Age differences in responsiveness of brainstem chemosensitive neurons to extracellular pH changes

The sensitivity of neurons in the caudal chemosensitive area on the ventrolateral surface of the medulla oblongata (VMS) to extracellular pH changes was examined in newborn and young developing kittens and compared to that of adult cats. The pH was varied by superfusion of the VMS with mock cerebrospinal fluid (CSF) of pH 7.4 (control), 7.0 (acid) and 7.8 (alkaline). A total of 97 neuronal units in the three age groups changed their firing rates inversely in response to extracellular fluid (ECF) pH changes. The greatest sensitivity was found in the adult group where acid superfusion caused an increase in neuronal activity. The least sensitivity was observed in the newborn group (1-6 days old), whereas the young kitten group (4-6 weeks old) exhibited an intermediate sensitivity. Neurons of kittens older than 7 weeks of age demonstrated a response pattern characteristic of the adult group. Neurons of neonates older than seven days, exhibited a response pattern characteristic of the young kitten group.     

Prostaglandin E2 induced changes in renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat

Prostaglandin E2, when infused into the renal artery of the dog, is a vasodilator and increases both renal interstitial hydrostatic pressure and sodium excretion. Similar studies in the rat, however, have been inconclusive. The present study examined the effect of prostaglandin E2 infusion into the renal interstitium, by means of a chronically implanted matrix, on renal blood flow, renal interstitial hydrostatic pressure and sodium excretion in the rat. Prostaglandin E2 was continuously infused directly into the kidney interstitium to mimic endogenous prostaglandin E2 production by renal cells. The maximum change in each of these parameters occurred when 10(-5) M PGE2 was infused. Renal blood flow increased from 4.70 +/- 0.91 to 5.45 +/- 0.35 ml/min (p less than 0.05) while renal interstitial hydrostatic pressure decreased from 3.9 +/- 0.4 to 2.6 +/- 0.5 mmHg (p less than 0.05) and fractional excretion of sodium decreased from 1.02 +/- 0.20 to 0.61 +/- 0.12% (p less than 0.05). Thus, the present study demonstrates that renal interstitial infusion of prostaglandin E2 increases total renal blood flow but decreases both renal interstitial hydrostatic pressure and urinary sodium excretion in the rat.     

Transgenetic studies implicate interactions between homologous PrP isoforms in scrapie prion replication

Transgenic (Tg) mice expressing both Syrian hamster (Ha) and mouse (Mo) prion protein (PrP) genes were used to probe the mechanism of scrapie prion replication. Four Tg lines expressing HaPrP exhibited distinct incubation times ranging from 48 to 277 days, which correlated inversely with HaPrP mRNA and HaPrPC. Bioassays of Tg brain extracts showed that the prion inoculum dictates which prions are synthesized de novo. Tg mice inoculated with Ha prions had approximately 10(9) ID50 units of Ha prions per gram of brain and less than 10 units of Mo prions. Conversely, Tg mice inoculated with Mo prions synthesized Mo prions but not Ha prions. Similarly, Tg mice inoculated with Ha prions exhibited neuropathologic changes characteristic of hamsters with scrapie, while Mo prions produced changes similar to those in non-Tg mice. Our results argue that species specificity of scrapie prions resides in the PrP sequence and prion synthesis is initiated by a species-specific interaction between PrPSc in the inoculum and homologous PrPC.     

What is the relationship between the endothelium derived relaxant factor and nitric oxide?

Nitric oxide gas in solution (NO) relaxes blood vessels with similar actions and pharmacodynamics as the endothelium derived relaxant factor (EDRF) and has been proposed to be a component of the materials released from stimulated endothelial cells. Certain data however suggest that EDRF and NO may not be identical. In some non-vascular smooth muscles, NO and EDRF exhibit markedly different pharmacologic profiles. Furthermore the interaction of EDRF and NO with anion exchange resins differ. The hypothesis that EDRF is identical to nitric oxide gas in solution or a nitrogen oxide containing compound is discussed.     

Kinetics of the sodium-dependent glutamine transporter in human intestinal cell confluent monolayers.

The intestinal epithelium metabolism of glutamine plays a critical role in inter-organ nitrogen flow. Although it is known that glutamine is the primary oxidative energy source and nucleotide precursor in intestinal cells, the luminal uptake of glutamine by the apical surface of enterocytes is poorly understood. In this study we have uncovered the sodium-dependent transporter system responsible for L-glutamine uptake by the apical membrane of a human intestinal epithelial cell line. The sodium-dependent Michaelis constant (Km) = 247 +/- 45 microM glutamine, and Jmax = 4.44 +/- 0.65 x 10(-9) mole min-1(mg protein)-1 (37 degrees C). Glutamine shares the transporter with alanine, as demonstrated by unlabeled glutamine inhibition of [3H]alanine uptake kinetics with a purely competitive-type inhibition pattern, and glutamine inhibition Ki = 205 +/- 18 microM by Dixon analysis. The inhibition pattern for a series of amino acid analogs indicated that this intestinal apical membrane sodium-dependent transporter for glutamine is distinct from any other transport system found in membranes of non-intestinal cells.     

Preliminary study of the distribution of the toxic elements As,Cd, and Hg in human hair and tissues by RNAA

In order to study the relationships between trace element concentrations of hair and internal body burdens, a radiochemical NAA technique has been used for determination of the elements As, Cd, and Hg in autopsy samples of liver, kidney-cortex, lung, and hair from 24 male persons who died by accident. High significant positive correlations were observed between the As concentration in hair and in kidney-cortex, and between Cd and Zn concentrations in kidney-cortex. The contents of Cd, both for lung and kidney-cortex, were related to the smoking habits of the subjects.

     

皮层第二体感区下行活动对尾核神经元伤害性反应的影响

本实验用清醒麻痹的家猫观察到,皮层第二体感区(SⅡ区)的下行活动对尾核痛相关单位的自发放电和伤害性反应均有影响。在35个痛相关单位中,刺激SⅡ区后,62.7％的自发放电受到影响(p<0.05)。在72个痛相关单位中,刺激SⅡ区后,77.8％的伤害性反应受到抑制(p<0.01),其中抑制痛兴奋单位的伤害性反应最为明显。而用利多卡因局部阻滞SⅡ区后,33个痛相关单位中,51.5％的伤害性反应增强(p<0.01)。本结果提示:(1)SⅡ区的下行活动不仅对尾核痛相关单位的自发活动有影响,而且对痛相关单位的伤害性反应有以抑制为主的下行性调制作用。(2)在正常机能状态下,SⅡ区对伤害性信息向尾核的传递有一定的紧张性的下行性抑制作用。     

高温厌氧条件下纤维素的直接乙醇发酵

本文介绍了出分解纤维素的嗜热厌氧菌Clostridium celluloflavus sp.nov.直接发酵纤维素产乙醇的初步研究、发酵于60℃下进仃,其主要产物为乙醇、乙酸、氢气和二氧化碳。文中介绍了间歇发酵的若干特征与影响发酵的因素,1％纤维素发酵至120小时,大约有70％纤维素被分解;乙醇的转化率约为0.36g/g降解纤维素;发酵液中乙醇浓度达到56至61mM。发酵中乙醇与乙酸浓度的比值因发酵时间与其它发酵条件的不同而不同。     

Integration host factor amplifies the induction of the aceBAK operon of Escherichia coli by relieving IclR repression.

A binding site for integration host factor (IHF) was identified upstream of the aceBAK promoter. Under inducing conditions, IHF activates aceB::lacZ expression by opposing IclR repression. In contrast, IHF has little effect on aceB::lacZ expression under repressing conditions. The ability of IHF to relieve repression under inducing but not repressing conditions allows this protein to amplify the induction of aceBAK.     

Use of green fluorescent protein to visualize the early events of symbiosis between Rhizobium meliloti and alfalfa (Medicago sativa).

A gene encoding a variant of green fluorescent protein (GFP) of Aequorea victoria was put under the control of a promoter which is constitutive in Rhizobium meliloti. The heterologous GFP gene was expressed at high levels during all stages of symbiosis, allowing R. meliloti cells to be visualized as they grew in the rhizosphere, on the root surface, and inside infection threads. In addition, nodules that were infected with bacteria which were synthesizing GFP fluoresced when illuminated with blue light. GFP-tagged bacteria could be seen inside infection threads, providing the opportunity to measure the growth rate and determine the patterns of growth of R. meliloti residing inside its host plant.