Indication of drier periods on Mars from the chemistry and mineralogy of atmospheric dust

The ubiquitous atmospheric dust on Mars is well mixed by periodic global dust storms, and such dust carries information about the environment in which it once formed and hence about the history of water on Mars. The Mars Exploration Rovers have permanent magnets to collect atmospheric dust for investigation by instruments on the rovers. Here we report results from M?ssbauer spectroscopy and X-ray fluorescence of dust particles captured from the martian atmosphere by the magnets. The dust on the magnets contains magnetite and olivine; this indicates a basaltic origin of the dust and shows that magnetite, not maghemite, is the mineral mainly responsible for the magnetic properties of the dust. Furthermore, the dust on the magnets contains some ferric oxides, probably including nanocrystalline phases, so some alteration or oxidation of the basaltic dust seems to have occurred. The presence of olivine indicates that liquid water did not play a dominant role in the processes that formed the atmospheric dust.     

Direct dating of Early Upper Palaeolithic human remains from Mladec

The human fossil assemblage from the Mladec Caves in Moravia (Czech Republic) has been considered to derive from a middle or later phase of the Central European Aurignacian period on the basis of archaeological remains (a few stone artefacts and organic items such as bone points, awls, perforated teeth), despite questions of association between the human fossils and the archaeological materials and concerning the chronological implications of the limited archaeological remains. The morphological variability in the human assemblage, the presence of apparently archaic features in some specimens, and the assumed early date of the remains have made this fossil assemblage pivotal in assessments of modern human emergence within Europe. We present here the first successful direct accelerator mass spectrometry radiocarbon dating of five representative human fossils from the site. We selected sample materials from teeth and from one bone for 14C dating. The four tooth samples yielded uncalibrated ages of approximately 31,000 14C years before present, and the bone sample (an ulna) provided an uncertain more-recent age. These data are sufficient to confirm that the Mladec human assemblage is the oldest cranial, dental and postcranial assemblage of early modern humans in Europe and is therefore central to discussions of modern human emergence in the northwestern Old World and the fate of the Neanderthals.     

High frequency of human cytomegalovirus (HCMV)-specific CD8+-T cells detected in a healthy CMV-seropositive donor

Human cytomegalovirus (HCMV) persists after infection but is controlled by cellular immune responses, particularly by CD8⁺ T cells. If infected individuals are immunosuppressed, HCMV can be reactivated. Upon testing the blood of healthy donors with human lymphocyte antigen tetramers, we found one individual with about 50 % of his CD8⁺ T cells being specific for the immunodominant pp65 epitope NLVPMVATV. Over a period of 2 years the high level of HCMV-specific T cells was maintained, and no HCMV DNA could be detected. At one timepoint, however, HCMV-specific DNA was detected, while 65 % of CD8⁺ T cells were specific for HCMV. When virus was detectable, a lower percentage of HCMV-specific CD8⁺ T cells showed interferon γ (IFN-γ) production after peptide stimulation in vitro. These data suggest that HCMV reactivation may also occur in immunocompetent persons, accompanied by the presence of HCMV-specific CD8⁺ T cells which are not producing IFNγ, and therefore potentially anergic or in vivo exhausted. Received 6 March 2002; received after revision 15 April 2002; accepted 17 April 2002     

The endogenous cannabinoid system controls extinction of aversive memories

Acquisition and storage of aversive memories is one of the basic principles of central nervous systems throughout the animal kingdom. In the absence of reinforcement, the resulting behavioural response will gradually diminish to be finally extinct. Despite the importance of extinction, its cellular mechanisms are largely unknown. The cannabinoid receptor 1 (CB1) and endocannabinoids are present in memory-related brain areas and modulate memory. Here we show that the endogenous cannabinoid system has a central function in extinction of aversive memories. CB1-deficient mice showed strongly impaired short-term and long-term extinction in auditory fear-conditioning tests, with unaffected memory acquisition and consolidation. Treatment of wild-type mice with the CB1 antagonist SR141716A mimicked the phenotype of CB1-deficient mice, revealing that CB1 is required at the moment of memory extinction. Consistently, tone presentation during extinction trials resulted in elevated levels of endocannabinoids in the basolateral amygdala complex, a region known to control extinction of aversive memories. In the basolateral amygdala, endocannabinoids and CB1 were crucially involved in long-term depression of GABA (gamma-aminobutyric acid)-mediated inhibitory currents. We propose that endocannabinoids facilitate extinction of aversive memories through their selective inhibitory effects on local inhibitory networks in the amygdala.     

The structure of theAspidosperma alkaloid compactinervine

Zusammenfassung Es wird über die Isolierung eines neuen Alkaloids — Compactinervin — aus der brasilianischen Apocynaceen-ArtAspidosperma compactinervium Kuhlm. berichtet. Durch massenspektroskopische und Kernresonanz-Messungen und chemische Umwandlungen konnte gezeigt werden, dass es sich beim Compactinervin um 19,20-Dihydroxy-19,20-dihydro-akuammicin handelt. Seine vollständige Stereochemie sowie die des verwandten Alkaloids Lochneridin konnte abgeleitet werden. Compactinervin stellt die erste Verbindung vom Akuammicin-Typ dar, die aus einerAspidosperma-Art isoliert worden ist.

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Paper XLI in the seriesAlkaloid Studies. For paper XL seeB. Gilbert, J. A. Brissolese, J. M. Wilson, H. Budzikiewicz, L. J. Durham, andC. Djerassi, Chem. and Ind.1962, 1949.

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Financial assistance in support of the joint research effort on Brazilian plants between Stanford University and the Instituto de Quimica Agricola was provided by the Rockefeller Foundation. Additional financial aid from the National Institutes of Health (grants AM 04257 and 2G-682) is gratefully acknowledged.     

Organic analysis of the Pueblito de Allende meteorite

It appears unlikely that the organic material detected in the meteorite that fell in Mexico last year can have been introduced by contamination.     

Primary cancer of the liver in rats after subcutaneous implantation of pellets of progesterone and testosterone propionate

Résumé Le carcinome hépatocellulaire du type trabéculaire a paru dans 2 rats sur 5, 745 jours après l'implantation de boulettes de progestérone cristallin et de propionate de testostérone, pesant 8 à 10 mg chacune. Un de ces rats a développé un carcinome provenant de l'épithélium d'une bronchiole respiratoire. L'absence d'une cholangiofibrosite antécédente, d'une nécrose ou d'une cirrhose hors de l'endroit de la tumeur du foie chez les rats soumis aux épreuves expérimentales, peut nécessiter un nouvel examen de la signification des lésions hépatiques comme facteur prédisposant au cancer chez l'homme.