Synthesis and antimalarial activity of new atovaquone derivatives

In this paper we describe the design and synthesis of 18 derivatives of the antimicrobial atovaquone which were substituted at the 3-hydroxy group by ester and ether functions. The compounds were evaluated in vitro for their activity against the growth of Plasmodium falciparum, the malaria causing parasite. All the compounds showed potent activity, with IC₅₀ values in the range of 1.25–50 nM, comparable to those of atovaquone and much higher than chloroquine or quinine.     

Performance in population models for count data,part II: A new SAEM algorithm

Analysis of count data from clinical trials using mixed effect analysis has recently become widely used. However, algorithms available for the parameter estimation, including LAPLACE and Gaussian quadrature (GQ), are associated with certain limitations, including bias in parameter estimates and the long analysis runtime. The stochastic approximation expectation maximization (SAEM) algorithm has proven to be a very efficient and powerful tool in the analysis of continuous data. The aim of this study was to implement and investigate the performance of a new SAEM algorithm for application to count data. A new SAEM algorithm was implemented in MATLAB for estimation of both, parameters and the Fisher information matrix. Stochastic Monte Carlo simulations followed by re-estimation were performed according to scenarios used in previous studies (part I) to investigate properties of alternative algorithms (Plan et al., 2008, Abstr 1372 []). A single scenario was used to explore six probability distribution models. For parameter estimation, the relative bias was less than 0.92% and 4.13% for fixed and random effects, for all models studied including ones accounting for over- or under-dispersion. Empirical and estimated relative standard errors were similar, with distance between them being <1.7% for all explored scenarios. The longest CPU time was 95 s for parameter estimation and 56 s for SE estimation. The SAEM algorithm was extended for analysis of count data. It provides accurate estimates of both, parameters and standard errors. The estimation is significantly faster compared to LAPLACE and GQ. The algorithm is implemented in Monolix 3.1, (beta-version available in July 2009).     

Microscopic haematuria as a relative contraindication for tranexamic acid

Tranexamic acid has been advocated for patients with severe bleeding tendency due to thrombocytopenia not responding to platelet transfusions. Macroscopic haematuria is a well-known contraindication for its use in such patients. We present three clinical cases with microscopic haematuria, in whom tranexamic acid caused problems of clot formation in the urinary tract, indicating that microscopic haematuria should also be considered as a contraindication for tranexamic acid.     

Visual system of a naturally microphthalmic mammal: The blind mole rat,Spalax ehrenbergi

Retinal projections and visual thalamo-cortical connections were studied in the subterranean mole rat, belonging to the superspecies Spalax ehrenbergi, by anterograde and retrograde tracing techniques. Quantitative image analysis was used to estimate the relative density and distribution of retinal input to different primary visual nuclei. The visual system of Spalax presents a mosaic of both regressive and progressive morphological features. Following intraocular injections of horseradish peroxidase conjugates, the retina was found to project bilaterally to all visual structures described as receiving retinal afferents in non-fossorial rodents. Structures involved in form analysis and visually guided behaviors are reduced in size by more than 90%, receive a sparse retinal innervation, and are cytoarchitecturally poorly differentiated. The dorsal lateral geniculate nucleus, as defined by cyto- and myelo-architecture, cytochrome oxidase, and acetylcholinesterase distribution as well as by afferent and efferent connections, consists of a narrow sheet 3–5 neurons thick, in the dorsal thalamus. Connections with visual cortex are topographically organized but multiple cortical injections result in widespread and overlapping distributions of geniculate neurons, thus indicating that the cortical map of visual space is imprecise. The superficial layers of the superior colliculus are collapsed to a single layer, and the diffuse ipsilateral distribution of retinal afferents also suggests a lack of precise retinotopic relations. In the pretectum, both the olivary pretectal nucleus and the nucleus of the optic tract could be identified as receiving ipsilateral and contralateral retinal projections. The ventral lateral geniculate nucleus is also bilaterally innervated, but distinct subdivisions of this nucleus or the intergeniculate leaflet could not be distinguished. The retina sends a sparse projection to the dorsal and lateral terminal nuclei of the accessory optic system. The medial terminal nucleus is not present. In contrast to the above, structures of the “non-image forming” visual pathway involved in photoperiodic perception are well developed in Spalax. The suprachiasmatic nucleus receives a bilateral projection from the retina and the absolute size, cytoarchitecture, density, and distribution of retinal afferents in Spalax are comparable with those of other rodents. A relatively hypertrophied retinal projection is observed in the bed nucleus of the stria terminalis. Other regions which receive sparse visual input include the lateral and anterior hypothalamic areas, the retrochiasmatic region, the sub-paraventricular zone, the paraventricular hypothalamic nucleus, the anteroventral and anterodorsal nuclei, the lateral habenula, the mediodorsal nucleus, and the basal telencephalon. These results indicate that the apparently global morphological regression of the visual system conceals a selective expansion of structures related to functions of photoperiodic perception and photo-neuroendocrine regulation. We suggest that the evolution of an atrophied eye and reduced visual system is an adaptively advantageous response to the unique subterranean environment. Factors favoring regression include mechanical aspects, metabolic constraints, and competition between sensory systems. The primary advantage of sensory atrophy is the metabolic economy gained by the reduction of visual structures which do not contribute significantly to the animal's fitness. © 1993 Wiley-Liss, Inc.     

Cocaine tolerance: Interactions among random-ratio and random-interval reinforcement-schedule parameters and repeated exposure to cocaine

Food-deprived pigeons were trained to peck a key under either a three-component multiple random-ratio 5, random-ratio 25, random-ratio 125 schedule or a three-component multiple random-interval 10-sec, random-interval 30-sec, random-interval 125-sec schedule of food presentation. Following determination of acute effects of cocaine (1.0-13.0 mg/kg), are-sponse-rate-reducing dose was given before each daily session. Once performance under conditions of daily administration had become stable, other doses occasionally were substituted for the usual daily dose so that dose effects could be assessed. Tolerance, i.e., a rightward shift in the dose-effect curve was observed in all subjects. For subjects studied under the random-ratio schedules, however, the robustness of the tolerance usually was related to the schedule-parameter value; tolerance was great at lower random values. By contrast, subjects whose responding was maintained by random-interval schedules were less likely to show tolerance that was schedule-parameter dependent. The results also provide suggestive evidence that dose may be an important factor in determining effects of repeated cocaine exposure; repeated administration of larger doses may be less likely to result in tolerance than similar exposure to smaller doses.     

Long-term structural alterations to endothelial cells in vein-to-artery grafts: a quantitative electron microscopic study

The intracellular structure of endothelium lining vein-to-artery grafts in rats was analysed, using transmission electron microscopy and morphometry, to determine the ultrastructural adaptations of endothelial cells in this altered vascular environment. Autogenous 4-mm sections of iliolumbar veins were inserted microsurgically into the left common iliac arteries of 16 male Wistar rats. At 3, 6, 26 and 52 weeks the cytoplasmic-vesicular, mitochondrial and rough endoplasmic reticular contents of endothelial cells lining the grafts, the opposite iliac arteries and the remaining ilio-lumbar veins were analysed morphometrically. There was a significant increase in the amount of all these cytoplasmic structures in endothelial cells at 3, 6 and 26 weeks; at 52 weeks there was also a significant increase in the volumes of mitochondria and cytoplasmic vesicles, but not in rough endoplasmic reticulum. It was concluded that the ultrastructure of endothelial cells lining these grafts is changed chronically after graft insertion, and we propose that this may be attributable to altered haemodynamic stresses within the graft.