective attention tasks show varying responses dependent on stimuli and performance accuracy. From membrane voltage and ion channel equations, we derive a phase oscillator model for LC neurons. Average spiking probabilities of a pool of cells over many trials are then computed via a probability density formulation. These show that: (1) Post-stimulus response is elevated in populations with lower spike rates; (2) Responses decay exponentially due to noise and variable pre-stimulus spike rates; and (3) Shorter stimuli preferentially cause depressed post-activation spiking. These results allow us to propose mechanisms for the different LC responses observed across behavioral and task conditions, and to make explicit the role of baseline firing rates and the duration of task-related inputs in determining LC response.     

Skin tight: cell adhesion in the epidermis of Caenorhabditis elegans

The powerful genetics, genomics and microscopy tools available for C. elegans make it well suited to studying how epithelial cells adhere to one another and the extracellular matrix, and how the integrated, simultaneous activities of multiple cell adhesion complexes function to shape an organism. Recent studies using forward and reverse genetics have shed light on how phylogenetically conserved cell adhesion complexes, such as the cadherin/catenin complex, claudins, the Discs large complex and hemidesmosome-like attachment structures, regulate epithelial cell adhesion, providing new insights into conserved cell adhesion mechanisms in higher eukaryotes.     

Patency of the preterm fetal ductus arteriosus is regulated by endothelial nitric oxide synthase and is independent of vasa vasorum in the mouse

Patency of the fetal ductus arteriosus (DA) is maintained in an environment of low relative oxygen tension and a preponderance of vasodilating forces. In addition to prostaglandins, nitric oxide (NO), a potent vasodilator in the pulmonary and systemic vasculatures, has been implicated in regulation of the fetal DA. To further define the contribution of NO to DA patency, the expression and function of NO synthase (NOS) isoforms were examined in the mouse DA on days 17-19 of pregnancy and after birth. Our results show that endothelial NOS (eNOS) is the predominant isoform expressed in the mouse DA and is localized in the DA endothelium by in situ hybridization. Despite rapid constriction of the DA after birth, eNOS expression levels were unchanged throughout the fetal and postnatal period. Pharmacological inhibition of prostaglandin vs. NO synthesis in vivo showed that the preterm fetal DA on day 16 is more sensitive to NOS inhibition than the mature fetal DA on day 19, whereas prostaglandin inhibition results in marked DA constriction on day 19 but minimal effects on the day 16 DA. Combined prostaglandin and NO inhibition caused additional DA constriction on day 16. The contribution of vasa vasorum to DA regulation was also examined. Immunoreactive platelet endothelial cell adhesion molecule and lacZ tagged FLK1 localized to DA endothelial cells but revealed the absence of vasa vasorum within the DA wall. Similarly, there was no evidence of vasa vasorum by vascular casting. These studies indicate that eNOS is the primary source of NO in the mouse DA and that vasomotor tone of the preterm fetal mouse DA is regulated by eNOS-derived NO and is potentiated by prostaglandins. In contrast to other species, mechanisms for DA patency and closure appear to be independent of any contribution of the vasa vasorum.     

Quantitative real-time RT-PCR demonstrates that handling stress can lead to rapid increases of gill-associated virus (GAV) infection levels in Penaeus monodon

Gill-associated virus (GAV) of the black tiger prawn Penaeus monodon has been implicated as a cause of periodic production losses in Australia since 1996. We report here the development of a real-time quantitative RT-PCR (qRT-PCR) for GAV. A dilution series of in vitro transcribed RNA was used to determine the sensitivity limit of the qRT-PCR and as a standard for GAV quantification. A linear relationship between cycle threshold (Ct) values and input RNA was obtained over a wide concentration range between 4.86 x 10(9) and 0.5 template copies per reaction, the latter being the test detection limit. The qRT-PCR was used to follow the progression of GAV levels in a group of 15 adult male P. monodon with chronic GAV infections that were super-infected by intramuscular injection of an inoculum containing high levels of GAV. By Day 9 post-injection, cumulative mortalities reached 100% (15/15) in the GAV-injected prawns and 40% (2/5) in placebo-injected prawns. Spermatophores were collected at the beginning, and together with other tissues, at the end of the trial. Prawns were also bled at regular intervals to collect circulating haemocytes. The qRT-PCR revealed that GAV loads increased significantly in haemocytes collected from both the control and super-infected prawns (p = 0.010). This increase was significantly higher in the super-infected prawns (p = 0.047). The rapid increase in GAV levels in super-infected P. monodon was expected. However, the increase in the control prawns was not, and indicates that repetitive bleeding and handling stress can stimulate GAV proliferation in chronically infected P. monodon.     

Benzimidazolone p38 inhibitors

The synthesis and in vitro p38 alpha activity of a novel series of benzimidazolone inhibitors is described. The p38 alpha SAR is consistent with a mode of binding wherein the benzimidazolone carbonyl serves as the H-bond acceptor to Met109 of p38 alpha in a manner analogous to the pyridine nitrogen of prototypical pyridylimidazole p38 inhibitors. Potent p38 alpha activity comparable to that of several previously reported p38 inhibitors is observed for this novel chemotype.     

CVT-4325: a potent fatty acid oxidation inhibitor with favorable oral bioavailability

New inhibitors of palmitoyl-CoA oxidation are based on the introduction of nitrogen heterocycles in the ‘Western Portion’ of the molecule. SAR studies led to the discovery of CVT-4325 (shown), a potent FOXi (IC₅₀ = 380 nM rat mitochondria) with favorable PK properties (F = 93%, t_1/2 = 13.6 h, dog).     

The yeast Apq12 protein affects nucleocytoplasmic mRNA transport

An important step in mRNA biogenesis is the export of mRNA from the nucleus to the cytoplasm. In this work, we provide evidence that the previously uncharacterized gene APQ12 functions in nucleocytoplasmic mRNA transport in Saccharomyces cerevisiae. First, apq12delta strains manifest 3' hyperadenylated mRNA similar to other previously characterized RNA export mutants. Second, bulk poly(A)+ RNA is retained in the nucleus in apq12delta cells. Third, an Apq12p-GFP chimeric protein is localized to the nuclear periphery. Fourth, mRNA in apq12delta cells is stabilized, consistent with a defect in the rate of nuclear export. Interestingly, apq12delta mutants are severely compromised for growth and display atypical cell morphology. Because this aberrant cell morphology is not seen with other viable export mutants, Apq12p must have either an additional cellular function, or preferentially impinge on the export of mRNAs regulating cell growth. Together, these findings support a role for APQ12 in nucleocytoplasmic transport of mRNA.