Effect of one night of sleep loss on changes in tumor necrosis factor alpha (TNF-α) levels in healthy men

Total sleep deprivation in humans is associated with increased daytime sleepiness, decreased performance, elevations in inflammatory cytokines, and hormonal/metabolic disturbances. To assess the effects of 40 h of total sleep deprivation (TSD) under constant and well controlled conditions, on plasma levels of TNF-α and its receptor (TNFR1), interleukin-6 (IL-6), cortisol and C-reactive protein (CRP), sleepiness and performance, 12 healthy men (29±3 years) participated in a 5-days sleep deprivation experiment (two control nights followed by a night of sleep loss and one recovery night). Between 0800 and 2300 (i.e. between 25 and 40 h of sleep deprivation), a serial of blood sampling, multiple sleep latency, subjective levels of sleepiness and reaction time tests were completed before (day 2: D2) and after (day 4: D4) one night of sleep loss. We showed that an acute sleep deprivation (i.e. after 34 and 37 h of sleep deprivation) induced a significant increase in TNF-α (P<0.01), but there were no significant changes in TNFR1, IL-6, cortisol and CRP. In conclusion, our study in which constant and controlled experimental conditions were realized with healthy subjects and in absence of psychological or physical stressors, an acute total sleep deprivation (from 34 h) was sufficient to induce secretion of pro-inflammatory cytokine such as TNF-α, a marker more described in chronic sleep restriction or deprivation and as mediators of excessive sleepiness in humans in pathological conditions.

A practical synthesis of (+)-discodermolide and analogues: fragment union by complex aldol reactions

A practical stereocontrolled synthesis of (+)-discodermolide (1) has been completed in 10.3% overall yield (23 steps longest linear sequence). The absolute stereochemistry of the C(1)-C(6) (7), C(9)-C(16) (8), and C(17)-C(24) (9) subunits was established via substrate-controlled, boron-mediated, aldol reactions of the chiral ethyl ketones 10, 11, and 12. Key fragment coupling reactions were a lithium-mediated, anti-selective, aldol reaction of aryl ester 8 (under Felkin-Anh induction from the aldehyde component 9), followed by in situ reduction to produce the 1,3-diol 40, and a (+)-diisopinocampheylboron chloride-mediated aldol reaction of methyl ketone 7 (overturning the inherent substrate induction from the aldehyde component 52) to give the (7S)-adduct 58. The flexibility of our overall strategy is illustrated by the synthesis of a number of diastereomers and structural analogues of discodermolide, which should serve as valuable probes for structure-activity studies.

[Cerebral cortical blood flow during parabolic maneuvers]

Cerebral cortical blood flow (CBF) was measured in 6 rabbits during parabolic flight maneuvers (20 s of weightlessness). During the first seconds of weightlessness, CBF increased up to 100% when compared with CBF at 1 G. Since this transient increase (5 s) was not modified when propranolol or pentobarbital was given to the animals, one can hypothesize that it was not related to stress.

Cerebral cortical blood flow during loss of consciousness induced by gravitational stress in rhesus monkeys

We investigated the influence of +Gz acceleration (head-to-foot inertial forces) onset on cerebral cortical blood flow (CBF) of rhesus monkeys to study the mechanisms underlying +Gz-induced loss of consciousness (G-LOC). CBF was measured through a chronic cranial window by laser-Doppler flowmetry and electrodes in contact with the dura mater were used to detect G-LOC (suppression of the cortical electrical activity). The animals were centrifuged up to +12 Gz with different G-onset rate until G-LOC occurred. G-LOC was preceded by a 2-5 s decrease in CBF. At G-LOC detection, CBF was not related to G-onset rate (mean CBF change: -76 +/- 9% of control value). We conclude that G-LOC results from cerebral ischemia rather than from mechanical stresses applied to the brain.

Effect of modafinil on cerebral blood flow of anaesthetised rats. Comparison with amphetamine

This experiment compares the cardio- and cerebrovascular effects of modafinil and amphetamine administered to rats. Injections of 300 mg/kg and 600 mg/kg modafinil i.p. had no major effect. In contrast, injection of D-amphetamine sulfate (5 mg/kg i.v.) induced a long-lasting rise in heart rate and in mean arterial blood pressure (MABP). Amphetamine administration also elicited a 70-min-long increase in cortical cerebral blood flow which was proportional to the increase in MABP. We conclude that, contrary to amphetamine, modafinil has no effect on perfusion in the cerebral cortex of anaesthetised rats.

Is the acetazolamide test valid for quantitative assessment of maximal cerebral autoregulatory vasodilation? An experimental study

BACKGROUND AND PURPOSE

The cerebral vasodilating effect of acetazolamide (ACZ) injection has been used as an index of the autoregulatory vasodilation (or cerebral perfusion reserve). The question of whether the ACZ test assesses the maximal autoregulatory vasodilating capacity is not definitely resolved. The effects of ACZ injection on this reserve at a dose producing maximal vasodilation have never been evaluated and may help to resolve this problem.

METHODS

The effect of ACZ injection on cerebral blood flow (CBF) autoregulation was tested in anesthetized rats. A pilot experiment evaluated the dose-effect relationship of injected ACZ, cumulative doses (n=4, group 1), and independent bolus doses (n=6, group 2). CBF was estimated by laser-Doppler flowmetry, and cerebrovascular resistance (CVR) was calculated from mean arterial blood pressure (MABP) and from CBF (expressed as a percentage of baseline CBF). A bolus of ACZ of 21 mg/kg produced the maximal cerebral vasodilation that could be obtained by ACZ administration. In the main experiment, MABP was lowered from 110 to 20 mm Hg by stepwise bleeding in 3 groups of 6 animals treated 10 minutes before bleeding by injection of saline (group 3), 7 mg/kg ACZ (group 4), or 21 mg/kg ACZ (group 5).

RESULTS

The CVR-MABP relationship was linear in all groups, indicating that CBF autoregulation was still effective after ACZ administration.

CONCLUSIONS

These results indicate that maximal ACZ-induced cerebral vasodilation is not quantitatively equivalent to maximal autoregulatory vasodilating capacity in anesthetized rats.

Total Synthesis of the Antimicrotubule Agent (+)-Discodermolide Using Boron-Mediated Aldol Reactions of Chiral Ketones

With a similar mechanism of action to taxol, the title compound 1 is a particularly promising candidate for development in cancer chemotherapy. This efficient synthesis, based on stereocontrolled aldol reactions, should help to overcome the scarce natural supply of 1 from the rare sponge source.

[Effect of biflow-induced ventilation (BIFIV) on cerebral cortical blood flow in anesthesized rabbits with intracranial hypertension]

This study compared the effect of biflow-induced ventilation (BIFIV) and conventional mechanical ventilation (CMV) on cerebral cortical blood flow (CBF) of six anaesthetized rabbits with an intracranial pressure (ICP) at 45 mmHg. BIFIV did not improve CBF during increased ICP when compared to CMV.

Cerebral cortical blood flow in rabbits during parabolic flights (hypergravity and microgravity)

We studied the effect of gravity on cerebral cortical blood flow (CBF), mean arterial blood pressure (BPa) and heart rate in six rabbits exposed to parabolic flights. The CBF was obtained using a laser-Doppler probe fixed on to a cranial window. Before weightlessness, the animals were exposed to chest-to-back directed acceleration (1.8-2.0 g). The CBF values were expressed as a percentage of CBFo (mean CBF during 60 s before the 1st parabola). Propranolol (1 mg x kg[-1] i.v.) was given after the 11th parabola and pentobarbital (12-15 mg x kg[-1] i.v.) after the 16th parabola. Before the administration of the drugs, CBF increased (P < 0.01) during hypergravity [i.e. maximal CBF 151 (SD 64)% CBFo. Simultaneously BPa increased [maximal BPa, 119 (SD 11) mmHg (P < 0.01)]. At the onset of weightlessness, CBF and BPa reached maximal values [194 (SD 96)% CBFo (P < 0.01) and 127 (SD 19) mmHg, (P < 0.01) respectively]. The microgravity-induced increase in CBF was transient since CBF returned to its baseline value after 8 (SD 2) s of microgravity. After propranolol administration, CBF was not statistically different during hypergravity but an elevation of CBF was still observed in weightlessness. The increases in CBF and BPa also persisted during weightlessness after pentobarbital administration. These data would indicate that CBF of nonanesthetized rabbits increases during the first seconds of weightlessness and demonstrate the involvement of rapid active regulatory mechanisms since CBF returned to control values within 8 (SD 2) s. We concluded that this elevation in blood flow was not related to stress because it persisted after the administration of propranolol and pentobarbital.

Hormonal response to restraint in rhesus monkeys

The purpose of this study was to characterize the hormonal responses to a restraining system in four adult male rhesus monkeys (Macaca mulatta) in preparation for a spaceflight project. After the monkeys were accustomed to food and water (Phase I), blood-volume-regulating hormones were measured during three phases: 10 days in a metabolic cage (Phase II), 16 days sitting in a restrained position in a specially designed metabolism chair (Phase III) and 10 days in metabolic cage (Phase IV). An increase of active renin (30%) and vasopressin (25%) was observed at the end of Phase III. A decrease of atrial natriuretic peptide (ANP), urodilatin, and sodium excretion occurred during the first days of Phase III. Catecholamines were unchanged. A dramatic increase (tenfold) in urinary excretion of growth hormone occurred during all of Phase III and at the beginning of Phase IV. These findings are similar to those found in man during isolation inactivity and during confinement stress.

A restraining system for rhesus monkeys used in space research

A new chronic restraining system has been designed specifically for male rhesus monkeys (8-13 kg) housed in weightlessness for scientific purposes. The restraining system consists of a coat (jacket and skirt) and a chair. The system separates the thorax from the lower part of the body, and allows large movements of the upper part of the body. The macaque can feed and groom itself, and can also sleep in close-to-normal position.

Cortical blood flow and +Gz acceleration in conscious rabbits

We examined whether superficial cortical blood flow (CBF) of nonanesthetized rabbits (n = 11) is affected by gravitational (G) stress. Blood flow was measured by laser-Doppler flowmetry through a chronic Plexiglas window implanted over the parietal cortex. Mean arterial blood pressure (MABP) was recorded via an aortic catheter with the pressure transducer situated at the level of the head. The electrocorticogram (ECoG) was also studied in seven rabbits. The animals were exposed to tail-to-head acceleration [6, 10, 15, and 20 G acceleration (Gz) for 1 min]. MABP fell with increasing acceleration (regression line equation: MABP = -7.0 Gz + 129.1; P < 0.001, r = 0.85), whereas CBF was statistically either not different from or greater than control. In one rabbit exposed to 20 Gz, high voltage and slow waves were observed on the ECoG and these changes were preceded by a decrease in CBF to 66% of control. We conclude that the stress and the siphon effect may account for the maintenance of elevated CBF despite low or negative MABP until the occurrence of vascular collapse that induces loss of consciousness.

Spreading depression reversibly impairs autoregulation of cortical blood flow

The experiment examines whether the mechanisms responsible for the autoregulation of cerebral blood flow (CBF) in response to hypotension were affected during the initial phase of cortical spreading depression (CSD). CSD was induced by a cortical pinprick in anesthetized rabbits, and CBF was measured by laser-Doppler flowmetry through a chronically implanted Plexiglas window. The reactivity to CO2 and papaverine was also studied before and after CSD. Fifteen minutes after CSD, autoregulatory vasodilation was reduced (P < 0.01). This impairment was reversible, since the autoregulatory response was restored 35 min after CSD. The time course of the reactivity to papaverine after CSD paralleled the autoregulatory response, with a significant correlation between the two reactivities (r = 0.47; P < 0.01). Conversely, the reactivity to CO2 was significantly reduced after CSD (P < 0.001) and remained affected for at least 95 min. We conclude that the mechanisms underlying autoregulation are transiently disturbed by CSD and that these mechanisms are not mediated by an accumulation of CO2 but seem instead to be related to an increase in adenosine 3',5'-cyclic monophosphate concentration.

Effect of nimodipine on the autoregulation of cerebral blood flow studied by laser-Doppler flowmetry

The present work examines whether nimodipine impairs autoregulation of CBF during hypotension. The CBF of 16 anesthetized rabbits was measured with a laser-Doppler flowmetry probe placed on the external surface of a plexiglas window, chronically inserted in the skull. Autoregulation was triggered by aortic bleeding. First, the effects of three doses of nimodipine (1, 3 and 10 micrograms/kg) and the solvent were studied in 10 rabbits in which MABP was maintained at 50 mmHg for one minute. Second, 10 micrograms/kg i.v. nimodipine was administered to 6 rabbits in which MABP was kept at 30 mmHg for one minute. Before bleeding, the 10 micrograms/kg dose significantly decreased MABP (from 96 +/- 11 mmHg to 81 +/- 11 mmHg, P < 0.01) and increased CBF (from 104 +/- 20% to 147 +/- 25%, P < 0.01) as compared to the solvent. In the first set of experiments, only the 10 micrograms/kg dose suppressed the autoregulatory vasodilation, but CBF was not different from control (84 +/- 17% versus 87 +/- 12%), probably because of the previous induced vasodilation. In the second set of experiments, active vasodilation occurred and the CBF during hypotension was not different from control (72 +/- 26% versus 65 +/- 11%). We conclude that under nimodipine the triggering of the active autoregulatory vasodilation is dependent on both the severity of hypotension and the previous nimodipine-induced vasodilation.

Rapid autoregulation of cerebral blood flow: a laser-Doppler flowmetry study

The mechanisms underlying autoregulation of CBF were studied in 19 rabbits using laser-Doppler flowmetry. A cranial plexiglas window was chronically inserted in the skull with dental cement under general anesthesia. The animals then were reanesthetized 5-7 days later and subjected to aortic bleeding while CBF was measured with the probe placed on the window. In the first set of experiments, MABP was decreased (from 90 to 30 mm Hg) and was maintained constant for 1 min. During the first seconds, CBF followed the steep decrease of MABP. Then, CBF increased and reached a plateau within 3-13 s, depending on the severity of hypotension. Hyperemia occurred when blood was restored, and the CBF recovered from this posthypotensive hyperemia with a rapid phase (within 2 s) and a slow phase (total recovery within 1 min). The lower limit of autoregulation was found to be 40 mm Hg. An increase in CBF due to papaverine showed that vasodilation was not maximal below this limit. In the second set of experiments, the rabbits were subjected to four episodes of hypotension at 40 mm Hg each but of different durations (from 2-3 to 60 s). The posthypotensive hyperemia was not influenced by the duration of hypotension, but the time of the total recovery phase increased with the duration of hypotension. We conclude that there exist rapid adaptive mechanisms leading to autoregulation and that the vasodilation is not dependent upon the duration of hypotension.

Transport aircraft crew and decompression hazards: study of a positive pressure schedule

The protection of the transport aircraft crew against cabin decompression hazards at high altitude (Z less than 45,000 ft) (13,700 m) is achieved by positive pressure breathing (PPB). Currently, many PPB schedules are used. Our research was performed to propose a PPB schedule, using the hypothesis of a decompression at high altitude, including a stay at the flight level and an emergency descent at the rate of 15,000 ft.min-1. The measures were arterial oxygen saturation, heart rate, speech capabilities, and psychomotor performance. The tests were conducted up to 45,000 ft. They show that the best protection at 45,000 ft is afforded when the PPB is included between 2 and 2.5 kPa (15 to 18.75 mm Hg).

[Use of primates in space physiology: a luxury or necessity?]

Microgravity induces a number of disorders in cardiovascular, muscle-skeletal vestibular, immunitary and hematopoietic systems. Considering the limited extent of experiments on man in space, use of animals models, and especially primates seems to be a necessity.