ADRA2A is involved in neuro‐endocrine regulation of bone resorption

Adrenergic stimulation is important for osteoclast differentiation and bone resorption. Previous research shows that this happens through β2‐adrenergic receptor (AR), but there are conflicting evidence on presence and role of α2A‐AR in bone. The aim of this study was to investigate the presence of α2A‐AR and its involvement in neuro‐endocrine signalling of bone remodelling in humans. Real‐time polymerase chain reaction (PCR) and immunohistochemistry were used to investigate α2A‐AR receptor presence and localization in bone cells. Functionality of rs553668 and rs1800544 single nucleotide polymorphism SNPs located in α2A‐AR gene was analysed by qPCR expression on bone samples and luciferase reporter assay in human osteosarcoma HOS cells. Using real‐time PCR, genetic association study between rs553668 A>G and rs1800544 C>G SNPs and major bone markers was performed on 661 Slovenian patients with osteoporosis. α2A‐AR is expressed in osteoblasts and lining cells but not in osteocytes. SNP rs553668 has a significant influence on α2A‐AR mRNA level in human bone samples through the stability of mRNA. α2A‐AR gene locus associates with important bone remodelling markers (BMD, CTX, Cathepsin K and pOC). The results of this study are providing comprehensive new evidence that α2A‐AR is involved in neuro‐endocrine signalling of bone turnover and development of osteoporosis. As shown by our results the neurological signalling is mediated through osteoblasts and result in bone resorption. Genetic study showed association of SNPs in α2A‐AR gene locus with bone remodelling markers, identifying the individuals with higher risk of development of osteoporosis.     

Comparative thermodynamic analysis of thrombin interaction with anti-thrombin aptamers and their heterodimeric construct

Aptamers interacting selectively with the anion-binding exosites 1 and 2 of thrombin were merged into dimeric oligonucleotide constructs by means of a poly-(dT)-linker of 35 nucleotides (nt) in length. Complexes of thrombin with the aptamers and their hetero- and homodimeric constructs were measured using an optical biosensor Biacore-3000. The K _D values obtained for the hetero- and homodimeric constructs were correspondingly 25–30- and 2–3-fold lower than those for the primary aptamers. Analysis of temperature dependencies of the K _D values within the temperature interval of 10–40°C has shown that affinity increases with the temperature decrease. The values of the enthalpy change ΔH upon formation of complexes of thrombin with the aptamers and the heterodimeric construct were basically the same. The value of the entropy change ΔS upon complex formation of thrombin with the aptamer heterodimeric construct was 1.5–2-fold higher than the ΔS values for the complexes with the aptamers. The complex formation and dissociation rates increased with the elevation of temperature from 10 to 37°C. However, at both temperatures the dissociation rate for the complex of thrombin with the heterodimeric construct was evidently lower that for the complexes with the aptamers.     

Temporal and spatial dynamics in a northern tallgrass prairie

It is well established that plants and soil properties are interdependent. What is less known is the degree to which the distribution of plant and soil properties, in both space and time, match one another. We assessed plant community and soil conditions in permanent sample plots in a tallgrass prairie community from 2002 to 2008. Redundancy analysis showed that the dominant grass species were associated with changes in elevation, soil pH, and gravimetric water content, but not nitrogen or phosphate. Indicator species analysis suggested the community is best described by four cluster types, with half of the plots changing community type over the 6-year sampling period. These cluster types were generally spatially aggregated, with semivariograms showing a range from 80 to 346 m. This degree of spatial structuring was observed in the elevation and soil water content data, but not in measures of soil inorganic N or P. This suggests that natural plant communities do not necessarily show a strong correspondence to all soil variables, especially those that vary rapidly in time and space. The dynamic nature of vegetation patch distribution, combined with their size, may contribute to the loss of species from small tallgrass prairie reserves.     

Differences in corticosterone level due to inter-food interval length: implications for schedule-induced polydipsia

The purpose of this study was to determine the effects of different food-reinforcement schedules on plasma corticosterone (CORT), and its possible involvement in the acquisition and maintenance of schedule-induced polydipsia (SIP). In Experiment 1, three groups of rats were submitted to two different fixed-interval (FI) schedules with inter-food intervals of 30 and 120 s, and to a massed-feeding presentation for 40 days until SIP was well stabilized. In Experiment 2, six groups of rats were exposed to the same schedules, FI 30s and FI 120s, and to the massed-feeding condition, but no water bottles were presented. CORT levels were determined on Days 3 and 40. Results of Experiment 1 indicated that FI 30s schedule, but not FI 120s or the massed-feeding condition, induces excessive drinking from Day 3. Results in Experiment 2 indicated that CORT levels were similar for all the groups on Day 3. However, only animals on the FI 30s schedule did increase their CORT levels on Day 40, with no variation in the hormone in the other two conditions, FI 120s and massed-feeding presentations. The data are discussed in terms of the implications of these results for hypotheses of SIP as anxiolitic behavior.     

Stable isotope evidence for impala Aepyceros melampus diets at Akagera National Park,Rwanda

Stable isotope analysis of tooth enamel was used to investigate the relative proportions of grass and browse in seasonal and overall diets of impala Aepyceros melampus at Akagera National Park, Rwanda. Bulk enamel samples suggest that on average, impala ate c. 86% C₄ grass year‐round, far more than in most previously studied impala populations across Africa. Intra‐tooth samples show that seasonal changes in the proportion of C₄ grass versus C₃ browse are minimal (c. 10%), the diet being dominated by C₄ grass year‐round in contrast to other impala populations that consume ≥50% browse during the dry season. Intra‐tooth oxygen isotope values track carbon isotope changes to a moderate degree, but are not patterned clearly enough to permit identification of wet versus dry seasons. As other studies have shown that impala select high‐protein diets, the foraging behaviour at Akagera is probably because of the availability of palatable grass for much of the year in the edaphic grasslands around the lacustrine environments of the eastern portions of Akagera National Park.     

Photoaptameric heterodimeric constructs as a new approach to enhance the efficiency of formation of photocrosslinks with a target protein

Using DNA aptamers selectively recognizing anion-binding exosites 1 and 2 of thrombin as a model, it has been demonstrated that their conjugation by a poly-(dT)-linker (ranging from 5 to 65 nucleotides (nt) in length) to produce aptamer heterodimeric constructs results into affinity enhancement. At the linker lengths ranged from 35 to 55 nt the apparent dissociation constants (K _D^app) measured using the optical biosensor Biacore-3000 for complexes of thrombin with the heterodimeric constructs reached minimum values (K _D^app) = 0.2–0.4 nM), which were approximately 30-fold less than for the complexes with the initial aptamers. A photoaptamer heterodimeric construct was designed connecting photoaptamer and aptamer sequences with the poly-(dT)-linker of 35 nt long. The photoaptamer used could form photo-induced cross-links with the exosite 2 of thrombin and the aptamer could bind to the exosite 1. The (K _D^app value for the photoaptamer construct was approximately 40-fold less than that for the primary photoaptamer (5.3 and 190 nM, respectively). Upon exposure of the equimolar mixtures of thrombin with the photoaptamer construct to the UV radiation at 308 nm the equal yield of the crosslinked complexes was observed at concentrations, which were lower by two orders of magnitude than in the case of the primary photoaptamer. It was found that concurrently with crosslinking to thrombin a photo-induced inactivation of the photoaptamer occurs presumably due to formation of the intermolecular crosslinking.     

Prior exposure to a single stress session facilitates subsequent contextual fear conditioning in rats. Evidence for a role of corticosterone

Previous studies showed that exposure of rats to chronic restraint stress for 21 days enhances subsequent contextual fear conditioning. Since recent evidence suggest that this effect is not dependent on stress-induced neurodegenerative processes, but to elevated training-elicited glucocorticoid release in chronically stressed animals, we aimed to explore here whether a single exposure to restraint stress, which is not expected to induce neuronal damage, would also affect contextual fear conditioning. We also questioned whether post-training corticosterone levels might be associated with any potential effect of stress on fear conditioning. Adult male Wistar rats were exposed to acute restraint stress for 2 h and, two days later, trained in the contextual fear conditioning task, under training conditions involving either moderate (0.4 mA shock) or high (1 mA shock) stress levels. The results showed that acute stress enhanced conditioned freezing at both training conditions, although data from the 1 mA shock intensity experiment only approached significance. Stressed animals were shown to display higher post-training corticosterone levels. Furthermore, the facilitating effect of prior stress was not evident when animals were trained in the hippocampal-independent auditory-cued conditioning task. Therefore, these findings support the idea that stress experiences preceding exposure to new types of stressors facilitate the development of contextual fear conditioning. They also indicate that not only repeated, but also a single exposure to aversive stimulation is sufficient to facilitate context-dependent fear conditioning, and suggest that increased glucocorticoid release at training might be implicated in the mechanisms mediating the memory facilitating effects induced by prior stress experiences.     

Towards a quantitative free flow electrophoresis and its application to particle size separations

The possibility to quantify free-flow electrophoresis (FFE) data was explored in application to 6 negatively charged polystyrene size standards in the size range of 73 to 762 nm diameter. Peak fraction numbers in FFE were shown to be proportional to mobilities of the particles, determined by capillary zone electrophoresis in the identical buffer. Standard deviations of peak fraction numbers demonstrate a high degree of intra-experimental reproducibility while inter-experimentally, a variability of 1 to 5 peak fraction numbers within 28 fractions was found. A relative mobility (Rf) scale for peak identification in FFE based on the free mobility of the dye, SPADNS, allowed for the utilization of the entire electrophoretic migration path but failed to improve the precision of fraction numbers in view of the substantial zone spreading of the dye. Mobility differences between particles increased upon lowering the ionic strength of the electrophoretic buffer. Peak width increased with particle size in inverse relation to ionic strength.     

Cryptic diversity in forest shrews of the genus Myosorex from southern Africa,with the description of a new species and comments on Myosorex tenuis

Forest or mouse shrews (Myosorex) represent a small but important radiation of African shrews generally adapted to montane and/or temperate conditions. The status of populations from Zimbabwe, Mozambique, and the north of South Africa has long been unclear because of the variability of traits that have traditionally been ‘diagnostic’ for the currently recognized South African taxa. We report molecular (mitochondrial DNA and nuclear DNA), craniometric, and morphological data from newly collected series of Myosorex from Zimbabwe (East Highlands), Mozambique (Mount Gorogonsa, Gorongosa National Park), and the Limpopo Province of South Africa (Soutpansberg Range) in the context of the available museum collections from southern and eastern Africa and published DNA sequences. Molecular data demonstrate close genetic similarity between populations from Mozambique and Zimbabwe, and this well‐supported clade (herein described as a new species, M yosorex meesteri sp. nov. ) is the sister group of all South African taxa, except for Myosorex longicaudatus Meester & Dippenaar, 1978. Populations of Myosorex in Limpopo Province (herein tentatively assigned to Myosorex cf. tenuis) are cladistically distinct from both Myosorex varius (Smuts, 1832) and Myosorex cafer (Sundevall, 1846), and diverged from M. varius at approximately the same time (2.7 Mya) as M. cafer and Myosorex sclateri Thomas & Schwann, 1905 diverged (2.4 Mya). Morphometric data are mostly discordant with the molecular data. For example, clearly distinct molecular clades overlap considerably in craniometric variables. On the other hand, extreme size differentiation occurs between genetically closely related populations in the Soutpansberg Range, which coincides with the bissection of the mountain range by the dry Sand River Valley, indicating the potential for strong intraspecific phenotypic divergence in these shrews. © 2013 The Linnean Society of London     

A Key Role for Nectin-1 in the Ventral Hippocampus in Contextual Fear Memory

Nectins are cell adhesion molecules that are widely expressed in the brain. Nectin expression shows a dynamic spatiotemporal regulation, playing a role in neural migratory processes during development. Nectin-1 and nectin-3 and their heterophilic trans-interactions are important for the proper formation of synapses. In the hippocampus, nectin-1 and nectin-3 localize at puncta adherentia junctions and may play a role in synaptic plasticity, a mechanism essential for memory and learning. We evaluated the potential involvement of nectin-1 and nectin-3 in memory consolidation using an emotional learning paradigm. Rats trained for contextual fear conditioning showed transient nectin-1—but not nectin-3—protein upregulation in synapse-enriched hippocampal fractions at about 2 h posttraining. The upregulation of nectin-1 was found exclusively in the ventral hippocampus and was apparent in the synaptoneurosomal fraction. This upregulation was induced by contextual fear conditioning but not by exposure to context or shock alone. When an antibody against nectin-1, R165, was infused in the ventral-hippocampus immediately after training, contextual fear memory was impaired. However, treatment with the antibody in the dorsal hippocampus had no effect in contextual fear memory formation. Similarly, treatment with the antibody in the ventral hippocampus did not interfere with acoustic memory formation. Further control experiments indicated that the effects of ventral hippocampal infusion of the nectin-1 antibody in contextual fear memory cannot be ascribed to memory non-specific effects such as changes in anxiety-like behavior or locomotor behavior. Therefore, we conclude that nectin-1 recruitment to the perisynaptic environment in the ventral hippocampus plays an important role in the formation of contextual fear memories. Our results suggest that these mechanisms could be involved in the connection of emotional and contextual information processed in the amygdala and dorsal hippocampus, respectively, thus opening new venues for the development of treatments to psychopathological alterations linked to impaired contextualization of emotions.