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K K Andersen

Publications and source records attributed to K K Andersen.

10 recordsLinked to original sources
PubMed2005

Nicotine and clozapine selectively reverse a PCP-induced deficit of PPI in BALB/cByJ but not NMRI mice: comparison with risperidone.

Schizophrenic patients have deficits in prepulse inhibition (PPI) that may be alleviated by smoking/nicotine. The effect of nicotinic agents on PPI in rodents is equivocal and few studies in mice have been reported. Thus, we assessed nicotine's (0.03-1mg/kg) effect on PPI in five mouse strains with no effects. We next determined if nicotine would reverse a phencyclidine (PCP)-induced deficit of PPI in BALB/cByJ and NMRI mice. BALB/cByJ mice have a low density of [(125)I]alpha-bungaratoxin binding in the hippocampus and poor inhibitory gating of auditory evoked potentials (AEPs), a model related to PPI. At 1mg/kg, nicotine selectively reversed the PCP-induced deficit of PPI in BALB/cByJ mice. The pharmacokinetic profile of nicotine (T(1/2), C(max), T(max) and AUC) was identical in both strains, obviating this as a factor for the strain-dependent effect observed. Moreover, 1mg/kg nicotine inhibited in vivo [(3)H]epibatidine binding with the same time-course in both strains, indicating no difference in brain "kinetics". Since high doses of nicotine were effective in BALB/cByJ mice a role for low-affinity nicotinic receptors, e.g. alpha(7) receptors, is plausible. Clozapine, but not risperidone, also only reversed the PCP deficit of PPI in BALB/cByJ. Clozapine and nicotine also enhance inhibitory gating of AEPs in DBA/2 mice, and clozapine's effect is antagonized by an alpha(7) antagonist. Our data and previous evidence possibly suggest a role for low-affinity nicotinic receptors in the effects of clozapine and nicotine. Furthermore, BALB/cByJ mice may represent a model to test the effects of nicotinic agents acting at low-affinity nicotinic receptors.

Animals↗
PubMed2005

Global iron connections between desert dust, ocean biogeochemistry, and climate.

The environmental conditions of Earth, including the climate, are determined by physical, chemical, biological, and human interactions that transform and transport materials and energy. This is the "Earth system": a highly complex entity characterized by multiple nonlinear responses and thresholds, with linkages between disparate components. One important part of this system is the iron cycle, in which iron-containing soil dust is transported from land through the atmosphere to the oceans, affecting ocean biogeochemistry and hence having feedback effects on climate and dust production. Here we review the key components of this cycle, identifying critical uncertainties and priorities for future research.

Atmosphere↗
PubMed2004

High-resolution record of Northern Hemisphere climate extending into the last interglacial period.

Two deep ice cores from central Greenland, drilled in the 1990s, have played a key role in climate reconstructions of the Northern Hemisphere, but the oldest sections of the cores were disturbed in chronology owing to ice folding near the bedrock. Here we present an undisturbed climate record from a North Greenland ice core, which extends back to 123,000 years before the present, within the last interglacial period. The oxygen isotopes in the ice imply that climate was stable during the last interglacial period, with temperatures 5 degrees C warmer than today. We find unexpectedly large temperature differences between our new record from northern Greenland and the undisturbed sections of the cores from central Greenland, suggesting that the extent of ice in the Northern Hemisphere modulated the latitudinal temperature gradients in Greenland. This record shows a slow decline in temperatures that marked the initiation of the last glacial period. Our record reveals a hitherto unrecognized warm period initiated by an abrupt climate warming about 115,000 years ago, before glacial conditions were fully developed. This event does not appear to have an immediate Antarctic counterpart, suggesting that the climate see-saw between the hemispheres (which dominated the last glacial period) was not operating at this time.

Journal Article↗
PubMed2003

Essential Bacillus subtilis genes.

To estimate the minimal gene set required to sustain bacterial life in nutritious conditions, we carried out a systematic inactivation of Bacillus subtilis genes. Among approximately 4,100 genes of the organism, only 192 were shown to be indispensable by this or previous work. Another 79 genes were predicted to be essential. The vast majority of essential genes were categorized in relatively few domains of cell metabolism, with about half involved in information processing, one-fifth involved in the synthesis of cell envelope and the determination of cell shape and division, and one-tenth related to cell energetics. Only 4% of essential genes encode unknown functions. Most essential genes are present throughout a wide range of Bacteria, and almost 70% can also be found in Archaea and Eucarya. However, essential genes related to cell envelope, shape, division, and respiration tend to be lost from bacteria with small genomes. Unexpectedly, most genes involved in the Embden-Meyerhof-Parnas pathway are essential. Identification of unknown and unexpected essential genes opens research avenues to better understanding of processes that sustain bacterial life.

Bacillus subtilis↗
PubMed1998

One of two osmC homologs in Bacillus subtilis is part of the sigmaB-dependent general stress regulon.

In this report we present the identification and analysis of two Bacillus subtilis genes, yklA and ykzA, which are homologous to the partially RpoS-controlled osmC gene from Escherichia coli. The yklA gene is expressed at higher levels in minimal medium than in rich medium and is driven by a putative vegetative promoter. Expression of ykzA is not medium dependent but increases dramatically when cells are exposed to stress and starvation. This stress-induced increase in ykzA expression is absolutely dependent on the alternative sigma factor sigmaB, which controls a large stationary-phase and stress regulon. ykzA is therefore another example of a gene common to the RpoS and sigmaB stress regulons of E. coli and B. subtilis, respectively. The composite complex expression pattern of the two B. subtilis genes is very similar to the expression profile of osmC in E. coli.

Bacillus subtilis↗
PubMed1998

Exposure margin in skeletal radiography and its effect on tube tilt compensation.

OBJECTIVE: To examine the rationale for and necessity of adjusting the film focal distance when X-ray angulation is employed during a radiographic study, and to determine the sensitivity of human interpreters to overall differences in film density and the correlation, if any, with digital analysis of radiographic films. DESIGN AND SETTING: The study was performed in the radiology department at Logan College of Chiropractic in St. Louis, Missouri. A standard X-ray phantom of the hand and wrist and several aluminum step wedges were exposed from 10% to 250% of baseline exposure intensity using equipment commonly found in a field doctor's practice. EVALUATION: The films were independently rated for overall image quality on a visual analog scale by five board-certified chiropractice radiologists. The films were also digitized, and selected regions analyzed on a computer. RESULTS: The panel of radiologists was able to consistently grade exposure intensity differences of approximately 10% relative change between films. The perceived density was directly proportional to the logarithm of the exposure intensity, as would be predicted from theoretical film response characteristics. The range of "acceptable" image quality was determined to lie between -40% and +60% of the baseline technique. CONCLUSIONS: This study validated the empirically derived tube tilt correction factor of 1 in of vertical adjustment per 5 degrees of tube angulation for tube tilts greater than or equal to 20 degrees. Underexposure impaired the interpretation of radiographs more than overexposure. Experienced human observers were able to reliably discriminate exposure differences on the order of 10% relative change when presented with complex grey-scale images, such as plain film radiographs.

Chiropractic↗
PubMed1986

Histamine challenge in asthmatics at 07.00-12.00-17.00 and 22.00 h.

Nine adult asthmatics were challenged with histamine four times during the same day, at 07.00, 12.00, 17.00 and 22.00 h. A dose of histamine, which had induced a fall in FEV1 greater than 20%, when inhaled a few days before the study day, was used. The baseline values before the inhalations varied through the day. FEV1 was on average 1.9 liter at 07.00, 2.2 l. at 12.00, 2.2 l. at 17.00 and 2.0 l. at 22.00 h. The average decrease in per cent from the baseline after the inhalation of histamine was 27% at 07.00, 33% at 12.00, 29% at 17.00 and 28% at 22.00 h. A statistically significant difference in baseline FEV1 was measured during the day, but no statistically significant difference was found in the percentage decrease in FEV1 after inhalation of histamine, when measured at 07.00, 12.00, 17.00 and 22.00 h.

Adult↗