The effects of visual input on open-loop and closed-loop postural control mechanisms

In an earlier posturographic investigation (Collins and De Luca 1993) it was proposed that open-loop and closed-loop control mechanisms are involved in the regulation of undisturbed, upright stance. In this study, stabilogram-diffusion analysis was used to examine how visual input affects the operational characteristics of these control mechanisms. Stabilogram-diffusion analysis leads to the extraction of repeatable center-of-pressure (COP) parameters that can be directly related to the resultant steady-state behavior and functional interaction of the neuromuscular mechanisms underlying the maintenance of erect posture. Twenty-five healthy male subjects (aged 19–30 years) were included in the study. An instrumented force platform was used to measure the time-varying displacements of the COP under each subject's feet during quiet standing. The subjects were tested under eyes-open and eyes-closed conditions. The COP trajectories were analyzed as one-dimensional and two-dimensional random walks, according to stabilogram-diffusion analysis. Using this technique, it was found that visual input affects the performance of the postural control system in one of two different ways — either it significantly modifies the steady-state behavior of the open-loop postural control mechanisms, or it significantly alters the characteristics of the other closed-loop feedback mechanisms that are involved in balance control. This result is interpreted as an indication that the visual system is integrated into the postural control system in one of two different ways. The experimental population was roughly evenly divided between these two schemes. For the first group (13 of 25 subjects), visual input principally caused a decrease in the effective stochastic activity of the open-loop control mechanisms in both the mediolateral and anteroposterior directions. For the second group (12 of 25 subjects), visual input caused an increase in the effective stochastic activity and uncorrelated behavior of the closed-loop control mechanisms in the anteroposterior direction only. On the basis of these results, it is hypothesized that visual input, in both schemes, serves to decrease the stiffness of the musculoskeletal system. In the former case, this may be accomplished by decreasing the level of muscular activity across the joints of the lower limb, whereas, in the latter case, reduced stiffness may be achieved by reducing the gain(s) of the other postural feedback mechanisms, i.e., the proprioceptive and/or vestibular systems. Using stabilogram-diffusion analysis, it was also found that the two groups of subjects behaved similarly under eyes-closed conditions. This result suggests that the open-loop postural control mechanisms and reflex-based feedback systems, respectively, of healthy, young individuals are organized in functionally equivalent ways.     

Independent contributions of the orienting of attention,fixation offset and bilateral stimulation on human saccadic latencies

In a series of experiments we examined the effects of the endogenous orienting of visual attention on human saccade latency. Three separate manipulations were performed: the orienting of visual attention, the prior offset of fixation (gap paradigm) and the bilateral presentation of saccade targets. Each of these manipulations was shown to make an independent contribution to saccade latency. In experiments 1 and 2 subjects were instructed to orient their attention covertly to a location by a verbal pre-cue; targets could appear in the attended hemifield (valid) or in the non-attended hemifield (invalid) together with a no-instruction (neutral) condition. Saccades were made under fixation gap and overlap conditions, to either single targets or two bilaterally presented targets which appeared at equal and opposite eccentricities in both hemifields. The results showed a large increase (cost) of saccade latency to invalid targets and a small non-significant decrease (benefit) of saccade latency to valid targets. The cost associated with invalid targets replicates the meridian crossing effect shown in manual reaction time experiments and is consistent with the hemifield inhibition and premotor models of attentional orienting. The use of a gap procedure produced a generalised facilitation of saccade latency, which was not modified by the prior orienting of visual attention. The magnitude of the gap effect was similar for saccades made to attended and non-attended stimulis. This suggests that the gap effect may be due to ocular motor disengagement, or a warning signal effect, rather than to the prior disengagement of visual attention. When two targets were presented simultaneously, one in each hemifield, saccade latency was slowed compared with the single target condition. The magnitude of this slowing was unaffected by the prior orienting of visual attention or by the fixation condition. The slowing was examined in more detail in experiment 3, by presenting targets with brief offset delays. The latency increase was maximal if the two targets were presented simultaneously and decreased if the distractor appeared at short intervals (20–80 ms) before or after the saccade target onset. If the non-attended stimulus was presented at greater intervals (160, 240 ms) before the saccade target, then a facilitation effect was observed. This demonstrates that the onset of a distractor in the non-attended hemifield can have both an inhibitory and a facilitatory effect on a saccade production.     

“生精胶囊”对大鼠的生精作用的研究

本文用病理学的计数方法研究了“生精胶囊”对大鼠的生精作用。结果表明“生精胶囊”能明显增加睾丸曲细精管内生殖细胞数目、睾丸内精子数目、曲细精管数量及其直径和曲细精管内细胞层数,增加精子活率而对初级精母细胞直径及精子活动力无明显影响。为临床该药治疗“男性不育少精症”提供了科学依据。     

Interaction of class III antiarrhythmic drugs with muscarinic M2 and M3 receptors: radioligand binding and functional studies

We have recently reported that class III antiarrhythmic drugs inhibit the muscarinic acetylcholine (ACh) receptor-operated K⁺ current (I _K, ACh) in guinea-pig atrial cells by different molecular mechanisms. The data obtained from the patch-clamp study suggest that d,l-sotalol inhibits I _{K, ACh} by blocking the muscarinic receptors, whereas MS-551 inhibits the K⁺ current by blocking the muscarinic receptors and depressing the function of the K⁺ channel itself and/or the guanine nucleotide-binding protein (G protein). This study was undertaken to determine whether the class III antiarrhythmic drugs d,l-sotalol and MS-551 interact with the muscarinic receptors of cardiac and peripheral tissues. Both drugs inhibited concentration dependently the specific [³H]N-methylscopolamine ([³H]-NMS) binding to membrane preparations obtained from guinea-pig atria and submandibular glands. The competition curves of these drugs for [³H]-NMS binding to glandular membranes were monophasic, suggesting competition with [³H]-NMS at a single site. Although the competition curve of d,l-sotalol for [³H]-NMS binding to atrial membranes was monophasic, that of MS-551 was biphasic and showed high- and low-affinity states of binding. d,l-Sotalol showed slightly, but significantly, higher affinity for cardiac-type muscarinic receptors (M₂) than for glandular-type muscarinic receptors (M₃). The inhibition constant (K _i) for MS-551 in glandular membranes was also slightly greater than the high-affinity K _i value for the drug in atrial membranes. In guinea-pig left atria and ilea, d,l-sotalol shifted the concentration-response curves for the negative inotropic effect and the contracting effect of carbachol in a parallel manner. The slopes of Schild plot were not significantly different from unity, suggesting competitive antagonism, and the pA₂ for d,l-sotalol in left atria was slightly greater than that in ilea. MS-551 also shifted the concentration response curve for the negative inotropic effect of carbachol in atrial preparations to a greater extent than that for the contracting effect in ileal preparations, although MS-551 failed to show a pure competitive antagonism. These results suggest that both d,l-sotalol and MS-551 interact with cardiac M₂ and peripheral M₃ receptors, and that at high concentrations they exert anticholinergic activity in cardiac and peripheral tissues.     

Effect ofd-fenfluramine on the indole contents of the rat brain after treatment with different inducers of cytochrome P450 isoenzymes

The effects of pretreatment with inducers of hepatic cytochrome P450 isoenzymes (phenobarbital, dexamethasone and-naphthoflavone) on the metabolism ofd-fenfluramine (d-F) and its acute and long-lasting indole-depleting effects were studied in rats, in an effort to obtain further information on the importance of hepatic drug metabolism in relation to its neurochemical actions. Twenty-four hours after the last dose of each inducer, rats were injected withd-F hydrochloride (5 mg/kg, IP) and killed at various times thereafter for parallel determination of indoles and drug concentrations in plasma and brain. Additional rats were treated as above and killed 1 week afterd-F hydrochloride (5 and 10 mg/kg) to study the recovery of indole in the cortex, a particularly sensitive brain area. Phenobarbital and-naphthoflavone and, to a lesser degree, dexamethasone, stimulated the metabolism ofd-F, as evidenced by a decrease in plasma and brain areas under the curve (AUC) compared to vehicle-treated rats. This indicated that multiple isoenzymes are capable of mediating the drug's metabolism, primarily byN-dealkylation tod-norfenfluramine (d-NF). None of the inducers raised plasma and brain AUC of the nor-derivative, and in fact phenobarbital and particularly-naphthoflavone reduced it. These different effects were even apparent in rats givend-NF (2.5 mg/kg), indicating that both phenobarbital and-naphthoflavone also stimulate the sequential metabolism of the nor-metabolite (byN-deamintaion) which, however, is apparently enhanced most actively by-naphthoflavone-inducible forms of P-450. Total active brain concentrations (d-F+d-NF) after the different pretreatments were in the order of-naphthoflavone < phenobarbital < dexamethasone vehicle. Interestingly,-naphthoflavone rapidly reversed the depletion of brain indoles caused byd-F (andd-NF); phenobarbital provided partial protection and dexamethasone did not appreciably modify either the acute or long-term neurochemical effects of the drug. The fact that phenobarbital affectedd-NF kinetics less than-naphthoflavone, and provided only partial protection against the acute and long-lasting neurochemical effects of high doses ofd-F, further stresses the critical role ofd-NF in the neurochemical outcome of its parent drug. These findings support the view that the degree and duration of the indole-depleting effects are related to critical brain concentrations of the parent compound and its nor-derivative, and provide indirect evidence that hepatic metabolites other thand-NF are unlikely to play any role in the neurochemical effects of high doses ofd-F in rats.     

Natural helping functions of lay health advisors in breast cancer education

Summary The Save Our Sisters Project builds on the roles of 95 natural helpers to increase mammography screening among older African American women in a NC county. Natural helpers are lay people to whom others naturally turn for advice, emotional support, and tangible aid. Findings from 14 focus group interviews showed that older women seek out these individuals when they have a female-specific concern, rather than or before seeking help from professionals. The characteristics of natural helpers, revealed in the findings, were used to identify and recruit them to become trained lay health advisors in breast cancer education. Through the SOS Project, natural helpers provide a community-based system of care and social support that complements the more specialized role of health professionals; linking them to women through places and ways that no health professional could begin to acquire. The three roles of lay health advisors are: (1) to assist individuals in their social networks with needs that are difficult for professionals to address; (2) to negotiate with professionals for support from the health system; and (3) to mobilize the resources of associations in their community to sustain support from the health system.     

Effect of 5-(p-hydroxyphenyl)-5-phenylhydantoin (p-HPPH) enantiomers,major metabolites of phenytoin,on the occurrence of chronic-gingival hyperplasia: in vivo and in vitro study

The purpose of this study was to assess the possible role of the (R)- and (S)- enantiomers of the phenytoin metabolite p-HPPH in the pathogenesis of gingival hyperplasia (GH). About 98% of circulating p-HPPH is in the (S)-form. There were significant differences between patients with and without GH in (R)-p-HPPH level (0.055 vs 0.042 g·ml^–1), both enantiomer/racemate level ratios, and R/S enantiomeric ratio (0.0313 vs 0.0232); an increase in serum (R)-p-HPPH level was observed in patients with GH. In separate experiments, the effect of p-HPPH enantiomers on the proliferation of the normal human dermal fibroblast was studied. The in vitro study showed that (R)-p-HPPH selectively stimulated fibroblast growth. The results suggest that the least abundant metabolite, (R)-p-HPPH, is the most toxic with respect to gingival hyperplasia.     

Functionally intact in vitro preparation generating respiratory activity in neonatal and mature mammals

The present report describes a novel rhythmically active brainstem slice preparation that generates respiratory activity spontaneously in both mice and rats of varying maturational states. The brainstems of neonatal (0–4 days) and mature (3–8 weeks) mice and rats were isolated and a 600- to 750-m thick slice cut to include the dorsomedial and the ventrolateral regions of the complete rostro-caudal extent of the medulla. This plane of section we have termed tilted-sagittal. Rhythmically discharging neurones were recorded extracellularly from both the dorsal and ventral regions of the slice. The recording sites of these neurones were found in the hypoglossal motonucleus (XII) and in areas of the ventrolateral medulla that includes the ventral respiratory group (VRG) region. Histological examination revealed the preservation of neuronal structures important for cardiorespiratory regulation and reflex control including the nucleus of the solitary tract as well as the nucleus ambiguus. In addition, pontine structures including the A5 region were also preserved. Rhythmic activity was found only in slices where the ambiguual column was preserved in its entirety. The mean frequency of discharge of XII neurones was 20 and 10 bursts per minute in neonates and mature rodents respectively. In preparations of mature animals we demonstrate that this frequency increased significantly (P<0.05) by either raising temperature from 29°C to 38°C (54%), elevating extracellular potassium concentration from 4 to 7.5 mM (52%), blocking potassium channels (20%) or decreasing pH from 7.4 to 7.0 (18%). The burst duration to frequency ratio of XII and VRG rhythmic neurones was similar and therefore indicative of a common brainstem oscillator. Consistent with this finding was that rhythmic activity in the VRG persisted despite removal of the dorsomedial region of the slice. In contrast, rhythmic XII neurones became tonic following mechanical disconnection of the VRG.     

工频电磁场对人体免疫功能的作用

目的　探讨工频电磁场对人体免疫功能的影响。方法　检测２５ 例长期工作在３ ×１０５ Ｖ超高压环境中的工作人员与５ 例正常对照者的外周血Ｔ 淋巴细胞分泌白细胞介素２（ＩＬ２） 活性,白细胞介素２ 受体（ＩＬ２Ｒ） 表达;单核／ 巨噬细胞抗体依赖的细胞介导的细胞毒（ＡＤＣＣ） 效应,白细胞介素１５（ＩＬ１５） 活性;血清中ＩｇＧ、ＩｇＡ、ＩｇＭ 的水平。结果　（１） 观察组ＩＬ２ 活性为（３６２ ±７８） Ｕ／ｍｌ,明显高于对照组［（２５４ ±６７）Ｕ／ｍｌ］ ,差异有显著性（ Ｐ ＜ ０ ．０５） 。（２） 观察组ＩＬ２Ｒ 表达比率为２８ ．４ ％ ±３ ．２ ％ ,对照组为２２ ．８ ％ ±１０ ．７ ％ ,差异无显著性（ Ｐ ＞ ０ ．０５） 。（３） 观察组单核／ 巨噬细胞ＡＤＣＣ 效应及ＩＬ１５ 分泌水平均有增强或增高的趋势,但差异无显著性（ Ｐ ＞ ０ ．０５） 。（４） 观察组血清中ＩｇＧ 水平为（１０ ．３７ ±１ ．２８）ｇ／Ｌ,明显高于对照组［（８ ．８９ ±１ ．８８）ｇ／Ｌ］ ,差异有显著性（ Ｐ ＜ ０ ．０５） ,而血清中ＩｇＡ、Ｉｇ Ｍ 水平与对照组比较,差异无显著性（ Ｐ ＞ ０ ．０５） 。结论　长期工作在工频电磁场环境中人员的Ｔ     

13年室间质控菌株鉴定工作的实践和体会

为了提高菌株鉴定水平, 我们自1985～1998 年参加了省临检中心细菌室间质控工作, 共鉴定下发菌株142 株,鉴定正确131 株(占92.25% ), 误检11 株(7.75% )。本文总结了鉴定工作的经验, 并对误检原因进行分析。认为理论、实践和学科新进展是提高鉴定水平的关键