Topographic distribution of direct and hippocampus- mediated entorhinal cortex activity evoked by olfactory tract stimulation

Olfactory information is central for memory-related functions, such as recognition and spatial orientation. To understand the role of olfaction in learning and memory, the distribution and propagation of olfactory tract-driven activity in the parahippocampal region needs to be characterized. We recently demonstrated that repetitive stimulation of the olfactory tract in the isolated guinea pig brain preparation induces an early direct activation of the rostrolateral entorhinal region followed by a delayed response in the medial entorhinal cortex (EC), preceded by the interposed activation of the hippocampus. In the present study we performed a detailed topographic analysis of both the early and the delayed entorhinal responses induced by patterned stimulation of the lateral olfactory tract in the isolated guinea pig brain. Bi-dimensional maps of EC activity recorded at 128 recording sites with 4 x 4 matrix electrodes (410 microm interlead separation) sequentially placed in eight different positions, showed (i) an early (onset at 16.09 +/- 1.2 ms) low amplitude potential mediated by the monosynaptic LOT input, followed by (ii) an associative potential in the rostral EC which originates from the piriform cortex (onset at 33.2 +/- 2.3 ms), and (iii) a delayed potential dependent on the previous activation of the hippocampus. The sharp component of the delayed response had an onset latency between 52 and 63 ms and was followed by a slow wave. Laminar profile analysis demonstrated that in the caudomedial EC the delayed response was associated with two distinct current sinks located in deep and in superficial layers, whereas in the rostrolateral EC a small-amplitude sink could be detected in the superficial layers exclusively. The present report demonstrates that the output generated by the hippocampal activation is unevenly distributed across different EC subregions and indicates that exclusively the medial and caudal divisions receive a deep-layer input from the hippocampus. In the rostrolateral EC, specific network interactions may be generated by the convergence of the direct olfactory input and the olfaction-driven hippocampal output.     

Structural and Tribological Assessment of Biomedical 316 Stainless Steel Subjected to Pulsed-Plasma Surface Modification: Comparison of LPBF 3D Printing and Conventional Fabrication

The structural features and nanoindentation/tribological properties of 316 stainless steel fabricated by conventional rolling and laser-based powder bed fusion (LPBF) were comparatively investigated regarding the effect of surface-pulsed plasma treatment (PPT). PPT was performed using an electrothermal axial plasma accelerator under a discharge voltage of 4.5 kV and a pulse duration of 1 ms. Optical microscopy, scanning electron microscopy, X-ray diffraction, nanoindentation measurements and tribological tests were applied to characterize the alloys. The LPBF steel presented almost the same modulus of elasticity and double the hardness of rolled steel. However, the LPBF steel manifested lower dry-sliding wear resistance compared with its wrought counterpart due to its porous structure and non-metallic inclusions. Conversely, LPBF steel showed three times higher wear resistance under sliding in simulated body fluid (SBF), as compared with wrought steel. PPT led to steel modification through surface melting to a depth of 22–26 μm, which resulted in a fine cellular structure. PPT moderately improved the dry-sliding wear resistance of LPBF steel by fusion of pores on its surface. On the other hand, PPT had almost no effect on the SBF-sliding wear response of the steel. The modification features were analyzed using a computer simulation of plasma-induced heating.     

Casting Welding from Magnesium Alloy Using Filler Materials That Contain Scandium

Based on the results achieved in systematic studies of structure formation and the formation of multicomponent phases, a scandium-containing filler metal from system alloy Mg-Zr-Nd for welding of aircraft casting was developed. The influence of scandium in magnesium filler alloy on its mechanical and special properties, such as long-term strength at elevated temperatures, was studied by the authors. It is established that modification of the magnesium alloy with scandium in an amount between 0.05 and 0.07% allows a fine-grained structure to be obtained, which increases its plasticity up to 70% and heat resistance up to 1.8 times due to the formation of complex intermetallic phases and the microalloying of the solid solution. Welding of the aircraft castings made of magnesium alloy with scandium-containing filler material allows obtaining a weld with a dense homogeneous fusion zone and the surrounding area without any defects. The developed filler material for welding surface defects (cracks, chips, etc.) formed during operation on aircraft engine bodies makes it possible to restore cast body parts and reuse them. The proposed filler material composition with an improved set of properties for the welding of body castings from Mg-Zr-Nd system alloy for aircraft engines makes it possible to increase their reliability and durability in general, extend the service life of aircraft engines, and obtain a significant economic effect.     

Calcium signaling in endocardial and epicardial ventricular myocytes from streptozotocin-induced diabetic rats

Aims/IntroductionAbnormalities in Ca²⁺ signaling have a key role in hemodynamic dysfunction in diabetic heart. The purpose of this study was to explore the effects of streptozotocin (STZ)‐induced diabetes on Ca²⁺ signaling in epicardial (EPI) and endocardial (ENDO) cells of the left ventricle after 5–6 months of STZ injection.Materials and MethodsWhole‐cell patch clamp was used to measure the L‐type Ca²⁺ channel (LTCC) and Na⁺/Ca²⁺ exchanger currents. Fluorescence photometry techniques were used to measure intracellular free Ca²⁺ concentration.ResultsAlthough the LTCC current was not significantly altered, the amplitude of Ca²⁺ transients increased significantly in EPI‐STZ and ENDO‐STZ compared with controls. Time to peak LTCC current, time to peak Ca²⁺ transient, time to half decay of LTCC current and time to half decay of Ca²⁺ transients were not significantly changed in EPI‐STZ and ENDO‐STZ myocytes compared with controls. The Na⁺/Ca²⁺ exchanger current was significantly smaller in EPI‐STZ and in ENDO‐STZ compared with controls.ConclusionsSTZ‐induced diabetes resulted in an increase in amplitude of Ca²⁺ transients in EPI and ENDO myocytes that was independent of the LTCC current. Such an effect can be attributed, at least in part, to the dysfunction of the Na⁺/Ca²⁺ exchanger. Additional studies are warranted to improve our understanding of the regional impact of diabetes on Ca²⁺ signaling, which will facilitate the discovery of new targeted treatments for diabetic cardiomyopathy.     

FESTUNG: A MATLAB / GNU Octave Toolbox for the Discontinuous Galerkin Method. Part IV: Generic Problem Framework and Model-Coupling Interface

This is the fourth installment in our series on implementing the discontinuous Galerkin (DG) method as an open source MATLAB / GNU Octave toolbox. Similarly to its predecessors, this part presents new features for application developers employing DG methods and follows our strategy of relying on fully vectorized constructs and supplying a comprehensive documentation. The specific focus of the current work is the newly added generic problem implementation framework and the highly customizable model-coupling interface for multi-domain and multi-physics simulation tools based on this framework. The functionality of the coupling interface in the FESTUNG toolbox is illustrated using a two-way coupled free-surface / groundwater flow system as an example application.     

From the Cover: Benthic invaders control the phosphorus cycle in the world’s largest freshwater ecosystem

The productivity of aquatic ecosystems depends on the supply of limiting nutrients. The invasion of the Laurentian Great Lakes, the world’s largest freshwater ecosystem, by dreissenid (zebra and quagga) mussels has dramatically altered the ecology of these lakes. A key open question is how dreissenids affect the cycling of phosphorus (P), the nutrient that limits productivity in the Great Lakes. We show that a single species, the quagga mussel, is now the primary regulator of P cycling in the lower four Great Lakes. By virtue of their enormous biomass, quagga mussels sequester large quantities of P in their tissues and dramatically intensify benthic P exchanges. Mass balance analysis reveals a previously unrecognized sensitivity of the Great Lakes ecosystem, where P availability is now regulated by the dynamics of mussel populations while the role of the external inputs of phosphorus is suppressed. Our results show that a single invasive species can have dramatic consequences for geochemical cycles even in the world’s largest aquatic ecosystems. The ongoing spread of dreissenids across a multitude of lakes in North America and Europe is likely to affect carbon and nutrient cycling in these systems for many decades, with important implications for water quality management.

Invasive species are well known to impact many aspects of ecosystems, including biodiversity, food web structure, and ecosystem functioning (1). The Laurentian Great Lakes, the largest freshwater ecosystem on Earth, serve as a dramatic example of large-scale reorganization of geochemical cycles by an invader. Following the establishment of zebra and quagga (dreissenid) mussels in littoral areas of the Great Lakes in the late 1980s, nutrients and productivity were redirected to the nearshore (2), while pelagic primary productivity declined by as much as 70% (3–7). Having outcompeted zebra mussels, quagga mussels now are abundant in most of the bottom areas in all of the Great Lakes except Lake Superior, often at densities exceeding 10,000 individuals per square meter (8–11). The expansion of quagga mussels coincided with unexplained changes in the abundances and distributions of other benthos (12) and modifications to the structure and phenology of the phytoplankton community (13) and food web structure (14, 15). Less attention was given to observations that pelagic concentrations of phosphorus (P), the productivity-limiting nutrient in the Great Lakes, decreased even while external P inputs remained steady (16, 17). The dynamics of P have practical importance because regulation of P inputs from the watershed has been the primary tool for managing water quality in the Great Lakes. In particular, reductions in P loadings are credited for the recovery from eutrophic conditions of the 1970s, and a further 40% reduction has been proposed recently to curtail recurring algal blooms in Lake Erie (18).However, will the dreissenid-colonized lakes respond to further reductions in P input in the same way they did in the past? The unprecedented changes in the Great Lakes induced by dreissenids warrant a reevaluation of P cycling and budgets, which need to account for mussel biomass and modified benthic–pelagic exchanges. The problem extends well beyond the Great Lakes: dreissenids have now been documented in thousands of inland lakes and rivers in North America (19) and Europe (20, 21) and may affect freshwater nutrient dynamics on continental scales.The dynamics of P concentrations in lake water are regulated by the balance of P sources and sinks. These include inputs from the watershed, removal with outflow, and net burial in sediments (16, 22). The role of the benthic system is significant. Sediments can recycle a large fraction of the deposited P and resupply it to the water column. Before the dreissenid invasion, this recycled fraction of P sedimentation varied from as little as 10% in Lake Michigan to as much as 60% in Lake Erie (16), contributing 15 to 48% of all (internal and external) phosphorus inputs to the water column (16). The efficiency of sedimentary P recycling also determines the inertia with which P concentrations in the water column respond to external inputs (16). When only a small fraction of the deposited P is recycled, total phosphorus (TP) concentrations respond with time lags of only a few years, even in large lakes (16). Recent TP dynamics in the Great Lakes, however, seems to have been decoupled from external P loadings (17), with change beginning shortly after the dreissenid invasion.Aquatic consumers can strongly impact the cycling of nutrients (23–26). High abundances of dreissenid mussels in particular can modify the sediment–water exchanges of phosphorus. As epibenthic filter feeders, dreissenids continually remove particulate P from bottom water (27). Most (∼90%) of the ingested phosphorus is remobilized (28): apart from a small portion incorporated into soft tissue and shell, P is either excreted into the water column in dissolved form or egested onto the sediment surface as feces and pseudofeces (27, 29, 30). The egested P is quickly remineralized to dissolved P via microbial decomposition (31). Mussel biomass P becomes mobilized over longer time scales through decomposition of dead tissues, release of gametes, and dissolution of shells (32). All of these processes modify the natural exchanges of P between sediments and water column, potentially affecting whole-system P mass balance. However, the effects of dreissenids on the sedimentary P fluxes have been evaluated in the Great Lakes only locally (27, 29, 30), and possibilities of regime-changing tipping points (33) or hysteresis in the geochemical dynamics have not been explored.Here, we show that the increase of invasive mussel biomass and consequent enhancement of benthic P fluxes have pushed the Great Lakes into a new dynamic regime where P concentrations and fluxes are controlled by mussel physiology and population dynamics, while responses to external phosphorus inputs have become muted. This regime is sensitive to biological perturbations, responds more slowly to external regulation, and presents unique challenges to managing these large ecosystems.     

Cellular correlates of spontaneous periodic events in the medial entorhinal cortex of the in vitro isolated guinea pig brain

Periodic potentials characterized by fast oscillations superimposed on a slow complex event are typically observed in cortical structures during sleep and anaesthesia. In the entorhinal cortex (EC) similar spontaneous periodic events (SPEs) have been described both in vivo and in vitro. Simultaneous extracellular and intracellular recordings from superficial neurons of the entorhinal cortex of the isolated Hartley guinea pig brain preparation demonstrated that SPEs recur with a periodicity of 2-10 s and correlate to neuronal firing superimposed on a depolarizing plateau that lasts 0.7-1 s. During SPEs, putative interneurons in all layers discharged high frequency firing (> 100 Hz), whereas no activity was observed in principal neurons of deep entorhinal cortex layers. Linear correlation analysis demonstrated a tight relationship between the fast component of the extracellular SPE and subthreshold oscillatory activity/neuronal firing in both superficial neurons and putative interneurons; firing of deep principal cells was independent from SPEs occurrence. The present study demonstrates that recurrent spontaneous events analogous to periodic activity observed during sleep/anaesthesia are generated in the entorhinal cortex by the interactions between superficial neurons and interneurons.