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At least 1,513 records · Page 84Linked to original sources
PubMed2005

[Behavioral changes of rats under rotation stimulation].

OBJECTIVE: To assess the specification and efficiency of rotation sickness indices by monitoring changes of behaviors in rats under rotation stimulation. METHOD: SD rats were stimulated by Crampton model with different time courses. Pica or kaolin consumption (KC), conditioned taste aversion (CTA) or saccharine water ingestion (SWI), 2 h food ingestion (2hFI), and open-field test (OFT) scores were observed. RESULT: Apparent changes of the four indices were observed after rotation stimulation. SWI, OFT scores and 2hFI decreased exponentially with increase of duration of the motion stimulation. KC increased linearly with the increase of time within 12 h stimulation. After 18 h stimulation, KC decreased to a level even lower than that after 6 or 12 h stimulation. The adjusted correlation between changes of the indices and duration of stimulation within 12 h are: 0.94 for KC, 0.54 for SWI, 0.44 for 2hFI and 0.34 for OFT. The maximum efficiency of the four indices appeared at 6-hour stimulation: 70% for KC, 90% for SWI, 80% for 2hFI and 95% for OFT. CONCLUSION: It is found that pica and CTA were more specific than the other indices. They may serve as primary indices and can be combined with the secondary indices such as 2hFI or OFT. Six hours is the optimal duration of stimulation by Crampton model for rotation sickness studies.

Animals↗
PubMed2005

Countermeasure for space flight effects on immune system: nutritional nucleotides.

Microgravity and its environment have adverse effects on the immune system. Abnormal immune responses observed in microgravity may pose serious consequences, especially for the recent directions of NASA for long-term space missions to Moon, Mars and deep Space exploration. The study of space flight immunology is limited due to relative inaccessibility, difficulty of performing experiments in space, and inadequate provisions in this area in the United States and Russian space programs (Taylor 1993). Microgravity and stress experienced during space flights results in immune system aberration (Taylor 1993). In ground-based mouse models for some of the microgravity effects on the human body, hindlimb unloading (HU) has been reported to cause abnormal cell proliferation and cytokine production (Armstrong et al., 1993, Chapes et al. 1993). In this report, we document that a nutritional nucleotide supplementation as studied in ground-based microgravity analogs, has potential to serve as a countermeasure for the immune dysfunction observed in space travel.

Animals↗
PubMed2004

The mechanism [correction of mehanism] of spatial [correction of spetial] orientation in conditions of G-stress.

Six test subjects were subjected to lateral (+Gy) and longitudinal-lateral (+Gz/+Gy) accelerations in a centrifuge with a rotation radius of 6.55 m. During rotation, test subjects were instructed to indicate the position of subjective visual vertical. Results of this study demonstrated that during exposure to +Gy and +Gz/+Gy accelerations, the direction of the indicated subjective vertical approached the direction of the resultant acceleration vector when the lateral component increased. This observed effect decreases with an increase of the longitudinal component of the acceleration. It was suggested that exposure to (i.e. "pulling") high lateral acceleration (up to 2-3 Gy) in highly maneuverable aircraft can hinder spatial orientation of a pilot due to this persistent illusory spatial position as reported above. Our analysis showed that the process of spatial orientation under the conditions of G-load influence becomes more difficult and it is depending on the compromise between visual and vestibular-proprioceptive inputs. On account of this finding, it may be proposed that under conditions of G-load influence, pilots that rely primarily on visual perception may be exposed to higher risk of spatial disorientation.

Acceleration↗
PubMed2004

Changes in the gaze fixation reaction in rhesus monkeys during the initial stage of water immersion.

The gaze fixation reaction was studied in three rhesus monkeys before and during thermoneutral (34.5 degrees C) water immersion to the mid-chest level. The angular vestibulo-ocular reflex gain increased and the head angular velocity decreased significantly in all monkeys in 5 h after the start of immersion. Additionally, one animal was immersed to the neck level. Two hours in the condition of more pronounced support deprivation decreased significantly angular velocity of the head but not increased the angular vestibulo-ocular reflex gain. Therefore, support deprivation act upon the head movement control first.

Animals↗
PubMed2004

Signal transduction in T cells: an overview.

The mitogenic in vitro activation of human peripheral blood lymphocytes is severely depressed in space as well as in models of low gravity conditions on ground. The mechanism of T-cell activation is very complex; 3 signals are required for full activation. A series of experiments performed in space and in modeled low gravity on ground have shown that a failure in the delivery of the second signal--interleukin-2--is one of the reasons for the impaired activation. The cytoskeleton plays a key role in several steps of the mitogenic activation; (1) in the binding of the mitogen to the cell membrane and the subsequent patching and capping of the receptors, and (2) in the transduction of the signals from the membrane to the nucleus. Changes in the cytoskeletal structures of vimentin and tubulin observed in cells exposed to low gravity conditions may have influenced the correct signal transduction.

Antigens, CD↗
PubMed2004

Effect of microgravity changes on virus infection in mice.

We have analyzed the effect of stress caused by the exposure of BALB/c mice to microgravity change on the susceptibility to herpes simplex virus type 1 (HSV-1) infection. Mice exposed to microgravity for 10 seconds showed a decreased rate of survival from HSV-1 infection. Murine interferon (MuIFN) administration to mice after exposure to microgravity partly diminished the decrease in survival. After repeated exposure to microgravity, mice showed tolerance to the stress. These results indicate that microgravity-stress leads to a down regulation of resistance to virus infection in relation to the modulation of the central nerve system in mice. Responsibility of the immune system dependent on cytokines, including IFN, for down regulation of the resistance is also suggested. Tail-suspended mice were also less resistant to virus infection.

Adaptation, Physiological↗
PubMed2004

Brief exposure to -2 Gz reduces cerebral blood flow velocity during subsequent +2 Gz acceleration.

In order to determine the implication of the cerebral vasoconstriction occurring under -Gz acceleration in the mechanism of the push-pull effect, four healthy male non-pilots were submitted to a control centrifugation at +2 Gz, and then to an experimental run with identical +2 Gz plateau, but preceded by -2 Gz exposure. Cerebral blood flow velocity (CBFV), pulsatility index, and resistance index (RI) were continually measured with a transcranial Doppler instrument. The decrease in blood pressure and in CBFV was more important during the experimental run, when the change in RI was not different. We concluded that the cerebral vasoconstriction occurring under -2 Gz exposure seems not to be a major contributor in the mechanism of the push-pull effect appearing during subsequent +2 Gz acceleration.

Blood Pressure↗
PubMed2004

ECG voltage modifications as response to gravity changes.

The aim of the study was to analyze ECG (QRS) voltage responses to body fluid shift due to gravity chances. Acute changes in gravity were created by two ways: 1) changes in gravity value during parabolic flights (within 27 subjects 45 ECG have been analyzed); 2) changes in gravity direction due to rotation of the body during postural tests (within 11 subjects 14 ECG have been analyzed). Results and conclusions. Gravity change leads to body fluid shift and changes of intrathoracic organs and tissues electroconduction. It influences on ECG voltage. During parabolic flights in up-right position: R amplitude in Z axis increases in hypergravity (+0.19 mV) and decreases in microgravity (-0.24 mV). During postural tests, R amplitude in Z axis increases in orthostatic position (+0.09 mV) and decreases in antiorthostatic position (-0.025 mV). Changes in QRS voltage during parabolic flights are more important than during postural tests. This could be due to more effective blood redistribution during parabolic flights.

Adult↗
PubMed2004

Effect of two-week tail suspension on forelimb and hindlimb [correction of hindlimd] small arteries in rats.

This study was aimed at comparing the effect of 2-week tail suspension on the characteristics of median artery and saphenous artery isolated from forelimb and hindlimb, accordingly. The segments of arteries were mounted in two-channel myograph for recording their isometric wall tension. In post-suspension rats segments of saphenous artery showed augmented sensitivity to noradrenaline and serotonin. More than two-fold decreased of EC50 was observed both before and after endothelium removal. Along with that, the sensitivity of median artery segments to vasoconstrictors was similar in post-suspension and control rats. However, the diameter of relaxed median artery in post-suspension rats was increased. Relaxation to acetylcholine compared to controls was augmented in both vascular regions of post-suspension rats being more pronounced in saphenous artery preparations.

Acetylcholine↗
PubMed2004

The autonomous regulation system functional reserves evaluation in 7-day head down bedrest.

The heart rate variability estimation was used for autonomous regulation diagnostic in the 7-day head down bedrest experiment (HDBR). The new device "Pneumocard" and the fix respirations test were applied. The growth of sympathetic activity of autonomous nervous system and reduction of functional reserves of regulation mechanisms were observed in the microgravity modeling by HDBR. The analysis of the individual data had shown, that at two volunteers with most significant growth of SI after the experiment the orthostatic intolerance was observed. The data received in experiment confirm a hypothesis that growth of sympathetic activity in microgravity is accompanied by reduction of regulation mechanisms functional reserves is prognostic unfavorable.

Aerospace Medicine↗
PubMed2004

Brain vessels in the rats exposed to primary and repeated tail-suspension. Minimization of structural changes after repeated exposure.

The aim of study was histological examination of brain vessels in the rats exposed to repeated tail-suspension (TS). The rats were subjected to 30-day TS, then readapted to horizontal position for 30 days and again exposed to 14-day TS simultaneously with the rats which were underwent to 14-day TS for the first time. 30-day TS induced in brain vessels the adaptive changes hindering the excessive blood inflow to brain--spasm and hypertrophy of muscle-elastic valves in extra- and intracerebral arteries and also the destructive changes--loss of vascular tone in extra- and intracerebral arteries, plethora in extra- and intracerebral veins, intracerebral venules and capillaries, conglutination of erythrocytes in capillaries, plasmatization of veins and capillaries and edema of brain tissue pointing out in total the increase in blood inflow to the brain and difficulty of blood outflow. After 30-day readaptation of TS-rats to horizontal position only adaptive changes in extracerebral arteries and intracerebral capillaries (cell proliferation) and edema of brain tissue were revealed. After repeated, 14-day TS in spite of new redistribution of blood to the head, in contrast to the vessel alterations after primary 14-day TS, the adaptive and destructive changes in brain vessels were lack, excluding only moderate plethora of intracerebral veins, cell proliferation in capillaries and weak signs of edema.

Adaptation, Physiological↗
PubMed2004

Hemodynamic changes in post-suspension rats during gradual hemorrhage.

We examined the changes of hemodynamic parameters in nembutal-anesthetized rats during gradual hemorrhage (2 ml/100 g body weight during 30 min). In control rats blood pressure began to decline starting from 3rd min of bleeding and from 5th min it was accompanied by cardiac deceleration. Hindlimb vascular resistance was only slightly increased up to 15th min (by 20-30%) and then began to grow drastically. Less prominent changes of hemodynamics were observed in post-suspension rats. The results indicate that when activity of sympathetic nervous system is blunted with anesthetic post-suspension rats demonstrate higher hemodynamic stability during acute hemorrhage.

Animals↗
PubMed2004

Afferent and peripheral control of muscle fiber properties during gravitational unloading.

The present paper covers two series of the experiment studies performed in attempt to analyze the support-triggered cellular mechanisms, controlling the maintenance of tonic muscle fiber characteristics. Exposure to 7 day dry immersion induced significant decline of the human soleus single fiber peak isometric tension and the Ca(2+)-sensitivity of myofibrils. 30-40% losses of the relative content of titin and nebulin were found after immersion. The application of the plantar support stimulation device prevented all these alterations. In the second experimental series the treatment of hindlimb suspended rats with the Ca(2+)-binding agent (EGTA) allowed to prevent or attenuate all the above mentioned unloading-induced soleus fiber alterations. Thus it is concluded that resting Ca2+ accumulation in the unloaded fibers may be among the mechanisms involved in the changes of fiber properties during unloading.

Animals↗
PubMed2004

Load-dependent regulation of neuromuscular system.

Roles of gravitational loading, sarcomere length, and/or tension development on the electromyogram (EMG) of soleus and afferent neurogram recorded at the L5 segmental level of spinal cord were investigated during parabolic flight of a jet airplane or hindlimb suspension in conscious rats. Both EMG and neurogram levels were increased when the gravity levels were elevated from 1-G to 2-G during the parabolic flight. They were decreased when the hindlimbs were unloaded by exposure to actual microgravity or by suspension. These phenomena were related to passive shortening of muscle fibers and/or sarcomeres. Unloading-related decrease in sarcomere length was greater at the central rather than the proximal and distal regions of fibers. These activities and tension development were not detected when the mean sarcomere length was less than 2.03 micrometers. It is suggested that load-dependent regulation of neuromuscular system is related to the tension development which is influenced by sarcomere length.

Animals↗