Presence of atrial natriuretic factor and cyclic guanosine monophosphate in saliva. Comparison of plasma and salivary concentrations during a head-down tilt

Using a specific and sensitive radio-immunoassay involving separation and extraction procedures, we measured the concentration of saliva and plasma atrial natriuric factor (ANF) and cyclic guanosine monophosphate (cGMP) in men before and during a 10 h head-down tilt at -6 degrees. Saliva values closely correlated with plasma for ANF (r = 0.7-0.95) and for cGMP (r = 0.65-1). During this dynamic test, the mean concentrations of ANF and cGMP were significantly higher after 15 and 45 min, respectively, this increase persisting for 3.5 h. We concluded that the concentration of ANF in saliva may be significantly affected by a marked fluid shift from the lower to the upper half of the body. This is the first time that the presence of ANF and cGMP has been demonstrated in saliva. The great advantage of studying saliva is that it can be obtained non-invasively in athletes or during space flight. This methodology will be used during the Soviet-French space flight (Antares Project) planned for 1992.     

Baboons (Papio papio) spontaneously process the first-order but not second-order configural properties of faces

A two-alternative forced-choice discrimination task was used to assess whether baboons (N=7) spontaneously process qualitative (i.e., first-order) or quantitative (i.e., second-order) variations in the configural arrangement of facial features. Experiment 1 used as test stimuli second-order pictorial faces of humans or baboons in which the mouth and the eyes were rotated upside down relative to the normal face. Baboons readily discriminated two different normal faces but did not discriminate a normal face from its second-order modified version. Experiment 2 used human or baboon faces for which the first-order configural properties had been distorted by reversing the location of the eyes and mouth within the face. Discrimination was prompt with these stimuli. Experiment 3 replicated some of the conditions and the results of experiment 1, thus ruling out possible effects of learning. It is concluded that baboons are more adept at spontaneously processing first- than second-order configural facial properties, similar to what is known in the human developmental literature.     

Cryoelectron Microscopy Structure of Purified γ-Secretase at 12 Å Resolution

γ-Secretase, an integral membrane protein complex, catalyzes the intramembrane cleavage of the β-amyloid precursor protein (APP) during the neuronal production of the amyloid β-peptide. As such, the protease has emerged as a key target for developing agents to treat and prevent Alzheimer's disease. Existing biochemical studies conflict on the oligomeric assembly state of the protease complex, and its detailed structure is not known. Here, we report that purified active human γ-secretase in digitonin has a total molecular mass of ∼ 230 kDa when measured by scanning transmission electron microscopy. This result supports a complex that is monomeric for each of the four component proteins. We further report the three-dimensional structure of the γ-secretase complex at 12 Å resolution as obtained by cryoelectron microscopy and single-particle image reconstruction. The structure reveals several domains on the extracellular side, three solvent-accessible low-density cavities, and a potential substrate-binding surface groove in the transmembrane region of the complex.     

Complex functions of the brain

Over the course of the last 50 years it has been possible to solve a number of basic problems in neurobiology. Interest is now turning more and more to problems concerning so-called “higherρ brain functions, including cognition. Examples from the visual system in primates are presented. First relatively elementary problems are illustrated, such as how long it takes to perceive an object or to respond to a stimulus or combinations of stimuli. Top-down modification of perception by expectation is demonstrated in an illusion of misdirected gaze. Interdisciplinary questions straddling the sciences and the humanities are also approached, such as which part of the brain mediates conscious perception. Finally, the problem of causality and freedom of will is addressed, taking into account the knowledge accumulated in the neurosciences during the last 5 decades.     

Synergistic transmembrane insertion of the heterodimeric PGLa/magainin 2 complex studied by solid-state NMR

The skin secretions of amphibians are a rich source of antimicrobial peptides. The two antimicrobial peptides PGLa and magainin 2, isolated from the African frog Xenopus laevis, have been shown to act synergistically by permeabilizing the membranes of microorganisms. In this report, the literature on PGLa is extensively reviewed, with special focus on its synergistically enhanced activity in the presence of magainin 2. Our recent solid state ²H NMR studies of the orientation of PGLa in lipid membranes alone and in the presence of magainin 2 are described in detail, and some new data from 3,3,3-²H₃-L-alanine labeled PGLa are included in the analysis.     

Lower limb postures resembling sitting and standing alter lumbar angles along the passive stiffness curve

In vivo lumbar passive stiffness is often used to assess time-dependent changes in lumbar tissues and to define the neutral zone. We tested the hypothesis that flexing the hips would alter tension in hip and spine musculature, leading to a more extended passive stiffness curve (i.e., right-shifted), without changes in lumbar stiffness. Twenty participants underwent side-lying passive testing with the lower limbs positioned in Stand, Kneel, and Sit representative postures. Moment-angle curves were constructed from the lumbar angles and the moment at L4/5 and partitioned into three zones. Partially supporting our hypothesis, lumbar stiffness within the low and transition stiffness zones was similar between the Stand and Sit. Contrary to our hypothesis, lumbar angles were significantly larger in the Sit compared to the Stand and Kneel postures at the first and second breakpoints, with average differences of 9.3° or 27.2% of passive range of motion (%PassRoM) in flexion and 5.6° or 16.6 %PassRoM in extension. Increased flexion in the Sit may be linked to increased posterior pelvic tilt and associated lower lumbar vertebrae flexion. Investigators must ensure consistent pelvis and hip positioning when measuring lumbar stiffness. Additionally, the adaptability of the neutral zone to pelvis posture, particularly between standing and sitting, should be considered in ergonomic applications.     

错觉图形组成成分间的亮度对比和颜色对比对错觉程度的影响

用定量的心理物理测量方法,研究了错觉图形组成成分间的亮度对比和颜色对比方位错觉、长度觉及面积错觉幅度的影响。测试结果表明：与通常的错觉效应相比,当错觉图形组成成分间存在亮度对比或颜色对比（等亮度）时,受试者的错觉程度明显降低;其中,当存在颜色对比时,方位错觉的下降幅度更为显著,达到６９．３％。此外还观察到,在单纯亮度对比条件下,只需１．８％和５．３％的低对比度即可分别产生轮廓和边缘错觉;但在等亮度     

Structure of human complement C8, a precursor to membrane attack

Complement component C8 plays a pivotal role in the formation of the membrane attack complex (MAC), an important antibacterial immune effector. C8 initiates membrane penetration and coordinates MAC pore formation. High-resolution structures of C8 subunits have provided some insight into the function of the C8 heterotrimer; however, there is no structural information describing how the intersubunit organization facilitates MAC assembly. We have determined the structure of C8 by electron microscopy and fitted the C8α-MACPF (membrane attack complex/perforin)-C8γ co-crystal structure and a homology model for C8β-MACPF into the density. Here, we demonstrate that both the C8γ protrusion and the C8α-MACPF region that inserts into the membrane upon activation are accessible.