The glutamate/GABA-glutamine cycle: aspects of transport, neurotransmitter homeostasis and ammonia transfer

Neurons are metabolically handicapped in the sense that they are not able to perform de novo synthesis of neurotransmitter glutamate and gamma-aminobutyric acid (GABA) from glucose. A metabolite shuttle known as the glutamate/GABA-glutamine cycle describes the release of neurotransmitter glutamate or GABA from neurons and subsequent uptake into astrocytes. In return, astrocytes release glutamine to be taken up into neurons for use as neurotransmitter precursor. In this review, the basic properties of the glutamate/GABA-glutamine cycle will be discussed, including aspects of transport and metabolism. Discussions of stoichiometry, the relative role of glutamate vs. GABA and pathological conditions affecting the glutamate/GABA-glutamine cycling are presented. Furthermore, a section is devoted to the accompanying ammonia homeostasis of the glutamate/GABA-glutamine cycle, examining the possible means of intercellular transfer of ammonia produced in neurons (when glutamine is deamidated to glutamate) and utilized in astrocytes (for amidation of glutamate) when the glutamate/GABA-glutamine cycle is operating. A main objective of this review is to endorse the view that the glutamate/GABA-glutamine cycle must be seen as a bi-directional transfer of not only carbon units but also nitrogen units.     

Changes in gray matter induced by learning--revisited

Background

Recently, activation-dependant structural brain plasticity in humans has been demonstrated in adults after three months of training a visio-motor skill. Learning three-ball cascade juggling was associated with a transient and highly selective increase in brain gray matter in the occipito-temporal cortex comprising the motion sensitive area hMT/V5 bilaterally. However, the exact time-scale of usage-dependant structural changes occur is still unknown. A better understanding of the temporal parameters may help to elucidate to what extent this type of cortical plasticity contributes to fast adapting cortical processes that may be relevant to learning.

Principal Findings

Using a 3 Tesla scanner and monitoring whole brain structure we repeated and extended our original study in 20 healthy adult volunteers, focussing on the temporal aspects of the structural changes and investigated whether these changes are performance or exercise dependant. The data confirmed our earlier observation using a mean effects analysis and in addition showed that learning to juggle can alter gray matter in the occipito-temporal cortex as early as after 7 days of training. Neither performance nor exercise alone could explain these changes.

Conclusion

We suggest that the qualitative change (i.e. learning of a new task) is more critical for the brain to change its structure than continued training of an already-learned task.     

Leveraging substrate flexibility and product selectivity of acetogens in two‐stage systems for chemical production

Carbon dioxide (CO₂) stands out as sustainable feedstock for developing a circular carbon economy whose energy supply could be obtained by boosting the production of clean hydrogen from renewable electricity. H₂‐dependent CO₂ gas fermentation using acetogenic microorganisms offers a viable solution of increasingly demonstrated value. While gas fermentation advances to achieve commercial process scalability, which is currently limited to a few products such as acetate and ethanol, it is worth taking the best of the current state‐of‐the‐art technology by its integration within innovative bioconversion schemes. This review presents multiple scenarios where gas fermentation by acetogens integrate into double‐stage biotechnological production processes that use CO₂ as sole carbon feedstock and H₂ as energy carrier for products'' synthesis. In the integration schemes here reviewed, the first stage can be biotic or abiotic while the second stage is biotic. When the first stage is biotic, acetogens act as a biological platform to generate chemical intermediates such as acetate, formate and ethanol that become substrates for a second fermentation stage. This approach holds the potential to enhance process titre/rate/yield metrics and products'' spectrum. Alternatively, when the first stage is abiotic, the integrated two‐stage scheme foresees, in the first stage, the catalytic transformation of CO₂ into C₁ products that, in the second stage, can be metabolized by acetogens. This latter scheme leverages the metabolic flexibility of acetogens in efficient utilization of the products of CO₂ abiotic hydrogenation, namely formate and methanol, to synthesize multicarbon compounds but also to act as flexible catalysts for hydrogen storage or production.

Carbon dioxide recycling is a compelling need and microbial carbon dioxide fixation in value‐added compounds is a valuable opportunity. Fermentation of CO₂ gas streams using acetogenic bacteria is consolidating as a key biotechnology to move toward a cyclic carbon economy. Throughout the review, we pinpointed an ample range of products that are technically attainable by reframing a CO₂‐based gas fermentation process within a two‐stage context with the aim of highlighting some avenues available for fruitful exploitation of the current technology.     

Chromosomenaberrationen bei Pflanzen und ihre genetische Wirkung

Ohne ZusammenfassungReferat auf der Tagung der Deutschen Gesellschaft für Vererbungswissenschaft, Würzburg, 26. September 1938.     

Task partitioning in swarms of robots: an adaptive method for strategy selection

Task partitioning is the decomposition of a task into two or more sub-tasks that can be tackled separately. Task partitioning can be observed in many species of social insects, as it is often an advantageous way of organizing the work of a group of individuals. Potential advantages of task partitioning are, among others: reduction of interference between workers, exploitation of individuals?? skills and specializations, energy efficiency, and higher parallelism. Even though swarms of robots can benefit from task partitioning in the same way as social insects do, only few works in swarm robotics are dedicated to this subject. In this paper, we study the case in which a swarm of robots has to tackle a task that can be partitioned into a sequence of two sub-tasks. We propose a method that allows the individual robots in the swarm to decide whether to partition the given task or not. The method is self-organized, relies on the experience of each individual, and does not require explicit communication between robots. We evaluate the method in simulation experiments, using foraging as testbed. We study cases in which task partitioning is preferable and cases in which it is not. We show that the proposed method leads to good performance of the swarm in both cases, by employing task partitioning only when it is advantageous. We also show that the swarm is able to react to changes in the environmental conditions by adapting the behavior on-line. Scalability experiments show that the proposed method performs well across all the tested group sizes.     

Chromosomes and reproductive behaviour of Finnish Taraxacum agamospecies

Material consisting of 157 accessions of 69 Finnish Taraxacum agamospecies, representing 7 sections, was grown in an experimental field for comparison of certain botanical and nutritional characteristics. This paper gives the collecting data as well as cytological and reproductive characteristics of the material. The largest section Taraxacum (Vulgariu ) was represented by 60 agamospecies, 59 of them triploid (2n = 24) and one tetraploid (T. penicilliforme , 2n = 32). The tetraploid and 37 triploids were chromosome counted for the first time. The diploid sexual species T. obtusilobum from Sweden was included for comparison. Other sections consisted of 3 triploids and 6 tetraploids, 3 tetraploid species of the section Erythrosperma being chromosome counted for the first time. Seedlings with deviating numbers were occasionally found. A banding technique of the chromosomes was developed but it did not allow the exact identification of other than the satellite chromosomes. Species-specific features were found in the flowering phenology and in several pollen characteristics (stainability, mean and variability of the size). There were indications of genetic variation within certain agamospecies in pollen characteristics. Isolated and emasculated (mostly only isolated) flower heads gave mostly a full seed set, which indicates obligate, autonomous agamospermy. Lower seed sets of T. adami, T. dahlstedtii and T. hamatiforme in isolation may be a sign of facultative apomixis in these species, requiring further study.     

Molecular and morphometric analyses identify new lineages within a large Eumida (Annelida) species complex

We report on two new lineages of the Eumida sanguinea complex from Great Britain and describe one of them as a new species using a multilocus approach, including the mitochondrial DNA COI-5P and the nuclear markers ITS (ITS1, 5.8S rRNA and ITS2) and 28S rRNA. The molecular analysis placed Eumida mackiei sp. nov. in a monophyletic clade with 19.1% (COI), 10.1% (ITS) and 1.7% (28S) mean distance to its nearest neighbour. Molecular diagnoses were also applied to nine lineages within the E. sanguinea complex. This was complemented with morphometric data employing multivariate statistical analysis and the incorporation of statistical dissimilarities against three other described species from the complex. Eumida mackiei sp. nov. can be distinguished from E. notata and E. maia by the larger distance between the eyes and differences in morphometric proportions mainly in the dorsal and ventral cirri as well as in the prostomial appendages. E. sanguinea sensu stricto failed to produce a cluster of its own in the morphometric analysis, probably due to juvenile bias. Integrative taxonomy provided strong evidence to formally describe a new cryptic species that can now be used in biomonitoring or other relevant ecological research.