Highly sensitive assay for the measurement of serotonin in microdialysates using capillary high-performance liquid chromatography with electrochemical detection

A highly sensitive isocratic capillary high-performance liquid chromatographic (HPLC) method with electrochemical detection (ED) for the simultaneous measurement of serotonin (5-hydroxytryptamine, 5-HT) and its metabolite 5-hydroxyindole-3-acetic acid (5-HIAA) in microdialysates has been developed using a 0.5 mm i.d. capillary column and a 11-nL detection cell. This method, validated on both pharmacological and analytical bases, can be performed using injection volumes as low as 1 microL. The limits of detection were 5.6 x 10(-11)mol/L and 3.0 x 10(-9)mol/L for 5-HT and 5-HIAA. Several applications of the present method are given on microdialysates from rodent brain and human spinal cord.     

Bipolar resistivity profiling of 3D tissue culture

We describe a new low-cost technique for continuous monitoring of the thickness of biofilms and tissue cultures, and we demonstrate the advantage of using electrodes of different dimensions to probe different depths of a sample. We have used electric impedance spectroscopy to monitor keratinocyte stem cells (YF29) growing on an array of Ti/Pt coplanar microelectrodes. The thickness of the sample was reconstructed by fitting the measurements to theoretical curves. We have developed an algorithm for the rapid calculation of the resistance through a multilayered sample. This algorithm is based on conformal mapping and the serial partial capacitance technique. The validity of the technique was tested by measuring the sedimentation rate of an alumina powder. Sample thicknesses between 10 and 80 microm could be measured with a resolution of a few microns using the device.     

Flexible polyimide microelectrode array for in vivo recordings and current source density analysis

This work presents implantable, flexible polymer-based probes with embedded microelectrodes for acute and chronic neural recordings in vivo, as tested on rodents. Acute recordings using this array were done in mice under urethane anesthesia and compared to those made using silicon-based probes manufactured at the Center for Neural Communication Technology, University of Michigan. The two electrode arrays yielded similar results. Recordings with chronically implanted polymer-based electrodes were performed for 60 days post-surgically in awake, behaving rats. The microelectrodes were used to monitor local field potentials and capture laminar differences in function of cortex and hippocampus, and produced response waveforms of undiminished amplitude and signal-to-noise ratios 8 weeks after chronic implantation. The polymer-based electrodes could also be connected to a lesion current to mark specific locations in the tissue. Current source density (CSD) analysis from the recordings depicted a source - sink-composition. Tissue response was assessed 8 weeks after insertion by immunochemical labeling with glial fibrillary acidic protein (GFAP) to identify astrocytes, and histological analysis showed minimal tissue reaction to the implanted structures.     

Prey synchronize their vigilant behaviour with other group members

It is generally assumed that an individual of a prey species can benefit from an increase in the number of its group''s members by reducing its own investment in vigilance. But what behaviour should group members adopt in relation to both the risk of being preyed upon and the individual investment in vigilance? Most models assume that individuals scan independently of one another. It is generally argued that it is more profitable for each group member owing to the cost that coordination of individual scans in non-overlapping bouts of vigilance would require. We studied the relationships between both individual and collective vigilance and group size in Defassa waterbuck, Kobus ellipsiprymnus defassa, in a population living under a predation risk. Our results confirmed that the proportion of time an individual spent in vigilance decreased with group size. However, the time during which at least one individual in the group scanned the environment (collective vigilance) increased. Analyses showed that individuals neither coordinated their scanning in an asynchronous way nor scanned independently of one another. On the contrary, scanning and non-scanning bouts were synchronized between group members, producing waves of collective vigilance. We claim that these waves are triggered by allelomimetic effects i.e. they are a phenomenon produced by an individual copying its neighbour''s behaviour.     

Learning influences host choice in tsetse

A learning capacity for feeding is described in many insect species including vectors of diseases, but has never been reported in tsetse flies (Diptera, Glossinidae), the cyclic vectors of human (sleeping sickness) and animal trypanosomoses in Africa. Repeated feeding on the same host species by a disease vector is likely to increase the within-species disease-transmission risk, but to decrease it between species. An experiment with cattle and reptiles in a stable provides evidence that the species of host selected for the second blood meal in tsetse flies depends on the host encountered for the first blood meal when the between-meal interval is 2 days. This preference disappears when the between-meal interval is extended to 3 days. The energetic advantages of this acquired preference and its importance in trypanosomoses epidemiology are discussed.     

In vivo imaging of malaria parasites in the murine liver

The form of the malaria parasite inoculated by the mosquito, called the sporozoite, transforms inside the host liver into thousands of a new form of the parasite, called the merozoite, which infects erythrocytes. We present here a protocol to visualize in vivo the behavior of Plasmodium berghei parasites in the hepatic tissue of the murine host. The use of GFP-expressing parasites and a high-speed spinning disk confocal microscope allows for the acquisition of four-dimensional images, which provide a time lapse view of parasite displacement and development in tissue volumes. These data can be analyzed to give information on the early events of sporozoite penetration of the hepatic tissue, that is, sporozoite gliding in the liver sinusoids, crossing the sinusoidal barrier, gliding in the parenchyma and traversal of hepatocytes, and invasion of a final hepatocyte, as well as the terminal events of merosome and merozoite release from infected hepatocytes. Combined with the use of mice expressing fluorescent cell types or cell markers, the system will provide useful information not only on the primary infection process, but also on parasite interactions with the host immune cells in the liver.     

Evidence of strong stabilizing effects on the evolution of boreoeutherian (Mammalia) dental proportions

The dentition is an extremely important organ in mammals with variation in timing and sequence of eruption, crown morphology, and tooth size enabling a range of behavioral, dietary, and functional adaptations across the class. Within this suite of variable mammalian dental phenotypes, relative sizes of teeth reflect variation in the underlying genetic and developmental mechanisms. Two ratios of postcanine tooth lengths capture the relative size of premolars to molars (premolar–molar module, PMM), and among the three molars (molar module component, MMC), and are known to be heritable, independent of body size, and to vary significantly across primates. Here, we explore how these dental traits vary across mammals more broadly, focusing on terrestrial taxa in the clade of Boreoeutheria (Euarchontoglires and Laurasiatheria). We measured the postcanine teeth of N = 1,523 boreoeutherian mammals spanning six orders, 14 families, 36 genera, and 49 species to test hypotheses about associations between dental proportions and phylogenetic relatedness, diet, and life history in mammals. Boreoeutherian postcanine dental proportions sampled in this study carry conserved phylogenetic signal and are not associated with variation in diet. The incorporation of paleontological data provides further evidence that dental proportions may be slower to change than is dietary specialization. These results have implications for our understanding of dental variation and dietary adaptation in mammals.