Simulation of the hippocampal theta rhythm

Centre of Theoretical and Computational Neuroscience, University of Plymouth, UK Basing on the hypothesis about the mechanisms of the theta rhythm generation, the article presents mathematical and computational models of theta activity in the hippocampus. The problem of the theta rhythm modeling is nontrivial because the slow theta oscillations (about 5 Hz) should be generated by a neural system composed of frequently firing neural populations. We studied a model of neural pacemakers in the septum. In this model, the pacemaker follows the frequency of the external signal if this frequency does not deviate too far from the natural frequency of the pacemaker, otherwise the pacemaker returns to the frequency of its own oscillations. These results are in agreement with the experimental records of medial septum neurons. Our model of the septal pacemaker of the theta rhythm is based on the hypothesis that the hippocampal theta appears as a result of the influence of the assemblies of neurons in the medial septum which are under control of pacemaker neurons. Though the model of the pacemaker satisfies many experimental facts, the synchronization of activity in different neural assemblies of the model is not as strong as it should be. Another model of the theta generation is based on the anatomical data about the existence of the inhibitory GABAergic loop between the medial septum and the hippocampus. This model shows stable oscillations at the frequency of the theta rhythm in a broad range of parameter values. It also provides explanation to the experimental data about the variation of the frequency and the amplitude of the theta rhythm under different external stimulations of the system. The role of the theta rhythm for information processing in the hippocampus is discussed.     

Energy state and its control on seed development: starch accumulation is associated with high ATP and steep oxygen gradients within barley grains

The role of oxygen and energy state in development and storage activity of cereal grains is an important issue, but has remained largely uninvestigated due to the lack of appropriate analytical methods. Metabolic profiling, bioluminescence-based in situ imaging of ATP, and oxygen-sensitive microsensors were combined here to investigate barley seed development. For the first time temporal and spatial maps of O2 and ATP distribution in cereal grains were determined and related to the differentiation pattern. Steep O2 gradients were demonstrated and strongly hypoxic regions were detected within the caryopsis (<0.1% of atmospheric saturation). Growing lateral and peripheral regions of endosperm remained well-supplied with O2 due to pericarp photosynthesis. ATP distribution in the developing grain was coupled to endosperm differentiation. High ATP concentrations were associated with the local onset of starch storage within endosperm, while low ATP overlapped with the hypoxic regions. Temporally, the building of steep gradients in ATP coincided with overall elevating metabolite levels, specific changes in the metabolite profiles (glycolysis and citrate cycle), and channelling of metabolic fluxes towards storage (increase of starch accumulation rate). These findings implicate an inhomogenous spatial arrangement of metabolic activity within the caryopsis. It is suggested that the local onset of starch storage is coupled with the accumulation of ATP and elevated metabolic activity. Thus, the ATP level reflects the metabolic state of storage tissue. On the basis of these findings, a hypothetical model for the regulation of starch storage in barley seeds is proposed.     

Seed-specific expression of a bacterial phosphoenolpyruvate carboxylase in Vicia narbonensis increases protein content and improves carbon economy

An ambitious aim in plant breeding and biotechnology is to increase the protein content of crop seeds used for food and feed. Using an approach to manipulate assimilate partitioning, we succeeded in elevating the protein content in legume seeds up to 50%. Transgenic bean plants were generated which express a Corynebacterium glutamicum phosphoenolpyruvate carboxylase (PEPC) in a seed-specific manner. The bacterial enzyme was not feedback inhibited by malate. Transgenic seeds showed a higher [14C]-CO2 uptake and about a threefold increased incorporation of labelled carbon into proteins. Changed metabolite profiles of maturing cotyledons indicated a shift of metabolic fluxes from sugars/starch into organic acids and free amino acids. These changes were consistent with an increased carbon flow through the anaplerotic pathway catalysed by PEPC. Consequently, transgenic seeds accumulated up to 20% more protein per gram seed dry weight. Additionally, seed dry weight was higher by 20%-30%. We conclude that PEPC in seeds is a promising target for molecular plant breeding.     

The effect of sodium cyanate-modified hemoglobin oxygen affinity on the heat resistance of rats]

Regression analysis of relationship between rat hemoglobin-oxygen affinity (HOA) and rectal temperature has shown a close positive correlation of these parameters. Heat resistance (HR) was examined in rats with HOA elevated by sodium cyanate in order to recognize the contribution of HOA to a process of body heat adaptation. Our data suggest that HR of treated rats was larger than in control animals. These results are discussed in relation with antioxidant type of the cyanate elevation in HOA.     

A Noninvasive Platform for Imaging and Quantifying Oil Storage in Submillimeter Tobacco Seed

While often thought of as a smoking drug, tobacco (Nicotiana spp.) is now considered as a plant of choice for molecular farming and biofuel production. Here, we describe a noninvasive means of deriving both the distribution of lipid and the microtopology of the submillimeter tobacco seed, founded on nuclear magnetic resonance (NMR) technology. Our platform enables counting of seeds inside the intact tobacco capsule to measure seed sizes, to model the seed interior in three dimensions, to quantify the lipid content, and to visualize lipid gradients. Hundreds of seeds can be simultaneously imaged at an isotropic resolution of 25 µm, sufficient to assess each individual seed. The relative contributions of the embryo and the endosperm to both seed size and total lipid content could be assessed. The extension of the platform to a range of wild and cultivated Nicotiana species demonstrated certain evolutionary trends in both seed topology and pattern of lipid storage. The NMR analysis of transgenic tobacco plants with seed-specific ectopic expression of the plastidial phosphoenolpyruvate/phosphate translocator, displayed a trade off between seed size and oil concentration. The NMR-based assay of seed lipid content and topology has a number of potential applications, in particular providing a means to test and optimize transgenic strategies aimed at the manipulation of seed size, seed number, and lipid content in tobacco and other species with submillimeter seeds.The use of tobacco (Nicotiana spp.) dates back to the Mayan civilization (Zagorevski and Loughmiller-Newman, 2012) and in modern times still retains a primary place, as measured by monetary value, among nonfood crop species. Given the well-documented health risks associated with smoking tobacco, finding alternative uses for the crop represents an active area of research. The ease of its genetic transformation (the species was the first plant to be successfully transformed some 30 years ago by Zambryski et al. [1983]) has prompted a suggestion that it might be used as a vehicle for the synthesis of high-value pharmaceutical compounds (Borisjuk et al., 1999; Davoodi-Semiromi et al., 2009; Morandini et al., 2011) and enzymes (Verma et al., 2010; Agrawal et al., 2011). Its potential biomass production can reach 170 tons ha⁻¹ per year in some commercial varieties (Schillberg et al., 2003), a level that is attractive in the context of biofuel production (Usta, 2005; Andrianov et al., 2010).Tobacco seed is conventionally considered to have no commercial use, but a production level of up to approximately 1.2 tons ha⁻¹ has been documented in the literature (Patel et al., 1998). The seed contains as much as 40% lipid (Frega et al., 1991), consisting mainly of triacylglycerols with a predominant contribution, about 75%, of linoleic acid. Tobacco seed lipid can be blended with mineral diesel fuel without any need for engine modification or fuel preheating (Usta, 2005). The conversion of tobacco into an energy crop can take advantage of a well-developed biotechnology infrastructure (Gadani et al., 2003). Molecular markers have been applied to characterize the genetic diversity present in breeding germplasm (Ren and Timko, 2001; Fricano et al., 2012). Furthermore, a dense marker-based genetic map has been derived (Bindler et al., 2011), and substantial volumes of DNA sequences have been deposited in the public domain (www.pngg.org/tgi/).Studying the biology of lipid deposition in tobacco seed (tissue specificity, seed size, and architecture) is hampered by the small size of the seed (typically <1 mm in diameter; Fig. 1A) and the large number of seeds formed within each capsule. Preexisting approaches to characterize the internal structure of seeds and to quantify the lipid fraction within them (Borisjuk et al., 2011, 2012; Horn et al., 2011a, 2012) are not readily applicable to small seeds. To the best of our knowledge, there is no method available for the noninvasive lipid imaging in submillimeter oilseeds as those of the genus Nicotiana.Open in a separate windowFigure 1.Variability in seed lipid content as estimated using TD-NMR in a range of Nicotiana species. A, Typical seed size of (from left to right) oat, soybean, oilseed rape, and tobacco. B, The geographical provenance of wild (red) and cultivated (green) Nicotiana spp. accessions. C, Seed lipid content expressed as a percentage of seed dry weight (DW).Our work describes how NMR can be exploited to provide a noninvasive platform for the in vivo analysis of tobacco seed. The method allows for both the characterization of seed architecture and the assessment of tissue-specific lipid storage capacity without any seed destruction. The simultaneous imaging of some hundreds of seeds can be achieved at a level of resolution sufficient to assess each seed individually. The method has been applied to investigate lipid deposition in the endosperm and embryo of the seed of various Nicotiana species as well as transgenic tobacco plants, thereby uncovering a previously unrecognized trade off between seed growth and lipid storage.     

Imaging heterogeneity of membrane and storage lipids in transgenic Camelina sativa seeds with altered fatty acid profiles

Engineering compositional changes in oilseeds is typically accomplished by introducing new enzymatic step(s) and/or by blocking or enhancing an existing enzymatic step(s) in a seed‐specific manner. However, in practice, the amounts of lipid species that accumulate in seeds are often different from what one would predict from enzyme expression levels, and these incongruences may be rooted in an incomplete understanding of the regulation of seed lipid metabolism at the cellular/tissue level. Here we show by mass spectrometry imaging approaches that triacylglycerols and their phospholipid precursors are distributed differently within cotyledons and the hypocotyl/radicle axis in embryos of the oilseed crop Camelina sativa, indicating tissue‐specific heterogeneity in triacylglycerol metabolism. Phosphatidylcholines and triacylglycerols enriched in linoleic acid (C18:2) were preferentially localized to the axis tissues, whereas lipid classes enriched in gadoleic acid (C20:1) were preferentially localized to the cotyledons. Manipulation of seed lipid compositions by heterologous over‐expression of an acyl–acyl carrier protein thioesterase, or by suppression of fatty acid desaturases and elongases, resulted in new overall seed storage lipid compositions with altered patterns of distribution of phospholipid and triacylglycerol in transgenic embryos. Our results reveal previously unknown differences in acyl lipid distribution in Camelina embryos, and suggest that this spatial heterogeneity may or may not be able to be changed effectively in transgenic seeds depending upon the targeted enzyme(s)/pathway(s). Further, these studies point to the importance of resolving the location of metabolites in addition to their quantities within plant tissues.