Synaptic Adhesion Molecules Regulate the Integration of New Granule Neurons in the Postnatal Mouse Hippocampus and their Impact on Spatial Memory.

Postnatal hippocampal neurogenesis induces network remodeling and may participate to mechanisms of learning. In turn, the maturation and survival of newborn neurons is regulated by their activity. Here, we tested the effect of a cell-autonomous overexpression of synaptic adhesion molecules on the maturation and survival of neurons born postnatally and on hippocampal-dependent memory performances. Families of adhesion molecules are known to induce pre- and post-synaptic assembly. Using viral targeting, we overexpressed three different synaptic adhesion molecules, SynCAM1, Neuroligin-1B and Neuroligin-2A in newborn neurons in the dentate gyrus of 7- to 9-week-old mice. We found that SynCAM1 increased the morphological maturation of dendritic spines and mossy fiber terminals while Neuroligin-1B increased spine density. In contrast, Neuroligin-2A increased both spine density and size as well as GABAergic innervation and resulted in a drastic increase of neuronal survival. Surprisingly, despite increased neurogenesis, mice overexpressing Neuroligin-2A in new neurons showed decreased memory performances in a Morris water maze task. These results indicate that the cell-autonomous overexpression of synaptic adhesion molecules can enhance different aspects of synapse formation on new neurons and increase their survival. Furthermore, they suggest that the mechanisms by which new neurons integrate in the postnatal hippocampus conditions their functional implication in learning and memory

Enduring neurobehavioral effects induced by microbiota depletion during the adolescent period

Peer ReviewedThe gut microbiota is an essential regulator of many aspects of host physiology. Disruption of gut microbial communities affects gut-brain communication which ultimately can manifest as changes in brain function and behaviour. Transient changes in gut microbial composition can be induced by various intrinsic and extrinsic factors, however, it is possible that enduring shifts in the microbiota composition can be achieved by perturbation at a timepoint when the gut microbiota has not fully matured or is generally unstable, such as during early life or ageing. In this study, we investigated the effects of 3-week microbiota depletion with antibiotic treatment during the adolescent period and in adulthood. Following a washout period to restore the gut microbiota, behavioural and molecular hallmarks of gut-brain communication were investigated. Our data revealed that transient microbiota depletion had long-lasting effects on microbiota composition and increased anxiety-like behaviour in mice exposed to antibiotic treatment during adolescence but not in adulthood. Similarly, gene expression in the amygdala was more severely affected in mice treated during adolescence. Taken together these data highlight the vulnerability of the gut microbiota during the critical adolescent period and the long-lasting impact manipulations of the microbiota can have on gene expression and behaviour in adulthood.Science Foundation Irelan

The Campanian Ignimbrite/Y5 Tephra Layer – A Regional Stratigraphic Marker for Isotope Stage 3 Deposits in the Lower Danube Region, Romania

A number of volcanic ash layers embedded in Pleistocene loess and fluvial deposits of the lower Jiu and Olt valleys in south-western Romania have been analyzed for glass chemical compositions and general chronological relations. The WDS-EPMA chemical analyses document remarkably similar major and minor element compositions at the four investigated sites, and total alkali–silica diagrams ascribe these volcanic ashes a phonolite to trachyte affinity. A comparison with the Quaternary Carpathian volcanism chemical data refutes this volcanic field as the primary source, even though earlier works have tentatively taken some of these volcanic ashes as evidence of volcanic activity in this particular field. Instead, the chemical data suggest an origin in the Campi Flegrei volcanic province in Italy, and a comparison with chemical data from proximal and distal outcrops of the Campanian Ignimbrite/Y5 tephra confirm that the ash layers presented here are distal occurrences of this widespread tephra layer. The Campanian Ignimbrite/Y5 tephra is the product of one of the largest late Quaternary explosive events in the Mediterranean, and is consistently dated elsewhere to about 39–40 ka. It is one of the most important chronologic/stratigraphic markers of western Eurasia that provide an independent basis for establishing age–depth relationships for the embedding deposits. Optical luminescence age estimates obtained at two of the investigated sites further confirm that these volcanic ash occurrences represent a regionally synchronous depositional event, around 40 ka. These results highlight the important role that the Campanian Ignimbrite/Y5 tephra could play as marker horizon at sub-continental scale, providing that more potential tephra locations such as these from the Pleistocene sedimentary deposits in the Lower Danube region are chemically and chronologically constrained

Evidence for Bronze Age and Medieval tin placer mining in the Erzgebirge mountains, Saxony (Germany)

Abstract Tin is an essential raw material both for the copper–tin alloys developed during the Early Bronze Age and for the casting of tableware in the Medieval period. Secondary geological deposits in the form of placers (cassiterite) provide easily accessible sources but have often been reworked several times during land-use history. In fact, evidence for the earliest phase of tin mining during the Bronze Age has not yet been confirmed for any area in Europe, stimulating an ongoing debate on this issue. For this study, a broad range of methods (sedimentology, pedology, palynology, anthracology, OSL/14C-dating, and micromorphology) was applied both within the extraction zone of placer mining and the downstream alluvial sediments at Schellerhau site in the upper eastern Erzgebirge (Germany). The results indicate that the earliest local removal of topsoil and processing of cassiterite-bearing weathered granite occurred already in the early second millennium BC, thus coinciding with the early and middle Bronze Age period. Placer mining resumed in this area during the Medieval period, probably as early as the 13th century AD. A peak of alluvial sedimentation during the mid-15th century AD is probably related to the acquisition of this region by the Elector of Saxony and the subsequent promotion of mining

Past human impact in a mountain forest: Geoarchaeology of a medieval glass production and charcoal hearth site in the Erzgebirge, Germany

Since the twelfth century, forest areas in the upper reaches of the low mountain ranges of central Europe provided an important source of wood and charcoal especially for mining and smelting as well as glass production. In this case study from a site in the upper Erzgebirge region (Ore Mountains), results from archeological, geophysical, pedo-sedimentological, geochemical, anthracological, and palynological analyses have been closely linked to allow for a diachronic reconstruction of changing land use and varying intensities of human impact with a special focus on the fourteenth to the twentieth century. While human presence during the thirteenth century can only be assumed from archeological material, the establishment of glass kilns together with quartz mining shafts during the fourteenth century has left behind more prominent traces in the landscape. However, although glass production is generally assumed to have caused intensive deforestation, the impact on this site appears rather weak compared to the sixteenth century onwards, when charcoal production, probably associated with emerging mining activities in the region, became important. Local deforestation and soil erosion has been associated mainly with this later phase of charcoal production and may indicate that the human impact of glass production is sometimes overestimated

Palaeosols and their cover sediments of a glacial landscape in northern central Europe: Spatial distribution, pedostratigraphy and evidence on landscape evolution

Knowledge of the distribution, types and properties of buried soils, i.e. palaeosols, is essential in understanding how lowlands in northern central Europe have changed over past millennia. This is an indispensable requirement for evaluating long-term human impact including soil erosion and land-cover dynamics. In the Serrahn area (62 km2), a young glacial landscape representative for northeastern Germany and part of the Müritz National Park, 26 pedosedimentary sections were documented and analysed. To this end, a multiproxy-approach was applied using pedology, micromorphology, geochronology, and palaeoecology. Statistical and spatial analyses of c. 5200 soil profiles, of which 10% contain palaeosols, show that buried soils cover an area of 5.7 km2, i.e. 9% of the area studied. Most palaeosols are Cambisols, Arenosols and Gleysols. Palaeosols are mainly covered by aeolian and colluvial sands, as well as by lacustrine sands and peat. Radiocarbon and luminescence dating together with palynological and anthracological data reveal that former land surfaces were dominantly buried through erosion triggered by human activity in the late Holocene. In addition, but to a clearly smaller extent, Lateglacial/early Holocene palaeosols and cover sediments occur. Following Medieval clear-cutting and intensive land use, the study area is today again widely forested. The high share of buried land surfaces detected here is expected to be representative for the hilly glacial landscapes even in the wider region, i.e. in northern central Europe, and should be considered in soil mapping, soil carbon budgeting and assessments of past human impact