EXPOSE, an Astrobiological Exposure Facility on the International Space Station - from Proposal to Flight

Following an European Space Agency announcement of opportunity in 1996 for ”Externally mounted payloads for 1st utilization phase” on the International Space Station (ISS), scientists working in the fields of astrobiology proposed experiments aiming at long-term exposure of a variety of chemical compounds and extremely resistant microorganisms to the hostile space environment. The ESA exposure facility EXPOSE was built and an operations´ concept was prepared. The EXPOSE experiments were developed through an intensive pre-flight experiment verification test program. 12 years later, two sets of astrobiological experiments in two EXPOSE facilities have been successfully launched to the ISS for external exposure for up to 1.5 years. EXPOSE-E, now installed at the balcony of the European Columbus module, was launched in February 2008, while EXPOSE-R took off to the ISS in November 2008 and was installed on the external URM-D platform of the Russian Zvezda module in March 2009.     

Design, optimization, realization, and analysis of an in vitro system for the exposure of embryonic stem cells at 1.71 GHz

The aim of this study was to develop an exposure system which enables in vitro experiments to be conducted under variously modulated radiofrequency exposures. Based on the evaluation of different possible systems, it was decided to realize a system based on rectangular waveguides. The system was optimized for the following parameters: (1) homogeneity of the cell exposure, (2) simultaneous exposure of several Petri dishes, (3) efficiency, (4) strict environmental control, (5) quick and easy access to the Petri dishes, (6) cost, and (7) simple operation by non-engineering personnel. The implemented control software enables investigation of a wide spectrum of amplitude modulation schemes between 0.1 Hz and 1 kHz, including the modulation schemes of current and future digital mobile communication systems as well as other exposure protocols. The system described has been initially utilized for a study on the differentiation and cell functions of embryonic stem cells. Detailed numerical and experimental dosimetry and environmental tests have demonstrated that it meets all target objectives. The entire system including the sham exposure system fits into a single incubator. It enables the carrying out of various experiments designed to test biological responses to RF exposures at 1.2-1.7 GHz by using various modulation schemes and long term exposure protocols as well as simultaneous data logging.     

Effect of photoperiod length on body mass and testicular growth in the house sparrow (Passer domesticus) and brahminy myna (Sturnus pagodarum)

Two experiments studied the relative effects on body mass and testicular growth of stimulatory photoperiods applied simultaneously to two photosensitive species, the house sparrow (Passer domesticus) and brahminy myna (Sturnus pagodarum). Experiment 1 on the house sparrow consisted of two parts. In experiment 1A, beginning on 24 March 2002, short day pretreated sparrows were exposed for 12 weeks to 13L: 11D (13 h light: 11 h darkness), 20L: 4D and NDL (control). Experiment 1B was similar to 1A except that it used sparrows that were not treated with short days. This experiment was repeated at three different times in the year. Beginning on 29 December 2002 (for 24 weeks), 26 March 2003 (for 12 weeks) and 16 August 2003 (for 8 weeks), sparrows captured from the wild and acclimated to captive condition for 1 week were exposed to 13L: 11D and 20L: 4D. Each time, a group was maintained in NDL and served as the control. Experiment 2 was performed on myna and used an identical protocol. Beginning on 24 March 2002, myna that were captured from the wild and acclimated to captivity conditions were exposed for 16 weeks to 13L: 11D and 20L: 4D; a group was maintained in NDL and served as the control. There was photostimulation and subsequent regression of the testes on all day lengths except in the August group of experiment 1B. The effect on body mass was variable. Interestingly, however, the response to 20L:4D was relatively smaller as compared to 13L:11D. Taken together, these results confirm that the two species use photoperiods in control of their reproductive cycle, and tend to indicate that exposure to unnatural long photoperiods may in fact be unfavorable and could compromise gonadal growth and development.     

Stoichiometry of lipid-protein interaction and integral membrane protein structure

The stoichiometries of lipid-protein interaction obtained from spin label electron spin resonance experiments with integral membrane proteins are compared with simple geometric models for the intramembranous perimeter that are based on the predicted numbers of transmembrane helices. Deviations from the predicted values provide evidence for oligomerization of the protein in the membrane and/or more complex arrangements of the transmembrane segments. Received: 16 January 1997 / Accepted: 5 March 1997     

The influence of density on frequency-dependent food selection: a comparison of four experiments with wild birds

We compare the results of four experiments, conducted at different times and with different protocols, that explored the relationship between frequency-dependent selection and prey density in wild birds feeding on artificial populations of coloured baits. One (experiment 4) used pastry baits that differed only in the presence or absence of a red stripe, and this experiment provided no evidence for any kind of selective behaviour. The other three experiments used green and brown baits, and they all provided evidence for a trend towards increasing anti-apostatic selection with high densities (>100 baits m^–2). However, one of these (experiment 3) provided no evidence for frequency-dependent selection at low densities (0.5–20 baits m^–2), while the other two experiments concurred in suggesting a trend towards increasing apostatic selection with low densities (down to 2 baits m^–2). Together, these experiments both support and qualify the published findings of experiment 1 that frequency- dependent selection by wild birds on bait populations is modified by density. Experiment 4 indicates that frequency-dependent selection may break down entirely if bait types are too similar, while experiment 3 indicates that some details of this trend with density will depend either on the protocol used or on exogenous changes in the birds’ feeding behaviour. Received: 1 September 1999 / Accepted: 22 March 2000     

Effects of neuropathic and non-neuropathic isomers of tricresyl phosphate and their microsomal activation on the production of axon-like processes by differentiating mouse N2a neuroblastoma cells

The aim of this work was to investigate the sublethal neuropathic effects of tricresyl phosphate (TCP: mixed isomers), triorthocresyl phosphate (TO:CP) and triparacresyl phosphate (TP:CP) on differentiating mouse N2a neuroblastoma cells. This was achieved by a combination of measurements of cell viability, axon outgrowth and the levels of cytoskeletal proteins detectable on western blots of extracts from cells induced to differentiate in the presence and absence of the compounds. In a time-course experiment TCP inhibited the outgrowth of axon-like processes following exposure times of 24 h or longer. Dose-response experiments indicated that TCP and TO:CP exhibited similar sustained levels of toxicity following both 24 and 48 h exposure, with no significant difference between their respective IC(50) values. By contrast, TP:CP demonstrated a transient effect on the outgrowth of axon-like processes, which was detectable after 24 but not 48 h of exposure. Isomer-specific patterns of toxicity were also evident at earlier time-points, with only the ortho isomer showing significant levels of inhibition of axon outgrowth following 4-8 h exposure. Probing of western blots with antibodies against cytoskeletal proteins indicated that the inhibition of axon outgrowth by these compounds was associated with a sustained reduction in the levels of phosphorylated neurofilament heavy chain. The inhibitory effect on axon outgrowth of TO:CP but not TP:CP was enhanced in the presence of a microsomal activation system. Since TO:CP is the most neuropathic of the isomers of TCP in vivo, differentiating N2a cells provide a useful cellular system for mechanistic studies of the neurodegenerative effects of this organophosphate.     

The diapause syndrome in the seed-eating caterpillar of Coleophora alticolella

Adult emergence in Coleophora alticolella held at 15 °C was accelerated by exposure to L18:D6 in autumn and midwinter. The effect decreased during winter and exposure of individuals, held at low temperature over winter, to L18:D6 or L6:D18 at 15 °C at the end of March resulted in the same mean emergence date. Long daylength experienced at 5 °C did not promote emergence nor did exposure to low temperature during winter. The number of adults emerging increased with the length of time cultures were held on short day but was always below 50% of the larvae. When larvae were exposed to L18:D6 and L6:D18 at 15 °C at the end of March, on long day 61% adults emerged and 39% remained in diapause, whereas on short day, 25% became adult and 75% remained diapausing larvae. The possibility of cohort splitting, with some individuals undergoing prolonged diapause, is discussed.     

Low-Frequency Electromagnetic Fields Alter the Replication Cycle of MS2 Bacteriophage

The effect of exposure to 60-Hz electromagnetic fields (EMFs) on RNA coliphage MS2 replication was studied. EMF exposure commenced when the bacterial cultures were inoculated with the phage (t = 0). In 12 experiments in which the strength of the field was 5 G, a significant delay in phage yield was found in the EMF-exposed cultures 45–65 min after inoculation, compared with control cultures. However, the EMF did not alter the final phage concentration. Experiments at 25 G (N = 5) suggested that the stronger field resulted in both impeded phage replication and increased phage yield. No differences between test groups were found in experiments involving sham-EMF exposure, thereby indicating that the results obtained with the EMFs were not due to systematic error. It appears that MS2, which codes for only four proteins, is the simplest biological system in which an EMF-induced effect has been demonstrated. The MS2 system is, therefore, conducive to follow-up studies aimed at understanding the level and nature of the underlying interaction process, and perhaps to biophysical modeling of the interaction process. Received: 26 August 1997 / Accepted: 17 November 1997     

RBE for carcinogenesis following exposure to high LET radiation

Stochastic radiation effects following exposure to heavy ions and other high linear energy transfer (LET) radiation in space are a matter of concern when the long-term consequences of space flights are considered. This paper is an overview of the relevant literature, emphasizing uncertainties entailed from estimates of relative biological effectiveness (RBE) for different experiment end-points, making the choice of a single weighting factor for the prediction of cancer risk in man extremely difficult. Life-span-shortening studies in mice exposed to heavy ions and ongoing large-scale experiments in monkeys exposed to protons suggest that RBEs for all cancers are lower than 5. This does not exclude a much higher RBE for rare tumors such as brain tumors in monkeys or promoted Harderian gland tumours in mice at LET >80 keV/µm. Skin cancer studies in rats exposed to neon or argon resulted in similar RBE. Exposure to fission neutrons led to high RBE in all species, not excluding values much higher than 20 for specific cancers such as lung tumors in mice and all cancers in rats. The estimate of maximal RBE is, however, extremely dependent on the hypothesis made on the shape of the dose-response curves in the lower range of doses. These results suggest that neutrons may be the most hazardous component of high-LET radiation. There is only limited evidence from cancer experiments that LET >150 keV/µm results in highly decreased efficiency, but this has been found for bone cancer induction following exposure to fission fragments.Invited paper presented at the International Symposium on Heavy Ion Research: Space, Radiation Protection and Therapy, Sophia-Antipolis, France, 21–24 March 1994     

Ornithine decarboxylase activity of L929 cells after exposure to continuous wave or 50 Hz modulated radiofrequency radiation--a replication study

A replication study with some extensions was made to confirm enhancement of ornithine decarboxylase (ODC) activity in murine L929 fibroblasts after radiofrequency (RF) field exposure reported in earlier studies. L929 cells purchased from two cell banks were exposed for 2, 8, or 24 h to continuous wave or DAMPS (burst modulated at 50 Hz, with 33% duty cycle) signals at specific absorption rate (SAR) levels of 2.5 or 6.0 W/kg. Exposures were carried out in Crawford and waveguide chambers, at frequencies 835 and 872 MHz, respectively. The results did not confirm findings of previous studies reporting increased ODC activity in RF-exposed cells. When Crawford cell exposure system was used, ODC activity was either not affected (in the case of 8 or 24 h exposures) or decreased after 2 h exposure at the highest SAR level (6 W/kg). The decrease was most pronounced when cooling with air flow was not used, and is most likely related to increased temperature. The minor methodological differences (use of antibiotics, increased sensitivity of ODC assay) are not likely to explain the inconsistency of the findings of the present and previous studies. Different results were obtained in experiments with the waveguide system that involves more efficient temperature control. In this exposure system, ODC activity was increased after 8 h exposure at 6 W/kg. Further studies are warranted to explore whether this finding reflects a true non-thermal effect. The present study did not provide evidence for modulation-specific effects reported in earlier studies.