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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Collisional desorption of NO by fast O atoms

Surface-adsorbed NO figures largely in the mechanism that produces visible glow around spacecraft in low Earth orbit (LEO). In view of the potential interference to optical observations such a glow represents, we have investigated the collision-induced desorption of NO from Al, Ni, and Z306 Chemglaze-coated surfaces at 96 K by hyperthermal (8 km/s) oxygen atoms. The removal of surface NO was followed by the monitoring of the visible fluorescence of electronically excited NO2 produced through the surface-mediated reaction O + NO. A variability in collisional desorption rate with material was observed. The limited data suggest a removal efficiency of 4 to 8% of the impinging O atom flux. Implications for the atmospheric scouring of contaminants from external surfaces of LEO spacecraft are discussed.

Sonnenfroh, David M.↗
NASA NTRS1995

Evolution of the biosynthesis of the branched-chain amino acids

The origins of the biosynthetic pathways for the branched-chain amino acids cannot be understood in terms of the backwards development of the present acetolactate pathway because it contains unstable intermediates. We propose that the first biosynthesis of the branched-chain amino acids was by the reductive carboxylation of short branched chain fatty acids giving keto acids which were then transaminated. Similar reaction sequences mediated by nonspecific enzymes would produce serine and threomine from the abundant prebiotic compounds glycolic and lactic acids. The aromatic amino acids may also have first been synthesized in this way, e.g. tryptophan from indole acetic acid. The next step would have been the biosynthesis of leucine from alpha-ketoisovalerc acid. The acetolactate pathway developed subsequently. The first version of the Krebs cycle, which was used for amino acid biosynthesis, would have been assembled by making use fo the reductive carboxylation and leucine biosynthesis enzymes, and completed with the development of a single new enzyme, succinate dehydrogenase. This evolutionary scheme suggests that there may be limitations to inferring the origins of metabolism by a simple back extrapolation of current pathways.

Keefe, Anthony D.↗
NASA NTRS1995

Structure of mass-loading shocks. 2: Comparison of theory and observation at comet Halley

The multifluid diffusive model of G. P. Zank et al. (1994), which describes the interaction of the solar wind with a cometary plasma in the outer coma, has been used to model the structure of the Halley bow shock. The theoretical results are compared to in situ observations made by Giotto. We compare the solar wind and cometary ion number densities and pressures upstream and through the quasi-perpendicular and quasi-parallel shocks (observed on the inbound and outbound legs of the encounter, respectively). In general, good agreement is found between theory and observations in terms of shock structure, strength, and location, especially for the quasi-parallel shock. The comparison between tha quasi-perpendicular shock observations and theory is complicated by the apparently nonstationary behavior of the shock, a feature which has been remarked upon by other investigators. The cometary bow shock appears to be an excellent example of an energetic-particle-mediated shock where the energetic particles comprise less than 10% of the total number density.

Zank, G. P.↗
NASA NTRS1994

UV-A/Blue-Light responses in algae

All life on earth depends on light. A variety of photoreceptors capture the light for a wide range of reactions. Photosynthetic organisms absorb the light necessary for energy transformation and charge separation facilitating photosynthesis. In addition to the bulk pigments there is a great diversity of photoreceptors present in minute concentrations that control development, metabolism and orientation of plants and microorganisms. Based on its spectral absorbance, the well-studied phytochrome system acts in the RL (red light) region as well as in the UV-A/BL (blue light) region where the above mentioned reactions are mediated by a variety of photoreceptors whose natures are largely unknown. Phyllogenetically the UV-A/BL photoreceptors seem to be more ancient pigments that eventually were replaced by the phytochrome system. However, there are many reports that suggest a coaction between the UV-A/BL receptors and the phytochrome system. In several cases the UV-A/BL activation is the prerequisite for the phytochrome reaction. Historically it was the German botanist Julius Sachs who first discovered in 1864 that phototropism in plants was due to BL reactions. It took over 70 years until Bunning (1937) and Galston and Baker (1949) rediscovered the BL response. Since then, an ever-increasing attention has been paid to this effect. In this contribution, the general aspect of UV-A/BL responses and especially the responsiveness of algae will be covered.

Senger, Horst↗
NASA NTRS1994

Effects of light on brain and behavior

It is obvious that light entering the eye permits the sensory capacity of vision. The human species is highly dependent on visual perception of the environment and consequently, the scientific study of vision and visual mechanisms is a centuries old endeavor. Relatively new discoveries are now leading to an expanded understanding of the role of light entering the eye in addition to supporting vision, light has various nonvisual biological effects. Over the past thirty years, animal studies have shown that environmental light is the primary stimulus for regulating circadian rhythms, seasonal cycles, and neuroendocrine responses. As with all photobiological phenomena, the wavelength, intensity, timing and duration of a light stimulus is important in determining its regulatory influence on the circadian and neuroendocrine systems. Initially, the effects of light on rhythms and hormones were observed only in sub-human species. Research over the past decade, however, has confirmed that light entering the eyes of humans is a potent stimulus for controlling physiological rhythms. The aim of this paper is to examine three specific nonvisual responses in humans which are mediated by light entering the eye: light-induced melatonin suppression, light therapy for winter depression, and enhancement of nighttime performance. This will serve as a brief introduction to the growing database which demonstrates how light stimuli can influence physiology, mood and behavior in humans. Such information greatly expands our understanding of the human eye and will ultimately change our use of light in the human environment.

Brainard, George C.↗
NASA NTRS1995

Pick-up ion pressure gradients modulating the solar wind dynamics

Neutral interstellar atoms penetrate deeply into the inner heliosphere before they become ionized by various processes. As ions they are picked-up by the frozen-in magnetic fields and are convected outwards with the solar wind plasma. Thereby the primary plasma flow is mass, momentum, and energy-loaded. The dynamics of the distant multi-constituent solar wind is, however, not solely determined by these loading processes, but is also affected by the wave-mediated pick-up ion pressure gradients derivable from the pick-up ion distribution function. The action of the radial components of these pressures essentially counter balances the decelerating effect of the solar wind momentum loading, diminishing strongly the deceleration of the distant solar wind. Furthermore the latitudinal components of the pick-up ion pressures induce latitudinal forces acting on the multiconstituent solar plasma outflow and inducing nonradial bulk flow components. The enforced nonradial outflow geometry on the upwind hemisphere may partly be responsible for the magnetic flux deficit which was claimed since several years in the PIONEER-10 magnetic flux data.

Fahr, Hans J.↗
NASA NTRS1994

Experiment K-7-31: Studies of Vestibular Primary Afferents and Eye Movements in Normal, Hypergravity and Hypogravity - Axon Cosmos Flight 2044

Fourteen days of active head movements in microgravity appear to modify the gain and neural adaptation properties of the horizontal semicircular canals in the rhesus monkey. This is the first demonstration of adaptive plasticity in the sensory receptor. Reversing prisms, for example, do not modify the gain of the primary afferent response. Pulse yaw rotation, sinusoidal rotation, and sum of sinusoidal rotation testing during the first day following recovery revealed that the gain of a sample of afferents was significantly greater than the gain derived from afferent responses obtained during pre-flight and control monkey testing. There was no strong evidence of tilt sensitivity in the sample of afferents that we tested either during the pre-flight or control tests or during the first day post-flight. Two irregular afferents tested on postflight day 2 showed changes with tilt but the responses were not systematic. The spontaneous discharge did not change following flight. Mean firing rate and coefficient of variation remained constant during the post flight tests and was near the value measured during pre flight tests. The change in gain of horizontal canal afferents might be adaptive. The animals were required to look at a target for food. This required active head and eye movements. Active head movements have been shown to be hypometric and eye movements have been shown to be hypermetric during the first few days of past Cosmos flights (see introduction). It might be that the increased gain in the horizontal semicircular canals permit accurate target acquisition during hypometric head movements by driving the eyes to greater angles for smaller angles of head movement. The mechanism by which the semicircular canals recalibrate (increase their gain) is unknown. The efferent vestibular system is a logical candidate. Horizontal nystagmus during rotation about an earth vertical axis with the horizontal semicircular canals in the plane of rotation produced the same response during postflight day 1 and post-flight day 9. But when the head was pitched down 45? the nystagmus slow phase velocity was greater and the duration was about twice during post-flight day 1. Apparently, this response involving the interaction of the horizontal and vertical semicircular canals and the otoliths did not recalibrate during post-flight day 1. The 'DC' bias of the slow phase velocity of the horizontal nystagmus during constant velocity horizontal axis rotation was roughly 4 times for one flight monkey and roughly 2 times for the other on post-flight day 1 compared to post-flight day 9. These results suggest that the otolith mediated response during constant velocity rotation also did not recalibrate on post-flight day 1.

Correia, M. J.↗
NASA NTRS1996

Mechanisms of insulin action on sympathetic nerve activity

Insulin resistance and hyperinsulinemia may contribute to the development of arterial hypertension. Although insulin may elevate arterial pressure, in part, through activation of the sympathetic nervous system, the sites and mechanisms of insulin-induced sympathetic excitation remain uncertain. While sympathoexcitation during insulin may be mediated by the baroreflex, or by modulation of norepinephrine release from sympathetic nerve endings, it has been shown repeatedly that insulin increases sympathetic outflow by actions on the central nervous system. Previous studies employing norepinephrine turnover have suggested that insulin causes sympathoexcitation by acting in the hypothalamus. Recent experiments from our laboratory involving direct measurements of regional sympathetic nerve activity have provided further evidence that insulin acts in the central nervous system. For example, administration of insulin into the third cerebralventricle increased lumbar but not renal or adrenal sympathetic nerve activity in normotensive rats. Interestingly, this pattern of regional sympathetic nerve responses to central neural administration of insulin is similar to that seen with systemic administration of insulin. Further, lesions of the anteroventral third ventricle hypothalamic (AV3V) region abolished increases in sympathetic activity to systemic administration of insulin with euglycemic clamp, suggesting that AV3V-related structures are critical for insulin-induced elevations in sympathetic outflow.

Muntzel, Martin S.↗
NASA NTRS1995

Simulated Microgravity Increases Cutaneous Blood Flow in the Head and Leg of Humans

The cutaneous micro-circulation vasodilates during acute 6 deg. head-down tilt (HDT, simulated microgravity) relative to upright conditions, more in the lower body than in the upper body. We expected that relative magnitudes of and differences between upper and lower body cutaneous blood flow elevation would be sustained during initial acclimation to simulated microgravity. We measured cutaneous micro-vascular blood flow with laser-Doppler flowmetry at the leg (over the distal tibia) and cheek (over the zygomatic arch) of eight healthy men before, during, and after 24 h of HDT. Results were calculated as a percentage of baseline value (100% measured during pre-tilt upright sitting). Cutaneous blood flow in the cheek increased significantly to 165 +/- 37% (mean + SE, p less than 0.05) at 9-12 h HDT, then returned to near baseline values by 24 h HDT (114 +/- 29%, NSD), despite increased local arterial pressure. Microvascular flow in the leg remained significantly elevated above baseline throughout 24 h HDT (427 +/- 85% at 3 h HDT and 215 +/- 142% at 24 h HDT, p less than 0.05). During the 6-h upright sitting recovery period, cheek and leg blood flow levels returned to near pre-tilt baseline values. Because hydrostatic effects of HDT increase local arterial pressure at the carotid sinus, baroreflex-mediated withdrawal of sympathetic tone probably contributed to increased microvascular flows at the head and leg during HDT. In the leg, baroreflex effects combined with minimal stimulation of local veno-arteriolar and myogenic autoregulatory vasoconstriction to elicit relatively larger and more sustained increases in cutaneous flow during HDT. In the cheek, delayed myogenic vasoconstriction and/or humoral effects apparently compensated for flow elevation by 24 h of HDT. Therefore, localized vascular adaptations to gravity probably explain differences in acclimation of lower and upper body blood flow to HDT and actual microgravity.

Stout, M. Shannon↗
NASA NTRS1995

Simulated Microgravity Increases Cutaneous Blood Flow in the Head and Leg of Humans

The cutaneous microcirculation vasodilates during acute 6 degree head-down tilt (HDT, simulated microgravity) relative to upright conditions, more in the lower body than in the upper body. Cutaneous microvascular blood flow was measured with laser-Doppler flowmetry at the leg (over the distal tibia) and cheek (over the zygomatic arch) of eight healthy men before, during, and after 24 h of HDT. Results were calculated as a percentage of baseline value (100% measured during pre-tilt upright sitting). Cutaneous blood flow in the cheek increased significantly to 165 +/- 37% (mean +/- SE, p less than 0.05) at 9-12 h HDT, then returned to near baseline values by 24 h HDT (114 +/- 29%, NSD), despite increased local arterial pressure. Microvascular flow in the leg remained significantly elevated above baseline througout 24 h HDT (427 +/- 85% at 3 h HDT and 215 +/- 142% at 24 h HDT, p less than 0.05). During the 6-h upright sitting recovery period, cheek and leg blood flow levels returned to near pre-tilt baseline values. Because hydrostatic effects of HDT increase local arterial pressure at the carotid sinus, baroreflex-mediated withdrawal of sympathetic tone probably contributed to increased microvascular flows at the head and leg during HDT. In the leg baroreflex effects combined with minimal stimulation of local veno-arteriolar and myogenic autoregulatory vasoconstriction to elicit relatively larger and more sustained increases in cutaneous flow during HDT. In the cheek, delayed myogenic vasoconstriction and/or hurmonal effects apparently compensated for flow elevation by 24 h of HDT. Therefore, localized vascular adaptations to gravity probably explain differences in acclimation of lower and upper body blood flow to HDT and actual microgravity.

Stout, M. Shannon↗
NASA NTRS1993

Monoclonal Antibody Testing for Cancer Metastasis

Malignant cells are characterized by the ability to invade surrounding normal tissues. Tumor invasion is abetted by proteolytic enzymes that have been correlated with recurrent disease and metastasis. These enzymes are involved in a cascade of proteolytic interactions with other enzymes and inhibitors which allow cancer cells to dissolve surrounding extracellular matrix, thereby enabling the cells to rapidly invade adjacent tissues and migrate to metastatic sites distant from the primary tumor. Among these proteases are the plasminogen activators (PA), collagenase IV, faminase, and in some cases cathepsin D, which together mediate key steps in the invasion process of metastasis. Cells which have the selective advantage for invasion and metastasis are those capable of regulating their proteolytic activity and proliferation. Cells in the process of invasion would be probably down-regulated for proliferation, but subsequent to attachment and adhesion at a distant site, would then be in a proliferative mode, up-regulating DNA replication. Urokinase (uPA) can be present in the tissues in several molecular forms. The inactive proenzyme is a single chain protein (scuPA) that is cleaved at Lys. 158 to form the double chain, high molecular weight active form (HMW-uPA) of 54 kD. A low molecular weight form (LMW-uPA) can also be produced by cleavage of the HMW-U PA at Lys. 135 - Lys. 136 giving a 35 kD active enzyme. Recently, it has been shown that the HMW active form of urokinase, bound to the tumor cell membrane, is responsible for the local lysis of the extracellular matrix, hence the tissue invasion mechanism for metastasis (Andreasen et al, 19861. Receptor- (membrane) bound uPA is twice as efficient (catalytically) as free fluid-phase uPA. Tho unbound uPA and the LMW form is not responsible for most of the local dissolution of extracellular matrix in the immediate vicinity of the metastatic tumor cell. High levels of urokinase (greater than 3.49 ng/mg of total protein) extracted from breast tumor tissues have recently been shown, together with plasminogen activator inhibitor 1 (PAI-1), to be a good prognostic indicator for high risk of recurrence and shorter patient survival times. In this project, we have attempted to develop immunocytochemical methodologies for the clinical assessment of the expression of urokinase plasminogen activator, which has been implicated to be important for initial steps in tumor invasion, and to relate it to cell proliferation and DNA replication at the single-cell level.

Source record↗
NASA NTRS1995

Chimeric Plant Calcium/Calmodulin-Dependent Protein Kinase Gene with a Neural Visinin-Like Calcium-Binding Domain

Calcium, a universal second messenger, regulates diverse cellular processes in eukaryotes. Ca-2(+) and Ca-2(+)/calmodulin-regulated protein phosphorylation play a pivotal role in amplifying and diversifying the action of Ca-2(+)- mediated signals. A chimeric Ca-2(+)/calmodulin-dependent protein kinase (CCaMK) gene with a visinin-like Ca-2(+)- binding domain was cloned and characterized from lily. The cDNA clone contains an open reading frame coding for a protein of 520 amino acids. The predicted structure of CCaMK contains a catalytic domain followed by two regulatory domains, a calmodulin-binding domain and a visinin-like Ca-2(+)-binding domain. The amino-terminal region of CCaMK contains all 11 conserved subdomains characteristic of serine/threonine protein kinases. The calmodulin-binding region of CCaMK has high homology (79%) to alpha subunit of mammalian Ca-2(+)/calmodulin-dependent protein kinase. The calmodulin-binding region is fused to a neural visinin-like domain that contains three Ca-2(+)-binding EF-hand motifs and a biotin-binding site. The Escherichia coli-expressed protein (approx. 56 kDa) binds calmodulin in a Ca-2(+)-dependent manner. Furthermore, Ca-45-binding assays revealed that CCaMK directly binds Ca-2(+). The CCaMK gene is preferentially expressed in developing anthers. Southern blot analysis revealed that CCaMK is encoded by a single gene. The structural features of the gene suggest that it has multiple regulatory controls and could play a unique role in Ca-2(+) signaling in plants.

Patil, Shameekumar↗
NASA NTRS1984

A Role for Presynaptic alpha(sub 2)-Adrenoceptors in Angiotensin 2-Induced Drinking in Rats

Studies from this laboratory have shown that either central or peripheral administration of clonidine, the alpha(sub 2)-adrenoceptor agonist, can attenuate a variety of dipsogenic stimuli in rats. Further, yohimbine and tolazoline, alpha(sub 2)-adrenoceptor antagonists, augment the drinking response to both peripherally administered isoproterenol and angiotensin 2. Studies reported here establish a dose-inhibition relationship between the dose of clonidine administered (2 to 32 micrograms/kg) intracerebroventricularly (IVT) and inhibition of the drinking response to peripherally administered angiotensin 2 (200 micrograms/kg, SC). DI(sub 50) was approximately 4 micrograms/kg. Yohimbine (300 micrograms/kg, SC) reversed the antidipsogenic effect of centrally administered clonidine (32 micrograms/kg, IVT) on angiotensin 2-induced (200 micrograms/kg, SC) water intake. Phenylephrine, an alpha(sub 2)-adrenoceptor agonist, administered IVT (40 and 80 micrograms/kg) also inhibited angiotensin 2-induced drinking in a dose-related fashion. The antidipsogenic effect of phenylephfine (80 micrograms/kg) was blocked by administration of yohimbine (100 micrograms/kg, SC). Thus, this effect of phenylephrine most likely occurs by way of alpha(sub 2)- adrenoceptors. These results support a role for the pre-synaptic alpha(sub 2)-adrenoceptor in the mediation of drinking in rats. Activation of alpha(sub 2)-adrenoceptors is accompanied by reduced water intake while inhibition of these receptors enhances water intake.

Fregly, Melvin J.↗
NASA NTRS1997

The Effects of Liquid Cooling Garments on Post-Space Flight Orthostatic Intolerance

Post space flight orthostatic intolerance among Space Shuttle crew members following exposure to extended periods of microgravity has been of significant concern to the safety of the shuttle program. Following the Challenger accident, flight crews were required to wear launch and entry suits (LES). It was noted that overall, there appeared to be a higher degree of orthostatic intolerance among the post-Challenger crews (approaching 30%). It was hypothesized that the increased heat load incurred when wearing the LES, contributed to an increased degree of orthostatic intolerance, possibly mediated through increased peripheral vasodilatation triggered by the heat load. The use of liquid cooling garments (LCG) beneath the launch and entry suits was gradually implemented among flight crews in an attempt to decrease heat load, increase crew comfort, and hopefully improve orthostatic tolerance during reentry and landing. The hypothesis that the use of the LCG during reentry and landing would decrease the degree of orthostasis has not been previously tested. Operational stand-tests were performed pre and post flight to assess crewmember's cardiovascular system's ability to respond to gravitational stress. Stand test and debrief information were collected and databased for 27 space shuttle missions. 63 crewpersons wearing the LCG, and 70 crewpersons not wearing the LCG were entered into the database for analysis. Of 17 crewmembers who exhibited pre-syncopal symptoms at the R+O analysis, 15 were not wearing the LCG. This corresponds to a 21% rate of postflight orthostatic intolerance among those without the LCG, and a 3% rate for those wearing LCG. There were differences in these individual's average post-flight maximal systolic blood pressure, and lower minimal Systolic Blood pressures in those without LCG. Though other factors, such as type of fluid loading, and exercise have improved concurrently with LCG introduction, from this data analysis, it appears that LCG usage provided a significant degree of protection from post-flight orthostatic intolerance.

Billica, Roger↗
NASA NTRS1997

The Role of GH/IGF-I Axis in Muscle Homeostasis During Weightlessness

Exposure to reduced gravity during space travel profoundly alters the loads placed on bone and muscle. Astronauts suffer significant losses of muscle and bone strength during weightlessness. Exercise as a countermeasure is only partially effective in remedying severe muscle atrophy and bone demineralization. Similar wasting of muscles and bones affects people on Earth during prolonged bed rest or immobilization due to injury. In the absence of weight bearing activity, atrophy occurs primarily in the muscles that act in low power, routine movements and in maintaining posture. Hormonal disfunction could contribute in part to the loss of muscle and bone during spaceflight. Reduced levels of human Growth Hormone (hGH) were found in astronauts during space flight, as well as reduced GH secretory activity was observed from the anterior pituitary in 7-day space flight rats. Growth hormone has been shown to be required for maintenance of muscle mass and bone mineralization, in part by mediating the biosynthesis IGF-I, a small polypeptide growth factor. IGF biosynthesis and secretion plays an important role in potentiating muscle cell differentiation and has been shown to drive the expression of myogenin, a myogenic specific basic helix-loop-helix factor. IGF-I has also been shown to have an important role in potentiating muscle regeneration, repair and adult muscle hypertrophy.

Schwartz, Robert J.↗
NASA NTRS1992

A Reevaluation of the Vestibulo-Ocular Reflex: New Ideas of its Purpose, Properties, Neural Substrate, and Disorders

Conventional views of the Vestibulo-Ocular Reflex (VOR) have emphasized testing with caloric stimuli and by passively rotating patients at low frequencies in a chair. The properties of the VOR tested under these conditions differ from the performance of this reflex during the natural function for which it evolved-locomotion. Only the VOR (and not visually mediated eye movements) can cope with the high-frequency angular and linear perturbations of the head that occur during locomotion; this is achieved by generating eye movements at short latency (less than 16 msec). Interpretation of vestibular testing is enhanced by the realization that, although the di- and trisynaptic components of the VOR are essential for this short-latency response, the overall accuracy and plasticity of the VOR depend upon a distributed, parallel network of neurons involving the vestibular nuclei. Neurons in this network variously encode inputs from the labyrinthine semicircular canals and otoliths, as well as from the visual and somatosensory systems. The central vestibular pathways branch to contact vestibular cortex (for perception) and the spinal cord (for control of posture). Thus, the vestibular nuclei basically coordinate the stabilization of gaze and posture, and contribute to the perception of verticality and self-motion. Consequently, brainstem disorders that disrupt the VOR cause not just only nystagmus, but also instability of posture (eg, increased fore-aft sway in patients with downbeat nystagmus) and disturbance of spatial orientation (eg, tilt of the subjective visual vertical in Wallenberg's syndrome).

Leigh, R. John↗
NASA NTRS1997

Membrane-Based Functions in the Origin of Cellular Life

If peptides consist of nonpolar residues only, they become inserted into the nonpolar phase. As demonstrated by the example of the leucine undecamer, such peptides fold into an a-helix as they partition into the nonpolar medium. The folding proceeds through an intermediate, called the 310-helix, which remains in equilibrium with the a-helix. This process represents a simple, protobiologically relevant example of environmentally-mediated self-organization of biological molecules. Once in the nonpolar environment, the peptides can readily change their orientation with respect to the interface from parallel to perpendicular, especially in response to local electric fields. The ability of nonpolar peptides to modify both the structure and orientation with changing external conditions may have provided a simple mechanism of transmitting signals from the environment to the interior of a protocell.

Wilson, Michael↗
NASA NTRS1996

Spaceflight Associated Apoptosis

Lymphoid tissues have been shown to atrophy in rats flown on Russian spaceflights. Histological examination indicated evidence for cell degradation. Lymphoid tissues from rats flown on Spacelab Life Sciences-2 mission were analyzed for apoptosis by evidence of fragmented lymphocytes, which could be engulfed by macrophages, or DNA strand breaks using the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay. Apoptosis was not detected in the thymus and spleen collected inflight or from the synchronous ground rats but was detected in the thymus, spleen and inguinal lymph node of the flight animals on recovery. These results indicate that the apoptosis observed in the lymphatic tissues of the rats on recovery could have been induced by the gravitational stress of reentry, corroborating the findings from the early space-flight observations.

Ichiki, Albert T.↗