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Biomedical subjects

C Sebastian

Publications and source records attributed to C Sebastian.

At least 19 recordsLinked to original sources
PubMed2002

Crickets in space: morphological, physiological and behavioral alterations induced by space flight and hypergravity.

"Crickets in Space" was a Neurolab experiment by which the balance between genetic programs and the gravitational environment for the development of a gravity sensitive neuronal system was studied. The model character of crickets was justified by their external gravity receptors, identified position-sensitive interneurons (PSI) and gravity-related compensatory head response, and by the specific relation of this behavior to neuronal arousal systems activated by locomotion. These advantages allowed to study the impact of modified gravity on cellular processes in a complex organism. Eggs, 1st, 4th and 6th stage larvae of Acheta domesticus were used. Post-flight experiments revealed a low susceptibility of the behavior to micro- and hypergravity while the physiology of the PSI was significantly affected. Immunocytological investigations revealed a stage-dependent sensitivity of thoracic GABAergic motoneurons to 3 g-conditions concerning their soma sizes but not their topographical arrangement. The morphology of neuromuscular junctions was not affected by 3 g-hypergravity. Peptidergic neurons from cerebral sensorimotor centers revealed no significant modifications by microgravity (micro g). The contrary physiological and behavioral results indicate a facilitation of 1 g-readaptation originating from accessory gravity, proprioceptive and visual sense organs. Absence of anatomical modifications point to an effective time window of micro g or 3 g-expo-sure related to the period of neuronal proliferation. The analysis of basic mechanisms of how animals and man adapt to altered gravitational conditions will profit from a continuation of the project "Crickets in Space".

Adaptation, Physiological↗
PubMed2002

Adaptation of the macular vestibuloocular reflex to altered gravitational conditions in a fish (Oreochromis mossambicus).

Young fish (Oreochromis mossambicus) were exposed to microgravity (micro g) for 9 to 10 days, or to hypergravity (hg) for 9 days. For several weeks after termination of micro g and hg, the roll-induced static vestibuloocular reflex (rVOR) was recorded. In stage 11/12-fish, the rVOR amplitude (angle between the maximal up and down movement of an eye during a complete 360 degree lateral roll) of micro g-animals increased significantly by 25% compared to 1 g-controls during the first post-flight week but decreased to the control level during the second post-flight week. Microgravity had no effect in stage 14/16 fish on the rVOR amplitude. After 3 g-exposure, the rVOR amplitude was significantly reduced for both groups compared to their 1 g-controls. Readaptation to 1 g-condition was completed during the second post-3 g week. We postulate a critical period during which the development of the macular vestibuloocular reflex depends on gravitational input, and which is limited by the first appearance of the rVOR. At this period of early development, exposure to microgravity sensitizes the vestibular system while hypergravity desensitizes it.

Adaptation, Physiological↗
PubMed2001

Altered gravitational forces affect the development of the static vestibuloocular reflex in fish (Oreochromis mossambicus).

Young fish (Oreochromis mossambicus) were exposed to microgravity (micro g) for 9 to 10 days during space missions STS-55 and STS-84, or to hypergravity (hg) for 9 days. Young animals (stages 11-12), which had not yet developed the roll-induced static vestibuloocular reflex (rVOR) at micro g- and hg-onset, and older ones (stages 14-16), which had already developed the rVOR, were used. For several weeks afterwards, the rVOR was recorded after termination of mug and hg. Here are the main results: (1) In the stage 11-12 fish, the rVOR gain (response angle/roll angle) measured for roll angles 15 degrees, 30 degrees, and 45 degrees was not affected by microgravity if animals were rolled from the horizontal to the inclined posture, but was increased significantly if animals were rolled in the opposite manner. The rVOR amplitude (maximal eye movement during a complete 360 degrees roll) of micro g animals increased significantly by 25% compared to 1g controls during the first postflight week, but decreased to the control level during the second postflight week. Microgravity had no effect in stage 14-16 fish on either rVOR gain or amplitude. (2) After 3g exposure, both rVOR gain and amplitude were significantly reduced for both stage 11-12 and stage 15 fish. One g readaptation was completed during the second post-3g week. Hypergravity at 2 or 2.5 g had no effect. (3) Hypergravity at all three levels tested (2g, 2.5g, and 3g) accelerated the morphological development as assessed by external morphological markers. Exposure to micro g- or 3g-periods during an early developmental period modifies the physiological properties of the neuronal network underlying the static rVOR; in susceptible developmental stages, these modifications include sensitization by microgravity and desensitization by hypergravity.

Animals↗
PubMed2001

Features of vestibuloocular reflex modulations induced by altered gravitational forces in tadpoles (Xenopus laevis).

In Xenopus laevis tadpoles, we studied the static vestibuloocular reflex (rVOR) in relation to modifications of the gravitational environment to find basic mechanisms of how altered gravitational forces (AGF) affect this reflex. Animals were exposed to microgravity during space flight or hypergravity (3g) for 4 to 12 days. Basic observations were that (1)the development of the rVOR is significantly affected by altered gravitational conditions, (2) the duration of 1g-readaptation depends on the strength of the test stimulus, (3) microgravity induces malformations of the body which are related to the rVOR depression. Future studies are based on the hypotheses (1) that the vestibular nuclei play a key roll in the adaptation to AGF conditions, (2) that the stimulus transducing systems in the sense organ are affected by AGF conditions, and (3) that fertilized eggs will be converted to normal adults guided by physiological and morphological set points representing the genetic programs. Developmental retardation or acceleration, or otherwise occurring deviations from standard development during embryonic and postembryonic life will activate genes that direct the developmental processes towards normality.

Adaptation, Physiological↗
PubMed2000

Rapid upregulation of caspase-3 in rat spinal cord after injury: mRNA, protein, and cellular localization correlates with apoptotic cell death.

Although the precise mechanisms explaining loss of, and failure to regain, function after spinal cord injury are unknown, there is increasing interest in the role of "secondary cell death." One prevalent theme in cell loss in other regions of the CNS involves apoptosis executed by the intracellular caspase proteases. A recent study demonstrated that spinal cord injury rapidly increased the activation of caspase-3. Our previous studies demonstrated peak apoptosis in three of four cellular compartments 3 days after controlled contusion in the rat. We have extended these analyses to include enzyme and substrate studies of caspase subfamilies both in rostral and in caudal adjacent segments compared to the lesion site. Although presumed activation of programmed proenzyme is considered the mechanism for enhanced caspases, our novel analyses were designed to detect upregulation of gene expression. We surveyed traumatically injured spinal cord for caspase family messages with a modified differential mRNA display approach and found that the caspase-3 (CASP3) message was present and upregulated severalfold after injury. Our results clearly demonstrate that cell death in the spinal cord occurs after posttranslational activation of caspases that follow, at least for caspase-3, initial upregulation of CASP3 mRNA levels.

Animals↗
PubMed1999

Light-dependent suppression of the vestibulo-ocular reflex during development.

In the fish Oreochromis mossambicus, light conditions affect the development of the roll-induced vestibuloocular reflex (rVOR). During development under continous light-dark conditions the rVOR amplitude, which is the maximum eye movement during a complete 360 degrees lateral roll, shows a secondary drop after a first peak at stage 17 by 64% (36.3 degrees at stage 17; 13.0 degrees at stage 20). This drop was shifted by 2 stages to older postembryonal stages and was 33% (29.2 degrees at stage 20; 19.5 degrees at stage 22) less pronounced in animals which were exposed to complete darkness for several days. Because the period of rVOR diminution is sensitive to light conditions, it is likely that outgrowing visual projection fibres reorganize the neuronal network underlying visual-vestibular behavior thus transiently suppressing the rVOR.

Animals↗
PubMed1998

The minimum duration of microgravity experience during space flight which affects the development of the roll induced vestibulo-ocular reflex in an amphibian (Xenopus laevis).

In tadpoles of Xenopus laevis, the effects of microgravity on the development of the roll-induced vestibuloocular reflex (rVOR) was investigated. Special attention was focused on sensitive periods and the minimum duration of microgravity exposure by which the development of the rVOR is affected. The peak-to-peak excursion (rVOR amplitude) of the rVOR characteristic for a lateral 360 degrees roll was used to describe microgravity effects. Fertilization of all eggs was performed 40 h before launch. Tadpoles were exposed to microgravity either during the first (MC-group) or second half of the mission (CM-group), or throughout the 9-day mission (MM-group). Inflight, 1G-gravity was simulated by a centrifuge (CC-group). After termination of the mission, the rVOR amplitude was only reduced in the MM-group with respect to the 1 G-inflight and 1 G-ground control by approximately 20-30% while both the MC- and CM-groups were not affected by the 4-day and 5-day microG exposure, respectively. However, CM-tadpoles like MM-tadpoles showed malformation of their body characterized by a dorsal bended tail. It disappeared in both groups within 2 weeks after landing. The difference between the rVOR amplitudes of the experimental groups disappeared within 5 weeks after landing. The results demonstrate that microgravity retards the development of the rVOR if it lasted longer than 4 days but that tadpoles are susceptible even for shorter periods as shown by the malformation of the body.

Animals↗
PubMed1998

Large pulmonary vein varix diagnosed by transesophageal echocardiography: an unusual site for thrombus in atrial fibrillation.

An elderly man with pulmonary vein varix and atrial fibrillation is described. The diagnosis of pulmonary varix, a localized dilatation of pulmonary vein, was made by transesophageal echocardiography. The patient had chronic atrial fibrillation, and transesophageal echocardiography demonstrated thrombus in the pulmonary varix. In patients with atrial fibrillation, pulmonary varix may be an unusual site for thrombus formation.

Aged↗
PubMed1998

Severe symptomatic sinus bradycardia associated with mesalamine use.

A 29-yr-old white woman was hospitalized with bloody diarrhea secondary to ulcerative colitis. Within 24 h of receiving intravenous steroids, loperamide, and mesalamine, she developed symptomatic hypotension, severe sinus bradycardia, sinus pauses, and junctional escape beats. The hypotension and sinus bradycardia resolved after discontinuing mesalamine. She had a family history of conduction tissue disease but her exercise ECG and Holter studies were normal. She was rehospitalized 6 wk later with an exacerbation of ulcerative colitis and, within 8 h of receiving mesalamine, developed hypotension and severe sinus bradycardia, which resolved after stopping mesalamine. Thus mesalamine should be used with caution, especially in patients predisposed to cardiac conduction tissue disease.

Adult↗
PubMed1998

Choosing the most appropriate treatment for stable angina. Safety considerations.

The goals of stable angina pectoris treatment are: (i) symptom relief and increase in angina-free walking time; and (ii) reduction of mortality and adverse outcome. Strategies used for plaque stabilisation resulting in a reduction in cardiovascular mortality and morbidity are: smoking cessation; aspirin (acetylsalicylic acid); blood pressure control; lipid lowering agents when low density lipoprotein cholesterol is elevated despite dietary therapy; coronary bypass surgery in patients with left main stem disease or triple vessel coronary disease and diminished left ventricular function; and use of estrogen in postmenopausal women. For symptom relief and to increase angina-free walking time, long acting nitrates, beta-blockers, calcium antagonists and potassium channel openers can be used. Drugs from these 3 classes are all effective when used optimally and choice of initial therapy should consider the presence of concomitant disease and underlying left ventricular function. However, none of the long acting nitrates provide continuous prophylaxis because nitrate tolerance develops during long term therapy. In patients with uncomplicated stable angina, nitrates, beta-blockers and calcium antagonists are all effective. Intermittent nitrate therapy is not associated with tolerance, but headache is a common adverse effect and the patient is unprotected at night and in the early hours of the morning. Concomitant treatment with a beta-blocker may be beneficial if the patient experiences withdrawal or early morning angina. For patients with stable angina and hypertension, therapy with a beta-blocker or a calcium antagonist rather than nitrate is indicated. beta-Blockers are preferred in patients who have had a myocardial infarction, or in those with a history of supraventricular tachyarrhythmias. beta-Blockers may produce excessive slowing of the heart rate, fatigue and bronchospasm in susceptible patients. Calcium antagonists are indicated as initial therapy when beta-blockers are either not tolerated or contraindicated. beta-Blockers and nondihydropyridine calcium antagonists should not be used in patients with sinus bradycardia and those with greater than first degree atrioventricular (AV) block because of the possibility of further slowing of heart rate and/or the development of high grade AV block. When monotherapy with one class is ineffective or associated with adverse effects, the patient should be switched to another class rather than given an additional drug. Optimal monotherapy is often as effective as combination therapy. If maximum monotherapy is only partially effective, a combination therapy which is not additive in terms of adverse effects should be chosen. Triple therapy may be deleterious and no more effective than dual therapy.

Adrenergic beta-Antagonists↗
PubMed1996

A hypergravity related sensitive period during the development of the roll induced vestibuloocular reflex in an amphibian (Xenopus laevis).

In tadpoles of Xenopus laevis, the effects of an exposure to hypergravity on the development of the roll-induced static vestibuloocular reflex (rVOR) were investigated. Special attention was given to the onset of the 9 or 12 days lasting 3 g period during early life. Recordings of rVOR characteristics for complete 360 degrees rolls of the tadpoles started 24 h after the end of the 3 g period. The rVOR peak-to-peak amplitudes from the 3 g samples recorded at the 2nd and 3rd day after termination of the 3 g exposure agreed with that recorded from the 1 g reared tadpoles for the youngest group, but were reduced by 30% in the older tadpoles. During further development under 1 g condition, the rVOR amplitude of tadpoles with 3 g experience did not change if the 3 g exposure started before the first appearance of the rVOR, but increased if it had started thereafter, albeit on a lower level than that of the 1 g reared siblings. The results support the existence of a sensitive period for the rVOR development, and additionally demonstrate that the period during which the rVOR appeared for the first time is an important milestone for the development of adaptive properties of the underlying neuronal network.

Animals↗
PubMed1996

Altered gravitational experience during early periods of life affects the static vestibulo-ocular reflex of tadpoles of the southern clawed toad, Xenopus laevis Daudin.

The effects of altered gravitational forces (AGF) on the development of the static vestibulo-ocular reflex (VOR) were investigated in Xenopus laevis tadpoles exposed to hypergravity (1.4g; 3g) or microgravity conditions (German spacelab mission D-2) for 9-10 days. The effects of light conditions during development were also tested by exposing tadpoles to either complete darkness (DD) or 12:12 h light-dark conditions (LD). The static VOR was induced by lateral roll. The efficacy of the VOR circuit after termination of AGF conditions was described by the peak-to-peak amplitude of the sinusoidal VOR characteristics (i.e. amplitude). The static VOR was first observed at stage 41 for both LD and DD tadpoles. Its further development was retarded in the DD tadpoles compared with the LD tadpoles up to stage 48. Microgravity as well as hypergravity exposure caused a significant (P < 0.05, at least) decrease in the static VOR amplitude during the first week after termination of the AGF period. The decreases were 39.4% in the microgravity group, 16.2% in the 1.4g group and 24.9-42.9% in the 3g group compared with the 1g ground-reared siblings at the same developmental stages. The response deficits usually disappeared but persisted for at least 2 weeks in animals whose development was retarded by hypergravity exposure. It is postulated (i) that gravity exerts an important influence on the normal development of the roll-induced static VOR; (ii) that hypergravity exposure decreases the sensitivity of the gravity-sensitive system so that recordings under 1g conditions cause a weaker static VOR; and (iii) that the vestibulo-spinal pathway possesses a higher degree of plasticity than the vestibulo-ocular pathway.

Adaptation, Physiological↗