Three-dimensional ultrastructural analysis of the Saccharomyces cerevisiae mitotic spindle

The three dimensional organization of microtubules in mitotic spindles of the yeast Saccharomyces cerevisiae has been determined by computer-aided reconstruction from electron micrographs of serially cross-sectioned spindles. Fifteen spindles ranging in length from 0.6-9.4 microns have been analyzed. Ordered microtubule packing is absent in spindles up to 0.8 micron, but the total number of microtubules is sufficient to allow one microtubule per kinetochore with a few additional microtubules that may form an interpolar spindle. An obvious bundle of about eight interpolar microtubules was found in spindles 1.3-1.6 microns long, and we suggest that the approximately 32 remaining microtubules act as kinetochore fibers. The relative lengths of the microtubules in these spindles suggest that they may be in an early stage of anaphase, even though these spindles are all situated in the mother cell, not in the isthmus between mother and bud. None of the reconstructed spindles exhibited the uniform populations of kinetochore microtubules characteristic of metaphase. Long spindles (2.7-9.4 microns), presumably in anaphase B, contained short remnants of a few presumed kinetochore microtubules clustered near the poles and a few long microtubules extending from each pole toward the spindle midplane, where they interdigitated with their counterparts from the other pole. Interpretation of these reconstructed spindles offers some insights into the mechanisms of mitosis in this yeast.     

The emerging diversity of the electrophoretic types of Vibrio cholerae in the Western Hemisphere

Since the Latin American cholera epidemic began in 1991, 447 isolates of Vibrio cholerae O1 from the Western Hemisphere have been assayed by multilocus enzyme electrophoresis (MEE) to determine allelic variation among 16 enzyme-encoding genes. Two electrophoretic types (ETs) were identified among toxigenic isolates from Latin America: 323 were ET 4, the ET associated with the Latin American epidemic, and 29 were ET 3. Twenty-three of these ET 3 isolates had a distinctive antimicrobial resistance pattern also seen in isolates imported into the United States from Latin America and Southeast Asia. These resistant isolates had an identical ribotype and nearly identical pulsed-field gel electrophoresis (PFGE) patterns. Most nontoxigenic isolates analyzed were not precursors or descendants of toxigenic epidemic strains. MEE provided a population genetic frame-work for the interpretation of PFGE and ribotype data from the isolates in this study. All three methods identified 2 distinct strains of toxigenic V. cholerae O1 currently epidemic in Latin America.     

Inhibition of nitric oxide synthesis extends cerebrovascular autoregulation during hypertension

In anesthetized intact rats, cerebral blood flow is autoregulated until mean arterial blood pressure (MAP) exceeds 150 mmHg. At higher pressures cerebral blood flow breaks through autoregulation and rapidly increases. However, interruption of the arterial baroreceptor reflex eliminates breakthrough of autoregulation. Thus, breakthrough may reflect active rather than passive vasodilatation. We, therefore, sought to determine if breakthrough depends upon synthesis of the vasodilator nitric oxide. Thirty-eight anesthetized adult male Sprague-Dawley rats were studied. In all, MAP was raised by slow i.v. infusion of phenylephrine. In rats pretreated with the nitric oxide synthase inhibitor L-nitroarginine (L-NA; 22 mg/kg i.v.) or with a combination of L-NA plus D-arginine (D-Arg; 240 mg/kg i.v.), breakthrough did not occur even when MAP exceeded 185 mmHg (L-NA) and 165 mmHg (D-Arg). In contrast, breakthrough occurred in rats treated with L-NA plus L-arginine (L-Arg; 240 mg/kg i.v.) and in rats whose basal vascular tone had been increased by pretreatment with arginine vasopressin prior to infusion of phenylephrine. Removal of sympathetic innervation to cerebral vessels attenuated, but did not eliminate, effects of L-NA on breakthrough. Thus, vasodilatation seen with breakthrough of autoregulation depends upon release of nitric oxide or a nitric oxide donor.     

The virion host shutoff protein of herpes simplex virus inhibits reporter gene expression in the absence of other viral gene products

The virion host shutoff (vhs) function of herpes simplex virus induces degradation of host mRNAs at early times and rapid turnover of viral mRNAs throughout infection. Previous studies have shown that disruption of the UL41 gene abrogates vhs activity, but have not determined whether the UL41 polypeptide is the direct inducer of mRNA degradation or whether it is the only virion component required for this activity. In this paper we report that transfection of cells with UL41 inhibits expression of a cotransfected CAT reporter gene and that the inhibition is not dependent upon other viral genes. Inhibition of CAT expression was due to UL41-dependent reduction of CAT mRNA levels. UL41 alleles encoding polypeptides that lacked vhs activity during virus infections exhibited a similar lack of activity in transfected cells. The results indicate that the UL41 polypeptide is the direct inducer of host mRNA degradation following virus infection and that it is the only virion component directly required for this activity. A 382-amino-acid nonsense polypeptide missing the last 107 residues of UL41 lacked inhibitory activity, but was packaged into virions, while a 343-amino-acid nonsense polypeptide lacked both inhibitory activity and the ability to be packaged.     

Marking effects in Pavlovian trace conditioning.

[Correction Notice: An erratum for this article was reported in Vol 13(3) of Journal of Experimental Psychology: Animal Behavior Processes (see record 2008-10750-001). The last sentence in the second paragraph of the Discussion on page 128 should read as follows: "A second possibility is that in the marked ITI group, the marking of irrelevant events in the middle of the intertrial interval promoted associations between those events and food, which then interfered with the learning of an association between SI and food."] In four experiments we investigated pigeons' acquisition of a successive discrimination with a trace autoshaping procedure. The conditioned stimuli were 5-s presentations of colored key lights, one of which was followed by food after a 5-s delay. In Experiment 1, which used spatially defined cues, we found that acquisition of differential responding to the reinforced cue was facilitated when a brief flash of light immediately followed both reinforced and nonreinforced cues. Experiment 2 found a similar enhancement by the added light flash in a purely visual discrimination. Experiment 3 found that the flash facilitated learning only when presented immediately after the discriminative cues, and not when it occurred immediately before the cues or at the time of reinforcement. A fourth experiment found this facilitation effect only when the flash and reinforcement occurred on the same trial. These results are interpreted in terms of marking: The flash enhanced learning because it triggered a backward scan through recent memory to search for possible predictors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of sleeping in a chemical protective mask on sleep quality and cognitive performance

PURPOSE: We wanted to determine whether sleep is disrupted when soldiers sleep in a new chemical protective mask, the M40. Sleep quantity and quality, extent of protection provided by the mask during sleep, and next day performance were assessed. METHOD: After several days of training, 9 male soldiers slept with and without the M40 mask on four occasions. RESULTS: Soldiers were able to tolerate the mask for most or all of the night. However, sleep, as assessed by wrist-worn activity monitors, was significantly disturbed. Minutes (mean +/- SEM) of waking significantly increased, from 25 +/- 2.1 to 86 +/- 8.5 per night (p < 0.001), and number of awakenings rose from 8 +/- 0.6 to 20 +/- 0.9 (p < 0.0001). Soldiers reported that it took longer and was more difficult to fall asleep when wearing the mask. Errors on a choice reaction time task increased significantly and subjects reported greater fatigue and sleepiness the day after sleeping in the mask. Protection provided by the masks varied substantially among subjects and declined over the course of the study. Some soldiers were protected throughout the night but others were only protected intermittently. CONCLUSION: We conclude that sleeping in the chemical protective mask should only be done when necessary, given the adverse effects on sleep and daytime function, as well as the variability of protection, of the mask.     

Prescribing practice and policy for hypnotics: a model of pharmacy audit

A problem of overprescribing of hypnotic medication ('sleeping tablets') was identified and quantified within a department of health care for older people in a district general hospital. Data on the volume of prescribing were obtained from computerized pharmacy records, and this information was supplemented by a retrospective survey of case notes of 100 patients. Sixty per cent of patients were prescribed a hypnotic at some stage during their hospital stay. Twelve per cent were prescribed a sleeping tablet on admission on an 'as required' basis but never took this medication, suggesting that such prescribing was becoming routine. As part of an ongoing pharmacy audit within the department, a policy was implemented to try to improve prescribing habits. Following this, hypnotic prescribing fell, with the average monthly number of sleeping tablets prescribed falling from 2392 to 734. A further survey of 100 case notes showed overall prescribing had fallen to 25%, although 2% were still prescribed a hypnotic on admission but never took it.