Swelling,Elasticity and Spatial Inhomogeneity of Poly(N,N‐dimethylacrylamide) Hydrogels Formed at Various Polymer Concentrations

Summary: The equilibrium swelling degree, modulus of elasticity and the spatial inhomogeneity of poly(N,N‐dimethylacrylamide) (PDMAAm) hydrogels were investigated over the entire range of the initial monomer concentration. The degree of dilution of the networks after their preparation was denoted by ν, the volume fraction of crosslinked polymer after the gel preparation. The linear swelling ratio of the gels increased linearly with increasing ν. Depending on the value of ν, three different gel regimes were observed: (1) For ν < 0.3, increasing ν decreases the extent of cyclization during crosslinking so that the effective crosslink density of gels increases with rising ν. (2) For 0.3 < ν < 0.7, increasing ν reduces the accessibility of the pendant vinyl groups during crosslinking due to steric hindrance at high polymer concentrations. As a result, the effective crosslink density of gels decreases with increasing ν. (3) For ν > 0.7, the modulus of elasticity increases sharply with increasing ν due to the increasing extent of chain entanglements in this high concentration regime. Static light scattering measurements on the gels show that the degree of spatial gel inhomogeneity in PDMAAm gels attains a maximum value at ν = 0.06. The appearance of a maximum as well as the ν‐dependence of scattered light intensities from gels was successfully reproduced by the theory proposed by Panyukov and Rabin.

Effective crosslink density ν_e of the hydrogels shown as a function of ν.     

Fibre-type specific expression of fast and slow essential myosin light chain mRNAs in trained human skeletal muscles

The fibre-type specific expression patterns of fast and slow isoforms of essential (alkali) myosin light chains (ELC) was analysed in trained, untrained and pathological human muscles. Biopsies from m. vastus lateralis of moderately trained and untrained persons, as well as highly trained endurance and strength athletes were analysed, by in situ hybridization, for the expression of the `fast' ELC 1f/3f and the `slow' ELC 1sb. We wanted to investigate if changes in the fibre-type specific ELC mRNA pattern could be used as markers for training adaptation, especially, if the mRNA of the slow ELC 1sb isoform would appear in type IIA fibres as a result of endurance training (Baumann et al. 1987). We found the fast/slow ELC expression patterns in the fibre types to be remarkably stable. Physiological stress, even high training loads, did not affect it. No IIA fibres expressing ELC 1sb mRNA were found. They could be detected, however, in pathological muscle samples, where fast/slow ELC patterns not found in normal muscles were frequent. Our data suggest that in healthy muscles, only a subset of the theoretically possible combinations of myosin heavy and light chain isoforms are expressed at the level of their mRNAs.     

Cardiac stimulus intensity and heartbeat detection: Effects of tilt-induced changes in stroke volume

The effects of variations in stroke volume on the intensity of cardiac stimuli was examined in a series of three experiments that empolyed classical psychophsical methods to assess heartbeat detection. Stroke volume was manipulated by passive body tilt and recorded using impedance cardiography while subjects performed heartbeat detection tasks. The postural manipulation generated little or no change in contractility or momentum but did produce substantial changes in stroke volume. However, this potential source of variation in cardiac stimulus magnitude did not influence either the precision of heartbeat detection or the temporal location of heartbeat sensations. It is concluded that the intensity dimension of the heartbeat stimulus is not determined by stroke volume.     

Preferential VH/V lambda pairings occur in the available B cell repertoire of adult BALB/c mice.

To gain insights into the composition of the B cell repertoire, we have investigated VH gene family expression associated with individual light chains. For this purpose, we have examined the use of 12 VH gene families in a large collection of hybridomas expressing one of the four lambda light chains [lambda 1 (V1J1), lambda 2 (V2J2 and V x J2) and lambda 3 (V1J3)]. Our results show that the distribution of the VH families is very different from one lambda subtype to another. This suggests that a few substitutions between VL regions are sufficient to generate very different associated repertoires by strong selection mechanisms. Moreover, we assume that the global VH expression pattern is not random but rather composed of many preferential VH/VL associations.     

一种测量红细胞聚集的新方法

根据红细胞聚集时,可减少血样光散射表面的数目和光通过血样透射强度增加的原理,设计了一种新型的双圆筒式的红细胞聚集仪。该仪器具有测量速度快、测量精度高和重复性好等优点。它的产生,将为实验室和临床进行红细胞聚集的研究及检测,提供方便和可靠的测量。     

Effect of the phenol antioxidant katavidan on autooxidation of microsomes exposed to visible light

A study is performed of the effect of the phenol antioxidant katavidan on autooxidation of microsomes from rat liver exposed to visible light. It is shown that katavidan in a concentration of 10⁻³ M inhibits but in concentrations of 10⁻⁵–10⁻⁷ M stimulates autooxidation of microsomes. No stimulation is observed under conditions of dark incubation. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny, Vol. 118, № 10, pp. 393–394, October, 1994 Presented by I. P. Ashmarin, Member of the Russian Academy of Medical Sciences     

Sensitivity to mechanical stimuli and the role of general sensory and perceptual processes in heartbeat detection

Sensitivity to heartbeat sensations is commonly assessed using tasks that require individuals to judge the simultaneity of heartbeats and tones. In two experiments, we investigated the suitability of this paradigm for examining cardioception. In the first experiment, participants judged the simultaneity of near–threshold vibrations and suprathreshold tones. Precision in judging vibration–tone simultaneity was directly related to the detectability of the mechanical stimuli, thereby supporting use of the simultaneity paradigm to assess heartbeat detection. In the second experiment, we examined the influences of sensitivity to mechanical stimuli and the ability to make intermodality simultaneity judgments on the precision of heartbeat detection. We measured participants' vibrotactile thresholds, precision in judging light–tone simultaneity, and precision in judging heartbeat–tone simultaneity. The ability to judge the simultaneity of lights and tones accounted for 24.3% of the variance in precision of heartbeat detection, and mechanical sensitivity accounted for a further 8.5%.     

Morphological characterization of different human cervical mucus types using light and scanning electron microscopy

BACKGROUND: This study was conducted on human cervical mucus using light microscopy (LM) and scanning electron microscopy (SEM). The objective was the morphological characterization of the different mucus types, with samples taken from the lumen of the cervix and from the different secretory zones of the cervical mucosa. METHODS: A total of 230 samples from 195 women were spread out on slides and air dried. The phenomenon of 'ferning' was observed and assessed in these samples using both LM and SEM. Further samples from the lumen of the cervix and the different secretory crypts were spread out on cover slips and fixed with glutaraldehyde (2.5%) to be studied by SEM. RESULTS: The results show the presence of four different morphological mucus types, namely L, S, P and G, in both types of sample using dried and fixed techniques. CONCLUSIONS: Mucus from the lumen of the cervix appears to be a morphologically heterogeneous entity. It contains different types of secretions, the proportions of which vary throughout the menstrual cycle. The different mucosal types show different types of crystallization, different patterns of ultrastructure (probably related to the arrangement of the glycoprotein network) and are produced in different secretory zones of the crypts in the cervix.     

Processing of binaural stimuli by cat superior olivary complex neurons

Summary A method was developed to record stereotactically from the cat Superior Olivary Complex (SOC) using glass micropipettes. Sound stimulation was given through a closed system that permitted independent variation of interaural time (time) and intensity (int) differences. The most common binaural units found (n = 34) were ipsilateral excitatory, contralateral inhibitory (EI¹), cells of the Lateral Superior Olive (LSO). Some Medial Superior Olive (MSO) cells and presumed MSO ascending afferents were found but, as noted by other authors, we found it difficult to obtain single unit recordings from this nucleus. The LSO EI cells were mostly sensitive to higher frequencies and showed Peristimulus Time Histograms (PSTHs) consisting of a sharp On response followed by a plateau when stimulated with Best Frequency (BF) tone bursts or noise bursts. This On response was sensitive to time and int such that ipsilateral time lead or intensity increase resulted in a stronger response. The response reached a minimum around zero time or int. No sharp peaks or dips were seen in the physiological range needed for localization, instead the response increased with increasing ipsilateral lead or intensity to the maximum values tested (2048 s time, 30 dB int). In the physiological range the time and int response were complementary (both increasing response as ipsilaterality was increased). Provided enough sound energy in the unit's sensitive region was present, the same time curves were produced when BF tone bursts, masked tone bursts, sharp onset tone bursts or noise bursts were used. Changing the time of the carrier of the tone burst alone had no effect (except for one cell with a BF of 560 Hz), only the relative time of arrival of the stimulus envelope seemed to be important. In contrast to these LSO EI cells MSO-type units showed EI or EE predominantly low frequency phase-locked responses. When stimulated with interaurally phase shifted (pha) BF tones the unit response was a cyclic function of pha. Some cells (all that were tested, n = 6 including the 560 Hz LSO EI cell) showed these cyclic responses when stimulated with noise bursts or non-BF tones. However, these characteristic delays were not necessarily in the physiological range, i.e. we could find no evidence that these units were responding to time/pha values corresponding to a particular sound source direction. In both LSO and MSO it seems that integration of information higher in the CNS from a population of these cells is necessary for unambiguous coding of sound source direction. The time intensity trading ratios measured in two MSO type cells (11 and 26 /dB) were clearly different to those measured in LSO EI cells (n = 6, 99–550 s/dB). These ratios correspond approximately to those of the psychophysical time and int images measured by Hafter and Jeffress (1968).Supported by the Deutsche Forschungsgemeinschaft (SFB 45)     

Direct infant UV light exposure is associated with eczema and immune development

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