Polyplax serrata: Effects of limb disability on lousiness in mice: VI. Lack of tolerance after neonatal exposure

Mice restrained from grooming become heavily infested with lice. Ordinarily the hosts develop resistance to the infestation which results in limitation or extinction of louse populations. However, individual mice, the number depending on breed, die of anemia or, in some cases, become debilitated but survive with continuous heavy louse burdens. A similar condition of tolerance is occasionally seen in domestic animals. Experiments were conducted to determine whether heavy exposure to lice in the neonatal period could induce tolerance to the parasite. When adequate provision was made to prevent mortality from louse infestation, survival and acquisition of resistance developed at the same rate and to the same degree in neonatally exposed and in naïve mice.     

Ligand-induced interconversions of maize homoserine dehydrogenase among different states

The threonine-sensitive homoserine dehydrogenase has been isolated and extensively purified from shoots of Zea mays L. var. earliking. This enzyme is shown to be hysteretic under certain conditions. Progress curves of the NAD-dependent reaction catalyzed by the maize enzyme can be characterized by distinct lags prior to achievement of steady state velocities, reflecting transitions from less active species to a more active steady state form of the enzyme. Incubation of the enzyme for 1 min at 25 degrees C prior to initiation of the reaction profoundly influences the properties of the less active enzyme and the nature of the subsequent slow transitions during assay. When the feedback modifier, L-threonine, or KCl is included in the preincubation mixture, the transitions involve biomolecular association reactions. In the absence of either ligand, or in the presence of an appropriate mixture of both, a unimolecular transition occurs during assay. Three unique preincubation states of the enzyme have been identified on the basis of their response to substrates and effectors; whereas, the kinetic and regulatory properties of the steady state form of the enzyme are independent of preincubation conditions. Steady state can thus be achieved by three different transitions. Each transition is retarded by threonine and favored by substrates and potassium, although the effects of these compounds differ quantitatively. Under the conditions tested, monovalent cations have no effect on the steady state velocity of the enzyme. A model describing the relationships among the four unique states of the enzyme which is consistent with the present results and supported by previous observations is proposed.     

Diel,size-differential drift patterns of three macroinvertebrate species in the lower Mississippi River,Louisiana (USA)

We explored macroinvertebrate size-differential drift in the lower Mississippi River (a 9th order system). Because this river system is highly turbid, we hypothesized that visually-dependent vertebrate predators feeding on drifting organisms would be at a disadvantage. Thus, size-differential drift should not occur. For one 24-hour period in both January and April, six drift nets were used to sample surface drift. Nets were emptied once every four hours. Individual intra-ocular distances of three macroinvertebrate species (Hydropsyche orris: Trichoptera, Hexagenia limbata: Ephemeroptera, Macrobrachium ohione: Crustacea) were measured. Percentages of size classes in the drift were determined. In both months, large individuals of H. orris and H. limbata were prevalent in the nocturnal but scarce in the diurnal drift. In January, large M. ohione drifted regardless of time. In April, large M. ohione predominated the nocturnal drift. Our results could not be attributed solely to vertebrate predator avoidance. Other mechanisms such as diel microhabitat migration and current velocity may have accounted for the results.     

The involvement of cAMP in lymphocyte capping

We have observed that agents that are known to elevate intracellular levels of cAMP such as N⁶,O²-dibutyryl adenosine 3′,5′-cyclic monophosphoric acid (dbcAMP) and theophylline cause a remarkable stimulatory effect on the lymphocyte receptor mobility phenomenon. Increased intracellular concentration of cAMP enhances not only antibody-induced but also Con A-induced lymphocyte capping events in T-lymphoma cells. In addition, we have noted that N²,O²-dibutyryl guanosine 3′,5′-cyclic monophosphoric acid (dbcGMP) does not stimulate but actually slightly inhibits the receptor movement. Furthermore, we have determined cAMP levels to increase greater than twofold during ligand-induced capping using a radioimmunoassay. Therefore, our data strongly suggest that cyclic adenylic monophosphoric acid (and not cGMP) is specifically involved in the redistribution of lymphocyte membrane proteins induced by both antibody and Con A.     

Chromosome studies on mosses from Austria,Czechoslovakia and other parts of Central Europe

Summary Reports are made on chromosomes in forty-six species from sixteen families of mosses. The plants were collected from all Austrian provinces, except the Tyrol and Vorarlberg, from Bohemia, Moravia, Slovakia, Bavaria, and also from Hungary and Italy. In addition to number or numbers of chromosomes reported for each species, observations are made on chromosome morphology, staining characteristics and behavior in meiosis or mitosis. The lowest numbers yet found are reported forDicranum fuscescens, n=8, andTimmia bavarica, n=8+1 m. For the latter species the study was made from mitotic configurations, and offers evidence that m-chromosomes may be normal members of the gametophytic set. These investigations reveal for the first time m-chromosomes inDicranoweisia cirrata, Pottia lanceolata, Timmia bavarica, Orthotrichum pumilum, Homalothecium lutescens, Brachythecium velutinum, Rhyncostegium murale, Rhyncostegiella pumila, andHypnum cupressiforme. Although the generaBartramia andPlagiopus previously have been characterized by different numbers of chromosomes, n=8 and n=7 respectively, plants ofPlagiopus oederi from Carinthia and Moravia were found, however, to have n=8. One species,Isopterygium seligeri, and one variety,Orthotrichum anomalum var.saxatile, have not been studied previously.Grateful acknowledgement is made to (1) the United States National Science Foundation for partial support of this investigation by a grant of research funds (NSF GB 6725) to Duke University, and (2) the Botanisches Institut der Universität Wien for laboratory space, equipment and use of the herbarium and library.     

Diaphragmatic work of breathing in premature human infants

Present methods of assessing the work of breathing in human infants do not account for the added load when intercostal muscle activity is lost and rib cage distortion occurs. We have developed a technique for assessing diaphragmatic work in this circumstance utilizing measurements of transdiaphragmatic pressure and abdominal volume displacement. Eleven preterm infants without evidence of lung disease were studied. During periods of minimal rib cage distortion, inspiratory diaphragmatic work averaged 5.9 g X cm X ml-1, increasing to an average of 12.4 g X cm X ml-1 with periods of paradoxical rib cage motion (P less than 0.01). Inspiratory work was strongly correlated with the electrical activity of the diaphragm as measured from its moving time average (P less than 0.05). Assuming a mechanical efficiency of 4% in these infants, the caloric cost of diaphragmatic work may reach 10% of their basal metabolic rate in periods with rib cage distortion. When lung disease is superimposed, the increased metabolic demands of the diaphragm may predispose preterm infants to fatigue and may contribute to a failure to grow.