Aquatic fauna from the Takarkori rock shelter reveals the Holocene central Saharan climate and palaeohydrography.

The abundant faunal remains from the Takarkori rock shelter in the Tadrart Acacus region of southwestern Libya are described. The material that covers the period between 10,200 to 4650 years cal BP illustrates the more humid environmental conditions in the Central Sahara during early and middle Holocene times. Particular attention is focussed on the aquatic fauna that shows marked diachronic changes related to increasing aridification. This is reflected in the decreasing amount of fish remains compared to mammals and, within the fish fauna, by changes through time in the proportion of the species and by a reduction of fish size. The aquatic fauna can, in addition, be used to formulate hypotheses about the former palaeohydrographical network. This is done by considering the possible location of pre-Holocene relic populations combined with observations on the topography and palaeohydrological settings of the Central Sahara.

Mechanically induced calcium signaling in chondrocytes in situ.

Changes in intracellular calcium (Ca(2+)) concentration, also known as Ca(2+) signaling, have been widely studied in articular cartilage chondrocytes to investigate pathways of mechanotransduction. Various physical stimuli can generate an influx of Ca(2+) into the cell, which in turn is thought to trigger a range of metabolic and signaling processes. In contrast to most studies, the approach used in this study allows for continuous real time recording of calcium signals in chondrocytes in their native environment. Therefore, interactions of cells with the extracellular matrix (ECM) are fully accounted for. Calcium signaling was quantified for dynamic loading conditions and at different temperatures. Peak magnitudes of calcium signals were greater and of shorter duration at 37°C than at 21°C. Furthermore, Ca(2+) signals were involved in a greater percentage of cells in the dynamic compared to the relaxation phases of loading. In contrast to the time-delayed signaling observed in isolated chondrocytes seeded in agarose gel, Ca(2+) signaling in situ is virtually instantaneous in response to dynamic loading. These differences between in situ and in vitro cell signaling responses might provide crucial insight into the role of the ECM in providing pathways of mechanotransduction in the intact cartilage that are absent in isolated cells seeded in gel constructs.