La nutrition en conditions extrêmes

Nutritional reference intakes are build to cover the nutritional needs of the majority of the “normal“ population in a “normal“ environment. Much work is needed to define references for extreme situations. Beside extreme situations such as pathology, under or over nutrition, the study of other extreme conditions could lead to useful insights in pathophysiological mechanisms. Man adaptation to cold temperatures, altitude or spatial flights leads to the development of experimental models, the utility of which goes far beyond the studied conditions: the regulation of appetite and of the metabolisms of proteins, carbohydrates or calcium provides interesting examples.     

Analysis of saccadic short-term plasticity in three dimensions

The capacity for short-term adaptation is a well-established property of the horizontal (H) and vertical (V) components of saccades. It allows these directional components, which clearly serve the goal of foveation, to maintain their precision even under changing circumstances. Torsional (T) saccade components, on the other hand, which deal with the orientation of the target on the fovea, have hardly been investigated in adaptation experiments. They appear to be severely restricted by Listing's law during fixations and saccades. The main purpose of Listing's law is far from obvious but could be visual or oculomotor. Better knowledge of the adaptive capacity of the saccadic system in the torsional direction could throw new light on the functional significance of this interesting neural strategy. To study short-term plasticity in the torsional components of saccades, binocular 3D-eye positions were measured, using magnetic search foils. Five normal human subjects were instructed to make uni-directional refixation saccades, while they viewed a large visual scene. To induce a change in the torsional component, the complete stimulus was rapidly rotated during these saccades. We thoroughly investigated the torsional responses of the saccadic system, to see if any short-term adaptive response in torsional direction was induced, in which case the notion of a visual purpose for Listing's law would be strengthened. In none of our experiments, however, did we find any clear adaptive response in torsional direction. To further investigate the reliability of this result and to ascertain that our experimental conditions allowed classical gain adaptation, we also did experiments designed to achieve a combination of torsional adaptation and classic gain shortening in one of the directional components. While gain adaptation was very obvious, none of the experiments provided evidence for a short-term effect in torsion. We conclude that our experiments do not support a purely visual basis for Listing's law.     

高中生自我和谐与应对方式及其相互关系

目的了解高中生自我和谐、应对方式的特征及其相互关系,为开展心理健康教育提供依据。方法采用自我和谐量表及简易应对方式问卷,对755名高中生进行问卷调查。结果高中生总分和各因子分在性别、是否独生子女、城乡、文理科等方面差异均无统计学意义,自我和谐总分存在年级差异;积极应对和消极应对维度在性别、是否独生子女、城乡、文理科等方面差异均无统计学意义,消极应对维度存在年级差异。应对方式与自我和谐总分及分量表得分存在不同程度的相关。结论采用积极应对方式有助于促进高中生的自我和谐,而消极应对方式对自我和谐存在不利影响。     

À propos de la psychiatrie de liaison en cancérologie

The psychiatrists practice in consultation-liaison psychiatry is peculiar. The work requires him/her to adapt to the terrain: to seize the opportunity of intervening in one way or another he will be obliged simultaneously to abandon his dual position with the patient, to integrate into the medical team and, also, to take into account the physiological specificity of the illness and its psycho-social repercussions. Whether on a formal or informal register all is subtle and delicate in these liaison interventions. Cancer and cancerology even add their own specificity and constraints to this mode of exercise. Consultation-liaison remains, more particularly in cancerology, a practice of mediation and of conciliation confronted to the problematics of risk, of incertitude and of finiteness.     

Renal brush border sodium-sulfate cotransport in guinea pig: effect of age and diet

  Renal adaptation to changes in inorganic sulfate intake and age was studied by comparing sulfate uptake by proximal tubule brush border membrane vesicles (BBMV) from guinea pigs of different ages on relatively high- or low-sulfate diets. Adult (>60 days) or young guinea pigs (<25 days) were fed either a control diet (0.28% sulfur content), a sulfur-free diet, or a high-sulfate diet. After 5 days on the diet, BBMV were obtained and kinetic analysis of ³⁵sulfate uptake was determined. In adult guinea pigs, the low-sulfate diet produced a significant increase in apparent maximal velocity (V _max). In young guinea pigs, a lower sulfate intake did not appreciably increase V _max, but a high-sulfate intake produced a reduction in V _max. The affinity for sulfate (K _m) was not changed in either age group. The dietary sulfate intake did not alter sodium gradient dependent-D-glucose or ³²phosphate V _max. In conclusion, our data indicate that renal inorganic sulfate BBMV uptake is regulated and responds to conditions of increased need (i.e., during the growth phase in young animals and during periods of decreased sulfate availability in adult animals) by increasing BBMV V _max. Received September 9, 1994; received in revised form March 18, 1997; accepted March 20, 1997     

牙体修复材料体外充填密合度的扫描电镜研究

用扫描电镜直接观察及硅橡胶一环氧树脂扫描电镜复型技术观察银汞合金、ＥＢ复合树脂、玻璃离子粘固粉体外充填与釉质、牙骨／本质壁的边缘密合度。结果表明，与牙体组织呈化学性结合的玻璃离子粘固粉与釉质、牙骨／本质壁的密合度好，两壁之间无差别；ＥＢ复合树脂与釉质壁的边缘密合度与玻璃离子粘固粉相似，其缝隙明显小于牙骨／本质壁；银汞合金与釉质壁、牙骨／本质壁的边缘密合度差，且两壁之间无明显差别。     

Simulation of space adaptation syndrome on earth

Summary The three Spacelab D-1 Scientist Astronauts were exposed to a 11/2 h 3 g centrifuge run in the supine position, resulting in a linear 3 g acceleration in the x-direction. They used their space experience to evaluate their readapting to normal gravity and compared their observations with Space Adaptation Syndrome. After the centrifuge runs, the vestibular visual system appeared to be modified in a very specific and reproducible manner. Readapting to the normal 1 g environment took at least 6 h. During this period there was a striking similarity to the astronaut's experience during adaptation to weightlessness in space. A series of vestibular tests were then performed, confirming these subjective findings.     

Habituation and adaptation of the vestibuloocular reflex: a model of differential control by the vestibulocerebellum

Summary We habituated the dominant time constant of the horizontal vestibuloocular reflex (VOR) of rhesus and cynomolgus monkeys by repeated testing with steps of velocity about a vertical axis and adapted the gain of the VOR by altering visual input with magnifying and reducing lenses. After baseline values were established, the nodulus and ventral uvula of the vestibulocerebellum were ablated in two monkeys, and the effects of nodulouvulectomy and flocculectomy on VOR gain adaptation and habituation were compared. The VOR time constant decreased with repeated testing, rapidly at first and more slowly thereafter. The gain of the VOR was unaffected. Massed trials were more effective than distributed trials in producing habituation. Regardless of the schedule of testing, the VOR time constant never fell below the time constant of the semicircular canals (5 s). This finding indicates that only the slow component of the vestibular response, the component produced by velocity storage, was habituated. In agreement with this, the time constant of optokinetic after-nystagmus (OKAN) was habituated concurrently with the VOR. Average values for VOR habituation were obtained on a per session basis for six animals. The VOR gain was adapted by natural head movements in partially habituated monkeys while they wore ×2.2 magnifying or ×0.5 reducing lenses. Adaptation occurred rapidly and reached about ±30%, similar to values obtained using forced rotation. VOR gain adaptation did not cause additional habituation of the time constant. When the VOR gain was reduced in animals with a long VOR time constant, there were overshoots in eye velocity that peaked at about 6–8 s after the onset or end of constant-velocity rotation. These overshoots occurred at times when the velocity storage integrator would have been maximally activated by semicircular canal input. Since the activity generated in the canals is not altered by visual adaptation, this finding indicates that the gain element that controls rapid changes in eye velocity in the VOR is separate from that which couples afferent input to velocity storage. Nodulouvulectomy caused a prompt and permanent loss of habituation, returning VOR time constants to initial values. VOR gain adaptation, which is lost after flocculectomy, was unaffected by nodulouvulectomy. Flocculectomy did not alter habituation of the VOR or of OKAN. Using a simplified model of the VOR, the decrease in the duration of vestibular nystagmus due to habituation was related to a decrement in the dominant time constant of the velocity storage integrator (1/h ₀). Nodulouvulectomy, which reversed habituation, would be effected by decreasing h ₀, thereby increasing the VOR time constant. Small values of h ₀ would cause velocity storage to approach an ideal integrative process, leading the system to become unstable. By controlling the VOR time constant through habituation, the nodulus and uvula can stabilize the slow component of the VOR. VOR gain adaptation was related to a modification of the direct vestibular path gain g ₁, without altering the coupling to velocity storage g ₀ or its time constant (1/h ₀). The mismatched direct- and indirect-pathway gains simulated the overshoots in the dynamic response to a step in velocity, that were observed experimentally. We conclude that independent distributed elements in the VOR modify its dynamic response, under control of separate parts of the vestibulocerebellum.     

Adaptive modification of the vestibulo-ocular reflex by mental effort in darkness

Summary The vestibulo-ocular reflex (VOR) can be suppressed in darkness if a subject tries to imagine that he looks at a head fixed target. This mental suppression of VOR was used to induce adaptive changes in VOR gam during 3 h of active head oscillations in complete darkness. VOR gain changes were tested by asking the subject to look at a visual target; then passively or actively the head was turned in darkness while the subject fixated the same target. Corrective saccades occurring at the end of the movement when lights were turned on give an elegant measure of VOR gain. Three hours of training induced in 3 subjects a mean of 10.9% and 11.4% decrease of VOR gain for passive and active conditions, respectively. This demonstrates that reflex adaptation can be obtained without external cues, and probably with only an internal reconstruction of target and eye movement.     

Dependence of adaptation of the human vertical angular vestibulo-ocular reflex on gravity

We determined the spatial dependence of adaptive gain changes of the vertical angular vestibulo-ocular reflex (aVOR) on gravity in five human subjects. The gain was decreased for 1 h by sinusoidal oscillation in pitch about a spatial vertical axis in a subject-stationary surround with the head oriented left-side down. Gains were tested by sinusoidal oscillation about a spatial vertical axis while subjects were tilted in 15° increments from left- to right-side down positions through the upright. Changes in gain of the vertical component of the induced eye movements were expressed as a percentage of the preadapted values for the final analysis. Vertical aVOR gain changes were maximal in the position in which the gain had been adapted and declined progressively as subjects were moved from this position. Gain changes were plotted as a function of head orientation and fit with a sine function. The bias level of the fitted sines, i.e., the gravity-independent gain change, was –29±10% (SD). The gains varied around this bias as a function of head position by ±18±6%, which were the gravity-dependent gain changes. The gravity-dependent gain changes induced by only 1 h of adaptation persisted, gradually declining over several days. We conclude that there is a component of the vertical aVOR gain change in humans that is dependent on the head orientation in which the gain was adapted, and that this dependence can persist for substantial periods.