Further studies on the biological characteristics of an endogenous colon mitosis inhibitor: Comparison with some structurally related peptides

Previous work indicates that the colonic epithelial cell proliferation in mice is reversibly inhibited by the tripeptide pGlu-His-GlyOH found in aqueous extracts of the intestine. In the present study we examined the possible tissue specificity of the colon mitosis inhibitor. The mitotic rate in the small intestine, epidermis and forestomach in mice was registered after a single i.p. injection of the tripeptide. A significantly reduced rate of cell renewal was found at 18 h in the epidermis whereas no inhibition was observed in the forestomach or ileal epithelium. To investigate whether the amino acid sequence of the tripeptide is essential for the inhibitory effect, three structurally related bioactive peptides were tested and compared to the effect of CMI. CMI showed a bell-shaped dose-response relationship as previously shown, whereas the mitotic rate was not reduced in the colonie epithelium after treatment with either an epidermal mitosis inhibitory pentapeptide, or the dipeptide pGlu-GlyOH, or an analogue of luteinizing hormone-releasing hormone. The efficacy of the tripeptide was dependent on the basal rate of cell renewal in the colonie epithelium. When the tripeptide was given at the circadian nadir of cell proliferation a delayed reduction of the proliferative activity was observed at 6 h after treatment, whereas treatment when the rate of cell proliferation was at its circadian zenith gave an immediate mitotic inhibition.     

Population dynamics in changing environments: the case of an eruptive forest pest species

In recent decades we have seen rapid and co‐occurring changes in landscape structure, species distributions and even climate as consequences of human activity. Such changes affect the dynamics of the interaction between major forest pest species, such as bark beetles (Coleoptera: Curculionidae, Scolytinae), and their host trees. Normally breeding mostly in broken or severely stressed spruce; at high population densities some bark beetle species can colonise and kill healthy trees on scales ranging from single trees in a stand to multi‐annual landscape‐wide outbreaks. In Eurasia, the largest outbreaks are caused by the spruce bark beetle, Ips typographus (Linnaeus), which is common and shares a wide distribution with its main host, Norway spruce (Picea abies Karst.). A large literature is now available, from which this review aims to synthesize research relevant for the population dynamics of I. typographus and co‐occurring species under changing conditions. We find that spruce bark beetle population dynamics tend to be metastable, but that mixed‐species and age‐heterogeneous forests with good site‐matching tend to be less susceptible to large‐scale outbreaks. While large accumulations of logs should be removed and/or debarked before the next swarming period, intensive removal of all coarse dead wood may be counterproductive, as it reduces the diversity of predators that in some areas may play a role in keeping I. typographus populations below the outbreak threshold, and sanitary logging frequently causes edge effects and root damage, reducing the resistance of remaining trees. It is very hard to predict the outcome of interspecific interactions due to invading beetle species or I. typographus establishing outside its current range, as they can be of varying sign and strength and may fluctuate depending on environmental factors and population phase. Most research indicates that beetle outbreaks will increase in frequency and magnitude as temperature, wind speed and precipitation variability increases, and that mitigating forestry practices should be adopted as soon as possible considering the time lags involved.     

Multiple Forms of Choline Acetyltransferase from Rat Brain

WE have found that several different forms of choline acetyl-transferase (ChAc) from rat brain can be separated by isoelectric focusing. Such heterogeneity of ChAc is of particular interest in the context of its ultrastructural localization. Subcellular fractionation^1–4 and histochemistry⁵ have shown that the enzyme in rat, in conditions of low ionic strength and pH, adhered to several different membranous structures.     

Water economy in bird nests

Summary Nest humidity ( ) under an incubating bantam hen was measured at ambient ranging from 1.3 to 25.0 mmHg. Weight loss of eggs was recorded in clutches of varying size. Nest and ambient were also measured in wild incubating willow ptarmigan nests in dry and wet habitats.Nest increased linearly with ambient in a way predictable on the assumption that the water vapour conductance ( ) of brood patch skin, plumage and eggs were constant and independent of ambient . Nest was also dependent of clutch size. Egg dehydration was quantitatively predicted from measured values and the laws of diffusion.Our findings confirm earlier conclusions that the adult bird does not actively regulate nest at varying ambient . Birds can presumably achieve appropriate egg dehydration by a strategy combining nest site, nest construction, egg shell conductance and incubation behaviour which meets the requirements of their breeding climate.Abbreviations water vapur pressure - water vapur conductance - water flux     

Phenotypes of non-attached Pseudomonas aeruginosa aggregates resemble surface attached biofilm

For a chronic infection to be established, bacteria must be able to cope with hostile conditions such as low iron levels, oxidative stress, and clearance by the host defense, as well as antibiotic treatment. It is generally accepted that biofilm formation facilitates tolerance to these adverse conditions. However, microscopic investigations of samples isolated from sites of chronic infections seem to suggest that some bacteria do not need to be attached to surfaces in order to establish chronic infections. In this study we employed scanning electron microscopy, confocal laser scanning microscopy, RT-PCR as well as traditional culturing techniques to study the properties of Pseudomonas aeruginosa aggregates. We found that non-attached aggregates from stationary-phase cultures have comparable growth rates to surface attached biofilms. The growth rate estimations indicated that, independently of age, both aggregates and flow-cell biofilm had the same slow growth rate as a stationary phase shaking cultures. Internal structures of the aggregates matrix components and their capacity to survive otherwise lethal treatments with antibiotics (referred to as tolerance) and resistance to phagocytes were also found to be strikingly similar to flow-cell biofilms. Our data indicate that the tolerance of both biofilms and non-attached aggregates towards antibiotics is reversible by physical disruption. We provide evidence that the antibiotic tolerance is likely to be dependent on both the physiological states of the aggregates and particular matrix components. Bacterial surface-attachment and subsequent biofilm formation are considered hallmarks of the capacity of microbes to cause persistent infections. We have observed non-attached aggregates in the lungs of cystic fibrosis patients; otitis media; soft tissue fillers and non-healing wounds, and we propose that aggregated cells exhibit enhanced survival in the hostile host environment, compared with non-aggregated bacterial populations.     

Influence of body composition on the metabolic rate of nestling European shags (Phalacrocorax aristotelis)

During the early development of avian nestlings, their mass-specific resting metabolic rate (RMR) changes in a biphasic pattern with the peak value often being much higher than that expected for an adult bird of similar body mass. In the present study we examined the possible influence of variations in the size of internal organs in “setting” the high RMR and peak metabolic rate (PMR) during development in a large altricial species, the European shag (Phalacrocorax aristotelis). Thermoneutral RMR and cold-exposure induced PMR were measured in nestlings 15 days old, the age at which the highest RMR occurred during development. Body mass averaged 414 g. Mean values of RMR and PMR were 5.75 W and 9.08 W, respectively; the RMR value corresponds to approximately 250% of the expected value for an adult non-passerine bird of similar body mass. The masses of all the organs measured (breast and leg muscles, heart, liver, intestine, and kidney) varied isometrically with total body mass. However, large chicks had a significantly lower fractional water content than small chicks, suggesting that the former had achieved a higher level of functional maturity. In contrast to what has been suggested for adult birds in general, the heart and kidney masses of shag nestlings were not significantly correlated with the metabolic rates. The intestine length, in contrast, was highly and positively correlated with both the RMR and the PMR, i.e. intestine length was a better predictor of RMR and PMR than was total body mass. In addition, liver mass was positively correlated with RMR. The results of the present study suggest that the liver in particular may play a key role in establishing the high, mass-specific RMR which is attained during development in bird chicks. Our results also support previous suggestions that early in their development, altricial chicks mainly allocate energy to the growth of `energy-processing' organs (such as the intestine and liver) rather than to `energy-consuming' organs. Accepted: 3 March 1999     

Tricarboxylic Acid Cycle Activity Measured by <Superscript>13</Superscript>C Magnetic Resonance Spectroscopy in Rats Subjected to the Kaolin Model of Obstructed Hydrocephalus

Evaluating early changes in cerebral metabolism in hydrocephalus can help in the decision making and the timing of surgical intervention. This study was aimed at examining the tricarboxylic acid (TCA) cycle rate and ¹³C label incorporation into neurotransmitter amino acids and other compounds 2 weeks after rats were subjected to kaolin-induced progressive hydrocephalus. In vivo and ex vivo magnetic resonance spectroscopy (MRS), combined with the infusion of [1,6-¹³C]glucose, was used to monitor the time courses of ¹³C label incorporation into the different carbon positions of glutamate in the forebrains of rats with hydrocephalus as well as in those of controls. Metabolic rates were determined by fitting the measured data into a one-compartment metabolic model. The TCA cycle rate was 1.3 ± 0.2 μmoles/gram/minute in the controls and 0.8 ± 0.4 μmoles/gram/minute in the acute hydrocephalus group, the exchange rate between α-ketoglutarate and glutamate was 4.1 ± 2.5 μmoles/gram/minute in the controls and 2.7 ± 2.6 μmoles/gram/minute in the hydrocephalus group calculated from in vivo MRS. There were no statistically significant differences between these rates. Hydrocephalus caused a decrease in the amounts of glutamate, alanine and taurine. In addition, the concentration of the neuronal marker N-acetyl aspartate was decreased. ¹³C Labelling of most amino acids derived from [1,6-¹³C]glucose was unchanged 2 weeks after hydrocephalus induction. The only indication of astrocyte impairment was the decreased ¹³C enrichment in glutamine C-2. This study shows that hydrocephalus causes subtle but significant alterations in neuronal metabolism already early in the course of the disease. These sub-lethal changes, however, if maintained and if ongoing might explain the delayed and programmed neuronal damage as seen in chronic hydrocephalus.     

Body size changes among otters, Lutra lutra, in Norway: the possible effects of food availability and global warming

Using museum data of adult specimens whose sex, age, and locality are known, we studied temporal and geographical body size trends among the otter, Lutra lutra, in Norway. We found that body size of the otters increased during the last quarter of the twentieth century, and suggest that this trend is related to increased food availability from fish farming and possibly also to energy saving due to elevated sea temperatures. Birth year and death year explained 38.8 and 43.5%, respectively, of the variation in body size. Body size of otters was positively related to latitude, thus conforming to Bergmann’s rule.     

Infectious pancreatic necrosis virus VP5 is dispensable for virulence and persistence

Infectious pancreatic necrosis virus (IPNV) is the causative agent of infectious pancreatic necrosis (IPN) disease in salmonid fish. Recent studies have revealed variation in virulence between isolates of the Sp serotype, associated with certain residues of the structural protein VP2. The isolates are also highly heterogenic in the coding region of the nonstructural VP5 protein. To study the involvement of this protein in the pathogenesis of disease, we generated three recombinant VP5 mutant viruses using reverse genetics. The "wild-type" recombinant NVI15 (rNVI15) virus is virulent, having a premature stop codon at nucleotide position 427, putatively encoding a truncated 12-kDa VP5 protein, whereas rNVI15-15K virus encodes a 15-kDa protein. Recombinant rNVI15-deltaVP5 virus contains a mutation in the initiation codon of the VP5 gene that ablates the expression of VP5. Atlantic salmon postsmolts were challenged to study the virulence characteristics of the recovered viruses in vivo. The role of VP5 in persistent infection was investigated by challenging Atlantic salmon fry with the recovered viruses, as well as with the low-virulence field strain Sp103 and a naturally occurring VP5-deficient mutant of Sp103. The results show that VP5 is not required for viral replication in vivo, and its absence does not alter the virulence characteristics of the virus or the establishment of persistent IPNV infection.