Microbial degradation of oxalate in the gastrointestinal tracts of rats.

Rates of oxalate degradation by mixed bacterial populations in cecal contents from wild rats ranged from 2.5 to 20.6 mumol/g (dry weight) per h. The oxalate-degrading activity in cecal contents from three strains of laboratory rats (Long-Evans, Wistar, and Sprague-Dawley) from four commercial breeders was generally lower, ranging from 1.8 to 3.5 mumol/g (dry weight) of cecal contents per h. This activity did not increase when diets were supplemented with oxalate. When Sprague-Dawley rats from a fifth commercial breeder were fed an oxalate diet, rates of oxalate degradation in cecal contents increased from 2.0 to 23.1 mumol/g (dry weight) per h. Obligately anaerobic, oxalate-degrading bacteria, similar to ruminal strains of Oxalobacter formigenes, were isolated from the latter group of laboratory rats and from wild rats. Viable counts of these bacteria were as high as 10(8)/g (dry weight) of cecal contents, which was less than 0.1% of the total viable population. This report presents the first evidence for the presence of anaerobic oxalate-degrading bacteria in the cecal contents of rats and represents the first direct measurement of the concentration of these bacteria in the large bowel of monogastric animals. We propose that methods used for the maintenance of most commercial rat colonies often preclude the intestinal colonization of laboratory rats with anaerobic oxalate-degrading bacteria.     

Neurotensin receptors in canine intestinal smooth muscle: preparation of plasma membranes and characterization of (Tyr3-125I)-labelled neurotensin binding

To study the binding of (Tyr3-125I)-labelled neurotensin to intestinal muscle, plasma membranes have been purified from dog intestinal circular smooth muscle. Purification was done by differential centrifugation followed by separation on a sucrose gradient. Electron microscopic study revealed that the dissected circular muscles used as the source of membranes were free of myenteric plexus and that the plasma membrane fraction obtained was free of any mitochondria or synaptosomes. The fraction used was obtained at the interface of 14%-33% sucrose density on the gradient and was 25-times enriched in the plasma membrane marker enzyme 5'-nucleotidase activity as compared to post-nuclear supernatant. This fraction contained negligible activity of mitochondrial membrane marker enzyme cytochrome c oxidase and low activity of a putative endoplasmic reticulum marker enzyme NADPH-cytochrome-c reductase. This membrane fraction contained a high density of neurotensin binding sites. This binding was studied by kinetic and by saturation approaches. Analysis of data from saturation binding studies by the computer programs (EBDA and LIGAND) suggested the presence of a two-site model (Kd1 = 0.118 nM, Kd2 = 3.18 nM, Bmax1 = 9.73 fmol/mg and Bmax2 = 129.8 fmol/mg). A part of specifically bound neurotensin was rapidly dissociated. No cooperativity between the two receptor types could be detected. A kinetic analysis of binding gave the Kd value equal to 0.107 nM. Carboxy terminal amino acid residues 8-13 were found to be essential for the binding activity and replacement of Tyr11 by tryptophan reduced the affinity of the peptide by 10 times in displacement studies. Binding was modulated by sodium ions and a guanine nucleotide Gpp[NH]p. MgCl2, CaCl2 and KCl were also found to reduce the specific binding. Evidence was found of a high specific binding to another membrane fraction poor in plasma membranes and rich in synaptosomes. We concluded that plasma membrane of canine intestinal circular muscle contains neurotensin receptors with recognition properties distinct from those obtained in previous studies of neurotensin binding sites in murine tissues. Another neurotensin binding site may be present on neuronal membranes.     

Calcium and contractions of isolated smooth muscle cells from rat myometrium

Smooth muscle cells were isolated from estrogenized rat myometrium by collagenase digestion. Electron microscopic examination and measurement of cell lengths by image-splitting micrometry were carried out after fixation with acrolein. Mean lengths of cells before and after isolation were 81.7 and 66.9 micron, respectively. Responses of cells were compared with contractions of isolated strips recorded isometrically. Effects of carbachol and KCl were examined in 2 mM Ca, 2 mM Ca + 4 mM EGTA, and 2 mM Ca + 10(-8) M nitrendipine solution. Carbachol and KCl produced concentration-dependent shortening of isolated cells maximal at 30 s after addition. The concentrations of carbachol required to produce shortenings were about 100-fold less than those required to produce isometric contractions; but no major difference was observed in the concentration dependence of cell shortening and isometric contraction produced by potassium-induced depolarization. In 2 mM Ca solution, there was a phasic response, followed by a tonic response such that more than 50% of maximum cell shortening was maintained for 10 min. However, in 2 mM Ca + 4 mM EGTA or 10(-8) M nitrendipine, the tonic contraction was abolished and cells rapidly relaxed after 30 s. If carbachol was added to cells after varying times in the EGTA-containing solution, the ability to initiate a contraction declined exponentially with a half-time of 160 s. Effects of depolarization by KCl were examined in 2 mM Ca plus nitrendipine and 2 mM Ca + 4 mM EGTA solution. Shortening occurred in 2 mM Ca solution by depolarization but not if nitrendipine was added. Though shortening was not observed in 2 mM Ca + 4 mM EGTA solution by KCl, subsequent addition of carbachol induced shortening. These results suggested that there was an intracellular Ca store site from which Ca was released by carbachol and which was not affected by depolarization in the absence of external Ca. No evidence was obtained that the contraction persists in Ca2+-free medium in isolated cells, which is in agreement with previous findings in small muscle strips in which only a similar transient response was obtained.     

Intra-tree foraging behavior of Ceratitis capitata flies in relation to host fruit density and quality

We examined the intra-tree foraging behavior of individually-released, wild-population Mediterranean fruit flies (medflies), Ceratitis capitata (Wiedemann), on field-caged host trees bearing each of three different densities (0, 3, or 12 per tree) of non-infested host fruit (kumquat) or each of two levels of fruit quality (12 non-infested fruit or 12 fruit infested with eggs and covered with host marking pheromone). With increasing density of non-infested fruit, medflies tended to remain longer in trees, visit more fruit before leaving, oviposit more often, accept a proportionately smaller number of fruit visited, and emigrate sooner after the last egg was laid (i.e. have a shorter Giving-Up-Time). Medflies spent much less time, oviposited much less often, and exhibited a longer Giving-Up-Time on trees harboring pheromone-marked fruit than non-infested fruit. Variation in temperature within the range at which experiments were conducted (25–36°C) had little detectable influence on foraging behavior. We compare our findings with published findings on the intra-tree foraging behavior of another tephritid fly, Rhagoletis pomonella (Walsh), and with current foraging behavior theory. We discuss implications of our findings with respect to medfly management strategies, particularly fruit stripping in eradication programs and use of synthetic marking pheromone for control.

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Résumé Nous avons étudié le comportement de prospection dans un arbre, de femelles d'une population sauvage de C. capitata, libérées individuellement à l'intérieur de cages contenant des Eriobotrya japonica (kumquat), portant chacun 3 densités différentes de fruits no contaminés (0, 3, 12 par arbre) et chacun 2 niveaux de qualité de fruits: 12 fruits non infestés ou 12 fruits contaminés par des oeufs et recouverts de phéromone de marquage de l'hôte. C. capitata avait terndance à rester plus longtemps dans les arbres, à visiter plus de fruits avant le quitter, à pondre plus souvent, à accepter proportionnellement un nombre plus réduit de fruits déjà visités, à émigrer plus tôt après la ponte du dernier oeuf (c'est-à-dire à présenter un temps d'abandon plus bref), quand la densité des fruits non contaminés augmentait. C. capitata a dépensé beaucoup moins de temps, pondu beaucoup moins souvent, et présenté un temps d'abandon plus long sur les arbres portant des fruits marqués par la phéromone que sur ceux ayant des fruits non contaminés. Les variations de température dans la gamme de cells où les observations ont eu lieu (23–36°C) n'ont eu qu'une faible influence décelable sur le comportement de prospection. Nous avons comparé nos résultats avec ceux publiés sur la prospection à l'intérieur de l'arbre par une autre téphritide (Rhagoletis pomonella) et avec la théorie dominante sur le comportement de prospection. Nous discutons les conséquences de nos résultats sur les stratégies de lutte contre C. capitata, en particulier l'élimination des fruits dans les plans d'erradication et l'utilisation de phéromone synthétique de marquage.

     

Presence of nucleosomes inPenicillium chrysogenum

We have studied the chromatin structure ofPenicillium chrysogenum. This fungus presents the typical nucleosomal repeat and the core DNA size characteristic of all the eukaryotes. The repeat length (about 180 base pairs) is in the range of those obtained for most fungi (160–180 base pairs) and shorter than in higher eukaryotes. Knowledge aboutP. chrysogenum chromatin structure opens the way to the study of the mechanisms of genetic regulation in this filamentous fungus.     

The influence of crabs on litter processing in high intertidal mangrove forests in tropical Australia

Summary Measurements of litter fall and litter removal by crabs, in conjunction with estimates of litter decay by microbes and tidal export of litter from three high-intertidal mangrove forests were made during a year-long study in tropical northeastern Australia. In forests dominated by Ceriops tagal and Bruguiera exaristata, litter standing stocks remained low on the forest floor (mean 6 g·m^-2), although litter fall was high; 822 and 1022 g·m^-2·y^-1, respectively. Sesarmid crabs removed 580 (Ceriops) and 803 (Bruguiera) g·m^-2·y^-1, or 71 and 79%, of the total annual litter fall from the forest floor. Relative to the rate of litter removal by crabs, microbial turnover of whole, unshredded litter was insignificant, accounting for <1% of annual litter fall. Export of litter by tides was estimated to remove 194 (Ceriops) and 252 (Bruguiera) g·m^-2·y^-1 or 24 and 25% of annual litter fall. In a forest dominated by Avicenniamarina, in which an ocypodid crab was more abundant than sesarmids, litter standing stocks were higher (mean 84 g·m^-2) and crabs removed less litter; 173 g·m^-2·y^-1 or 33% of the annual litter fall of 519 g·m^-2·y^-1. Microbial turnover of intact litter was more important in the Avicennia forest (168 g·m^-2·y^-1 or 32% of annual litter fall), and tides exported 107 g·m^-2·y^-1 or 21% of litter production. In areas where sesarmid crabs were absent or rare in Ceriops forests, there were significantly higher standing stocks of litter and slower rates of leaf removal. Taking into account the probable assimilation efficiencies of sesarmid crabs feeding on mangrove leaves, we estimate that in Ceriops and Bruguiera forests leaf processing by crabs turns litter over at >75 times the rate of microbial decay alone, thus facilitating the high sediment bacterial productivity in these forests. The importance of litter processing by crabs increases with height in the intertidal in tropical Australia, in contrast to New World mangrove forests, where the reverse is true.Contribution No. 445 from the Australian Institute of Marine Science     

Auxin Physiology of the Tomato Mutant diageotropica

The tomato (Lycopersicon esculentum, Mill.) mutant diageotropica (dgt) exhibits biochemical, physiological, and morphological abnormalities that suggest the mutation may have affected a primary site of auxin perception or action. We have compared two aspects of the auxin physiology of dgt and wild-type (VFN8) seedlings: auxin transport and cellular growth parameters. The rates of basipetal indole-3-acetic acid (IAA) polar transport are identical in hypocotyl sections of the two genotypes, but dgt sections have a slightly greater capacity for IAA transport. 2,3,5-Triiodobenzoic acid and ethylene reduce transport in both mutant and wild-type sections. The kinetics of auxin uptake into VFN8 and dgt sections are nearly identical. These results make it unlikely that an altered IAA efflux carrier or IAA uptake symport are responsible for the pleiotropic effects resulting from the dgt mutation. The lack of auxin-induced cell elongation in dgt plants is not due to insufficient turgor, as the osmotic potential of dgt cell sap is less (more negative) than that of VFN8. An auxin-induced increase in wall extensibility, as measured by the Instron technique, only occurs in the VFN8 plants. These data suggest dgt hypocotyls suffer a defect in the sequence of events culminating in auxin-induced cell wall loosening.     

Postcranial adaptation and evolution in lorisidae

With the exception of leaping, lorises and galagos move in many similar ways although frequencies and styles differ. This peculiar locomotor distinction in two closely related subfamilies has profoundly altered their respective postcranial anatomies from their common ancestor. A comparison of postcranial adaptation in extant forms shows that lorises and galagos differ somewhat in forelimb mobility, but are more fundamentally disparate in hindlimb adaptation. Inferences concerning locomotor adaptation in the lorisid fossil record indicate a more generalized locomotor pattern which is more like that of extant cheirogaleids than either living galagos or lorises. Thus, vertical clinging and leaping in galagines and the slow-climbing and suspensory movements of lorisines appear to be evolutionarily recent innovations from a more generalized locomotor past.