Surface properties of fibrinogen and fibrin

By contact angle measurements on layers of fibrinogen and fibrin, it can be shown that the transformation from fibrinogen to fibrin is accompanied by a change in surface properties from very hydrophilic (fibrinogen) to moderately but definitely hydrophobic (fibrin). It is also shown that, contrary to serum albumin and gamma globulin, fibrinogen does not become more hydrophobic upon drying.     

A rod-shaped,gram-negative,propionigenic bacterium with a wide substrate range and the ability to fix molecular nitrogen

From estuarine mud a rod-shaped, motile, gram-negative, anaerobic bacterium was isolated (strain asp 66). Asp 66 fermented several substrates including glucose, fructose, malate, fumarate, citrate and aspartate. Fermentation products were acetate, propionate and presumably CO₂. Hydrogen was never formed nor utilized. Succinate conversion to propionate was catalyzed by cell suspensions but did not support growth. Asp 66 did not require vitamins and grew well in mineral media with a fermentable substrate. The pH range for growth was from 6.5 to 8.5. Temperature optimum was 27 to 30°C. The strain was able to fix N₂ as evidenced by its growth with N₂ as sole nitrogen source and its ability to reduce acetylene to ethylene. Cell-free extracts of cultures grown under air without shaking contained cytochrome(s) with absorption peaks at 523 nm and at 553 nm. The G+C content of the DNA was 60.8+-1 mol%. The taxonomic position of strain asp 66 is discussed.     

Aerobic nitrate and nitrite reduction in continuous cultures of Escherichia coli E4

Nitrate and nitrite was reduced by Escherichia coli E4 in a l-lactate (5 mM) limited culture in a chemostat operated at dissolved oxygen concentrations corresponding to 90–100% air saturation. Nitrate reductase and nitrite reductase activity was regulated by the growth rate, and oxygen and nitrate concentrations. At a low growth rate (0.11 h^–1) nitrate and nitrite reductase activities of 200 nmol · mg^–1 protein · min^–1 and 250 nmol · mg^–1 protein · min^–1 were measured, respectively. At a high growth rate (0.55 h^–1) both enzyme activities were considerably lower (25 and 12 nmol mg^–1 · protein · min^–1). The steady state nitrite concentration in the chemostat was controlled by the combined action of the nitrate and nitrite reductase. Both nitrate and nitrite reductase activity were inversely proportional to the growth rate. The nitrite reductase activity decreased faster with growth rate than the nitrate reductase. The chemostat biomass concentration of E. coli E4, with ammonium either solely or combined with nitrate as a source of nitrogen, remained constant throughout all growth rates and was not affected by nitrite concentrations. Contrary to batch, E. coli E4 was able to grow in continuous cultures on nitrate as the sole source of nitrogen. When cultivated with nitrate as the sole source of nitrogen the chemostat biomass concentration is related to the activity of nitrate and nitrite reductase and hence, inversely proportional to growth rate.     

The caudal spinal cord of coho salmon (Oncorhynchus kisutch): Immunocytochemical evidence of a “caudal serotoninergic system”

Summary The caudal spinal cord of the coho salmon was investigated by means of immunocytochemistry using antisera against serotonin, urotensin I, urotensin II, somatostatin and a urea-extract of bovine Reissner's fiber (AFRU). Populations of serotonin-immunoreactive (IR) neurons were found rostral and dorsal to the urophysis in close spatial association with caudal secretory neurons. Thick, smooth serotonin-IR processes extended toward the external surface of the spinal cord where they displayed conspicuous terminal dilatations. Thin, beaded serotonin-IR fibers appeared to innervate populations of caudal secretory and somatostatin-IR cerebrospinal fluid-contacting neurons. Most caudal neurosecretory cells displayed both urotensin I and urotensin II immunoreactivities; only a minority reacted exclusively with either urotensin I or urotensin II antisera. Urotensin II-IR and somatostatin-IR cerebrospinal fluid (CSF)-contacting neurons were found as an integral component of the central canal wall in the caudal spinal cord and filum terminale; their dendritic processes appeared to contact Reissner's fiber, which displayed a weak AFRU-immunoreactivity while inside the central canal, but became strongly reactive in the interior of the terminal ventricle as it formed the massa caudalis. The distribution of serotoninergic processes points to a regulatory role in the function of caudal secretory and CSF-contacting neurons and to a putative serotonin release into the subarachnoid space and/or meningeal vasculature. It is also suggested that the CSF-contacting neurons of the central canal may participate in a feedback mechanism controlling the secretory activity of the subcommissural organ.Supported by Grant A/1095-1 from the International Foundation for Science, Sweden, to C.Y.; Grant I/63-476 from Volkswagen-Stiftung to E.R.; and Grant S-85-39 from the Dirección de Investigaciones, Universidad Austral de Chile     

Oxidation of glycerol,lactate, and propionate by Propionibacterium freudenreichii in a poised-potential amperometric culture system

Growth of Propionibacterium freudenreichii was studied with glycerol, lactate, and propionate as energy sources and a three-electrode poised-potential amperometric electrode system with hexacyanoferrate (III) as mediator. In batch culture experiments with glycerol and lactate as substrates, hexacyanoferrate (III) was completely reduced. Growth yields increased and the fermentation patterns were shifted towards higher acetate formation with increasing hexacyanoferrate (III) concentrations (0.25–8.0 mM). In experiments with regulated electrodes, glycerol, lactate, and propionate were oxidized to acetate and CO₂, and the electrons were quantitatively transferred to the working electrode. Growth yields of 29.0, 13.4 and 14.2 g cell material per mol were calculated, respectively. The high cell yield obtained during propionate oxidation cannot be explained solely by substrate level phosphorylation indicating that additional energy was conserved via electron transport phosphorylation. Furthermore, this result indicated complete reversibility of the methyl-malonyl-CoA pathway in propionic acid bacteria.     

Analysis of a disease transmission model in a population with varying size

An S I R S epidemiological model with vital dynamics in a population of varying size is discussed. A complete global analysis is given which uses a new result to establish the nonexistence of periodic solutions. Results are discussed in terms of three explicit threshold parameters which respectively govern the increase of the total population, the existence and stability of an endemic proportion equilibrium and the growth of the infective population. These lead to two distinct concepts of disease eradication which involve the total number of infectives and their proportion in the population.Partially supported by NSF Grant No. DMS-8703631. This work was done while this author was visiting the University of VictoriaResearch supported in part by NSERC A-8965     

视前区微量注射吗啡对大鼠丘脑束旁核痛反应神经元电活动的影响

本实验观察了视前区(POA)内微量注入阿片样物质对丘脑束旁核(Pf)痛反应神经元电活动影响。结果如下:(1)POA 内微量注射高浓度吗啡(10μg/μl)能显著抑制 Pf 内大部分(20/26)痛兴奋神经元(PEN)的痛诱发放电,其中3个神经元注药后对伤害性刺激转变成抑制反应;POA 内微量注射低浓度吗啡(1μg/μl)也显著抑制 Pf 内大部分(19/23)PEN 的痛诱发放电。(2) POA 内微量注射两种浓度的吗啡,均使大多数痛抑制神经元(PIN,共27/33)的完全抑制时程缩短。上述结果提示,POA 内阿片样物质对 Pf 内痛反应神经元的电活动可能具有抑制作用。     

在双脉冲光刺激下瞳孔系统的采样控制特性

本文用实验揭示了瞳孔对光动态反应具有采样控制特性。实验中采用各种不同时间间隔的双脉冲光,以开环的方式(Maxwellian View)刺激瞳孔,当双脉冲之间间隔较长时,瞳孔反应相当于对双脉冲光的两次脉冲分别产生瞬态收缩;当双脉冲时间间隔短于0.6s 时,其反应就成了一次瞬态收缩,与单个光脉冲所引起的瞳孔反应一样。同—受试者的多次实验结果相同,不同受试者所得结果也基本一致。故瞳孔对脉冲刺激光引起反应后,必须至少约隔0.6s 才能对另一次脉冲光产生反应,这就说明了瞳孔动态反应具有离散的采样控制特性。实验还进一步证明,瞳孔系统的控制机制是双重模式的控制:不同的刺激条件下,瞳孔反应可呈现为瞬态反应(AC)或持续反应(DC),瞬态反应的 AC 通道为离散的采样控制,持续反应的 DC 通道为连续控制。     

Discrimination of jittered sonar echoes by the echolocating bat,Eptesicus fuscus: The shape of target images in echolocation

1. Behavioral experiments with jittering echoes examined acoustic images of sonar targets in the echolocating bat, Eptesicus fuscus, along the echo delay or target range axis. Echo phase, amplitude, bandwidth, and signal-to-noise ratio were manipulated to assess the underlying auditory processes for image formation. 2. Fine delay acuity is about 10 ns. Calibration and control procedures indicate that this represents temporal acuity rather than spectral discrimination. Jitter discrimination curves change in phase when the phase of one jittering echo is shifted by 180 degrees relative to the other, showing that echo phase is involved in delay estimation. At an echo detectability index of about 36 dB, fine acuity is 40 ns, which is approximately as predicted for the delay accuracy of an ideal receiver. 3. Compound performance curves for 0 degrees and 180 degrees phase conditions match the crosscorrelation function of the echoes. The locations of both 0 degrees and 180 degrees phase peaks in the performance curves shift along the time axis by an amount that matches neural amplitude-latency trading in Eptesicus, confirming a temporal basis for jitter discrimination.     

Regional distribution of DNA and RNA in rat brain: A sensitive determination using high-performance liquid chromatography with electrochemical detection

DNA and RNA contents in 20 brain regions or nuclei of the rat were determined by a highly sensitive method using high-performance liquid chromatography with electrochemical detection. The high DNA and RNA contents were found in the hypothalamic nuclei, especially the median eminence-arcuate nucleus. These results may be available for the preparation of nucleic acids as the regional control.