Centrifugation as a countermeasure during actual and simulated microgravity: a review

This paper summarizes what has been learned from studies of the effects of artificial gravity generated by centrifugation in actual and simulated weightless conditions. The experience of artificial gravity during actual space flight in animals and humans are discussed. Studies using intermittent centrifugation during bed rest and water immersion, as a way to maintain orthostatic tolerance and exercise capacity, are reviewed; their results indicate that intermittent centrifugation is a potential countermeasure for maintaining the integrity of these physiological functions in extended space missions. These results can help set guidelines for future experiments aimed at validating the regimes of centrifugation as a countermeasure for space missions. Current and future research projects using artificial gravity conditions in humans are discussed.

Polygalacturonase (pectinase), a new oilseed rape allergen

BACKGROUND

Type I hypersensitivity to rapeseed pollen allergens was described as the result of a cross-sensitization with various pollens that could constitute an aggravating factor in birch or grass pollen allergies. Recently, a few rapeseed pollen allergens were described. The aim of the present work was to identify new rapeseed pollen allergens by using two-dimensional gel analysis, microsequencing, and mass spectrometry.

METHODS

Water extractable proteins from oilseed rape pollen or stamen were separated by two-dimensional gel electrophoresis. The proteins were then electroblotted onto a nitrocellulose (NC) sheet. The NC sheets were successively incubated with (1) individual human sera pre-selected for their immunoglobulin E (IgE) reactivity to rapeseed pollen proteins, (2) alkaline phosphatase (AP)-conjugated goat anti-human IgE and (3) AP substrate. The allergens localized by this method were then identified by microsequencing and MALDI-TOF mass spectrometry analysis.

RESULTS

Of the 18 sera studied, five recognized a wide multispot zone with a molecular mass around 43 kD and pIs between 6.5 and 8.5. The results obtained with two representative sera are shown. From this zone, two isoforms of the polygalacturonase enzyme were identified by microsequencing. Confirmation was obtained through MALDI-TOF mass spectrometry analysis.

CONCLUSION

The present results allow the identification of a new rapeseed allergen that can be the main allergen for some patients.

Effects of cosmonaut vestibular training on vestibular function prior to spaceflight

The purpose of this study was to quantify the effects of repetitive Coriolis and cross-coupled stimulations, similar to the vestibular training the cosmonauts are exposed to prior to their spaceflight. on vestibular function in control subjects on Earth. Ten volunteers were passively rotated in yaw on a rotating chair while executing standardized pitch head-and-trunk movements. The chair stopped to change direction after 12 head-and-trunk movements were made. The runs were grouped in sessions of ten,which were repeated daily for 10 days. The severity of motion sickness was assessed by subjective judgment and measurements of skin pallor and salivary total protein concentration, and nystagmus was recorded. The severity of motion sickness and nystagmus decreased during cosmonaut vestibular training (CVT). One month after the end of CVT, nystagmus responses were still about 20-30% lower than control values. These results indicate that CVT induces a habituation of vestibular responses. One important implication of this experiment concerns space studies on cosmonauts who are exposed to such vestibular training prior to their spaceflight.

Perception of tilt (somatogravic illusion) in response to sustained linear acceleration during space flight

During the 1998 Neurolab mission (STS-90), four astronauts were exposed to interaural and head vertical (dorsoventral) linear accelerations of 0.5 g and 1 g during constant velocity rotation on a centrifuge, both on Earth and during orbital space flight. Subjects were oriented either left-ear-out or right-ear-out (Gy centrifugation), or lay supine along the centrifuge arm with their head off-axis (Gz centrifugation). Pre-flight centrifugation, producing linear accelerations of 0.5 g and 1 g along the Gy (interaural) axis, induced illusions of roll-tilt of 20 degrees and 34 degrees for gravito-inertial acceleration (GIA) vector tilts of 27 degrees and 45 degrees , respectively. Pre-flight 0.5 g and 1 g Gz (head dorsoventral) centrifugation generated perceptions of backward pitch of 5 degrees and 15 degrees , respectively. In the absence of gravity during space flight, the same centrifugation generated a GIA that was equivalent to the centripetal acceleration and aligned with the Gy or Gz axes. Perception of tilt was underestimated relative to this new GIA orientation during early in-flight Gy centrifugation, but was close to the GIA after 16 days in orbit, when subjects reported that they felt as if they were 'lying on side'. During the course of the mission, inflight roll-tilt perception during Gy centrifugation increased from 45 degrees to 83 degrees at 1 g and from 42 degrees to 48 degrees at 0.5 g. Subjects felt 'upside-down' during in-flight Gz centrifugation from the first in-flight test session, which reflected the new GIA orientation along the head dorsoventral axis. The different levels of in-flight tilt perception during 0.5 g and 1 g Gy centrifugation suggests that other non-vestibular inputs, including an internal estimate of the body vertical and somatic sensation, were utilized in generating tilt perception. Interpretation of data by a weighted sum of body vertical and somatic vectors, with an estimate of the GIA from the otoliths, suggests that perception weights the sense of the body vertical more heavily early in-flight, that this weighting falls during adaptation to microgravity, and that the decreased reliance on the body vertical persists early post-flight, generating an exaggerated sense of tilt. Since graviceptors respond to linear acceleration and not to head tilt in orbit, it has been proposed that adaptation to weightlessness entails reinterpretation of otolith activity, causing tilt to be perceived as translation. Since linear acceleration during in-flight centrifugation was always perceived as tilt, not translation, the findings do not support this hypothesis.

Distance perception within near visual space

We investigated the perception of distance of visual targets with constant size and luminance presented between 20 and 120 cm from subjects' eyes. When retinal disparity cues were present, the subjects could reproduce very accurately the distance of a seen reference in this area. When only extraretinal information was available, distance perception was still correct for distances of 40 cm or less. However, distances beyond 60 cm were underestimated. When forced to evaluate the distance between a reference and themselves, e.g. when evaluating the absolute distance or half the distance or twice the distance of a reference, subjects used an egocentric plane of reference located on average 10.4 cm in front of their eyes. Measurements of binocular eye movements indicated a clear relationship between vergence angle and target distance. The egocentric plane of reference at 10.4 cm also corresponds to the maximum achievable vergence. These results suggest that ocular convergence can be used as a reliable cue for distance within the arm's reaching space.

Ocular counterrolling induced by centrifugation during orbital space flight

During the 1998 Neurolab mission (STS-90), four astronauts were exposed to interaural centripetal accelerations (Gy centrifugation) of 0.5 g and 1 g during rotation on a centrifuge, both on Earth and during orbital space flight. Subjects were oriented either left-ear out or right-ear out, facing or back to motion. Binocular eye movements were measured in three dimensions using a video technique. On Earth, tangential centrifugation that produces 1 g of interaural linear acceleration combines with gravity to tilt the gravitoinertial acceleration (GIA) vector 45 degrees in the roll plane relative to the head vertical, generating a summed vector of 1.4 g. Before flight, this elicited mean ocular counterrolling (OCR) of 5.7 degrees. Due to the relative absence of gravity during flight, there was no linear acceleration along the dorsoventral axis of the head. As a result, during in-flight centrifugation, gravitoinertial acceleration was strictly aligned with the centripetal acceleration along the interaural axis. There was a small but significant decrease (mean 10%) in the magnitude of OCR in space (5.1 degrees). The magnitude of OCR during postflight 1 g centrifugation was not significantly different from preflight OCR (5.9 degrees). Findings were similar for 0.5 g centrifugation, but the OCR magnitude was approximately 60% of that induced by centrifugation at 1 g. OCR during pre- and postflight static tilt was not significantly different and was always less than OCR elicited by centrifugation of Earth for an equivalent interaural linear acceleration. In contrast, there was no difference between the OCR generated by in-flight centrifugation and by static tilt on Earth at equivalent interaural linear accelerations. These data support the following conclusions: (1) OCR is generated predominantly in response to interaural linear acceleration; (2) the increased OCR during centrifugation on Earth is a response to the head dorsoventral 1 g linear acceleration component, which was absent in microgravity. The dorsoventral linear acceleration could have activated either the otoliths or body-tilt receptors that responded to the larger GIA magnitude (1.4 g), to generate the increased OCR during centrifugation on Earth. A striking finding was that magnitude of OCR was maintained throughout and after flight. This is in contrast to most previous postflight OCR studies, which have generally registered decreases in OCR. We postulate that intermittent exposure to artificial gravity, in the form of the centripetal acceleration experienced during centrifugation, acted as a countermeasure to deconditioning of this otolith-ocular orienting reflex during the 16-day mission.

Changes in the vertical size of a three-dimensional object drawn in weightlessness by astronauts

The purpose of this study was to investigate the effects of weightlessness on mental representation of spatial cues. Two astronauts drew two groups of three-dimensional cubes with their eyes closed, one on Earth (preflight) and the other under weightless conditions during a 7-day orbital flight (inflight). Differences in the average height of the two groups of cubes were observed. The ratio of average length of the horizontal vs. the vertical lines of the inflight cubes increased significantly compared to that of the preflight cubes. The disappearance of the gravitational reference system, which determines on Earth the vertical direction, seems to influence the internal representation of the vertical dimension, (i. e. the height) of a three-dimensional object.

Quantitative measurement of bitagged recombinant proteins using an immunometric assay: application to an anti-substance P recombinant antibody

We have developed two different immunometric assays to directly quantify both the total and the active fractions of a recombinant antibody (single chain fragment variable, or ScFv) as obtained in a crude extract from an Escherichia coli expression system. For total determination, the assay is based on the simultaneous recognition of two different peptide Tag sequences (Ha-Tag and Myc-Tag) at each of the N- and C-terminal extremities of the recombinant protein. A monoclonal antibody (mAb 12CA5, directed against Ha-Tag), coated on microtiter plates, is used for capture, and the mAb 9E10 (directed against Myc-Tag), labeled with acetylcholinesterase (AChE, EC 3.1.1.7), acts as tracer. In parallel, for the determination of the active fraction, the capture is performed using microtiter plates coated with the antigen, while solid-phase-immobilized ScFv is measured using the same 9E10 tracer mAb. A synthetic peptide in which the two Tag sequences were joined was used as a standard, thus avoiding the laborious purification of a recombinant protein as reference. The method was applied to the direct measurement, in periplasmic extracts, of the total and active fractions of an ScFv produced at different induction temperatures.

[Severe obstetric complications nescessitating hospitalization and intensive care: a ten year retrospective study]

OBJECTIVES

To assess the serious maternal morbidity during pregnancy, delivery and post partum, which led to an hospitalization in a medical or surgical intensive care unit.

STUDY DESIGN

A Retrospective study was carried out on a period of ten years, from July 1986 to July 1996, in the University Teaching Hospital of Besançon.

PATIENTS

The criterions of inclusion come from the definition of the serious maternal morbidity decided by the Inserm: any admission of a pregnant woman in a medical or surgical intensive care unit in the 42 days of the post-partum, whatever the term of the pregnancy and the type of the post-partum, extra uterine pregnancy, spontaneous miscarriage and medical or voluntary abortion.

METHODS

Forty-six patient's medical file hospitalized in a medical or surgical intensive care unit between July, 1st 1986 and July, 31st 1996, have been studied.

RESULTS

The analysis of the cause underline the gravity of the pathologies handled with young patients and initially healthy, the short length of controlled ventilation and hospitalization, the avoidability of great number of transfer in an intensive care unit, and the lack of hospitalization due to anaesthesia. The frequency of hospitalisation in an intensive care unit during and after the pregnancy was estimated at 0.17% of lives births.

CONCLUSION

The serious maternal morbidity could be an indicator of the quality of the obstetrics cares which would complete the study of the maternal mortality. The potential gravity of the complication of the pregnancy and the delivery require better care of this patients.

Evaluation of a high IgE-responder mouse model of allergy to bovine beta-lactoglobulin (BLG): development of sandwich immunoassays for total and allergen-specific IgE, IgG1 and IgG2a in BLG-sensitized mice

An animal model of food allergy represents an important tool for studying the mechanisms of induction and repression of an allergic reaction, as well as for the development of an immunotherapy to prevent or minimize such an adverse reaction. IgE and IgG1 (Th2 response) vs. IgG2a (Th1 response) are good markers for the induction of an allergic response in mice. Nevertheless, while the total serum concentrations of these isotypes are easy to measure using classical sandwich immunoassays, this is not the case for allergen-specific isotypes. To develop an animal model of allergy to bovine beta-lactoglobulin (BLG), we set up quantitative assays for total and for allergen-specific IgE, IgG1 and IgG2a. Microtiter plates coated either with anti-isotype antibodies (Abs) or with allergen were used for Ab capture, while anti-isotype Fab' fragments coupled to acetylcholinesterase were used for visualization. These assays of anti-BLG specific Abs are original in two ways. First, assay calibration is performed using anti-BLG specific mAbs, thus allowing good quantification of the different isotypes and subclasses of serum antibodies. Second, the detection of all anti-BLG specific Abs, i.e., those recognizing both the native and denatured forms of the protein, is achieved through indirect coating of BLG using biotin-streptavidin binding. The present assays are quantitative, specific to the isotype (cross-reactivity <0.5%), very sensitive (detection limit in the 10 pg/ml range), and reproducible (coefficient of variation less than 10%). Applied to the humoral response in mice sensitized with BLG adsorbed on alum, these assays proved to be a very useful tool for monitoring high IgE-responder mice following BLG immunization, and for an immunotherapy directed at polarizing the immune response.

Yaw and pitch visual-vestibular interaction in weightlessness

Both yaw and pitch visual-vestibular interactions at two separate frequencies of chair rotation (0.2 and 0.8 Hz) in combination with a single velocity of optokinetic stimulus (36 degrees/s) were used to investigate the effects of sustained weightlessness on neural strategies adopted by astronaut subjects to cope with the stimulus rearrangement of spaceflight. Pitch and yaw oscillation in darkness at 0.2 and 0.8 Hz without optokinetic stimulation, and constant velocity linear optokinetic stimulation at 18, 36, and 54 degrees/s presented relative to the head with the subject stationary, were used as controls for the visual-vestibular interactions. The results following 8 days of space flight showed no significant changes in: (1) either the horizontal and vertical vestibulo-ocular reflex (VOR) gain, phase, or bias; (2) the yaw visual-vestibular response (VVR); or (3) the horizontal or vertical optokinetic (OKN) slow phase velocity (SPV). However, significant changes were observed: (1) when during pitch VVR at 0.2 Hz late inflight, the contribution of the optokinetic input to the combined oculomotor response was smaller than during the stationary OKN SPV measurements, followed by an increased contribution during the immediate postflight testing; and (2) when during pitch VVR at 0.8 Hz, the component of the combined oculomotor response due to the underlying vertical VOR was more efficiently suppressed early inflight and less suppressed immediately postflight compared with preflight observations. The larger OKN response during pitch VVR at 0.2 Hz and the better suppression of VOR during pitch VVR at 0.8 Hz postflight are presumably due to the increased role of vision early inflight and immediately after spaceflight, as previously observed in various studies. These results suggest that the subjects adopted a neural strategy to structure their spatial orientation in weightlessness by reweighting visual, otolith, and perhaps tactile/somatic signals.

Allergy to bovine beta-lactoglobulin: specificity of human IgE to tryptic peptides

BACKGROUND

Bovine beta-lactoglobulin (Blg) is a major cow's milk allergen. It is the main whey protein, without any counterpart in human milk. Blg chemical hydrolysates appeared to retain most of the immunoreactivity of the native protein. Allergenicity of Blg has already been shown to be associated with the four peptides derived from cyanogen bromide cleavage of Blg.

OBJECTIVES

To map the major allergenic epitopes (e.g. regions of the molecule able to bind IgE) on Blg using specific IgE from sera of 46 milk-allergic patients as a probe.

METHODS

Direct and competitive inhibition enzyme immunoassays involving immobilized native protein or purified peptides derived from Blg tryptic cleavage.

RESULTS

Several peptides capable of specifically binding human IgEs were identified and were classified according to the intensity and frequency of the responses. The major epitopes appeared to be fragments (41-60), (102-124) and (149-162) recognized by 92, 97 and 89% of sera, respectively, whilst a second group which contained the fragments (1-8) and (25-40) was recognized by 58 and 72% of the population. A third group, comprising peptides (9-14), (84-91) and (92-100), was still detected by more than 40% of sera.

CONCLUSION

Three peptides were identified as major epitopes, recognized by a large majority of human IgE antibodies. Numerous other epitopes are scattered all along the Blg sequence.

Effects of body orientation and rotation axis on pitch visual-vestibular interaction

Spatial transformations of the vestibular-optokinetic system must account for changes in head position with respect to gravity in order to produce compensatory oculomotor responses. The purpose of this experiment was to study the influence of gravity on the vestibulo-ocular reflex (VOR) in darkness and on visual-vestibular interaction in the pitch plane in human subjects using two different comparisons: (1) Earth-horizontal axis (EHA) rotation about an upright versus a supine body orientation, and (2) Earth-horizontal versus Earth-vertical (EVA) rotation axes. Visual-vestibular responses (VVR) were evaluated by measuring the slow phase velocity of nystagmus induced during sinusoidal motion of the body in the pitch plane (at 0.2 Hz and 0.8 Hz) combined with a constant-velocity vertical optokinetic stimulation (at +/- 36 degrees/s). The results showed no significant effect on the gain or phase of the VOR in darkness or on the VVR responses at 0.8 Hz between EHA upright and EHA supine body orientations. However, there was a downward shift in the VOR bias in darkness in the supine orientation. There were systematic changes in VOR and VVR between EHA and EVA for 0.2 Hz, including a reduced modulation gain, increased phase lead, and decreased bias during EVA rotation. The same trend was also observed at 0.8 Hz, but at a lesser extent, presumably due to the effects of eccentric rotation in our EVA condition and/or to the different canal input across frequencies. The change in the bias at 0.2 Hz between rotation in darkness and rotation with an optokinetic stimulus was greater than the optokinetic responses without rotation. During EHA, changes in head position relative to gravity preserve graviceptor input to the VVR regardless of body orientation. However, the modifications in VVR gain and phase when the rotation axis is aligned with gravity indicate that this graviceptive information is important for providing compensatory eye movements during visual-vestibular interaction in the pitch plane.

Alteration of eye movements and motion perception in microgravity

This review article summarizes the results of space research on eye movements and subjective perception during vestibular stimulation. Inflight and postflight changes in reflex eye movements gain are described for head angular rotation (yaw, pitch, and roll), linear acceleration, off-vertical axis rotation, and optokinetic stimulation. There is evidence that changes in eye movements in microgravity primarily occur for head movements in pitch or roll which normally stimulate the otolith organs on Earth, but the data are not conclusive. The relationship between the eye movements gain and self-motion perception remains to be determined. We advocate the use of a human on- and off-axis rotator combined with the measurements of both tri-dimensional eye movement and perceptual response as a method to systematically investigate the adaptive changes in vestibular function to microgravity.

Postural reactions induced by vertical motion of visual scenes and the effects of weightlessness

Postural reactions induced by vertical optokinetic stimulation were recorded for 5 subjects in a ground-based study, and for one astronaut before, during, and after a 25-day spaceflight. On the ground, the amplitude of visually-induced postural reactions generally increased with stimulus velocity and saturated around 60 degrees/s, with an angle of body tilt which never exceeded 2-3 degrees. For velocities higher than 20 degrees/s, backward body tilt during upgoing optokinetic stimulation was larger than forward body tilt during downgoing stimulation. In weightlessness, the angle of body tilt was reduced compared to ground values, but after the flight the postural reactions were larger than before the flight. If the limited angle of body tilt on Earth is due to an inhibition from the graviceptive inputs which do not confirm the visual inputs, the larger angle of tilt might reflect that this inhibition was less effective after spaceflight. This ineffectiveness might reflect a confusion between body tilt and translation as the result of adaptation to weightlessness.

Effects of hypergravity on optokinetic after-nystagmus and perceived direction of optokinetic stimulation

BACKGROUND

Previous observations made in parabolic flight and centrifuge studies have shown the presence of a vertical nystagmus (Lz-nystagmus) induced by changes in gravitoinertial forces, and its interaction with oculomotor reflexes.

HYPOTHESIS

This Lz-nystagmus is also responsible for the changes in optokinetic after-nystagmus (OKAN) and the subjective perception of optokinetic stimulation direction during hypergravity.

METHODS

OKAN was recorded during the 1.8-g phase of parabolic flight after exposure to horizontal or vertical optokinetic stimulation during the preceding 1.0-g or 0-g phases. Changes in the apparent direction of image motion in subjects presented with an optokinetic stimulus were investigated in another experiment where longer exposure to hypergravity was generated by flying an airplane along a spiral path.

RESULTS

In upright subjects, the time constant of OKAN with slow phase up decreased during 1.8 g, whereas the horizontal OKAN showed no change in 1.8 g compared with OKAN recorded in 1.0 g. When the subjects were lying on their left side, the OKAN with slow phase right (slow phase up with respect to gravity) decreased in 1.8 g. The subjects tested showed larger error in setting the optokinetic stimulus in a pure horizontal plane in 1.8 g than in 1.0 g. The error was also larger for oblique stimulus in 1.8 g than in 1.0 g, but no differences were seen for the vertical stimulation.

CONCLUSION

The changes in OKAN can be explained by an interaction between slow phase eye movements generated by OKAN and the Lz-nystagmus generated by change in the gravitational force level. The error of the perceived direction of the optokinetic stimulus measured during horizontal and oblique stimulation is also presumably due to the interaction between the visual system and the Lz-nystagmus generated by hypergravity.

Absence of vestibular habituation of the vestibulo-ocular reflex in the vertical plane in the cat

The effect of exposure to repeated angular velocity steps about the earth-vertical axis on the vertical vestibulo-ocular reflex (VOR) during onside pitch rotation was investigated in normal cats. By contrast with the VOR in the horizontal plane, the amplitude and duration of the vertical VOR did not progressively decrease throughout the repetition of velocity steps alternated in both directions. Instead, the amplitude of VOR decreased by about 40% during the very first trials in naive cats and then stayed unchanged with repeated stimuli. Habituation of the amplitude of the vertical VOR was observed when the velocity steps were always directed in the same direction. However, the duration of the vertical VOR did not show any signs of habituation. The habituation of the amplitude of the vertical VOR during unidirectional training was due to the progressive development of an initial inhibition of the VOR. This initial inhibition appeared much earlier during the bidirectional protocol, and was presumably responsible for the larger reduction in VOR amplitude observed during the very first session. These results support the model of two distinct mechanisms for VOR habituation, one producing an increasing inhibition of nystagmus, and the other depressing the response duration, and suggest that only the first mechanism is generated during repeated stimulation in the vertical plane. The low-frequency information provided by the velocity storage mechanism during onside pitch rotation, when the otoliths are positioned so they do not signal head tilt relative to gravity, could prevent a decrease in the overall response by the second mechanism.

Essential fatty acid deficiency in the pig: effects on eicosanoid basal levels and in vitro synthesis by the small intestine

The influence of nutritional essential fatty acid (EFA) deficiency on arachidonate metabolism by porcine small intestine has been studied. Great care was exercised in the manipulation of the jejunal wall to avoid artefactual metabolism of arachidonate. Thus, jejunal wall was frozen in liquid nitrogen after organ removal and washing, and subsequently lyophilized. This lyophilized tissue was used as starting material for all experiments, including organic solvent extractions (for basal level determinations) and reconstitution in aqueous buffer (for neosynthesis experiments). Feeding pigs with a low linoleate diet for 12 weeks resulted in a 36% diminution in the % of arachidonate in jejunal phospholipids. Basal levels of 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha), thromboxane B2 (TXB2), PGF2 alpha, PGE2, PGD2 and leukotriene B4 (LTB4) were not altered in the EFA-deficient state. However, we observed a significant lowering of the synthesis of each of these eicosanoids (except LTB4) by the EFA-deficient jejunum during brief (15s) in vitro neosynthesis experiments. The origin of arachidonate as a substrate of PG endoperoxide synthase, also named PGH synthase or cyclooxygenase (Cox) in these neosynthesis experiments is probably a non-esterified fatty acid pool since, (1) neosynthesis was not inhibited by the phospholipase A2 (PLA2) inhibitor parabromophenacylbromide, and (2) substantial amounts of arachidonic acid were found in the jejunum, frozen or lyophilized. Cox activity of the lyophilized jejunum and Cox content of liver and intestine microsomes were not modified in the EFA-deficient state.(ABSTRACT TRUNCATED AT 250 WORDS)