Dental use wear in extinct lemurs: evidence of diet and niche differentiation

A new technique for molar use-wear analysis is applied to samples of all 16 species of extinct lemurs with known dentitions, as well as to a large comparative sample of extant primates. This technique, which relies on the light refractive properties of wear pits and scratches as seen under a standard stereoscopic microscope, has shown itself to be effective in distinguishing the diets of ungulates and extant primates. We draw dietary inferences for each of the 16 extinct lemur species in our database. There is a strong phylogenetic signal, with the Palaeopropithecidae showing use-wear signatures similar to those of the Indriidae; extinct lemurids (Pachylemur spp.) showing striking similarities to extant lemurids (except Hapalemur spp.); and Megaladapis showing similarities to Lepilemur spp. Only the Archaeolemuridae have dietary signatures unlike those of any extant lemurs, with the partial exception of Daubentonia. We conclude that the Archaeolemuridae were hard-object feeders; the Palaeopropithecidae were seed predators, consuming a mixed diet of foliage and fruit to varying degrees; Pachylemur was a fruit-dominated mixed feeder, but not a seed predator; and all Megaladapis were leaf browsers. There is no molar use wear evidence that any of the extinct lemurs relied on terrestrial foods (C4 grasses, tubers, rhizomes). This has possible implications for the role of the disappearance of wooded habitats in the extinction of lemurs.     

Modal damping for monitoring bone integrity and osteoporosis

We applied a noninvasive method to assess bone structural integrity. The method is based on the measurement of the dynamic characteristics of the bone (quality factor and modal damping factor) by applying vibration excitation in the range of acoustic frequencies, in the form of an acoustic sweep signal. Excised sheep femora were tested to detect changes in modal damping, density (kg/m3), bone mineral density (kg/m2) and bone mineral (hydroxyapatite) percentage. The changes were recorded after each time of chemical treatment of the bones performed to gradually cause mineral removal, thus simulating osteoporosis. It was shown that the change in quality factor and damping was in all cases on average equal or greater to the change in all other measured characteristics, thus strengthening the potential of the proposed method to become a valuable assessment tool for monitoring bone integrity and osteoporosis.     

Living polypeptides

Block copolypeptides, which combine the self-assembly of block copolymers and the highly ordered 3D structures of proteins, are potential candidates for novel supramolecular structures and biotech applications, such as biosensors, tissue engineering, and selective drug delivery. The synthesis of model block copolypeptides through living nucleophilic/basic polymerization of alpha-amino acid N-carboxyanhydrides (NCAs) has been a challenge for more than fifty years, most probably due to traces of impurities in the system. This problem has been overcome, using high vacuum techniques in order to create and maintain the conditions necessary for the living polymerization of NCAs with primary amines. This method is a general one and opens avenues leading to novel, well-defined polypeptides with various architectures.     

Stimulation of Na+/H+ antiport and pyruvate kinase activities by high glucose concentration in human erythrocytes

This study aims to demonstrate the effect of high glucose concentrations on NHE-1 and PK activities and investigate the implicated signal transduction pathways. Erythrocytes drawn from healthy volunteers were incubated in the presence of 5 or 50 mM of glucose, fructose, galactose or mannitol. When appropriate, specific inhibitors of NHE-1, PKC or p42/44 MAPK were used. Erythrocyte NHE-1 activity has been estimated by fluorometrical determination of the intracellular pH and quantification of sodium uptake using 22Na. Pyruvate kinase activity was measured by a NADH-lactate dehydrogenase enzymatic assay. p42/44 MAPK activity was assessed with a specific enzyme linked immunosorbent assay (ELISA). Increased concentrations of glucose but not galactose, fructose or mannitol enhanced erythrocyte NHE-1, PK and p42/44 MAPK activity. Inhibition of PKC, counteracted these effects of glucose. Similarly, inhibition of NHE 1 abolished the effect of high glucose on PK and p42/44 MAPK as well. Finally, inhibition of p42/44 MAPK also hindered the effect of glucose on NHE-1 and PK activities. The data of the present study indicate an acute effect of glucose on signal transduction pathways in human erythrocytes. This pathway involves NHE-1, PKC, and p42/44 MAPK. A positive feedback between NHE 1 and p42/44 MAPK is suggested.     

Effects of longitudinal stretch on VSM tone and distensibility of muscular conduit arteries

With progressing age, large arteries diminish their longitudinal stretch, which in extreme cases results in tortuosity. Increased age is also associated with loss of vessel distensibility. We measured pressure-diameter curves from muscular porcine carotid arteries ex vivo at different longitudinal stretch ratios (lambda(z) = 1.4 and 1.8) and under different vascular smooth muscle (VSM) conditions (fully relaxed, normal VSM tone, and maximally contracted). Distensibility was found to be halved by decreasing longitudinal stretch from lambda(z) = 1.8 to 1.4 at physiological pressures. This counterintuitive observation is possible because highly nonlinear elastic modulus of the artery and anisotropic properties. Furthermore, a significantly larger basal VSM contraction was observed at lambda(z) = 1.8 than 1.4, although this was clearly not related to a myogenic response during inflation. This dependence of VSM tone to longitudinal stretch may have possible implications on the functional characteristics of the arterial wall.     

On the mechanism of thrombin-induced angiogenesis: involvement of alphavbeta3-integrin

Thrombin has been reported to be a potent angiogenic factor both in vitro and in vivo, and many of the cellular effects of thrombin may contribute to activation of angiogenesis. In this report we show that thrombin-treatment of human endothelial cells increases mRNA and protein levels of alphavbeta3-integrin. This thrombin-mediated effect is specific, dose dependent, and requires the catalytic site of thrombin. In addition, thrombin interacts with alphavbeta3 as demonstrated by direct binding of alphavbeta3 protein to immobilized thrombin. This interaction of thrombin with alphavbeta3-integrin, which is an angiogenic marker in vascular tissue, is of functional significance. Immobilized thrombin promotes endothelial cells attachment, migration, and survival. Antibody to alphavbeta3 or a specific peptide antagonist to alphavbeta3 can abolish all these alphavbeta3-mediated effects. Furthermore, in the chick chorioallantoic membrane system, the antagonist peptide to alphavbeta3 diminishes both basal and the thrombin-induced angiogenesis. These results support the pivotal role of thrombin in activation of endothelial cells and angiogenesis and may be related to the clinical observation of neovascularization within thrombi.     

Ultra high-resolution fMRI in monkeys with implanted RF coils

Spatiotemporally resolved functional MRI (fMRI) in animals can reveal how wide-spread neural networks are organized and accompanying electrophysiological recordings can show how small neural assemblies contribute to this organization. Here we present a novel technique that yields high-resolution structural and functional images of the monkey brain with small, tissue-compatible, intraosteally implantable radiofrequency coils. Voxel sizes as small as 0.0113 microl with high signal-to-noise and contrast-to-noise ratios were obtained, revealing both structural and functional cortical architecture in great detail. Up to a certain point, contrast sensitivity increased with decreasing voxel size, probably because of the decreased partial volume effects. Spatial specificity was demonstrated by the lamina-specific activation in experiments comparing responses to moving and flickering stimuli. The implications of this technique for combined fMRI/electrophysiology experiments and its limitations in terms of spatial coverage are discussed.     

Visual competition

Binocular rivalry--the alternations in perception that occur when different images are presented to the two eyes--has been the subject of intensive investigation for more than 160 years. The psychophysical properties of binocular rivalry have been well described, but newer imaging and electrophysiological techniques have not resolved the issue of where in the brain rivalry occurs. The most recent evidence supports a view of rivalry as a series of processes, each of which is implemented by neural mechanisms at different levels of the visual hierarchy. Although unanswered questions remain, this view of rivalry might allow us to resolve some of the controversies and apparent contradictions that have emerged from its study.     

The 1.76 A resolution crystal structure of glycogen phosphorylase B complexed with glucose, and CP320626, a potential antidiabetic drug

CP320626, a potential antidiabetic drug, inhibits glycogen phosphorylase in synergism with glucose. To elucidate the structural basis of synergistic inhibition, we determined the structure of muscle glycogen phosphorylase b (MGPb) complexed with both glucose and CP320626 at 1.76 A resolution, and refined to a crystallographic R value of 0.211 (R(free)=0.235). CP320626 binds at a novel allosteric site, which is some 33 A from the catalytic site, where glucose binds. The high resolution structure allows unambiguous definition of the conformation of the 1-acetyl-4-hydroxy-piperidine ring supported by theoretical energy calculations. Both CP320626 and glucose promote the less active T-state, thereby explaining their synergistic inhibition. Structural comparison of MGPb--glucose--CP320626 complex with liver glycogen phosphorylase a (LGPa) complexed with a related compound (CP403700) show that the ligand binding site is conserved in LGPa.     

Field parasitism of Ceratitis capitata larvae by Aganaspis daci in Chios, Greece

High parasitism rates were recorded in the Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) in pupae derived from field infested figs, on the Greek island of Chios in 1999 and 2000. Adult parasitoids were identified as Aganaspis daci (Weld) (Hymenoptera:Eucoilidae), previously known as Trybliographa daci (Weld). Approximately 45%of C. capitata pupae yielded adultparasitoid in both years and the totalmortality of pupae due to the parasitoid was62–65%. Development of male A. daci at25°C, reared on 3rd instar larvaeof C. capitata, was shorter than that of the female (34 and 37 days respectively). Average adultmale longevity was 4–5 days longer than female(16–17 to 11–12 days, respectively) and almostidentical in wild and F₁ parasitoids ofboth sexes. We suggest that A. daci maybe an efficient form of biological control ofC. capitata in the Mediterranean regionand probably in other areas.