Arachidonic Acid as a Possible Negative Feedback Inhibitor of Nicotinic Acetylcholine Receptors on Neurons

Neuronal acetylcholine receptors, being highly permeable to calcium, are likely to regulate calcium-dependent events in neurons. Arachidonic acid is a membrane-permeant second messenger that can be released from membrane phospholipids by phospholipases in a calcium-dependent manner. We show here that activation of neuronal acetylcholine receptors triggers release of 3H-arachidonic acid in a calcium-dependent manner from neurons preloaded with the fatty acid. Moreover, low concentrations of arachidonic acid reversibly inhibit the receptors and act most efficiently on receptors likely to have the highest permeability to calcium, namely receptors containing α7 subunits. Low concentrations of arachidonic acid also reversibly inhibit α7- containing receptors expressed in Xenopus oocytes following injection of α7 cRNA. The oocyte results indicate following injection of α7 cRNA. The oocyte results indicate that the inhibition is a feature of the receptors rather than a consequence of neuron-specific machinery. The inhibition is not mediated by specific metabolites of arachidonic acid because the effects can be mimicked by other fatty acids; their effectiveness correlates with their content of double bonds. In contrast to arachidonic effects on calcium currents, inhibition of neuronal nicotinic receptors by the fatty acid cannot be prevented by blocking production of free radicals or by inhibiting protein kinase C. An alternative mechanism is that arachidonic acid binds directly to the receptors or perturbs the local environment in such a manner as to constrain receptor function

Synaptic Currents Generated by Neuronal Acetylcholine Receptors Sensitive to α-Bungarotoxin

AbstractNicotinic acetylcholine receptors are widely distributed throughout the nervous system, but their functions remain largely unknown. One of the most abundant is a class of receptors that contains the α7 gene product, has a high relative permeability to calcium, and binds α-bungarotoxin. Here, we report that receptors sensitive to α-bungarotoxin, though concentrated in perisynaptic clusters on neurons, can generate a large amount of the synaptic current. Residual currents through other nicotinic receptors are sufficient to elicit action potentials, but with slower rise times. This demonstrates a postsynaptic response for α-bungarotoxin-sensitive receptors on neurons and suggests that the functional domain of the postsynaptic membrane is broader than previously recognized

Endogenous signaling through α7-containing nicotinic receptors promotes maturation and integration of adult-born neurons in the hippocampus

Neurogenesis in the dentate gyrus occurs throughout adult mammalian life and is essential for proper hippocampal function. Early in their development, adult-born neurons express homomeric α7-containing nicotinic acetylcholine receptors (α7-nAChRs) and receive direct cholinergic innervation. We show here that functional α7-nAChRs are necessary for normal survival, maturation, and integration of adult-born neurons in the dentate gyrus. Stereotaxic retroviral injection into the dentate gyrus of wild-type and α7-knock-out (α7KO) male and female mice was used to label and birthdate adult-born neurons for morphological and electrophysiological measures; BrdU (5-bromo-2-deoxyuridine) injections were used to quantify cell survival. In α7KO mice, we find that adult-born neurons develop with truncated, less complex dendritic arbors and display GABAergic postsynaptic currents with immature kinetics. The neurons also have a prolonged period of GABAergic depolarization characteristic of an immature state. In this condition, they receive fewer spontaneous synaptic currents and are more prone to die during the critical period when adult-born neurons are normally integrated into behaviorally relevant networks. Even those adult-born neurons that survive the critical period retain long-term dendritic abnormalities in α7KO mice. Interestingly, local infection with retroviral constructs to knockdown α7-mRNA mimics the α7KO phenotype, demonstrating that the relevant α7-nAChR signaling is cell autonomous. The results indicate a profound role for α7-nAChRs in adult neurogenesis and predict that α7-nAChR loss will cause progressive impairment in hippocampal circuitry and function over time as fewer neurons are added to the dentate gyrus and those that are added integrate less well.This work was supported by National Institutes of Health Grants NS012601 and N0S35469, and the Tobacco-Related Disease Research Program (16RT-0167). N.R.C. is a Tobacco-Related Disease Research Program predoctoral fellow. C.C.F. is a Fundação Calouste Gulbenkian Graduate Fellow. A.W.F. is a National Research Service Award predoctoral fellow. We thank Gouping Feng (Duke University, Durham, NC) for the GFP-reporter mouse line and Xiao-Yun Wang for expert technical assistance

Evolution of response dynamics underlying bacterial chemotaxis

© 2011 Soyer and Goldstein; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Background: The ability to predict the function and structure of complex molecular mechanisms underlying cellular behaviour is one of the main aims of systems biology. To achieve it, we need to understand the evolutionary routes leading to a specific response dynamics that can underlie a given function and how biophysical and environmental factors affect which route is taken. Here, we apply such an evolutionary approach to the bacterial chemotaxis pathway, which is documented to display considerable complexity and diversity.Results: We construct evolutionarily accessible response dynamics starting from a linear response to absolute levels of attractant, to those observed in current-day Escherichia coli. We explicitly consider bacterial movement as a two-state process composed of non-instantaneous tumbling and swimming modes. We find that a linear response to attractant results in significant chemotaxis when sensitivity to attractant is low and when time spent tumbling is large. More importantly, such linear response is optimal in a regime where signalling has low sensitivity. As sensitivity increases, an adaptive response as seen in Escherichia coli becomes optimal and leads to 'perfect' chemotaxis with a low tumbling time. We find that as tumbling time decreases and sensitivity increases, there exist a parameter regime where the chemotaxis performance of the linear and adaptive responses overlap, suggesting that evolution of chemotaxis responses might provide an example for the principle of functional change in structural continuity.Conclusions: Our findings explain several results from diverse bacteria and lead to testable predictions regarding chemotaxis responses evolved in bacteria living under different biophysical constraints and with specific motility machinery. Further, they shed light on the potential evolutionary paths for the evolution of complex behaviours from simpler ones in incremental fashion

An Open Source Simulation Model for Soil and Sediment Bioturbation

Bioturbation is one of the most widespread forms of ecological engineering and has significant implications for the structure and functioning of ecosystems, yet our understanding of the processes involved in biotic mixing remains incomplete. One reason is that, despite their value and utility, most mathematical models currently applied to bioturbation data tend to neglect aspects of the natural complexity of bioturbation in favour of mathematical simplicity. At the same time, the abstract nature of these approaches limits the application of such models to a limited range of users. Here, we contend that a movement towards process-based modelling can improve both the representation of the mechanistic basis of bioturbation and the intuitiveness of modelling approaches. In support of this initiative, we present an open source modelling framework that explicitly simulates particle displacement and a worked example to facilitate application and further development. The framework combines the advantages of rule-based lattice models with the application of parameterisable probability density functions to generate mixing on the lattice. Model parameters can be fitted by experimental data and describe particle displacement at the spatial and temporal scales at which bioturbation data is routinely collected. By using the same model structure across species, but generating species-specific parameters, a generic understanding of species-specific bioturbation behaviour can be achieved. An application to a case study and comparison with a commonly used model attest the predictive power of the approach

Metabolic Deficiences Revealed in the Biotechnologically Important Model Bacterium Escherichia coli BL21(DE3)

The Escherichia coli B strain BL21(DE3) has had a profound impact on biotechnology through its use in the production of recombinant proteins. Little is understood, however, regarding the physiology of this important E. coli strain. We show here that BL21(DE3) totally lacks activity of the four [NiFe]-hydrogenases, the three molybdenum- and selenium-containing formate dehydrogenases and molybdenum-dependent nitrate reductase. Nevertheless, all of the structural genes necessary for the synthesis of the respective anaerobic metalloenzymes are present in the genome. However, the genes encoding the high-affinity molybdate transport system and the molybdenum-responsive transcriptional regulator ModE are absent from the genome. Moreover, BL21(DE3) has a nonsense mutation in the gene encoding the global oxygen-responsive transcriptional regulator FNR. The activities of the two hydrogen-oxidizing hydrogenases, therefore, could be restored to BL21(DE3) by supplementing the growth medium with high concentrations of Ni2+ (Ni2+-transport is FNR-dependent) or by introducing a wild-type copy of the fnr gene. Only combined addition of plasmid-encoded fnr and high concentrations of MoO42− ions could restore hydrogen production to BL21(DE3); however, to only 25–30% of a K-12 wildtype. We could show that limited hydrogen production from the enzyme complex responsible for formate-dependent hydrogen evolution was due solely to reduced activity of the formate dehydrogenase (FDH-H), not the hydrogenase component. The activity of the FNR-dependent formate dehydrogenase, FDH-N, could not be restored, even when the fnr gene and MoO42− were supplied; however, nitrate reductase activity could be recovered by combined addition of MoO42− and the fnr gene. This suggested that a further component specific for biosynthesis or activity of formate dehydrogenases H and N was missing. Re-introduction of the gene encoding ModE could only partially restore the activities of both enzymes. Taken together these results demonstrate that BL21(DE3) has major defects in anaerobic metabolism, metal ion transport and metalloprotein biosynthesis

Total and CO-reactive heme content of actinorhizal nodules and the roots of some non-nodulated plants

The concentration of total and CO-reactive heme was measured in actinorhizal nodules from six different genera. This gave the upper limit to hemoglobin concentration in these nodules. Quantitative extraction of CO-reactive heme was achieved under anaerobic conditions in a buffer equilibrated with CO and containing Triton X-100. The concentration of CO-reactive heme in nodules of Casuarina and Myrica was approximately half of that found in legume nodules, whereas in Comptonia, Alnus and Ceanothus the concentrations of heme were about 10 times lower than in legume nodules. There was no detectable CO-reactive heme in Datisca nodules, but low concentrations were detected in roots of all non-nodulating plants examined, including Zea mays . Difference spectra of CO treated minus dithionite-reduced extracts displayed similar wavelengths of maximal and minimal light absorption for all extracts, and were consistent with those of a hemoglobin. The concentration of CO-reactive heme was not correlated to the degree to which CO inhibited nitrogenase activity nor was it affected by reducing the oxygen concentration in the rooting zone. However, there was a positive correlation between heme concentration and suberization or lignification of the walls of infected host cells. These observations demonstrate that, unlike legume nodules, high concentrations of heme or hemoglobin are not needed for active nitrogen fixation in most actinorhizal nodules. Nonetheless, a significant amount of CO-reactive heme is found in the nodules of Alnus, Comptonia, and Ceanothus, and in the roots of Zea mays . The identity and function of this heme is unknown.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43460/1/11104_2006_Article_BF02370943.pd

New literacy challenge for the twenty-first century: genetic knowledge is poor even among well educated

We live in an age of rapidly advancing genetic research. This research is generating new knowledge that has implications for personal health and well-being. The present study assessed the level of genetic knowledge and personal engagement with genetics in a large sample (N = 5404) of participants. Participants received secondary education in 78 countries, with the largest samples from Russia, the UK and the USA. The results showed significant group differences in genetic knowledge between different countries, professions, education levels and religious affiliations. Overall, genetic knowledge was poor. The questions were designed to assess basic genetic literacy. However, only 1.2% of participants answered all 18 questions correctly, and the average score was 65.5%. Genetic knowledge was related to peoples’ attitudes towards genetics. For example, those with greater genetic knowledge were on average more willing to use genetic knowledge for their personal health management. Based on the results, the paper proposes a number of immediate steps that societies can implement to empower the public to benefit from everadvancing genetic knowledge